Check in the pristine copy of ICU 4.6...

icu46/source/common/ucnvmbcs.c

+/*
+******************************************************************************
+*
+*   Copyright (C) 2000-2010, International Business Machines
+*   Corporation and others.  All Rights Reserved.
+*
+******************************************************************************
+*   file name:  ucnvmbcs.c
+*   encoding:   US-ASCII
+*   tab size:   8 (not used)
+*   indentation:4
+*
+*   created on: 2000jul03
+*   created by: Markus W. Scherer
+*
+*   The current code in this file replaces the previous implementation
+*   of conversion code from multi-byte codepages to Unicode and back.
+*   This implementation supports the following:
+*   - legacy variable-length codepages with up to 4 bytes per character
+*   - all Unicode code points (up to 0x10ffff)
+*   - efficient distinction of unassigned vs. illegal byte sequences
+*   - it is possible in fromUnicode() to directly deal with simple
+*     stateful encodings (used for EBCDIC_STATEFUL)
+*   - it is possible to convert Unicode code points
+*     to a single zero byte (but not as a fallback except for SBCS)
+*
+*   Remaining limitations in fromUnicode:
+*   - byte sequences must not have leading zero bytes
+*   - except for SBCS codepages: no fallback mapping from Unicode to a zero byte
+*   - limitation to up to 4 bytes per character
+*
+*   ICU 2.8 (late 2003) adds a secondary data structure which lifts some of these
+*   limitations and adds m:n character mappings and other features.
+*   See ucnv_ext.h for details.
+*
+*   Change history: 
+*
+*    5/6/2001       Ram       Moved  MBCS_SINGLE_RESULT_FROM_U,MBCS_STAGE_2_FROM_U,
+*                             MBCS_VALUE_2_FROM_STAGE_2, MBCS_VALUE_4_FROM_STAGE_2
+*                             macros to ucnvmbcs.h file
+*/
+
+#include "unicode/utypes.h"
+
+#if !UCONFIG_NO_CONVERSION && !UCONFIG_NO_LEGACY_CONVERSION
+
+#include "unicode/ucnv.h"
+#include "unicode/ucnv_cb.h"
+#include "unicode/udata.h"
+#include "unicode/uset.h"
+#include "ucnv_bld.h"
+#include "ucnvmbcs.h"
+#include "ucnv_ext.h"
+#include "ucnv_cnv.h"
+#include "umutex.h"
+#include "cmemory.h"
+#include "cstring.h"
+
+/* control optimizations according to the platform */
+#define MBCS_UNROLL_SINGLE_TO_BMP 1
+#define MBCS_UNROLL_SINGLE_FROM_BMP 0
+
+/*
+ * _MBCSHeader versions 5.3 & 4.3
+ * (Note that the _MBCSHeader version is in addition to the converter formatVersion.)
+ *
+ * This version is optional. Version 5 is used for incompatible data format changes.
+ * makeconv will continue to generate version 4 files if possible.
+ *
+ * Changes from version 4:
+ *
+ * The main difference is an additional _MBCSHeader field with
+ * - the length (number of uint32_t) of the _MBCSHeader
+ * - flags for further incompatible data format changes
+ * - flags for further, backward compatible data format changes
+ *
+ * The MBCS_OPT_FROM_U flag indicates that most of the fromUnicode data is omitted from
+ * the file and needs to be reconstituted at load time.
+ * This requires a utf8Friendly format with an additional mbcsIndex table for fast
+ * (and UTF-8-friendly) fromUnicode conversion for Unicode code points up to maxFastUChar.
+ * (For details about these structures see below, and see ucnvmbcs.h.)
+ *
+ *   utf8Friendly also implies that the fromUnicode mappings are stored in ascending order
+ *   of the Unicode code points. (This requires that the .ucm file has the |0 etc.
+ *   precision markers for all mappings.)
+ *
+ *   All fallbacks have been moved to the extension table, leaving only roundtrips in the
+ *   omitted data that can be reconstituted from the toUnicode data.
+ *
+ *   Of the stage 2 table, the part corresponding to maxFastUChar and below is omitted.
+ *   With only roundtrip mappings in the base fromUnicode data, this part is fully
+ *   redundant with the mbcsIndex and will be reconstituted from that (also using the
+ *   stage 1 table which contains the information about how stage 2 was compacted).
+ *
+ *   The rest of the stage 2 table, the part for code points above maxFastUChar,
+ *   is stored in the file and will be appended to the reconstituted part.
+ *
+ *   The entire fromUBytes array is omitted from the file and will be reconstitued.
+ *   This is done by enumerating all toUnicode roundtrip mappings, performing
+ *   each mapping (using the stage 1 and reconstituted stage 2 tables) and
+ *   writing instead of reading the byte values.
+ *
+ * _MBCSHeader version 4.3
+ *
+ * Change from version 4.2:
+ * - Optional utf8Friendly data structures, with 64-entry stage 3 block
+ *   allocation for parts of the BMP, and an additional mbcsIndex in non-SBCS
+ *   files which can be used instead of stages 1 & 2.
+ *   Faster lookups for roundtrips from most commonly used characters,
+ *   and lookups from UTF-8 byte sequences with a natural bit distribution.
+ *   See ucnvmbcs.h for more details.
+ *
+ * Change from version 4.1:
+ * - Added an optional extension table structure at the end of the .cnv file.
+ *   It is present if the upper bits of the header flags field contains a non-zero
+ *   byte offset to it.
+ *   Files that contain only a conversion table and no base table
+ *   use the special outputType MBCS_OUTPUT_EXT_ONLY.
+ *   These contain the base table name between the MBCS header and the extension
+ *   data.
+ *
+ * Change from version 4.0:
+ * - Replace header.reserved with header.fromUBytesLength so that all
+ *   fields in the data have length.
+ *
+ * Changes from version 3 (for performance improvements):
+ * - new bit distribution for state table entries
+ * - reordered action codes
+ * - new data structure for single-byte fromUnicode
+ *   + stage 2 only contains indexes
+ *   + stage 3 stores 16 bits per character with classification bits 15..8
+ * - no multiplier for stage 1 entries
+ * - stage 2 for non-single-byte codepages contains the index and the flags in
+ *   one 32-bit value
+ * - 2-byte and 4-byte fromUnicode results are stored directly as 16/32-bit integers
+ *
+ * For more details about old versions of the MBCS data structure, see
+ * the corresponding versions of this file.
+ *
+ * Converting stateless codepage data ---------------------------------------***
+ * (or codepage data with simple states) to Unicode.
+ *
+ * Data structure and algorithm for converting from complex legacy codepages
+ * to Unicode. (Designed before 2000-may-22.)
+ *
+ * The basic idea is that the structure of legacy codepages can be described
+ * with state tables.
+ * When reading a byte stream, each input byte causes a state transition.
+ * Some transitions result in the output of a code point, some result in
+ * "unassigned" or "illegal" output.
+ * This is used here for character conversion.
+ *
+ * The data structure begins with a state table consisting of a row
+ * per state, with 256 entries (columns) per row for each possible input
+ * byte value.
+ * Each entry is 32 bits wide, with two formats distinguished by
+ * the sign bit (bit 31):
+ *
+ * One format for transitional entries (bit 31 not set) for non-final bytes, and
+ * one format for final entries (bit 31 set).
+ * Both formats contain the number of the next state in the same bit
+ * positions.
+ * State 0 is the initial state.
+ *
+ * Most of the time, the offset values of subsequent states are added
+ * up to a scalar value. This value will eventually be the index of
+ * the Unicode code point in a table that follows the state table.
+ * The effect is that the code points for final state table rows
+ * are contiguous. The code points of final state rows follow each other
+ * in the order of the references to those final states by previous
+ * states, etc.
+ *
+ * For some terminal states, the offset is itself the output Unicode
+ * code point (16 bits for a BMP code point or 20 bits for a supplementary
+ * code point (stored as code point minus 0x10000 so that 20 bits are enough).
+ * For others, the code point in the Unicode table is stored with either
+ * one or two code units: one for BMP code points, two for a pair of
+ * surrogates.
+ * All code points for a final state entry take up the same number of code
+ * units, regardless of whether they all actually _use_ the same number
+ * of code units. This is necessary for simple array access.
+ *
+ * An additional feature comes in with what in ICU is called "fallback"
+ * mappings:
+ *
+ * In addition to round-trippable, precise, 1:1 mappings, there are often
+ * mappings defined between similar, though not the same, characters.
+ * Typically, such mappings occur only in fromUnicode mapping tables because
+ * Unicode has a superset repertoire of most other codepages. However, it
+ * is possible to provide such mappings in the toUnicode tables, too.
+ * In this case, the fallback mappings are partly integrated into the
+ * general state tables because the structure of the encoding includes their
+ * byte sequences.
+ * For final entries in an initial state, fallback mappings are stored in
+ * the entry itself like with roundtrip mappings.
+ * For other final entries, they are stored in the code units table if
+ * the entry is for a pair of code units.
+ * For single-unit results in the code units table, there is no space to
+ * alternatively hold a fallback mapping; in this case, the code unit
+ * is stored as U+fffe (unassigned), and the fallback mapping needs to
+ * be looked up by the scalar offset value in a separate table.
+ *
+ * "Unassigned" state entries really mean "structurally unassigned",
+ * i.e., such a byte sequence will never have a mapping result.
+ *
+ * The interpretation of the bits in each entry is as follows:
+ *
+ * Bit 31 not set, not a terminal entry ("transitional"):
+ * 30..24 next state
+ * 23..0  offset delta, to be added up
+ *
+ * Bit 31 set, terminal ("final") entry:
+ * 30..24 next state (regardless of action code)
+ * 23..20 action code:
+ *        action codes 0 and 1 result in precise-mapping Unicode code points
+ *        0  valid byte sequence
+ *           19..16 not used, 0
+ *           15..0  16-bit Unicode BMP code point
+ *                  never U+fffe or U+ffff
+ *        1  valid byte sequence
+ *           19..0  20-bit Unicode supplementary code point
+ *                  never U+fffe or U+ffff
+ *
+ *        action codes 2 and 3 result in fallback (unidirectional-mapping) Unicode code points
+ *        2  valid byte sequence (fallback)
+ *           19..16 not used, 0
+ *           15..0  16-bit Unicode BMP code point as fallback result
+ *        3  valid byte sequence (fallback)
+ *           19..0  20-bit Unicode supplementary code point as fallback result
+ *
+ *        action codes 4 and 5 may result in roundtrip/fallback/unassigned/illegal results
+ *        depending on the code units they result in
+ *        4  valid byte sequence
+ *           19..9  not used, 0
+ *            8..0  final offset delta
+ *                  pointing to one 16-bit code unit which may be
+ *                  fffe  unassigned -- look for a fallback for this offset
+ *                  ffff  illegal
+ *        5  valid byte sequence
+ *           19..9  not used, 0
+ *            8..0  final offset delta
+ *                  pointing to two 16-bit code units
+ *                  (typically UTF-16 surrogates)
+ *                  the result depends on the first code unit as follows:
+ *                  0000..d7ff  roundtrip BMP code point (1st alone)
+ *                  d800..dbff  roundtrip surrogate pair (1st, 2nd)
+ *                  dc00..dfff  fallback surrogate pair (1st-400, 2nd)
+ *                  e000        roundtrip BMP code point (2nd alone)
+ *                  e001        fallback BMP code point (2nd alone)
+ *                  fffe        unassigned
+ *                  ffff        illegal
+ *           (the final offset deltas are at most 255 * 2,
+ *            times 2 because of storing code unit pairs)
+ *
+ *        6  unassigned byte sequence
+ *           19..16 not used, 0
+ *           15..0  16-bit Unicode BMP code point U+fffe (new with version 2)
+ *                  this does not contain a final offset delta because the main
+ *                  purpose of this action code is to save scalar offset values;
+ *                  therefore, fallback values cannot be assigned to byte
+ *                  sequences that result in this action code
+ *        7  illegal byte sequence
+ *           19..16 not used, 0
+ *           15..0  16-bit Unicode BMP code point U+ffff (new with version 2)
+ *        8  state change only
+ *           19..0  not used, 0
+ *           useful for state changes in simple stateful encodings,
+ *           at Shift-In/Shift-Out codes
+ *
+ *
+ *        9..15 reserved for future use
+ *           current implementations will only perform a state change
+ *           and ignore bits 19..0
+ *
+ * An encoding with contiguous ranges of unassigned byte sequences, like
+ * Shift-JIS and especially EUC-TW, can be stored efficiently by having
+ * at least two states for the trail bytes:
+ * One trail byte state that results in code points, and one that only
+ * has "unassigned" and "illegal" terminal states.
+ *
+ * Note: partly by accident, this data structure supports simple stateful
+ * encodings without any additional logic.
+ * Currently, only simple Shift-In/Shift-Out schemes are handled with
+ * appropriate state tables (especially EBCDIC_STATEFUL!).
+ *
+ * MBCS version 2 added:
+ * unassigned and illegal action codes have U+fffe and U+ffff
+ * instead of unused bits; this is useful for _MBCS_SINGLE_SIMPLE_GET_NEXT_BMP()
+ *
+ * Converting from Unicode to codepage bytes --------------------------------***
+ *
+ * The conversion data structure for fromUnicode is designed for the known
+ * structure of Unicode. It maps from 21-bit code points (0..0x10ffff) to
+ * a sequence of 1..4 bytes, in addition to a flag that indicates if there is
+ * a roundtrip mapping.
+ *
+ * The lookup is done with a 3-stage trie, using 11/6/4 bits for stage 1/2/3
+ * like in the character properties table.
+ * The beginning of the trie is at offsetFromUTable, the beginning of stage 3
+ * with the resulting bytes is at offsetFromUBytes.
+ *
+ * Beginning with version 4, single-byte codepages have a significantly different
+ * trie compared to other codepages.
+ * In all cases, the entry in stage 1 is directly the index of the block of
+ * 64 entries in stage 2.
+ *
+ * Single-byte lookup:
+ *
+ * Stage 2 only contains 16-bit indexes directly to the 16-blocks in stage 3.
+ * Stage 3 contains one 16-bit word per result:
+ * Bits 15..8 indicate the kind of result:
+ *    f  roundtrip result
+ *    c  fallback result from private-use code point
+ *    8  fallback result from other code points
+ *    0  unassigned
+ * Bits 7..0 contain the codepage byte. A zero byte is always possible.
+ *
+ * In version 4.3, the runtime code can build an sbcsIndex for a utf8Friendly
+ * file. For 2-byte UTF-8 byte sequences and some 3-byte sequences the lookup
+ * becomes a 2-stage (single-index) trie lookup with 6 bits for stage 3.
+ * ASCII code points can be looked up with a linear array access into stage 3.
+ * See maxFastUChar and other details in ucnvmbcs.h.
+ *
+ * Multi-byte lookup:
+ *
+ * Stage 2 contains a 32-bit word for each 16-block in stage 3:
+ * Bits 31..16 contain flags for which stage 3 entries contain roundtrip results
+ *             test: MBCS_FROM_U_IS_ROUNDTRIP(stage2Entry, c)
+ *             If this test is false, then a non-zero result will be interpreted as
+ *             a fallback mapping.
+ * Bits 15..0  contain the index to stage 3, which must be multiplied by 16*(bytes per char)
+ *
+ * Stage 3 contains 2, 3, or 4 bytes per result.
+ * 2 or 4 bytes are stored as uint16_t/uint32_t in platform endianness,
+ * while 3 bytes are stored as bytes in big-endian order.
+ * Leading zero bytes are ignored, and the number of bytes is counted.
+ * A zero byte mapping result is possible as a roundtrip result.
+ * For some output types, the actual result is processed from this;
+ * see ucnv_MBCSFromUnicodeWithOffsets().
+ *
+ * Note that stage 1 always contains 0x440=1088 entries (0x440==0x110000>>10),
+ * or (version 3 and up) for BMP-only codepages, it contains 64 entries.
+ *
+ * In version 4.3, a utf8Friendly file contains an mbcsIndex table.
+ * For 2-byte UTF-8 byte sequences and most 3-byte sequences the lookup
+ * becomes a 2-stage (single-index) trie lookup with 6 bits for stage 3.
+ * ASCII code points can be looked up with a linear array access into stage 3.
+ * See maxFastUChar, mbcsIndex and other details in ucnvmbcs.h.
+ *
+ * In version 3, stage 2 blocks may overlap by multiples of the multiplier
+ * for compaction.
+ * In version 4, stage 2 blocks (and for single-byte codepages, stage 3 blocks)
+ * may overlap by any number of entries.
+ *
+ * MBCS version 2 added:
+ * the converter checks for known output types, which allows
+ * adding new ones without crashing an unaware converter
+ */
+
+static const UConverterImpl _SBCSUTF8Impl;
+static const UConverterImpl _DBCSUTF8Impl;
+
+/* GB 18030 data ------------------------------------------------------------ */
+
+/* helper macros for linear values for GB 18030 four-byte sequences */
+#define LINEAR_18030(a, b, c, d) ((((a)*10+(b))*126L+(c))*10L+(d))
+
+#define LINEAR_18030_BASE LINEAR_18030(0x81, 0x30, 0x81, 0x30)
+
+#define LINEAR(x) LINEAR_18030(x>>24, (x>>16)&0xff, (x>>8)&0xff, x&0xff)
+
+/*
+ * Some ranges of GB 18030 where both the Unicode code points and the
+ * GB four-byte sequences are contiguous and are handled algorithmically by
+ * the special callback functions below.
+ * The values are start & end of Unicode & GB codes.
+ *
+ * Note that single surrogates are not mapped by GB 18030
+ * as of the re-released mapping tables from 2000-nov-30.
+ */
+static const uint32_t
+gb18030Ranges[13][4]={
+    {0x10000, 0x10FFFF, LINEAR(0x90308130), LINEAR(0xE3329A35)},
+    {0x9FA6, 0xD7FF, LINEAR(0x82358F33), LINEAR(0x8336C738)},
+    {0x0452, 0x200F, LINEAR(0x8130D330), LINEAR(0x8136A531)},
+    {0xE865, 0xF92B, LINEAR(0x8336D030), LINEAR(0x84308534)},
+    {0x2643, 0x2E80, LINEAR(0x8137A839), LINEAR(0x8138FD38)},
+    {0xFA2A, 0xFE2F, LINEAR(0x84309C38), LINEAR(0x84318537)},
+    {0x3CE1, 0x4055, LINEAR(0x8231D438), LINEAR(0x8232AF32)},
+    {0x361B, 0x3917, LINEAR(0x8230A633), LINEAR(0x8230F237)},
+    {0x49B8, 0x4C76, LINEAR(0x8234A131), LINEAR(0x8234E733)},
+    {0x4160, 0x4336, LINEAR(0x8232C937), LINEAR(0x8232F837)},
+    {0x478E, 0x4946, LINEAR(0x8233E838), LINEAR(0x82349638)},
+    {0x44D7, 0x464B, LINEAR(0x8233A339), LINEAR(0x8233C931)},
+    {0xFFE6, 0xFFFF, LINEAR(0x8431A234), LINEAR(0x8431A439)}
+};
+
+/* bit flag for UConverter.options indicating GB 18030 special handling */
+#define _MBCS_OPTION_GB18030 0x8000
+
+/* bit flag for UConverter.options indicating KEIS,JEF,JIF special handling */
+#define _MBCS_OPTION_KEIS 0x01000
+#define _MBCS_OPTION_JEF  0x02000
+#define _MBCS_OPTION_JIPS 0x04000
+
+#define KEIS_SO_CHAR_1 0x0A
+#define KEIS_SO_CHAR_2 0x42
+#define KEIS_SI_CHAR_1 0x0A
+#define KEIS_SI_CHAR_2 0x41
+
+#define JEF_SO_CHAR 0x28
+#define JEF_SI_CHAR 0x29
+
+#define JIPS_SO_CHAR_1 0x1A
+#define JIPS_SO_CHAR_2 0x70
+#define JIPS_SI_CHAR_1 0x1A
+#define JIPS_SI_CHAR_2 0x71
+
+enum SISO_Option {
+    SI,
+    SO
+};
+typedef enum SISO_Option SISO_Option;
+
+static int32_t getSISOBytes(SISO_Option option, uint32_t cnvOption, uint8_t *value) {
+    int32_t SISOLength = 0;
+
+    switch (option) {
+        case SI:
+            if ((cnvOption&_MBCS_OPTION_KEIS)!=0) {
+                value[0] = KEIS_SI_CHAR_1;
+                value[1] = KEIS_SI_CHAR_2;
+                SISOLength = 2;
+            } else if ((cnvOption&_MBCS_OPTION_JEF)!=0) {
+                value[0] = JEF_SI_CHAR;
+                SISOLength = 1;
+            } else if ((cnvOption&_MBCS_OPTION_JIPS)!=0) {
+                value[0] = JIPS_SI_CHAR_1;
+                value[1] = JIPS_SI_CHAR_2;
+                SISOLength = 2;
+            } else {
+                value[0] = UCNV_SI;
+                SISOLength = 1;
+            }
+            break;
+        case SO:
+            if ((cnvOption&_MBCS_OPTION_KEIS)!=0) {
+                value[0] = KEIS_SO_CHAR_1;
+                value[1] = KEIS_SO_CHAR_2;
+                SISOLength = 2;
+            } else if ((cnvOption&_MBCS_OPTION_JEF)!=0) {
+                value[0] = JEF_SO_CHAR;
+                SISOLength = 1;
+            } else if ((cnvOption&_MBCS_OPTION_JIPS)!=0) {
+                value[0] = JIPS_SO_CHAR_1;
+                value[1] = JIPS_SO_CHAR_2;
+                SISOLength = 2;
+            } else {
+                value[0] = UCNV_SO;
+                SISOLength = 1;
+            }
+            break;
+        default:
+            /* Should never happen. */
+            break;
+    }
+
+    return SISOLength;
+}
+
+/* Miscellaneous ------------------------------------------------------------ */
+
+/**
+ * Callback from ucnv_MBCSEnumToUnicode(), takes 32 mappings from
+ * consecutive sequences of bytes, starting from the one encoded in value,
+ * to Unicode code points. (Multiple mappings to reduce per-function call overhead.)
+ * Does not currently support m:n mappings or reverse fallbacks.
+ * This function will not be called for sequences of bytes with leading zeros.
+ *
+ * @param context an opaque pointer, as passed into ucnv_MBCSEnumToUnicode()
+ * @param value contains 1..4 bytes of the first byte sequence, right-aligned
+ * @param codePoints resulting Unicode code points, or negative if a byte sequence does
+ *        not map to anything
+ * @return TRUE to continue enumeration, FALSE to stop
+ */
+typedef UBool U_CALLCONV
+UConverterEnumToUCallback(const void *context, uint32_t value, UChar32 codePoints[32]);
+
+/* similar to ucnv_MBCSGetNextUChar() but recursive */
+static UBool
+enumToU(UConverterMBCSTable *mbcsTable, int8_t stateProps[],
+        int32_t state, uint32_t offset,
+        uint32_t value,
+        UConverterEnumToUCallback *callback, const void *context,
+        UErrorCode *pErrorCode) {
+    UChar32 codePoints[32];
+    const int32_t *row;
+    const uint16_t *unicodeCodeUnits;
+    UChar32 anyCodePoints;
+    int32_t b, limit;
+
+    row=mbcsTable->stateTable[state];
+    unicodeCodeUnits=mbcsTable->unicodeCodeUnits;
+
+    value<<=8;
+    anyCodePoints=-1;  /* becomes non-negative if there is a mapping */
+
+    b=(stateProps[state]&0x38)<<2;
+    if(b==0 && stateProps[state]>=0x40) {
+        /* skip byte sequences with leading zeros because they are not stored in the fromUnicode table */
+        codePoints[0]=U_SENTINEL;
+        b=1;
+    }
+    limit=((stateProps[state]&7)+1)<<5;
+    while(b<limit) {
+        int32_t entry=row[b];
+        if(MBCS_ENTRY_IS_TRANSITION(entry)) {
+            int32_t nextState=MBCS_ENTRY_TRANSITION_STATE(entry);
+            if(stateProps[nextState]>=0) {
+                /* recurse to a state with non-ignorable actions */
+                if(!enumToU(
+                        mbcsTable, stateProps, nextState,
+                        offset+MBCS_ENTRY_TRANSITION_OFFSET(entry),
+                        value|(uint32_t)b,
+                        callback, context,
+                        pErrorCode)) {
+                    return FALSE;
+                }
+            }
+            codePoints[b&0x1f]=U_SENTINEL;
+        } else {
+            UChar32 c;
+            int32_t action;
+
+            /*
+             * An if-else-if chain provides more reliable performance for
+             * the most common cases compared to a switch.
+             */
+            action=MBCS_ENTRY_FINAL_ACTION(entry);
+            if(action==MBCS_STATE_VALID_DIRECT_16) {
+                /* output BMP code point */
+                c=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            } else if(action==MBCS_STATE_VALID_16) {
+                int32_t finalOffset=offset+MBCS_ENTRY_FINAL_VALUE_16(entry);
+                c=unicodeCodeUnits[finalOffset];
+                if(c<0xfffe) {
+                    /* output BMP code point */
+                } else {
+                    c=U_SENTINEL;
+                }
+            } else if(action==MBCS_STATE_VALID_16_PAIR) {
+                int32_t finalOffset=offset+MBCS_ENTRY_FINAL_VALUE_16(entry);
+                c=unicodeCodeUnits[finalOffset++];
+                if(c<0xd800) {
+                    /* output BMP code point below 0xd800 */
+                } else if(c<=0xdbff) {
+                    /* output roundtrip or fallback supplementary code point */
+                    c=((c&0x3ff)<<10)+unicodeCodeUnits[finalOffset]+(0x10000-0xdc00);
+                } else if(c==0xe000) {
+                    /* output roundtrip BMP code point above 0xd800 or fallback BMP code point */
+                    c=unicodeCodeUnits[finalOffset];
+                } else {
+                    c=U_SENTINEL;
+                }
+            } else if(action==MBCS_STATE_VALID_DIRECT_20) {
+                /* output supplementary code point */
+                c=(UChar32)(MBCS_ENTRY_FINAL_VALUE(entry)+0x10000);
+            } else {
+                c=U_SENTINEL;
+            }
+
+            codePoints[b&0x1f]=c;
+            anyCodePoints&=c;
+        }
+        if(((++b)&0x1f)==0) {
+            if(anyCodePoints>=0) {
+                if(!callback(context, value|(uint32_t)(b-0x20), codePoints)) {
+                    return FALSE;
+                }
+                anyCodePoints=-1;
+            }
+        }
+    }
+    return TRUE;
+}
+
+/*
+ * Only called if stateProps[state]==-1.
+ * A recursive call may do stateProps[state]|=0x40 if this state is the target of an
+ * MBCS_STATE_CHANGE_ONLY.
+ */
+static int8_t
+getStateProp(const int32_t (*stateTable)[256], int8_t stateProps[], int state) {
+    const int32_t *row;
+    int32_t min, max, entry, nextState;
+
+    row=stateTable[state];
+    stateProps[state]=0;
+
+    /* find first non-ignorable state */
+    for(min=0;; ++min) {
+        entry=row[min];
+        nextState=MBCS_ENTRY_STATE(entry);
+        if(stateProps[nextState]==-1) {
+            getStateProp(stateTable, stateProps, nextState);
+        }
+        if(MBCS_ENTRY_IS_TRANSITION(entry)) {
+            if(stateProps[nextState]>=0) {
+                break;
+            }
+        } else if(MBCS_ENTRY_FINAL_ACTION(entry)<MBCS_STATE_UNASSIGNED) {
+            break;
+        }
+        if(min==0xff) {
+            stateProps[state]=-0x40;  /* (int8_t)0xc0 */
+            return stateProps[state];
+        }
+    }
+    stateProps[state]|=(int8_t)((min>>5)<<3);
+
+    /* find last non-ignorable state */
+    for(max=0xff; min<max; --max) {
+        entry=row[max];
+        nextState=MBCS_ENTRY_STATE(entry);
+        if(stateProps[nextState]==-1) {
+            getStateProp(stateTable, stateProps, nextState);
+        }
+        if(MBCS_ENTRY_IS_TRANSITION(entry)) {
+            if(stateProps[nextState]>=0) {
+                break;
+            }
+        } else if(MBCS_ENTRY_FINAL_ACTION(entry)<MBCS_STATE_UNASSIGNED) {
+            break;
+        }
+    }
+    stateProps[state]|=(int8_t)(max>>5);
+
+    /* recurse further and collect direct-state information */
+    while(min<=max) {
+        entry=row[min];
+        nextState=MBCS_ENTRY_STATE(entry);
+        if(stateProps[nextState]==-1) {
+            getStateProp(stateTable, stateProps, nextState);
+        }
+        if(MBCS_ENTRY_IS_FINAL(entry)) {
+            stateProps[nextState]|=0x40;
+            if(MBCS_ENTRY_FINAL_ACTION(entry)<=MBCS_STATE_FALLBACK_DIRECT_20) {
+                stateProps[state]|=0x40;
+            }
+        }
+        ++min;
+    }
+    return stateProps[state];
+}
+
+/*
+ * Internal function enumerating the toUnicode data of an MBCS converter.
+ * Currently only used for reconstituting data for a MBCS_OPT_NO_FROM_U
+ * table, but could also be used for a future ucnv_getUnicodeSet() option
+ * that includes reverse fallbacks (after updating this function's implementation).
+ * Currently only handles roundtrip mappings.
+ * Does not currently handle extensions.
+ */
+static void
+ucnv_MBCSEnumToUnicode(UConverterMBCSTable *mbcsTable,
+                       UConverterEnumToUCallback *callback, const void *context,
+                       UErrorCode *pErrorCode) {
+    /*
+     * Properties for each state, to speed up the enumeration.
+     * Ignorable actions are unassigned/illegal/state-change-only:
+     * They do not lead to mappings.
+     *
+     * Bits 7..6:
+     * 1 direct/initial state (stateful converters have multiple)
+     * 0 non-initial state with transitions or with non-ignorable result actions
+     * -1 final state with only ignorable actions
+     *
+     * Bits 5..3:
+     * The lowest byte value with non-ignorable actions is
+     * value<<5 (rounded down).
+     *
+     * Bits 2..0:
+     * The highest byte value with non-ignorable actions is
+     * (value<<5)&0x1f (rounded up).
+     */
+    int8_t stateProps[MBCS_MAX_STATE_COUNT];
+    int32_t state;
+
+    uprv_memset(stateProps, -1, sizeof(stateProps));
+
+    /* recurse from state 0 and set all stateProps */
+    getStateProp(mbcsTable->stateTable, stateProps, 0);
+
+    for(state=0; state<mbcsTable->countStates; ++state) {
+        /*if(stateProps[state]==-1) {
+            printf("unused/unreachable <icu:state> %d\n", state);
+        }*/
+        if(stateProps[state]>=0x40) {
+            /* start from each direct state */
+            enumToU(
+                mbcsTable, stateProps, state, 0, 0,
+                callback, context,
+                pErrorCode);
+        }
+    }
+}
+
+U_CFUNC void
+ucnv_MBCSGetFilteredUnicodeSetForUnicode(const UConverterSharedData *sharedData,
+                                         const USetAdder *sa,
+                                         UConverterUnicodeSet which,
+                                         UConverterSetFilter filter,
+                                         UErrorCode *pErrorCode) {
+    const UConverterMBCSTable *mbcsTable;
+    const uint16_t *table;
+
+    uint32_t st3;
+    uint16_t st1, maxStage1, st2;
+
+    UChar32 c;
+
+    /* enumerate the from-Unicode trie table */
+    mbcsTable=&sharedData->mbcs;
+    table=mbcsTable->fromUnicodeTable;
+    if(mbcsTable->unicodeMask&UCNV_HAS_SUPPLEMENTARY) {
+        maxStage1=0x440;
+    } else {
+        maxStage1=0x40;
+    }
+
+    c=0; /* keep track of the current code point while enumerating */
+
+    if(mbcsTable->outputType==MBCS_OUTPUT_1) {
+        const uint16_t *stage2, *stage3, *results;
+        uint16_t minValue;
+
+        results=(const uint16_t *)mbcsTable->fromUnicodeBytes;
+
+        /*
+         * Set a threshold variable for selecting which mappings to use.
+         * See ucnv_MBCSSingleFromBMPWithOffsets() and
+         * MBCS_SINGLE_RESULT_FROM_U() for details.
+         */
+        if(which==UCNV_ROUNDTRIP_SET) {
+            /* use only roundtrips */
+            minValue=0xf00;
+        } else /* UCNV_ROUNDTRIP_AND_FALLBACK_SET */ {
+            /* use all roundtrip and fallback results */
+            minValue=0x800;
+        }
+
+        for(st1=0; st1<maxStage1; ++st1) {
+            st2=table[st1];
+            if(st2>maxStage1) {
+                stage2=table+st2;
+                for(st2=0; st2<64; ++st2) {
+                    if((st3=stage2[st2])!=0) {
+                        /* read the stage 3 block */
+                        stage3=results+st3;
+
+                        do {
+                            if(*stage3++>=minValue) {
+                                sa->add(sa->set, c);
+                            }
+                        } while((++c&0xf)!=0);
+                    } else {
+                        c+=16; /* empty stage 3 block */
+                    }
+                }
+            } else {
+                c+=1024; /* empty stage 2 block */
+            }
+        }
+    } else {
+        const uint32_t *stage2;
+        const uint8_t *stage3, *bytes;
+        uint32_t st3Multiplier;
+        uint32_t value;
+        UBool useFallback;
+
+        bytes=mbcsTable->fromUnicodeBytes;
+
+        useFallback=(UBool)(which==UCNV_ROUNDTRIP_AND_FALLBACK_SET);
+
+        switch(mbcsTable->outputType) {
+        case MBCS_OUTPUT_3:
+        case MBCS_OUTPUT_4_EUC:
+            st3Multiplier=3;
+            break;
+        case MBCS_OUTPUT_4:
+            st3Multiplier=4;
+            break;
+        default:
+            st3Multiplier=2;
+            break;
+        }
+
+        for(st1=0; st1<maxStage1; ++st1) {
+            st2=table[st1];
+            if(st2>(maxStage1>>1)) {
+                stage2=(const uint32_t *)table+st2;
+                for(st2=0; st2<64; ++st2) {
+                    if((st3=stage2[st2])!=0) {
+                        /* read the stage 3 block */
+                        stage3=bytes+st3Multiplier*16*(uint32_t)(uint16_t)st3;
+
+                        /* get the roundtrip flags for the stage 3 block */
+                        st3>>=16;
+
+                        /*
+                         * Add code points for which the roundtrip flag is set,
+                         * or which map to non-zero bytes if we use fallbacks.
+                         * See ucnv_MBCSFromUnicodeWithOffsets() for details.
+                         */
+                        switch(filter) {
+                        case UCNV_SET_FILTER_NONE:
+                            do {
+                                if(st3&1) {
+                                    sa->add(sa->set, c);
+                                    stage3+=st3Multiplier;
+                                } else if(useFallback) {
+                                    uint8_t b=0;
+                                    switch(st3Multiplier) {
+                                    case 4:
+                                        b|=*stage3++;
+                                    case 3:
+                                        b|=*stage3++;
+                                    case 2:
+                                        b|=stage3[0]|stage3[1];
+                                        stage3+=2;
+                                    default:
+                                        break;
+                                    }
+                                    if(b!=0) {
+                                        sa->add(sa->set, c);
+                                    }
+                                }
+                                st3>>=1;
+                            } while((++c&0xf)!=0);
+                            break;
+                        case UCNV_SET_FILTER_DBCS_ONLY:
+                             /* Ignore single-byte results (<0x100). */
+                            do {
+                                if(((st3&1)!=0 || useFallback) && *((const uint16_t *)stage3)>=0x100) {
+                                    sa->add(sa->set, c);
+                                }
+                                st3>>=1;
+                                stage3+=2;  /* +=st3Multiplier */
+                            } while((++c&0xf)!=0);
+                            break;
+                        case UCNV_SET_FILTER_2022_CN:
+                             /* Only add code points that map to CNS 11643 planes 1 & 2 for non-EXT ISO-2022-CN. */
+                            do {
+                                if(((st3&1)!=0 || useFallback) && ((value=*stage3)==0x81 || value==0x82)) {
+                                    sa->add(sa->set, c);
+                                }
+                                st3>>=1;
+                                stage3+=3;  /* +=st3Multiplier */
+                            } while((++c&0xf)!=0);
+                            break;
+                        case UCNV_SET_FILTER_SJIS:
+                             /* Only add code points that map to Shift-JIS codes corresponding to JIS X 0208. */
+                            do {
+                                if(((st3&1)!=0 || useFallback) && (value=*((const uint16_t *)stage3))>=0x8140 && value<=0xeffc) {
+                                    sa->add(sa->set, c);
+                                }
+                                st3>>=1;
+                                stage3+=2;  /* +=st3Multiplier */
+                            } while((++c&0xf)!=0);
+                            break;
+                        case UCNV_SET_FILTER_GR94DBCS:
+                            /* Only add code points that map to ISO 2022 GR 94 DBCS codes (each byte A1..FE). */
+                            do {
+                                if( ((st3&1)!=0 || useFallback) &&
+                                    (uint16_t)((value=*((const uint16_t *)stage3)) - 0xa1a1)<=(0xfefe - 0xa1a1) &&
+                                    (uint8_t)(value-0xa1)<=(0xfe - 0xa1)
+                                ) {
+                                    sa->add(sa->set, c);
+                                }
+                                st3>>=1;
+                                stage3+=2;  /* +=st3Multiplier */
+                            } while((++c&0xf)!=0);
+                            break;
+                        case UCNV_SET_FILTER_HZ:
+                            /* Only add code points that are suitable for HZ DBCS (lead byte A1..FD). */
+                            do {
+                                if( ((st3&1)!=0 || useFallback) &&
+                                    (uint16_t)((value=*((const uint16_t *)stage3))-0xa1a1)<=(0xfdfe - 0xa1a1) &&
+                                    (uint8_t)(value-0xa1)<=(0xfe - 0xa1)
+                                ) {
+                                    sa->add(sa->set, c);
+                                }
+                                st3>>=1;
+                                stage3+=2;  /* +=st3Multiplier */
+                            } while((++c&0xf)!=0);
+                            break;
+                        default:
+                            *pErrorCode=U_INTERNAL_PROGRAM_ERROR;
+                            return;
+                        }
+                    } else {
+                        c+=16; /* empty stage 3 block */
+                    }
+                }
+            } else {
+                c+=1024; /* empty stage 2 block */
+            }
+        }
+    }
+
+    ucnv_extGetUnicodeSet(sharedData, sa, which, filter, pErrorCode);
+}
+
+U_CFUNC void
+ucnv_MBCSGetUnicodeSetForUnicode(const UConverterSharedData *sharedData,
+                                 const USetAdder *sa,
+                                 UConverterUnicodeSet which,
+                                 UErrorCode *pErrorCode) {
+    ucnv_MBCSGetFilteredUnicodeSetForUnicode(
+        sharedData, sa, which,
+        sharedData->mbcs.outputType==MBCS_OUTPUT_DBCS_ONLY ?
+            UCNV_SET_FILTER_DBCS_ONLY :
+            UCNV_SET_FILTER_NONE,
+        pErrorCode);
+}
+
+static void
+ucnv_MBCSGetUnicodeSet(const UConverter *cnv,
+                   const USetAdder *sa,
+                   UConverterUnicodeSet which,
+                   UErrorCode *pErrorCode) {
+    if(cnv->options&_MBCS_OPTION_GB18030) {
+        sa->addRange(sa->set, 0, 0xd7ff);
+        sa->addRange(sa->set, 0xe000, 0x10ffff);
+    } else {
+        ucnv_MBCSGetUnicodeSetForUnicode(cnv->sharedData, sa, which, pErrorCode);
+    }
+}
+
+/* conversion extensions for input not in the main table -------------------- */
+
+/*
+ * Hardcoded extension handling for GB 18030.
+ * Definition of LINEAR macros and gb18030Ranges see near the beginning of the file.
+ *
+ * In the future, conversion extensions may handle m:n mappings and delta tables,
+ * see http://source.icu-project.org/repos/icu/icuhtml/trunk/design/conversion/conversion_extensions.html
+ *
+ * If an input character cannot be mapped, then these functions set an error
+ * code. The framework will then call the callback function.
+ */
+
+/*
+ * @return if(U_FAILURE) return the code point for cnv->fromUChar32
+ *         else return 0 after output has been written to the target
+ */
+static UChar32
+_extFromU(UConverter *cnv, const UConverterSharedData *sharedData,
+          UChar32 cp,
+          const UChar **source, const UChar *sourceLimit,
+          uint8_t **target, const uint8_t *targetLimit,
+          int32_t **offsets, int32_t sourceIndex,
+          UBool flush,
+          UErrorCode *pErrorCode) {
+    const int32_t *cx;
+
+    cnv->useSubChar1=FALSE;
+
+    if( (cx=sharedData->mbcs.extIndexes)!=NULL &&
+        ucnv_extInitialMatchFromU(
+            cnv, cx,
+            cp, source, sourceLimit,
+            (char **)target, (char *)targetLimit,
+            offsets, sourceIndex,
+            flush,
+            pErrorCode)
+    ) {
+        return 0; /* an extension mapping handled the input */
+    }
+
+    /* GB 18030 */
+    if((cnv->options&_MBCS_OPTION_GB18030)!=0) {
+        const uint32_t *range;
+        int32_t i;
+
+        range=gb18030Ranges[0];
+        for(i=0; i<sizeof(gb18030Ranges)/sizeof(gb18030Ranges[0]); range+=4, ++i) {
+            if(range[0]<=(uint32_t)cp && (uint32_t)cp<=range[1]) {
+                /* found the Unicode code point, output the four-byte sequence for it */
+                uint32_t linear;
+                char bytes[4];
+
+                /* get the linear value of the first GB 18030 code in this range */
+                linear=range[2]-LINEAR_18030_BASE;
+
+                /* add the offset from the beginning of the range */
+                linear+=((uint32_t)cp-range[0]);
+
+                /* turn this into a four-byte sequence */
+                bytes[3]=(char)(0x30+linear%10); linear/=10;
+                bytes[2]=(char)(0x81+linear%126); linear/=126;
+                bytes[1]=(char)(0x30+linear%10); linear/=10;
+                bytes[0]=(char)(0x81+linear);
+
+                /* output this sequence */
+                ucnv_fromUWriteBytes(cnv,
+                                     bytes, 4, (char **)target, (char *)targetLimit,
+                                     offsets, sourceIndex, pErrorCode);
+                return 0;
+            }
+        }
+    }
+
+    /* no mapping */
+    *pErrorCode=U_INVALID_CHAR_FOUND;
+    return cp;
+}
+
+/*
+ * Input sequence: cnv->toUBytes[0..length[
+ * @return if(U_FAILURE) return the length (toULength, byteIndex) for the input
+ *         else return 0 after output has been written to the target
+ */
+static int8_t
+_extToU(UConverter *cnv, const UConverterSharedData *sharedData,
+        int8_t length,
+        const uint8_t **source, const uint8_t *sourceLimit,
+        UChar **target, const UChar *targetLimit,
+        int32_t **offsets, int32_t sourceIndex,
+        UBool flush,
+        UErrorCode *pErrorCode) {
+    const int32_t *cx;
+
+    if( (cx=sharedData->mbcs.extIndexes)!=NULL &&
+        ucnv_extInitialMatchToU(
+            cnv, cx,
+            length, (const char **)source, (const char *)sourceLimit,
+            target, targetLimit,
+            offsets, sourceIndex,
+            flush,
+            pErrorCode)
+    ) {
+        return 0; /* an extension mapping handled the input */
+    }
+
+    /* GB 18030 */
+    if(length==4 && (cnv->options&_MBCS_OPTION_GB18030)!=0) {
+        const uint32_t *range;
+        uint32_t linear;
+        int32_t i;
+
+        linear=LINEAR_18030(cnv->toUBytes[0], cnv->toUBytes[1], cnv->toUBytes[2], cnv->toUBytes[3]);
+        range=gb18030Ranges[0];
+        for(i=0; i<sizeof(gb18030Ranges)/sizeof(gb18030Ranges[0]); range+=4, ++i) {
+            if(range[2]<=linear && linear<=range[3]) {
+                /* found the sequence, output the Unicode code point for it */
+                *pErrorCode=U_ZERO_ERROR;
+
+                /* add the linear difference between the input and start sequences to the start code point */
+                linear=range[0]+(linear-range[2]);
+
+                /* output this code point */
+                ucnv_toUWriteCodePoint(cnv, linear, target, targetLimit, offsets, sourceIndex, pErrorCode);
+
+                return 0;
+            }
+        }
+    }
+
+    /* no mapping */
+    *pErrorCode=U_INVALID_CHAR_FOUND;
+    return length;
+}
+
+/* EBCDIC swap LF<->NL ------------------------------------------------------ */
+
+/*
+ * This code modifies a standard EBCDIC<->Unicode mapping table for
+ * OS/390 (z/OS) Unix System Services (Open Edition).
+ * The difference is in the mapping of Line Feed and New Line control codes:
+ * Standard EBCDIC maps
+ *
+ *   <U000A> \x25 |0
+ *   <U0085> \x15 |0
+ *
+ * but OS/390 USS EBCDIC swaps the control codes for LF and NL,
+ * mapping
+ *
+ *   <U000A> \x15 |0
+ *   <U0085> \x25 |0
+ *
+ * This code modifies a loaded standard EBCDIC<->Unicode mapping table
+ * by copying it into allocated memory and swapping the LF and NL values.
+ * It allows to support the same EBCDIC charset in both versions without
+ * duplicating the entire installed table.
+ */
+
+/* standard EBCDIC codes */
+#define EBCDIC_LF 0x25
+#define EBCDIC_NL 0x15
+
+/* standard EBCDIC codes with roundtrip flag as stored in Unicode-to-single-byte tables */
+#define EBCDIC_RT_LF 0xf25
+#define EBCDIC_RT_NL 0xf15
+
+/* Unicode code points */
+#define U_LF 0x0a
+#define U_NL 0x85
+
+static UBool
+_EBCDICSwapLFNL(UConverterSharedData *sharedData, UErrorCode *pErrorCode) {
+    UConverterMBCSTable *mbcsTable;
+
+    const uint16_t *table, *results;
+    const uint8_t *bytes;
+
+    int32_t (*newStateTable)[256];
+    uint16_t *newResults;
+    uint8_t *p;
+    char *name;
+
+    uint32_t stage2Entry;
+    uint32_t size, sizeofFromUBytes;
+
+    mbcsTable=&sharedData->mbcs;
+
+    table=mbcsTable->fromUnicodeTable;
+    bytes=mbcsTable->fromUnicodeBytes;
+    results=(const uint16_t *)bytes;
+
+    /*
+     * Check that this is an EBCDIC table with SBCS portion -
+     * SBCS or EBCDIC_STATEFUL with standard EBCDIC LF and NL mappings.
+     *
+     * If not, ignore the option. Options are always ignored if they do not apply.
+     */
+    if(!(
+         (mbcsTable->outputType==MBCS_OUTPUT_1 || mbcsTable->outputType==MBCS_OUTPUT_2_SISO) &&
+         mbcsTable->stateTable[0][EBCDIC_LF]==MBCS_ENTRY_FINAL(0, MBCS_STATE_VALID_DIRECT_16, U_LF) &&
+         mbcsTable->stateTable[0][EBCDIC_NL]==MBCS_ENTRY_FINAL(0, MBCS_STATE_VALID_DIRECT_16, U_NL)
+    )) {
+        return FALSE;
+    }
+
+    if(mbcsTable->outputType==MBCS_OUTPUT_1) {
+        if(!(
+             EBCDIC_RT_LF==MBCS_SINGLE_RESULT_FROM_U(table, results, U_LF) &&
+             EBCDIC_RT_NL==MBCS_SINGLE_RESULT_FROM_U(table, results, U_NL)
+        )) {
+            return FALSE;
+        }
+    } else /* MBCS_OUTPUT_2_SISO */ {
+        stage2Entry=MBCS_STAGE_2_FROM_U(table, U_LF);
+        if(!(
+             MBCS_FROM_U_IS_ROUNDTRIP(stage2Entry, U_LF)!=0 &&
+             EBCDIC_LF==MBCS_VALUE_2_FROM_STAGE_2(bytes, stage2Entry, U_LF)
+        )) {
+            return FALSE;
+        }
+
+        stage2Entry=MBCS_STAGE_2_FROM_U(table, U_NL);
+        if(!(
+             MBCS_FROM_U_IS_ROUNDTRIP(stage2Entry, U_NL)!=0 &&
+             EBCDIC_NL==MBCS_VALUE_2_FROM_STAGE_2(bytes, stage2Entry, U_NL)
+        )) {
+            return FALSE;
+        }
+    }
+
+    if(mbcsTable->fromUBytesLength>0) {
+        /*
+         * We _know_ the number of bytes in the fromUnicodeBytes array
+         * starting with header.version 4.1.
+         */
+        sizeofFromUBytes=mbcsTable->fromUBytesLength;
+    } else {
+        /*
+         * Otherwise:
+         * There used to be code to enumerate the fromUnicode
+         * trie and find the highest entry, but it was removed in ICU 3.2
+         * because it was not tested and caused a low code coverage number.
+         * See Jitterbug 3674.
+         * This affects only some .cnv file formats with a header.version
+         * below 4.1, and only when swaplfnl is requested.
+         *
+         * ucnvmbcs.c revision 1.99 is the last one with the
+         * ucnv_MBCSSizeofFromUBytes() function.
+         */
+        *pErrorCode=U_INVALID_FORMAT_ERROR;
+        return FALSE;
+    }
+
+    /*
+     * The table has an appropriate format.
+     * Allocate and build
+     * - a modified to-Unicode state table
+     * - a modified from-Unicode output array
+     * - a converter name string with the swap option appended
+     */
+    size=
+        mbcsTable->countStates*1024+
+        sizeofFromUBytes+
+        UCNV_MAX_CONVERTER_NAME_LENGTH+20;
+    p=(uint8_t *)uprv_malloc(size);
+    if(p==NULL) {
+        *pErrorCode=U_MEMORY_ALLOCATION_ERROR;
+        return FALSE;
+    }
+
+    /* copy and modify the to-Unicode state table */
+    newStateTable=(int32_t (*)[256])p;
+    uprv_memcpy(newStateTable, mbcsTable->stateTable, mbcsTable->countStates*1024);
+
+    newStateTable[0][EBCDIC_LF]=MBCS_ENTRY_FINAL(0, MBCS_STATE_VALID_DIRECT_16, U_NL);
+    newStateTable[0][EBCDIC_NL]=MBCS_ENTRY_FINAL(0, MBCS_STATE_VALID_DIRECT_16, U_LF);
+
+    /* copy and modify the from-Unicode result table */
+    newResults=(uint16_t *)newStateTable[mbcsTable->countStates];
+    uprv_memcpy(newResults, bytes, sizeofFromUBytes);
+
+    /* conveniently, the table access macros work on the left side of expressions */
+    if(mbcsTable->outputType==MBCS_OUTPUT_1) {
+        MBCS_SINGLE_RESULT_FROM_U(table, newResults, U_LF)=EBCDIC_RT_NL;
+        MBCS_SINGLE_RESULT_FROM_U(table, newResults, U_NL)=EBCDIC_RT_LF;
+    } else /* MBCS_OUTPUT_2_SISO */ {
+        stage2Entry=MBCS_STAGE_2_FROM_U(table, U_LF);
+        MBCS_VALUE_2_FROM_STAGE_2(newResults, stage2Entry, U_LF)=EBCDIC_NL;
+
+        stage2Entry=MBCS_STAGE_2_FROM_U(table, U_NL);
+        MBCS_VALUE_2_FROM_STAGE_2(newResults, stage2Entry, U_NL)=EBCDIC_LF;
+    }
+
+    /* set the canonical converter name */
+    name=(char *)newResults+sizeofFromUBytes;
+    uprv_strcpy(name, sharedData->staticData->name);
+    uprv_strcat(name, UCNV_SWAP_LFNL_OPTION_STRING);
+
+    /* set the pointers */
+    umtx_lock(NULL);
+    if(mbcsTable->swapLFNLStateTable==NULL) {
+        mbcsTable->swapLFNLStateTable=newStateTable;
+        mbcsTable->swapLFNLFromUnicodeBytes=(uint8_t *)newResults;
+        mbcsTable->swapLFNLName=name;
+
+        newStateTable=NULL;
+    }
+    umtx_unlock(NULL);
+
+    /* release the allocated memory if another thread beat us to it */
+    if(newStateTable!=NULL) {
+        uprv_free(newStateTable);
+    }
+    return TRUE;
+}
+
+/* reconstitute omitted fromUnicode data ------------------------------------ */
+
+/* for details, compare with genmbcs.c MBCSAddFromUnicode() and transformEUC() */
+static UBool U_CALLCONV
+writeStage3Roundtrip(const void *context, uint32_t value, UChar32 codePoints[32]) {
+    UConverterMBCSTable *mbcsTable=(UConverterMBCSTable *)context;
+    const uint16_t *table;
+    uint32_t *stage2;
+    uint8_t *bytes, *p;
+    UChar32 c;
+    int32_t i, st3;
+
+    table=mbcsTable->fromUnicodeTable;
+    bytes=(uint8_t *)mbcsTable->fromUnicodeBytes;
+
+    /* for EUC outputTypes, modify the value like genmbcs.c's transformEUC() */
+    switch(mbcsTable->outputType) {
+    case MBCS_OUTPUT_3_EUC:
+        if(value<=0xffff) {
+            /* short sequences are stored directly */
+            /* code set 0 or 1 */
+        } else if(value<=0x8effff) {
+            /* code set 2 */
+            value&=0x7fff;
+        } else /* first byte is 0x8f */ {
+            /* code set 3 */
+            value&=0xff7f;
+        }
+        break;
+    case MBCS_OUTPUT_4_EUC:
+        if(value<=0xffffff) {
+            /* short sequences are stored directly */
+            /* code set 0 or 1 */
+        } else if(value<=0x8effffff) {
+            /* code set 2 */
+            value&=0x7fffff;
+        } else /* first byte is 0x8f */ {
+            /* code set 3 */
+            value&=0xff7fff;
+        }
+        break;
+    default:
+        break;
+    }
+
+    for(i=0; i<=0x1f; ++value, ++i) {
+        c=codePoints[i];
+        if(c<0) {
+            continue;
+        }
+
+        /* locate the stage 2 & 3 data */
+        stage2=((uint32_t *)table)+table[c>>10]+((c>>4)&0x3f);
+        p=bytes;
+        st3=(int32_t)(uint16_t)*stage2*16+(c&0xf);
+
+        /* write the codepage bytes into stage 3 */
+        switch(mbcsTable->outputType) {
+        case MBCS_OUTPUT_3:
+        case MBCS_OUTPUT_4_EUC:
+            p+=st3*3;
+            p[0]=(uint8_t)(value>>16);
+            p[1]=(uint8_t)(value>>8);
+            p[2]=(uint8_t)value;
+            break;
+        case MBCS_OUTPUT_4:
+            ((uint32_t *)p)[st3]=value;
+            break;
+        default:
+            /* 2 bytes per character */
+            ((uint16_t *)p)[st3]=(uint16_t)value;
+            break;
+        }
+
+        /* set the roundtrip flag */
+        *stage2|=(1UL<<(16+(c&0xf)));
+    }
+    return TRUE;
+ }
+
+static void
+reconstituteData(UConverterMBCSTable *mbcsTable,
+                 uint32_t stage1Length, uint32_t stage2Length,
+                 uint32_t fullStage2Length,  /* lengths are numbers of units, not bytes */
+                 UErrorCode *pErrorCode) {
+    uint16_t *stage1;
+    uint32_t *stage2;
+    uint8_t *bytes;
+    uint32_t dataLength=stage1Length*2+fullStage2Length*4+mbcsTable->fromUBytesLength;
+    mbcsTable->reconstitutedData=(uint8_t *)uprv_malloc(dataLength);
+    if(mbcsTable->reconstitutedData==NULL) {
+        *pErrorCode=U_MEMORY_ALLOCATION_ERROR;
+        return;
+    }
+    uprv_memset(mbcsTable->reconstitutedData, 0, dataLength);
+
+    /* copy existing data and reroute the pointers */
+    stage1=(uint16_t *)mbcsTable->reconstitutedData;
+    uprv_memcpy(stage1, mbcsTable->fromUnicodeTable, stage1Length*2);
+
+    stage2=(uint32_t *)(stage1+stage1Length);
+    uprv_memcpy(stage2+(fullStage2Length-stage2Length),
+                mbcsTable->fromUnicodeTable+stage1Length,
+                stage2Length*4);
+
+    mbcsTable->fromUnicodeTable=stage1;
+    mbcsTable->fromUnicodeBytes=bytes=(uint8_t *)(stage2+fullStage2Length);
+
+    /* indexes into stage 2 count from the bottom of the fromUnicodeTable */
+    stage2=(uint32_t *)stage1;
+
+    /* reconstitute the initial part of stage 2 from the mbcsIndex */
+    {
+        int32_t stageUTF8Length=((int32_t)mbcsTable->maxFastUChar+1)>>6;
+        int32_t stageUTF8Index=0;
+        int32_t st1, st2, st3, i;
+
+        for(st1=0; stageUTF8Index<stageUTF8Length; ++st1) {
+            st2=stage1[st1];
+            if(st2!=stage1Length/2) {
+                /* each stage 2 block has 64 entries corresponding to 16 entries in the mbcsIndex */
+                for(i=0; i<16; ++i) {
+                    st3=mbcsTable->mbcsIndex[stageUTF8Index++];
+                    if(st3!=0) {
+                        /* an stage 2 entry's index is per stage 3 16-block, not per stage 3 entry */
+                        st3>>=4;
+                        /*
+                         * 4 stage 2 entries point to 4 consecutive stage 3 16-blocks which are
+                         * allocated together as a single 64-block for access from the mbcsIndex
+                         */
+                        stage2[st2++]=st3++;
+                        stage2[st2++]=st3++;
+                        stage2[st2++]=st3++;
+                        stage2[st2++]=st3;
+                    } else {
+                        /* no stage 3 block, skip */
+                        st2+=4;
+                    }
+                }
+            } else {
+                /* no stage 2 block, skip */
+                stageUTF8Index+=16;
+            }
+        }
+    }
+
+    /* reconstitute fromUnicodeBytes with roundtrips from toUnicode data */
+    ucnv_MBCSEnumToUnicode(mbcsTable, writeStage3Roundtrip, mbcsTable, pErrorCode);
+}
+
+/* MBCS setup functions ----------------------------------------------------- */
+
+static void
+ucnv_MBCSLoad(UConverterSharedData *sharedData,
+          UConverterLoadArgs *pArgs,
+          const uint8_t *raw,
+          UErrorCode *pErrorCode) {
+    UDataInfo info;
+    UConverterMBCSTable *mbcsTable=&sharedData->mbcs;
+    _MBCSHeader *header=(_MBCSHeader *)raw;
+    uint32_t offset;
+    uint32_t headerLength;
+    UBool noFromU=FALSE;
+
+    if(header->version[0]==4) {
+        headerLength=MBCS_HEADER_V4_LENGTH;
+    } else if(header->version[0]==5 && header->version[1]>=3 &&
+              (header->options&MBCS_OPT_UNKNOWN_INCOMPATIBLE_MASK)==0) {
+        headerLength=header->options&MBCS_OPT_LENGTH_MASK;
+        noFromU=(UBool)((header->options&MBCS_OPT_NO_FROM_U)!=0);
+    } else {
+        *pErrorCode=U_INVALID_TABLE_FORMAT;
+        return;
+    }
+
+    mbcsTable->outputType=(uint8_t)header->flags;
+    if(noFromU && mbcsTable->outputType==MBCS_OUTPUT_1) {
+        *pErrorCode=U_INVALID_TABLE_FORMAT;
+        return;
+    }
+
+    /* extension data, header version 4.2 and higher */
+    offset=header->flags>>8;
+    if(offset!=0) {
+        mbcsTable->extIndexes=(const int32_t *)(raw+offset);
+    }
+
+    if(mbcsTable->outputType==MBCS_OUTPUT_EXT_ONLY) {
+        UConverterLoadArgs args={ 0 };
+        UConverterSharedData *baseSharedData;
+        const int32_t *extIndexes;
+        const char *baseName;
+
+        /* extension-only file, load the base table and set values appropriately */
+        if((extIndexes=mbcsTable->extIndexes)==NULL) {
+            /* extension-only file without extension */
+            *pErrorCode=U_INVALID_TABLE_FORMAT;
+            return;
+        }
+
+        if(pArgs->nestedLoads!=1) {
+            /* an extension table must not be loaded as a base table */
+            *pErrorCode=U_INVALID_TABLE_FILE;
+            return;
+        }
+
+        /* load the base table */
+        baseName=(const char *)header+headerLength*4;
+        if(0==uprv_strcmp(baseName, sharedData->staticData->name)) {
+            /* forbid loading this same extension-only file */
+            *pErrorCode=U_INVALID_TABLE_FORMAT;
+            return;
+        }
+
+        /* TODO parse package name out of the prefix of the base name in the extension .cnv file? */
+        args.size=sizeof(UConverterLoadArgs);
+        args.nestedLoads=2;
+        args.onlyTestIsLoadable=pArgs->onlyTestIsLoadable;
+        args.reserved=pArgs->reserved;
+        args.options=pArgs->options;
+        args.pkg=pArgs->pkg;
+        args.name=baseName;
+        baseSharedData=ucnv_load(&args, pErrorCode);
+        if(U_FAILURE(*pErrorCode)) {
+            return;
+        }
+        if( baseSharedData->staticData->conversionType!=UCNV_MBCS ||
+            baseSharedData->mbcs.baseSharedData!=NULL
+        ) {
+            ucnv_unload(baseSharedData);
+            *pErrorCode=U_INVALID_TABLE_FORMAT;
+            return;
+        }
+        if(pArgs->onlyTestIsLoadable) {
+            /*
+             * Exit as soon as we know that we can load the converter
+             * and the format is valid and supported.
+             * The worst that can happen in the following code is a memory
+             * allocation error.
+             */
+            ucnv_unload(baseSharedData);
+            return;
+        }
+
+        /* copy the base table data */
+        uprv_memcpy(mbcsTable, &baseSharedData->mbcs, sizeof(UConverterMBCSTable));
+
+        /* overwrite values with relevant ones for the extension converter */
+        mbcsTable->baseSharedData=baseSharedData;
+        mbcsTable->extIndexes=extIndexes;
+
+        /*
+         * It would be possible to share the swapLFNL data with a base converter,
+         * but the generated name would have to be different, and the memory
+         * would have to be free'd only once.
+         * It is easier to just create the data for the extension converter
+         * separately when it is requested.
+         */
+        mbcsTable->swapLFNLStateTable=NULL;
+        mbcsTable->swapLFNLFromUnicodeBytes=NULL;
+        mbcsTable->swapLFNLName=NULL;
+
+        /*
+         * The reconstitutedData must be deleted only when the base converter
+         * is unloaded.
+         */
+        mbcsTable->reconstitutedData=NULL;
+
+        /*
+         * Set a special, runtime-only outputType if the extension converter
+         * is a DBCS version of a base converter that also maps single bytes.
+         */
+        if( sharedData->staticData->conversionType==UCNV_DBCS ||
+                (sharedData->staticData->conversionType==UCNV_MBCS &&
+                 sharedData->staticData->minBytesPerChar>=2)
+        ) {
+            if(baseSharedData->mbcs.outputType==MBCS_OUTPUT_2_SISO) {
+                /* the base converter is SI/SO-stateful */
+                int32_t entry;
+
+                /* get the dbcs state from the state table entry for SO=0x0e */
+                entry=mbcsTable->stateTable[0][0xe];
+                if( MBCS_ENTRY_IS_FINAL(entry) &&
+                    MBCS_ENTRY_FINAL_ACTION(entry)==MBCS_STATE_CHANGE_ONLY &&
+                    MBCS_ENTRY_FINAL_STATE(entry)!=0
+                ) {
+                    mbcsTable->dbcsOnlyState=(uint8_t)MBCS_ENTRY_FINAL_STATE(entry);
+
+                    mbcsTable->outputType=MBCS_OUTPUT_DBCS_ONLY;
+                }
+            } else if(
+                baseSharedData->staticData->conversionType==UCNV_MBCS &&
+                baseSharedData->staticData->minBytesPerChar==1 &&
+                baseSharedData->staticData->maxBytesPerChar==2 &&
+                mbcsTable->countStates<=127
+            ) {
+                /* non-stateful base converter, need to modify the state table */
+                int32_t (*newStateTable)[256];
+                int32_t *state;
+                int32_t i, count;
+
+                /* allocate a new state table and copy the base state table contents */
+                count=mbcsTable->countStates;
+                newStateTable=(int32_t (*)[256])uprv_malloc((count+1)*1024);
+                if(newStateTable==NULL) {
+                    ucnv_unload(baseSharedData);
+                    *pErrorCode=U_MEMORY_ALLOCATION_ERROR;
+                    return;
+                }
+
+                uprv_memcpy(newStateTable, mbcsTable->stateTable, count*1024);
+
+                /* change all final single-byte entries to go to a new all-illegal state */
+                state=newStateTable[0];
+                for(i=0; i<256; ++i) {
+                    if(MBCS_ENTRY_IS_FINAL(state[i])) {
+                        state[i]=MBCS_ENTRY_TRANSITION(count, 0);
+                    }
+                }
+
+                /* build the new all-illegal state */
+                state=newStateTable[count];
+                for(i=0; i<256; ++i) {
+                    state[i]=MBCS_ENTRY_FINAL(0, MBCS_STATE_ILLEGAL, 0);
+                }
+                mbcsTable->stateTable=(const int32_t (*)[256])newStateTable;
+                mbcsTable->countStates=(uint8_t)(count+1);
+                mbcsTable->stateTableOwned=TRUE;
+
+                mbcsTable->outputType=MBCS_OUTPUT_DBCS_ONLY;
+            }
+        }
+
+        /*
+         * unlike below for files with base tables, do not get the unicodeMask
+         * from the sharedData; instead, use the base table's unicodeMask,
+         * which we copied in the memcpy above;
+         * this is necessary because the static data unicodeMask, especially
+         * the UCNV_HAS_SUPPLEMENTARY flag, is part of the base table data
+         */
+    } else {
+        /* conversion file with a base table; an additional extension table is optional */
+        /* make sure that the output type is known */
+        switch(mbcsTable->outputType) {
+        case MBCS_OUTPUT_1:
+        case MBCS_OUTPUT_2:
+        case MBCS_OUTPUT_3:
+        case MBCS_OUTPUT_4:
+        case MBCS_OUTPUT_3_EUC:
+        case MBCS_OUTPUT_4_EUC:
+        case MBCS_OUTPUT_2_SISO:
+            /* OK */
+            break;
+        default:
+            *pErrorCode=U_INVALID_TABLE_FORMAT;
+            return;
+        }
+        if(pArgs->onlyTestIsLoadable) {
+            /*
+             * Exit as soon as we know that we can load the converter
+             * and the format is valid and supported.
+             * The worst that can happen in the following code is a memory
+             * allocation error.
+             */
+            return;
+        }
+
+        mbcsTable->countStates=(uint8_t)header->countStates;
+        mbcsTable->countToUFallbacks=header->countToUFallbacks;
+        mbcsTable->stateTable=(const int32_t (*)[256])(raw+headerLength*4);
+        mbcsTable->toUFallbacks=(const _MBCSToUFallback *)(mbcsTable->stateTable+header->countStates);
+        mbcsTable->unicodeCodeUnits=(const uint16_t *)(raw+header->offsetToUCodeUnits);
+
+        mbcsTable->fromUnicodeTable=(const uint16_t *)(raw+header->offsetFromUTable);
+        mbcsTable->fromUnicodeBytes=(const uint8_t *)(raw+header->offsetFromUBytes);
+        mbcsTable->fromUBytesLength=header->fromUBytesLength;
+
+        /*
+         * converter versions 6.1 and up contain a unicodeMask that is
+         * used here to select the most efficient function implementations
+         */
+        info.size=sizeof(UDataInfo);
+        udata_getInfo((UDataMemory *)sharedData->dataMemory, &info);
+        if(info.formatVersion[0]>6 || (info.formatVersion[0]==6 && info.formatVersion[1]>=1)) {
+            /* mask off possible future extensions to be safe */
+            mbcsTable->unicodeMask=(uint8_t)(sharedData->staticData->unicodeMask&3);
+        } else {
+            /* for older versions, assume worst case: contains anything possible (prevent over-optimizations) */
+            mbcsTable->unicodeMask=UCNV_HAS_SUPPLEMENTARY|UCNV_HAS_SURROGATES;
+        }
+
+        /*
+         * _MBCSHeader.version 4.3 adds utf8Friendly data structures.
+         * Check for the header version, SBCS vs. MBCS, and for whether the
+         * data structures are optimized for code points as high as what the
+         * runtime code is designed for.
+         * The implementation does not handle mapping tables with entries for
+         * unpaired surrogates.
+         */
+        if( header->version[1]>=3 &&
+            (mbcsTable->unicodeMask&UCNV_HAS_SURROGATES)==0 &&
+            (mbcsTable->countStates==1 ?
+                (header->version[2]>=(SBCS_FAST_MAX>>8)) :
+                (header->version[2]>=(MBCS_FAST_MAX>>8))
+            )
+        ) {
+            mbcsTable->utf8Friendly=TRUE;
+
+            if(mbcsTable->countStates==1) {
+                /*
+                 * SBCS: Stage 3 is allocated in 64-entry blocks for U+0000..SBCS_FAST_MAX or higher.
+                 * Build a table with indexes to each block, to be used instead of
+                 * the regular stage 1/2 table.
+                 */
+                int32_t i;
+                for(i=0; i<(SBCS_FAST_LIMIT>>6); ++i) {
+                    mbcsTable->sbcsIndex[i]=mbcsTable->fromUnicodeTable[mbcsTable->fromUnicodeTable[i>>4]+((i<<2)&0x3c)];
+                }
+                /* set SBCS_FAST_MAX to reflect the reach of sbcsIndex[] even if header->version[2]>(SBCS_FAST_MAX>>8) */
+                mbcsTable->maxFastUChar=SBCS_FAST_MAX;
+            } else {
+                /*
+                 * MBCS: Stage 3 is allocated in 64-entry blocks for U+0000..MBCS_FAST_MAX or higher.
+                 * The .cnv file is prebuilt with an additional stage table with indexes
+                 * to each block.
+                 */
+                mbcsTable->mbcsIndex=(const uint16_t *)
+                    (mbcsTable->fromUnicodeBytes+
+                     (noFromU ? 0 : mbcsTable->fromUBytesLength));
+                mbcsTable->maxFastUChar=(((UChar)header->version[2])<<8)|0xff;
+            }
+        }
+
+        /* calculate a bit set of 4 ASCII characters per bit that round-trip to ASCII bytes */
+        {
+            uint32_t asciiRoundtrips=0xffffffff;
+            int32_t i;
+
+            for(i=0; i<0x80; ++i) {
+                if(mbcsTable->stateTable[0][i]!=MBCS_ENTRY_FINAL(0, MBCS_STATE_VALID_DIRECT_16, i)) {
+                    asciiRoundtrips&=~((uint32_t)1<<(i>>2));
+                }
+            }
+            mbcsTable->asciiRoundtrips=asciiRoundtrips;
+        }
+
+        if(noFromU) {
+            uint32_t stage1Length=
+                mbcsTable->unicodeMask&UCNV_HAS_SUPPLEMENTARY ?
+                    0x440 : 0x40;
+            uint32_t stage2Length=
+                (header->offsetFromUBytes-header->offsetFromUTable)/4-
+                stage1Length/2;
+            reconstituteData(mbcsTable, stage1Length, stage2Length, header->fullStage2Length, pErrorCode);
+        }
+    }
+
+    /* Set the impl pointer here so that it is set for both extension-only and base tables. */
+    if(mbcsTable->utf8Friendly) {
+        if(mbcsTable->countStates==1) {
+            sharedData->impl=&_SBCSUTF8Impl;
+        } else {
+            if(mbcsTable->outputType==MBCS_OUTPUT_2) {
+                sharedData->impl=&_DBCSUTF8Impl;
+            }
+        }
+    }
+
+    if(mbcsTable->outputType==MBCS_OUTPUT_DBCS_ONLY || mbcsTable->outputType==MBCS_OUTPUT_2_SISO) {
+        /*
+         * MBCS_OUTPUT_DBCS_ONLY: No SBCS mappings, therefore ASCII does not roundtrip.
+         * MBCS_OUTPUT_2_SISO: Bypass the ASCII fastpath to handle prevLength correctly.
+         */
+        mbcsTable->asciiRoundtrips=0;
+    }
+}
+
+static void
+ucnv_MBCSUnload(UConverterSharedData *sharedData) {
+    UConverterMBCSTable *mbcsTable=&sharedData->mbcs;
+
+    if(mbcsTable->swapLFNLStateTable!=NULL) {
+        uprv_free(mbcsTable->swapLFNLStateTable);
+    }
+    if(mbcsTable->stateTableOwned) {
+        uprv_free((void *)mbcsTable->stateTable);
+    }
+    if(mbcsTable->baseSharedData!=NULL) {
+        ucnv_unload(mbcsTable->baseSharedData);
+    }
+    if(mbcsTable->reconstitutedData!=NULL) {
+        uprv_free(mbcsTable->reconstitutedData);
+    }
+}
+
+static void
+ucnv_MBCSOpen(UConverter *cnv,
+              UConverterLoadArgs *pArgs,
+              UErrorCode *pErrorCode) {
+    UConverterMBCSTable *mbcsTable;
+    const int32_t *extIndexes;
+    uint8_t outputType;
+    int8_t maxBytesPerUChar;
+
+    if(pArgs->onlyTestIsLoadable) {
+        return;
+    }
+
+    mbcsTable=&cnv->sharedData->mbcs;
+    outputType=mbcsTable->outputType;
+
+    if(outputType==MBCS_OUTPUT_DBCS_ONLY) {
+        /* the swaplfnl option does not apply, remove it */
+        cnv->options=pArgs->options&=~UCNV_OPTION_SWAP_LFNL;
+    }
+
+    if((pArgs->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        /* do this because double-checked locking is broken */
+        UBool isCached;
+
+        umtx_lock(NULL);
+        isCached=mbcsTable->swapLFNLStateTable!=NULL;
+        umtx_unlock(NULL);
+
+        if(!isCached) {
+            if(!_EBCDICSwapLFNL(cnv->sharedData, pErrorCode)) {
+                if(U_FAILURE(*pErrorCode)) {
+                    return; /* something went wrong */
+                }
+
+                /* the option does not apply, remove it */
+                cnv->options=pArgs->options&=~UCNV_OPTION_SWAP_LFNL;
+            }
+        }
+    }
+
+    if(uprv_strstr(pArgs->name, "18030")!=NULL) {
+        if(uprv_strstr(pArgs->name, "gb18030")!=NULL || uprv_strstr(pArgs->name, "GB18030")!=NULL) {
+            /* set a flag for GB 18030 mode, which changes the callback behavior */
+            cnv->options|=_MBCS_OPTION_GB18030;
+        }
+    } else if((uprv_strstr(pArgs->name, "KEIS")!=NULL) || (uprv_strstr(pArgs->name, "keis")!=NULL)) {
+        /* set a flag for KEIS converter, which changes the SI/SO character sequence */
+        cnv->options|=_MBCS_OPTION_KEIS;
+    } else if((uprv_strstr(pArgs->name, "JEF")!=NULL) || (uprv_strstr(pArgs->name, "jef")!=NULL)) {
+        /* set a flag for JEF converter, which changes the SI/SO character sequence */
+        cnv->options|=_MBCS_OPTION_JEF;
+    } else if((uprv_strstr(pArgs->name, "JIPS")!=NULL) || (uprv_strstr(pArgs->name, "jips")!=NULL)) {
+        /* set a flag for JIPS converter, which changes the SI/SO character sequence */
+        cnv->options|=_MBCS_OPTION_JIPS;
+    }
+
+    /* fix maxBytesPerUChar depending on outputType and options etc. */
+    if(outputType==MBCS_OUTPUT_2_SISO) {
+        cnv->maxBytesPerUChar=3; /* SO+DBCS */
+    }
+
+    extIndexes=mbcsTable->extIndexes;
+    if(extIndexes!=NULL) {
+        maxBytesPerUChar=(int8_t)UCNV_GET_MAX_BYTES_PER_UCHAR(extIndexes);
+        if(outputType==MBCS_OUTPUT_2_SISO) {
+            ++maxBytesPerUChar; /* SO + multiple DBCS */
+        }
+
+        if(maxBytesPerUChar>cnv->maxBytesPerUChar) {
+            cnv->maxBytesPerUChar=maxBytesPerUChar;
+        }
+    }
+
+#if 0
+    /*
+     * documentation of UConverter fields used for status
+     * all of these fields are (re)set to 0 by ucnv_bld.c and ucnv_reset()
+     */
+
+    /* toUnicode */
+    cnv->toUnicodeStatus=0;     /* offset */
+    cnv->mode=0;                /* state */
+    cnv->toULength=0;           /* byteIndex */
+
+    /* fromUnicode */
+    cnv->fromUChar32=0;
+    cnv->fromUnicodeStatus=1;   /* prevLength */
+#endif
+}
+
+static const char *
+ucnv_MBCSGetName(const UConverter *cnv) {
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0 && cnv->sharedData->mbcs.swapLFNLName!=NULL) {
+        return cnv->sharedData->mbcs.swapLFNLName;
+    } else {
+        return cnv->sharedData->staticData->name;
+    }
+}
+
+/* MBCS-to-Unicode conversion functions ------------------------------------- */
+
+static UChar32
+ucnv_MBCSGetFallback(UConverterMBCSTable *mbcsTable, uint32_t offset) {
+    const _MBCSToUFallback *toUFallbacks;
+    uint32_t i, start, limit;
+
+    limit=mbcsTable->countToUFallbacks;
+    if(limit>0) {
+        /* do a binary search for the fallback mapping */
+        toUFallbacks=mbcsTable->toUFallbacks;
+        start=0;
+        while(start<limit-1) {
+            i=(start+limit)/2;
+            if(offset<toUFallbacks[i].offset) {
+                limit=i;
+            } else {
+                start=i;
+            }
+        }
+
+        /* did we really find it? */
+        if(offset==toUFallbacks[start].offset) {
+            return toUFallbacks[start].codePoint;
+        }
+    }
+
+    return 0xfffe;
+}
+
+/* This version of ucnv_MBCSToUnicodeWithOffsets() is optimized for single-byte, single-state codepages. */
+static void
+ucnv_MBCSSingleToUnicodeWithOffsets(UConverterToUnicodeArgs *pArgs,
+                                UErrorCode *pErrorCode) {
+    UConverter *cnv;
+    const uint8_t *source, *sourceLimit;
+    UChar *target;
+    const UChar *targetLimit;
+    int32_t *offsets;
+
+    const int32_t (*stateTable)[256];
+
+    int32_t sourceIndex;
+
+    int32_t entry;
+    UChar c;
+    uint8_t action;
+
+    /* set up the local pointers */
+    cnv=pArgs->converter;
+    source=(const uint8_t *)pArgs->source;
+    sourceLimit=(const uint8_t *)pArgs->sourceLimit;
+    target=pArgs->target;
+    targetLimit=pArgs->targetLimit;
+    offsets=pArgs->offsets;
+
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        stateTable=(const int32_t (*)[256])cnv->sharedData->mbcs.swapLFNLStateTable;
+    } else {
+        stateTable=cnv->sharedData->mbcs.stateTable;
+    }
+
+    /* sourceIndex=-1 if the current character began in the previous buffer */
+    sourceIndex=0;
+
+    /* conversion loop */
+    while(source<sourceLimit) {
+        /*
+         * This following test is to see if available input would overflow the output.
+         * It does not catch output of more than one code unit that
+         * overflows as a result of a surrogate pair or callback output
+         * from the last source byte.
+         * Therefore, those situations also test for overflows and will
+         * then break the loop, too.
+         */
+        if(target>=targetLimit) {
+            /* target is full */
+            *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+            break;
+        }
+
+        entry=stateTable[0][*source++];
+        /* MBCS_ENTRY_IS_FINAL(entry) */
+
+        /* test the most common case first */
+        if(MBCS_ENTRY_FINAL_IS_VALID_DIRECT_16(entry)) {
+            /* output BMP code point */
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            if(offsets!=NULL) {
+                *offsets++=sourceIndex;
+            }
+
+            /* normal end of action codes: prepare for a new character */
+            ++sourceIndex;
+            continue;
+        }
+
+        /*
+         * An if-else-if chain provides more reliable performance for
+         * the most common cases compared to a switch.
+         */
+        action=(uint8_t)(MBCS_ENTRY_FINAL_ACTION(entry));
+        if(action==MBCS_STATE_VALID_DIRECT_20 ||
+           (action==MBCS_STATE_FALLBACK_DIRECT_20 && UCNV_TO_U_USE_FALLBACK(cnv))
+        ) {
+            entry=MBCS_ENTRY_FINAL_VALUE(entry);
+            /* output surrogate pair */
+            *target++=(UChar)(0xd800|(UChar)(entry>>10));
+            if(offsets!=NULL) {
+                *offsets++=sourceIndex;
+            }
+            c=(UChar)(0xdc00|(UChar)(entry&0x3ff));
+            if(target<targetLimit) {
+                *target++=c;
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+            } else {
+                /* target overflow */
+                cnv->UCharErrorBuffer[0]=c;
+                cnv->UCharErrorBufferLength=1;
+                *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+                break;
+            }
+
+            ++sourceIndex;
+            continue;
+        } else if(action==MBCS_STATE_FALLBACK_DIRECT_16) {
+            if(UCNV_TO_U_USE_FALLBACK(cnv)) {
+                /* output BMP code point */
+                *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+
+                ++sourceIndex;
+                continue;
+            }
+        } else if(action==MBCS_STATE_UNASSIGNED) {
+            /* just fall through */
+        } else if(action==MBCS_STATE_ILLEGAL) {
+            /* callback(illegal) */
+            *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+        } else {
+            /* reserved, must never occur */
+            ++sourceIndex;
+            continue;
+        }
+
+        if(U_FAILURE(*pErrorCode)) {
+            /* callback(illegal) */
+            break;
+        } else /* unassigned sequences indicated with byteIndex>0 */ {
+            /* try an extension mapping */
+            pArgs->source=(const char *)source;
+            cnv->toUBytes[0]=*(source-1);
+            cnv->toULength=_extToU(cnv, cnv->sharedData,
+                                    1, &source, sourceLimit,
+                                    &target, targetLimit,
+                                    &offsets, sourceIndex,
+                                    pArgs->flush,
+                                    pErrorCode);
+            sourceIndex+=1+(int32_t)(source-(const uint8_t *)pArgs->source);
+
+            if(U_FAILURE(*pErrorCode)) {
+                /* not mappable or buffer overflow */
+                break;
+            }
+        }
+    }
+
+    /* write back the updated pointers */
+    pArgs->source=(const char *)source;
+    pArgs->target=target;
+    pArgs->offsets=offsets;
+}
+
+/*
+ * This version of ucnv_MBCSSingleToUnicodeWithOffsets() is optimized for single-byte, single-state codepages
+ * that only map to and from the BMP.
+ * In addition to single-byte optimizations, the offset calculations
+ * become much easier.
+ */
+static void
+ucnv_MBCSSingleToBMPWithOffsets(UConverterToUnicodeArgs *pArgs,
+                            UErrorCode *pErrorCode) {
+    UConverter *cnv;
+    const uint8_t *source, *sourceLimit, *lastSource;
+    UChar *target;
+    int32_t targetCapacity, length;
+    int32_t *offsets;
+
+    const int32_t (*stateTable)[256];
+
+    int32_t sourceIndex;
+
+    int32_t entry;
+    uint8_t action;
+
+    /* set up the local pointers */
+    cnv=pArgs->converter;
+    source=(const uint8_t *)pArgs->source;
+    sourceLimit=(const uint8_t *)pArgs->sourceLimit;
+    target=pArgs->target;
+    targetCapacity=(int32_t)(pArgs->targetLimit-pArgs->target);
+    offsets=pArgs->offsets;
+
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        stateTable=(const int32_t (*)[256])cnv->sharedData->mbcs.swapLFNLStateTable;
+    } else {
+        stateTable=cnv->sharedData->mbcs.stateTable;
+    }
+
+    /* sourceIndex=-1 if the current character began in the previous buffer */
+    sourceIndex=0;
+    lastSource=source;
+
+    /*
+     * since the conversion here is 1:1 UChar:uint8_t, we need only one counter
+     * for the minimum of the sourceLength and targetCapacity
+     */
+    length=(int32_t)(sourceLimit-source);
+    if(length<targetCapacity) {
+        targetCapacity=length;
+    }
+
+#if MBCS_UNROLL_SINGLE_TO_BMP
+    /* unrolling makes it faster on Pentium III/Windows 2000 */
+    /* unroll the loop with the most common case */
+unrolled:
+    if(targetCapacity>=16) {
+        int32_t count, loops, oredEntries;
+
+        loops=count=targetCapacity>>4;
+        do {
+            oredEntries=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            oredEntries|=entry=stateTable[0][*source++];
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+
+            /* were all 16 entries really valid? */
+            if(!MBCS_ENTRY_FINAL_IS_VALID_DIRECT_16(oredEntries)) {
+                /* no, return to the first of these 16 */
+                source-=16;
+                target-=16;
+                break;
+            }
+        } while(--count>0);
+        count=loops-count;
+        targetCapacity-=16*count;
+
+        if(offsets!=NULL) {
+            lastSource+=16*count;
+            while(count>0) {
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                --count;
+            }
+        }
+    }
+#endif
+
+    /* conversion loop */
+    while(targetCapacity > 0 && source < sourceLimit) {
+        entry=stateTable[0][*source++];
+        /* MBCS_ENTRY_IS_FINAL(entry) */
+
+        /* test the most common case first */
+        if(MBCS_ENTRY_FINAL_IS_VALID_DIRECT_16(entry)) {
+            /* output BMP code point */
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            --targetCapacity;
+            continue;
+        }
+
+        /*
+         * An if-else-if chain provides more reliable performance for
+         * the most common cases compared to a switch.
+         */
+        action=(uint8_t)(MBCS_ENTRY_FINAL_ACTION(entry));
+        if(action==MBCS_STATE_FALLBACK_DIRECT_16) {
+            if(UCNV_TO_U_USE_FALLBACK(cnv)) {
+                /* output BMP code point */
+                *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+                --targetCapacity;
+                continue;
+            }
+        } else if(action==MBCS_STATE_UNASSIGNED) {
+            /* just fall through */
+        } else if(action==MBCS_STATE_ILLEGAL) {
+            /* callback(illegal) */
+            *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+        } else {
+            /* reserved, must never occur */
+            continue;
+        }
+
+        /* set offsets since the start or the last extension */
+        if(offsets!=NULL) {
+            int32_t count=(int32_t)(source-lastSource);
+
+            /* predecrement: do not set the offset for the callback-causing character */
+            while(--count>0) {
+                *offsets++=sourceIndex++;
+            }
+            /* offset and sourceIndex are now set for the current character */
+        }
+
+        if(U_FAILURE(*pErrorCode)) {
+            /* callback(illegal) */
+            break;
+        } else /* unassigned sequences indicated with byteIndex>0 */ {
+            /* try an extension mapping */
+            lastSource=source;
+            cnv->toUBytes[0]=*(source-1);
+            cnv->toULength=_extToU(cnv, cnv->sharedData,
+                                    1, &source, sourceLimit,
+                                    &target, pArgs->targetLimit,
+                                    &offsets, sourceIndex,
+                                    pArgs->flush,
+                                    pErrorCode);
+            sourceIndex+=1+(int32_t)(source-lastSource);
+
+            if(U_FAILURE(*pErrorCode)) {
+                /* not mappable or buffer overflow */
+                break;
+            }
+
+            /* recalculate the targetCapacity after an extension mapping */
+            targetCapacity=(int32_t)(pArgs->targetLimit-target);
+            length=(int32_t)(sourceLimit-source);
+            if(length<targetCapacity) {
+                targetCapacity=length;
+            }
+        }
+
+#if MBCS_UNROLL_SINGLE_TO_BMP
+        /* unrolling makes it faster on Pentium III/Windows 2000 */
+        goto unrolled;
+#endif
+    }
+
+    if(U_SUCCESS(*pErrorCode) && source<sourceLimit && target>=pArgs->targetLimit) {
+        /* target is full */
+        *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+    }
+
+    /* set offsets since the start or the last callback */
+    if(offsets!=NULL) {
+        size_t count=source-lastSource;
+        while(count>0) {
+            *offsets++=sourceIndex++;
+            --count;
+        }
+    }
+
+    /* write back the updated pointers */
+    pArgs->source=(const char *)source;
+    pArgs->target=target;
+    pArgs->offsets=offsets;
+}
+
+static UBool
+hasValidTrailBytes(const int32_t (*stateTable)[256], uint8_t state) {
+    const int32_t *row=stateTable[state];
+    int32_t b, entry;
+    /* First test for final entries in this state for some commonly valid byte values. */
+    entry=row[0xa1];
+    if( !MBCS_ENTRY_IS_TRANSITION(entry) &&
+        MBCS_ENTRY_FINAL_ACTION(entry)!=MBCS_STATE_ILLEGAL
+    ) {
+        return TRUE;
+    }
+    entry=row[0x41];
+    if( !MBCS_ENTRY_IS_TRANSITION(entry) &&
+        MBCS_ENTRY_FINAL_ACTION(entry)!=MBCS_STATE_ILLEGAL
+    ) {
+        return TRUE;
+    }
+    /* Then test for final entries in this state. */
+    for(b=0; b<=0xff; ++b) {
+        entry=row[b];
+        if( !MBCS_ENTRY_IS_TRANSITION(entry) &&
+            MBCS_ENTRY_FINAL_ACTION(entry)!=MBCS_STATE_ILLEGAL
+        ) {
+            return TRUE;
+        }
+    }
+    /* Then recurse for transition entries. */
+    for(b=0; b<=0xff; ++b) {
+        entry=row[b];
+        if( MBCS_ENTRY_IS_TRANSITION(entry) &&
+            hasValidTrailBytes(stateTable, (uint8_t)MBCS_ENTRY_TRANSITION_STATE(entry))
+        ) {
+            return TRUE;
+        }
+    }
+    return FALSE;
+}
+
+/*
+ * Is byte b a single/lead byte in this state?
+ * Recurse for transition states, because here we don't want to say that
+ * b is a lead byte if all byte sequences that start with b are illegal.
+ */
+static UBool
+isSingleOrLead(const int32_t (*stateTable)[256], uint8_t state, UBool isDBCSOnly, uint8_t b) {
+    const int32_t *row=stateTable[state];
+    int32_t entry=row[b];
+    if(MBCS_ENTRY_IS_TRANSITION(entry)) {   /* lead byte */
+        return hasValidTrailBytes(stateTable, (uint8_t)MBCS_ENTRY_TRANSITION_STATE(entry));
+    } else {
+        uint8_t action=(uint8_t)(MBCS_ENTRY_FINAL_ACTION(entry));
+        if(action==MBCS_STATE_CHANGE_ONLY && isDBCSOnly) {
+            return FALSE;   /* SI/SO are illegal for DBCS-only conversion */
+        } else {
+            return action!=MBCS_STATE_ILLEGAL;
+        }
+    }
+}
+
+U_CFUNC void
+ucnv_MBCSToUnicodeWithOffsets(UConverterToUnicodeArgs *pArgs,
+                          UErrorCode *pErrorCode) {
+    UConverter *cnv;
+    const uint8_t *source, *sourceLimit;
+    UChar *target;
+    const UChar *targetLimit;
+    int32_t *offsets;
+
+    const int32_t (*stateTable)[256];
+    const uint16_t *unicodeCodeUnits;
+
+    uint32_t offset;
+    uint8_t state;
+    int8_t byteIndex;
+    uint8_t *bytes;
+
+    int32_t sourceIndex, nextSourceIndex;
+
+    int32_t entry;
+    UChar c;
+    uint8_t action;
+
+    /* use optimized function if possible */
+    cnv=pArgs->converter;
+
+    if(cnv->preToULength>0) {
+        /*
+         * pass sourceIndex=-1 because we continue from an earlier buffer
+         * in the future, this may change with continuous offsets
+         */
+        ucnv_extContinueMatchToU(cnv, pArgs, -1, pErrorCode);
+
+        if(U_FAILURE(*pErrorCode) || cnv->preToULength<0) {
+            return;
+        }
+    }
+
+    if(cnv->sharedData->mbcs.countStates==1) {
+        if(!(cnv->sharedData->mbcs.unicodeMask&UCNV_HAS_SUPPLEMENTARY)) {
+            ucnv_MBCSSingleToBMPWithOffsets(pArgs, pErrorCode);
+        } else {
+            ucnv_MBCSSingleToUnicodeWithOffsets(pArgs, pErrorCode);
+        }
+        return;
+    }
+
+    /* set up the local pointers */
+    source=(const uint8_t *)pArgs->source;
+    sourceLimit=(const uint8_t *)pArgs->sourceLimit;
+    target=pArgs->target;
+    targetLimit=pArgs->targetLimit;
+    offsets=pArgs->offsets;
+
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        stateTable=(const int32_t (*)[256])cnv->sharedData->mbcs.swapLFNLStateTable;
+    } else {
+        stateTable=cnv->sharedData->mbcs.stateTable;
+    }
+    unicodeCodeUnits=cnv->sharedData->mbcs.unicodeCodeUnits;
+
+    /* get the converter state from UConverter */
+    offset=cnv->toUnicodeStatus;
+    byteIndex=cnv->toULength;
+    bytes=cnv->toUBytes;
+
+    /*
+     * if we are in the SBCS state for a DBCS-only converter,
+     * then load the DBCS state from the MBCS data
+     * (dbcsOnlyState==0 if it is not a DBCS-only converter)
+     */
+    if((state=(uint8_t)(cnv->mode))==0) {
+        state=cnv->sharedData->mbcs.dbcsOnlyState;
+    }
+
+    /* sourceIndex=-1 if the current character began in the previous buffer */
+    sourceIndex=byteIndex==0 ? 0 : -1;
+    nextSourceIndex=0;
+
+    /* conversion loop */
+    while(source<sourceLimit) {
+        /*
+         * This following test is to see if available input would overflow the output.
+         * It does not catch output of more than one code unit that
+         * overflows as a result of a surrogate pair or callback output
+         * from the last source byte.
+         * Therefore, those situations also test for overflows and will
+         * then break the loop, too.
+         */
+        if(target>=targetLimit) {
+            /* target is full */
+            *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+            break;
+        }
+
+        if(byteIndex==0) {
+            /* optimized loop for 1/2-byte input and BMP output */
+            if(offsets==NULL) {
+                do {
+                    entry=stateTable[state][*source];
+                    if(MBCS_ENTRY_IS_TRANSITION(entry)) {
+                        state=(uint8_t)MBCS_ENTRY_TRANSITION_STATE(entry);
+                        offset=MBCS_ENTRY_TRANSITION_OFFSET(entry);
+
+                        ++source;
+                        if( source<sourceLimit &&
+                            MBCS_ENTRY_IS_FINAL(entry=stateTable[state][*source]) &&
+                            MBCS_ENTRY_FINAL_ACTION(entry)==MBCS_STATE_VALID_16 &&
+                            (c=unicodeCodeUnits[offset+MBCS_ENTRY_FINAL_VALUE_16(entry)])<0xfffe
+                        ) {
+                            ++source;
+                            *target++=c;
+                            state=(uint8_t)MBCS_ENTRY_FINAL_STATE(entry); /* typically 0 */
+                            offset=0;
+                        } else {
+                            /* set the state and leave the optimized loop */
+                            bytes[0]=*(source-1);
+                            byteIndex=1;
+                            break;
+                        }
+                    } else {
+                        if(MBCS_ENTRY_FINAL_IS_VALID_DIRECT_16(entry)) {
+                            /* output BMP code point */
+                            ++source;
+                            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+                            state=(uint8_t)MBCS_ENTRY_FINAL_STATE(entry); /* typically 0 */
+                        } else {
+                            /* leave the optimized loop */
+                            break;
+                        }
+                    }
+                } while(source<sourceLimit && target<targetLimit);
+            } else /* offsets!=NULL */ {
+                do {
+                    entry=stateTable[state][*source];
+                    if(MBCS_ENTRY_IS_TRANSITION(entry)) {
+                        state=(uint8_t)MBCS_ENTRY_TRANSITION_STATE(entry);
+                        offset=MBCS_ENTRY_TRANSITION_OFFSET(entry);
+
+                        ++source;
+                        if( source<sourceLimit &&
+                            MBCS_ENTRY_IS_FINAL(entry=stateTable[state][*source]) &&
+                            MBCS_ENTRY_FINAL_ACTION(entry)==MBCS_STATE_VALID_16 &&
+                            (c=unicodeCodeUnits[offset+MBCS_ENTRY_FINAL_VALUE_16(entry)])<0xfffe
+                        ) {
+                            ++source;
+                            *target++=c;
+                            if(offsets!=NULL) {
+                                *offsets++=sourceIndex;
+                                sourceIndex=(nextSourceIndex+=2);
+                            }
+                            state=(uint8_t)MBCS_ENTRY_FINAL_STATE(entry); /* typically 0 */
+                            offset=0;
+                        } else {
+                            /* set the state and leave the optimized loop */
+                            ++nextSourceIndex;
+                            bytes[0]=*(source-1);
+                            byteIndex=1;
+                            break;
+                        }
+                    } else {
+                        if(MBCS_ENTRY_FINAL_IS_VALID_DIRECT_16(entry)) {
+                            /* output BMP code point */
+                            ++source;
+                            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+                            if(offsets!=NULL) {
+                                *offsets++=sourceIndex;
+                                sourceIndex=++nextSourceIndex;
+                            }
+                            state=(uint8_t)MBCS_ENTRY_FINAL_STATE(entry); /* typically 0 */
+                        } else {
+                            /* leave the optimized loop */
+                            break;
+                        }
+                    }
+                } while(source<sourceLimit && target<targetLimit);
+            }
+
+            /*
+             * these tests and break statements could be put inside the loop
+             * if C had "break outerLoop" like Java
+             */
+            if(source>=sourceLimit) {
+                break;
+            }
+            if(target>=targetLimit) {
+                /* target is full */
+                *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+                break;
+            }
+
+            ++nextSourceIndex;
+            bytes[byteIndex++]=*source++;
+        } else /* byteIndex>0 */ {
+            ++nextSourceIndex;
+            entry=stateTable[state][bytes[byteIndex++]=*source++];
+        }
+
+        if(MBCS_ENTRY_IS_TRANSITION(entry)) {
+            state=(uint8_t)MBCS_ENTRY_TRANSITION_STATE(entry);
+            offset+=MBCS_ENTRY_TRANSITION_OFFSET(entry);
+            continue;
+        }
+
+        /* save the previous state for proper extension mapping with SI/SO-stateful converters */
+        cnv->mode=state;
+
+        /* set the next state early so that we can reuse the entry variable */
+        state=(uint8_t)MBCS_ENTRY_FINAL_STATE(entry); /* typically 0 */
+
+        /*
+         * An if-else-if chain provides more reliable performance for
+         * the most common cases compared to a switch.
+         */
+        action=(uint8_t)(MBCS_ENTRY_FINAL_ACTION(entry));
+        if(action==MBCS_STATE_VALID_16) {
+            offset+=MBCS_ENTRY_FINAL_VALUE_16(entry);
+            c=unicodeCodeUnits[offset];
+            if(c<0xfffe) {
+                /* output BMP code point */
+                *target++=c;
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+                byteIndex=0;
+            } else if(c==0xfffe) {
+                if(UCNV_TO_U_USE_FALLBACK(cnv) && (entry=(int32_t)ucnv_MBCSGetFallback(&cnv->sharedData->mbcs, offset))!=0xfffe) {
+                    /* output fallback BMP code point */
+                    *target++=(UChar)entry;
+                    if(offsets!=NULL) {
+                        *offsets++=sourceIndex;
+                    }
+                    byteIndex=0;
+                }
+            } else {
+                /* callback(illegal) */
+                *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+            }
+        } else if(action==MBCS_STATE_VALID_DIRECT_16) {
+            /* output BMP code point */
+            *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            if(offsets!=NULL) {
+                *offsets++=sourceIndex;
+            }
+            byteIndex=0;
+        } else if(action==MBCS_STATE_VALID_16_PAIR) {
+            offset+=MBCS_ENTRY_FINAL_VALUE_16(entry);
+            c=unicodeCodeUnits[offset++];
+            if(c<0xd800) {
+                /* output BMP code point below 0xd800 */
+                *target++=c;
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+                byteIndex=0;
+            } else if(UCNV_TO_U_USE_FALLBACK(cnv) ? c<=0xdfff : c<=0xdbff) {
+                /* output roundtrip or fallback surrogate pair */
+                *target++=(UChar)(c&0xdbff);
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+                byteIndex=0;
+                if(target<targetLimit) {
+                    *target++=unicodeCodeUnits[offset];
+                    if(offsets!=NULL) {
+                        *offsets++=sourceIndex;
+                    }
+                } else {
+                    /* target overflow */
+                    cnv->UCharErrorBuffer[0]=unicodeCodeUnits[offset];
+                    cnv->UCharErrorBufferLength=1;
+                    *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+
+                    offset=0;
+                    break;
+                }
+            } else if(UCNV_TO_U_USE_FALLBACK(cnv) ? (c&0xfffe)==0xe000 : c==0xe000) {
+                /* output roundtrip BMP code point above 0xd800 or fallback BMP code point */
+                *target++=unicodeCodeUnits[offset];
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+                byteIndex=0;
+            } else if(c==0xffff) {
+                /* callback(illegal) */
+                *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+            }
+        } else if(action==MBCS_STATE_VALID_DIRECT_20 ||
+                  (action==MBCS_STATE_FALLBACK_DIRECT_20 && UCNV_TO_U_USE_FALLBACK(cnv))
+        ) {
+            entry=MBCS_ENTRY_FINAL_VALUE(entry);
+            /* output surrogate pair */
+            *target++=(UChar)(0xd800|(UChar)(entry>>10));
+            if(offsets!=NULL) {
+                *offsets++=sourceIndex;
+            }
+            byteIndex=0;
+            c=(UChar)(0xdc00|(UChar)(entry&0x3ff));
+            if(target<targetLimit) {
+                *target++=c;
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+            } else {
+                /* target overflow */
+                cnv->UCharErrorBuffer[0]=c;
+                cnv->UCharErrorBufferLength=1;
+                *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+
+                offset=0;
+                break;
+            }
+        } else if(action==MBCS_STATE_CHANGE_ONLY) {
+            /*
+             * This serves as a state change without any output.
+             * It is useful for reading simple stateful encodings,
+             * for example using just Shift-In/Shift-Out codes.
+             * The 21 unused bits may later be used for more sophisticated
+             * state transitions.
+             */
+            if(cnv->sharedData->mbcs.dbcsOnlyState==0) {
+                byteIndex=0;
+            } else {
+                /* SI/SO are illegal for DBCS-only conversion */
+                state=(uint8_t)(cnv->mode); /* restore the previous state */
+
+                /* callback(illegal) */
+                *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+            }
+        } else if(action==MBCS_STATE_FALLBACK_DIRECT_16) {
+            if(UCNV_TO_U_USE_FALLBACK(cnv)) {
+                /* output BMP code point */
+                *target++=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+                byteIndex=0;
+            }
+        } else if(action==MBCS_STATE_UNASSIGNED) {
+            /* just fall through */
+        } else if(action==MBCS_STATE_ILLEGAL) {
+            /* callback(illegal) */
+            *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+        } else {
+            /* reserved, must never occur */
+            byteIndex=0;
+        }
+
+        /* end of action codes: prepare for a new character */
+        offset=0;
+
+        if(byteIndex==0) {
+            sourceIndex=nextSourceIndex;
+        } else if(U_FAILURE(*pErrorCode)) {
+            /* callback(illegal) */
+            if(byteIndex>1) {
+                /*
+                 * Ticket 5691: consistent illegal sequences:
+                 * - We include at least the first byte in the illegal sequence.
+                 * - If any of the non-initial bytes could be the start of a character,
+                 *   we stop the illegal sequence before the first one of those.
+                 */
+                UBool isDBCSOnly=(UBool)(cnv->sharedData->mbcs.dbcsOnlyState!=0);
+                int8_t i;
+                for(i=1;
+                    i<byteIndex && !isSingleOrLead(stateTable, state, isDBCSOnly, bytes[i]);
+                    ++i) {}
+                if(i<byteIndex) {
+                    /* Back out some bytes. */
+                    int8_t backOutDistance=byteIndex-i;
+                    int32_t bytesFromThisBuffer=(int32_t)(source-(const uint8_t *)pArgs->source);
+                    byteIndex=i;  /* length of reported illegal byte sequence */
+                    if(backOutDistance<=bytesFromThisBuffer) {
+                        source-=backOutDistance;
+                    } else {
+                        /* Back out bytes from the previous buffer: Need to replay them. */
+                        cnv->preToULength=(int8_t)(bytesFromThisBuffer-backOutDistance);
+                        /* preToULength is negative! */
+                        uprv_memcpy(cnv->preToU, bytes+i, -cnv->preToULength);
+                        source=(const uint8_t *)pArgs->source;
+                    }
+                }
+            }
+            break;
+        } else /* unassigned sequences indicated with byteIndex>0 */ {
+            /* try an extension mapping */
+            pArgs->source=(const char *)source;
+            byteIndex=_extToU(cnv, cnv->sharedData,
+                              byteIndex, &source, sourceLimit,
+                              &target, targetLimit,
+                              &offsets, sourceIndex,
+                              pArgs->flush,
+                              pErrorCode);
+            sourceIndex=nextSourceIndex+=(int32_t)(source-(const uint8_t *)pArgs->source);
+
+            if(U_FAILURE(*pErrorCode)) {
+                /* not mappable or buffer overflow */
+                break;
+            }
+        }
+    }
+
+    /* set the converter state back into UConverter */
+    cnv->toUnicodeStatus=offset;
+    cnv->mode=state;
+    cnv->toULength=byteIndex;
+
+    /* write back the updated pointers */
+    pArgs->source=(const char *)source;
+    pArgs->target=target;
+    pArgs->offsets=offsets;
+}
+
+/*
+ * This version of ucnv_MBCSGetNextUChar() is optimized for single-byte, single-state codepages.
+ * We still need a conversion loop in case we find reserved action codes, which are to be ignored.
+ */
+static UChar32
+ucnv_MBCSSingleGetNextUChar(UConverterToUnicodeArgs *pArgs,
+                        UErrorCode *pErrorCode) {
+    UConverter *cnv;
+    const int32_t (*stateTable)[256];
+    const uint8_t *source, *sourceLimit;
+
+    int32_t entry;
+    uint8_t action;
+
+    /* set up the local pointers */
+    cnv=pArgs->converter;
+    source=(const uint8_t *)pArgs->source;
+    sourceLimit=(const uint8_t *)pArgs->sourceLimit;
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        stateTable=(const int32_t (*)[256])cnv->sharedData->mbcs.swapLFNLStateTable;
+    } else {
+        stateTable=cnv->sharedData->mbcs.stateTable;
+    }
+
+    /* conversion loop */
+    while(source<sourceLimit) {
+        entry=stateTable[0][*source++];
+        /* MBCS_ENTRY_IS_FINAL(entry) */
+
+        /* write back the updated pointer early so that we can return directly */
+        pArgs->source=(const char *)source;
+
+        if(MBCS_ENTRY_FINAL_IS_VALID_DIRECT_16(entry)) {
+            /* output BMP code point */
+            return (UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+        }
+
+        /*
+         * An if-else-if chain provides more reliable performance for
+         * the most common cases compared to a switch.
+         */
+        action=(uint8_t)(MBCS_ENTRY_FINAL_ACTION(entry));
+        if( action==MBCS_STATE_VALID_DIRECT_20 ||
+            (action==MBCS_STATE_FALLBACK_DIRECT_20 && UCNV_TO_U_USE_FALLBACK(cnv))
+        ) {
+            /* output supplementary code point */
+            return (UChar32)(MBCS_ENTRY_FINAL_VALUE(entry)+0x10000);
+        } else if(action==MBCS_STATE_FALLBACK_DIRECT_16) {
+            if(UCNV_TO_U_USE_FALLBACK(cnv)) {
+                /* output BMP code point */
+                return (UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+            }
+        } else if(action==MBCS_STATE_UNASSIGNED) {
+            /* just fall through */
+        } else if(action==MBCS_STATE_ILLEGAL) {
+            /* callback(illegal) */
+            *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+        } else {
+            /* reserved, must never occur */
+            continue;
+        }
+
+        if(U_FAILURE(*pErrorCode)) {
+            /* callback(illegal) */
+            break;
+        } else /* unassigned sequence */ {
+            /* defer to the generic implementation */
+            pArgs->source=(const char *)source-1;
+            return UCNV_GET_NEXT_UCHAR_USE_TO_U;
+        }
+    }
+
+    /* no output because of empty input or only state changes */
+    *pErrorCode=U_INDEX_OUTOFBOUNDS_ERROR;
+    return 0xffff;
+}
+
+/*
+ * Version of _MBCSToUnicodeWithOffsets() optimized for single-character
+ * conversion without offset handling.
+ *
+ * When a character does not have a mapping to Unicode, then we return to the
+ * generic ucnv_getNextUChar() code for extension/GB 18030 and error/callback
+ * handling.
+ * We also defer to the generic code in other complicated cases and have them
+ * ultimately handled by _MBCSToUnicodeWithOffsets() itself.
+ *
+ * All normal mappings and errors are handled here.
+ */
+static UChar32
+ucnv_MBCSGetNextUChar(UConverterToUnicodeArgs *pArgs,
+                  UErrorCode *pErrorCode) {
+    UConverter *cnv;
+    const uint8_t *source, *sourceLimit, *lastSource;
+
+    const int32_t (*stateTable)[256];
+    const uint16_t *unicodeCodeUnits;
+
+    uint32_t offset;
+    uint8_t state;
+
+    int32_t entry;
+    UChar32 c;
+    uint8_t action;
+
+    /* use optimized function if possible */
+    cnv=pArgs->converter;
+
+    if(cnv->preToULength>0) {
+        /* use the generic code in ucnv_getNextUChar() to continue with a partial match */
+        return UCNV_GET_NEXT_UCHAR_USE_TO_U;
+    }
+
+    if(cnv->sharedData->mbcs.unicodeMask&UCNV_HAS_SURROGATES) {
+        /*
+         * Using the generic ucnv_getNextUChar() code lets us deal correctly
+         * with the rare case of a codepage that maps single surrogates
+         * without adding the complexity to this already complicated function here.
+         */
+        return UCNV_GET_NEXT_UCHAR_USE_TO_U;
+    } else if(cnv->sharedData->mbcs.countStates==1) {
+        return ucnv_MBCSSingleGetNextUChar(pArgs, pErrorCode);
+    }
+
+    /* set up the local pointers */
+    source=lastSource=(const uint8_t *)pArgs->source;
+    sourceLimit=(const uint8_t *)pArgs->sourceLimit;
+
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        stateTable=(const int32_t (*)[256])cnv->sharedData->mbcs.swapLFNLStateTable;
+    } else {
+        stateTable=cnv->sharedData->mbcs.stateTable;
+    }
+    unicodeCodeUnits=cnv->sharedData->mbcs.unicodeCodeUnits;
+
+    /* get the converter state from UConverter */
+    offset=cnv->toUnicodeStatus;
+
+    /*
+     * if we are in the SBCS state for a DBCS-only converter,
+     * then load the DBCS state from the MBCS data
+     * (dbcsOnlyState==0 if it is not a DBCS-only converter)
+     */
+    if((state=(uint8_t)(cnv->mode))==0) {
+        state=cnv->sharedData->mbcs.dbcsOnlyState;
+    }
+
+    /* conversion loop */
+    c=U_SENTINEL;
+    while(source<sourceLimit) {
+        entry=stateTable[state][*source++];
+        if(MBCS_ENTRY_IS_TRANSITION(entry)) {
+            state=(uint8_t)MBCS_ENTRY_TRANSITION_STATE(entry);
+            offset+=MBCS_ENTRY_TRANSITION_OFFSET(entry);
+
+            /* optimization for 1/2-byte input and BMP output */
+            if( source<sourceLimit &&
+                MBCS_ENTRY_IS_FINAL(entry=stateTable[state][*source]) &&
+                MBCS_ENTRY_FINAL_ACTION(entry)==MBCS_STATE_VALID_16 &&
+                (c=unicodeCodeUnits[offset+MBCS_ENTRY_FINAL_VALUE_16(entry)])<0xfffe
+            ) {
+                ++source;
+                state=(uint8_t)MBCS_ENTRY_FINAL_STATE(entry); /* typically 0 */
+                /* output BMP code point */
+                break;
+            }
+        } else {
+            /* save the previous state for proper extension mapping with SI/SO-stateful converters */
+            cnv->mode=state;
+
+            /* set the next state early so that we can reuse the entry variable */
+            state=(uint8_t)MBCS_ENTRY_FINAL_STATE(entry); /* typically 0 */
+
+            /*
+             * An if-else-if chain provides more reliable performance for
+             * the most common cases compared to a switch.
+             */
+            action=(uint8_t)(MBCS_ENTRY_FINAL_ACTION(entry));
+            if(action==MBCS_STATE_VALID_DIRECT_16) {
+                /* output BMP code point */
+                c=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+                break;
+            } else if(action==MBCS_STATE_VALID_16) {
+                offset+=MBCS_ENTRY_FINAL_VALUE_16(entry);
+                c=unicodeCodeUnits[offset];
+                if(c<0xfffe) {
+                    /* output BMP code point */
+                    break;
+                } else if(c==0xfffe) {
+                    if(UCNV_TO_U_USE_FALLBACK(cnv) && (c=ucnv_MBCSGetFallback(&cnv->sharedData->mbcs, offset))!=0xfffe) {
+                        break;
+                    }
+                } else {
+                    /* callback(illegal) */
+                    *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                }
+            } else if(action==MBCS_STATE_VALID_16_PAIR) {
+                offset+=MBCS_ENTRY_FINAL_VALUE_16(entry);
+                c=unicodeCodeUnits[offset++];
+                if(c<0xd800) {
+                    /* output BMP code point below 0xd800 */
+                    break;
+                } else if(UCNV_TO_U_USE_FALLBACK(cnv) ? c<=0xdfff : c<=0xdbff) {
+                    /* output roundtrip or fallback supplementary code point */
+                    c=((c&0x3ff)<<10)+unicodeCodeUnits[offset]+(0x10000-0xdc00);
+                    break;
+                } else if(UCNV_TO_U_USE_FALLBACK(cnv) ? (c&0xfffe)==0xe000 : c==0xe000) {
+                    /* output roundtrip BMP code point above 0xd800 or fallback BMP code point */
+                    c=unicodeCodeUnits[offset];
+                    break;
+                } else if(c==0xffff) {
+                    /* callback(illegal) */
+                    *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                }
+            } else if(action==MBCS_STATE_VALID_DIRECT_20 ||
+                      (action==MBCS_STATE_FALLBACK_DIRECT_20 && UCNV_TO_U_USE_FALLBACK(cnv))
+            ) {
+                /* output supplementary code point */
+                c=(UChar32)(MBCS_ENTRY_FINAL_VALUE(entry)+0x10000);
+                break;
+            } else if(action==MBCS_STATE_CHANGE_ONLY) {
+                /*
+                 * This serves as a state change without any output.
+                 * It is useful for reading simple stateful encodings,
+                 * for example using just Shift-In/Shift-Out codes.
+                 * The 21 unused bits may later be used for more sophisticated
+                 * state transitions.
+                 */
+                if(cnv->sharedData->mbcs.dbcsOnlyState!=0) {
+                    /* SI/SO are illegal for DBCS-only conversion */
+                    state=(uint8_t)(cnv->mode); /* restore the previous state */
+
+                    /* callback(illegal) */
+                    *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                }
+            } else if(action==MBCS_STATE_FALLBACK_DIRECT_16) {
+                if(UCNV_TO_U_USE_FALLBACK(cnv)) {
+                    /* output BMP code point */
+                    c=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+                    break;
+                }
+            } else if(action==MBCS_STATE_UNASSIGNED) {
+                /* just fall through */
+            } else if(action==MBCS_STATE_ILLEGAL) {
+                /* callback(illegal) */
+                *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+            } else {
+                /* reserved (must never occur), or only state change */
+                offset=0;
+                lastSource=source;
+                continue;
+            }
+
+            /* end of action codes: prepare for a new character */
+            offset=0;
+
+            if(U_FAILURE(*pErrorCode)) {
+                /* callback(illegal) */
+                break;
+            } else /* unassigned sequence */ {
+                /* defer to the generic implementation */
+                cnv->toUnicodeStatus=0;
+                cnv->mode=state;
+                pArgs->source=(const char *)lastSource;
+                return UCNV_GET_NEXT_UCHAR_USE_TO_U;
+            }
+        }
+    }
+
+    if(c<0) {
+        if(U_SUCCESS(*pErrorCode) && source==sourceLimit && lastSource<source) {
+            /* incomplete character byte sequence */
+            uint8_t *bytes=cnv->toUBytes;
+            cnv->toULength=(int8_t)(source-lastSource);
+            do {
+                *bytes++=*lastSource++;
+            } while(lastSource<source);
+            *pErrorCode=U_TRUNCATED_CHAR_FOUND;
+        } else if(U_FAILURE(*pErrorCode)) {
+            /* callback(illegal) */
+            /*
+             * Ticket 5691: consistent illegal sequences:
+             * - We include at least the first byte in the illegal sequence.
+             * - If any of the non-initial bytes could be the start of a character,
+             *   we stop the illegal sequence before the first one of those.
+             */
+            UBool isDBCSOnly=(UBool)(cnv->sharedData->mbcs.dbcsOnlyState!=0);
+            uint8_t *bytes=cnv->toUBytes;
+            *bytes++=*lastSource++;     /* first byte */
+            if(lastSource==source) {
+                cnv->toULength=1;
+            } else /* lastSource<source: multi-byte character */ {
+                int8_t i;
+                for(i=1;
+                    lastSource<source && !isSingleOrLead(stateTable, state, isDBCSOnly, *lastSource);
+                    ++i
+                ) {
+                    *bytes++=*lastSource++;
+                }
+                cnv->toULength=i;
+                source=lastSource;
+            }
+        } else {
+            /* no output because of empty input or only state changes */
+            *pErrorCode=U_INDEX_OUTOFBOUNDS_ERROR;
+        }
+        c=0xffff;
+    }
+
+    /* set the converter state back into UConverter, ready for a new character */
+    cnv->toUnicodeStatus=0;
+    cnv->mode=state;
+
+    /* write back the updated pointer */
+    pArgs->source=(const char *)source;
+    return c;
+}
+
+#if 0
+/*
+ * Code disabled 2002dec09 (ICU 2.4) because it is not currently used in ICU. markus
+ * Removal improves code coverage.
+ */
+/**
+ * This version of ucnv_MBCSSimpleGetNextUChar() is optimized for single-byte, single-state codepages.
+ * It does not handle the EBCDIC swaplfnl option (set in UConverter).
+ * It does not handle conversion extensions (_extToU()).
+ */
+U_CFUNC UChar32
+ucnv_MBCSSingleSimpleGetNextUChar(UConverterSharedData *sharedData,
+                              uint8_t b, UBool useFallback) {
+    int32_t entry;
+    uint8_t action;
+
+    entry=sharedData->mbcs.stateTable[0][b];
+    /* MBCS_ENTRY_IS_FINAL(entry) */
+
+    if(MBCS_ENTRY_FINAL_IS_VALID_DIRECT_16(entry)) {
+        /* output BMP code point */
+        return (UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+    }
+
+    /*
+     * An if-else-if chain provides more reliable performance for
+     * the most common cases compared to a switch.
+     */
+    action=(uint8_t)(MBCS_ENTRY_FINAL_ACTION(entry));
+    if(action==MBCS_STATE_VALID_DIRECT_20) {
+        /* output supplementary code point */
+        return 0x10000+MBCS_ENTRY_FINAL_VALUE(entry);
+    } else if(action==MBCS_STATE_FALLBACK_DIRECT_16) {
+        if(!TO_U_USE_FALLBACK(useFallback)) {
+            return 0xfffe;
+        }
+        /* output BMP code point */
+        return (UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+    } else if(action==MBCS_STATE_FALLBACK_DIRECT_20) {
+        if(!TO_U_USE_FALLBACK(useFallback)) {
+            return 0xfffe;
+        }
+        /* output supplementary code point */
+        return 0x10000+MBCS_ENTRY_FINAL_VALUE(entry);
+    } else if(action==MBCS_STATE_UNASSIGNED) {
+        return 0xfffe;
+    } else if(action==MBCS_STATE_ILLEGAL) {
+        return 0xffff;
+    } else {
+        /* reserved, must never occur */
+        return 0xffff;
+    }
+}
+#endif
+
+/*
+ * This is a simple version of _MBCSGetNextUChar() that is used
+ * by other converter implementations.
+ * It only returns an "assigned" result if it consumes the entire input.
+ * It does not use state from the converter, nor error codes.
+ * It does not handle the EBCDIC swaplfnl option (set in UConverter).
+ * It handles conversion extensions but not GB 18030.
+ *
+ * Return value:
+ * U+fffe   unassigned
+ * U+ffff   illegal
+ * otherwise the Unicode code point
+ */
+U_CFUNC UChar32
+ucnv_MBCSSimpleGetNextUChar(UConverterSharedData *sharedData,
+                        const char *source, int32_t length,
+                        UBool useFallback) {
+    const int32_t (*stateTable)[256];
+    const uint16_t *unicodeCodeUnits;
+
+    uint32_t offset;
+    uint8_t state, action;
+
+    UChar32 c;
+    int32_t i, entry;
+
+    if(length<=0) {
+        /* no input at all: "illegal" */
+        return 0xffff;
+    }
+
+#if 0
+/*
+ * Code disabled 2002dec09 (ICU 2.4) because it is not currently used in ICU. markus
+ * TODO In future releases, verify that this function is never called for SBCS
+ * conversions, i.e., that sharedData->mbcs.countStates==1 is still true.
+ * Removal improves code coverage.
+ */
+    /* use optimized function if possible */
+    if(sharedData->mbcs.countStates==1) {
+        if(length==1) {
+            return ucnv_MBCSSingleSimpleGetNextUChar(sharedData, (uint8_t)*source, useFallback);
+        } else {
+            return 0xffff; /* illegal: more than a single byte for an SBCS converter */
+        }
+    }
+#endif
+
+    /* set up the local pointers */
+    stateTable=sharedData->mbcs.stateTable;
+    unicodeCodeUnits=sharedData->mbcs.unicodeCodeUnits;
+
+    /* converter state */
+    offset=0;
+    state=sharedData->mbcs.dbcsOnlyState;
+
+    /* conversion loop */
+    for(i=0;;) {
+        entry=stateTable[state][(uint8_t)source[i++]];
+        if(MBCS_ENTRY_IS_TRANSITION(entry)) {
+            state=(uint8_t)MBCS_ENTRY_TRANSITION_STATE(entry);
+            offset+=MBCS_ENTRY_TRANSITION_OFFSET(entry);
+
+            if(i==length) {
+                return 0xffff; /* truncated character */
+            }
+        } else {
+            /*
+             * An if-else-if chain provides more reliable performance for
+             * the most common cases compared to a switch.
+             */
+            action=(uint8_t)(MBCS_ENTRY_FINAL_ACTION(entry));
+            if(action==MBCS_STATE_VALID_16) {
+                offset+=MBCS_ENTRY_FINAL_VALUE_16(entry);
+                c=unicodeCodeUnits[offset];
+                if(c!=0xfffe) {
+                    /* done */
+                } else if(UCNV_TO_U_USE_FALLBACK(cnv)) {
+                    c=ucnv_MBCSGetFallback(&sharedData->mbcs, offset);
+                /* else done with 0xfffe */
+                }
+                break;
+            } else if(action==MBCS_STATE_VALID_DIRECT_16) {
+                /* output BMP code point */
+                c=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+                break;
+            } else if(action==MBCS_STATE_VALID_16_PAIR) {
+                offset+=MBCS_ENTRY_FINAL_VALUE_16(entry);
+                c=unicodeCodeUnits[offset++];
+                if(c<0xd800) {
+                    /* output BMP code point below 0xd800 */
+                } else if(UCNV_TO_U_USE_FALLBACK(cnv) ? c<=0xdfff : c<=0xdbff) {
+                    /* output roundtrip or fallback supplementary code point */
+                    c=(UChar32)(((c&0x3ff)<<10)+unicodeCodeUnits[offset]+(0x10000-0xdc00));
+                } else if(UCNV_TO_U_USE_FALLBACK(cnv) ? (c&0xfffe)==0xe000 : c==0xe000) {
+                    /* output roundtrip BMP code point above 0xd800 or fallback BMP code point */
+                    c=unicodeCodeUnits[offset];
+                } else if(c==0xffff) {
+                    return 0xffff;
+                } else {
+                    c=0xfffe;
+                }
+                break;
+            } else if(action==MBCS_STATE_VALID_DIRECT_20) {
+                /* output supplementary code point */
+                c=0x10000+MBCS_ENTRY_FINAL_VALUE(entry);
+                break;
+            } else if(action==MBCS_STATE_FALLBACK_DIRECT_16) {
+                if(!TO_U_USE_FALLBACK(useFallback)) {
+                    c=0xfffe;
+                    break;
+                }
+                /* output BMP code point */
+                c=(UChar)MBCS_ENTRY_FINAL_VALUE_16(entry);
+                break;
+            } else if(action==MBCS_STATE_FALLBACK_DIRECT_20) {
+                if(!TO_U_USE_FALLBACK(useFallback)) {
+                    c=0xfffe;
+                    break;
+                }
+                /* output supplementary code point */
+                c=0x10000+MBCS_ENTRY_FINAL_VALUE(entry);
+                break;
+            } else if(action==MBCS_STATE_UNASSIGNED) {
+                c=0xfffe;
+                break;
+            }
+
+            /*
+             * forbid MBCS_STATE_CHANGE_ONLY for this function,
+             * and MBCS_STATE_ILLEGAL and reserved action codes
+             */
+            return 0xffff;
+        }
+    }
+
+    if(i!=length) {
+        /* illegal for this function: not all input consumed */
+        return 0xffff;
+    }
+
+    if(c==0xfffe) {
+        /* try an extension mapping */
+        const int32_t *cx=sharedData->mbcs.extIndexes;
+        if(cx!=NULL) {
+            return ucnv_extSimpleMatchToU(cx, source, length, useFallback);
+        }
+    }
+
+    return c;
+}
+
+/* MBCS-from-Unicode conversion functions ----------------------------------- */
+
+/* This version of ucnv_MBCSFromUnicodeWithOffsets() is optimized for double-byte codepages. */
+static void
+ucnv_MBCSDoubleFromUnicodeWithOffsets(UConverterFromUnicodeArgs *pArgs,
+                                  UErrorCode *pErrorCode) {
+    UConverter *cnv;
+    const UChar *source, *sourceLimit;
+    uint8_t *target;
+    int32_t targetCapacity;
+    int32_t *offsets;
+
+    const uint16_t *table;
+    const uint16_t *mbcsIndex;
+    const uint8_t *bytes;
+
+    UChar32 c;
+
+    int32_t sourceIndex, nextSourceIndex;
+
+    uint32_t stage2Entry;
+    uint32_t asciiRoundtrips;
+    uint32_t value;
+    uint8_t unicodeMask;
+
+    /* use optimized function if possible */
+    cnv=pArgs->converter;
+    unicodeMask=cnv->sharedData->mbcs.unicodeMask;
+
+    /* set up the local pointers */
+    source=pArgs->source;
+    sourceLimit=pArgs->sourceLimit;
+    target=(uint8_t *)pArgs->target;
+    targetCapacity=(int32_t)(pArgs->targetLimit-pArgs->target);
+    offsets=pArgs->offsets;
+
+    table=cnv->sharedData->mbcs.fromUnicodeTable;
+    mbcsIndex=cnv->sharedData->mbcs.mbcsIndex;
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        bytes=cnv->sharedData->mbcs.swapLFNLFromUnicodeBytes;
+    } else {
+        bytes=cnv->sharedData->mbcs.fromUnicodeBytes;
+    }
+    asciiRoundtrips=cnv->sharedData->mbcs.asciiRoundtrips;
+
+    /* get the converter state from UConverter */
+    c=cnv->fromUChar32;
+
+    /* sourceIndex=-1 if the current character began in the previous buffer */
+    sourceIndex= c==0 ? 0 : -1;
+    nextSourceIndex=0;
+
+    /* conversion loop */
+    if(c!=0 && targetCapacity>0) {
+        goto getTrail;
+    }
+
+    while(source<sourceLimit) {
+        /*
+         * This following test is to see if available input would overflow the output.
+         * It does not catch output of more than one byte that
+         * overflows as a result of a multi-byte character or callback output
+         * from the last source character.
+         * Therefore, those situations also test for overflows and will
+         * then break the loop, too.
+         */
+        if(targetCapacity>0) {
+            /*
+             * Get a correct Unicode code point:
+             * a single UChar for a BMP code point or
+             * a matched surrogate pair for a "supplementary code point".
+             */
+            c=*source++;
+            ++nextSourceIndex;
+            if(c<=0x7f && IS_ASCII_ROUNDTRIP(c, asciiRoundtrips)) {
+                *target++=(uint8_t)c;
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                    sourceIndex=nextSourceIndex;
+                }
+                --targetCapacity;
+                c=0;
+                continue;
+            }
+            /*
+             * utf8Friendly table: Test for <=0xd7ff rather than <=MBCS_FAST_MAX
+             * to avoid dealing with surrogates.
+             * MBCS_FAST_MAX must be >=0xd7ff.
+             */
+            if(c<=0xd7ff) {
+                value=DBCS_RESULT_FROM_MOST_BMP(mbcsIndex, (const uint16_t *)bytes, c);
+                /* There are only roundtrips (!=0) and no-mapping (==0) entries. */
+                if(value==0) {
+                    goto unassigned;
+                }
+                /* output the value */
+            } else {
+                /*
+                 * This also tests if the codepage maps single surrogates.
+                 * If it does, then surrogates are not paired but mapped separately.
+                 * Note that in this case unmatched surrogates are not detected.
+                 */
+                if(UTF_IS_SURROGATE(c) && !(unicodeMask&UCNV_HAS_SURROGATES)) {
+                    if(UTF_IS_SURROGATE_FIRST(c)) {
+getTrail:
+                        if(source<sourceLimit) {
+                            /* test the following code unit */
+                            UChar trail=*source;
+                            if(UTF_IS_SECOND_SURROGATE(trail)) {
+                                ++source;
+                                ++nextSourceIndex;
+                                c=UTF16_GET_PAIR_VALUE(c, trail);
+                                if(!(unicodeMask&UCNV_HAS_SUPPLEMENTARY)) {
+                                    /* BMP-only codepages are stored without stage 1 entries for supplementary code points */
+                                    /* callback(unassigned) */
+                                    goto unassigned;
+                                }
+                                /* convert this supplementary code point */
+                                /* exit this condition tree */
+                            } else {
+                                /* this is an unmatched lead code unit (1st surrogate) */
+                                /* callback(illegal) */
+                                *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                                break;
+                            }
+                        } else {
+                            /* no more input */
+                            break;
+                        }
+                    } else {
+                        /* this is an unmatched trail code unit (2nd surrogate) */
+                        /* callback(illegal) */
+                        *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                        break;
+                    }
+                }
+
+                /* convert the Unicode code point in c into codepage bytes */
+                stage2Entry=MBCS_STAGE_2_FROM_U(table, c);
+
+                /* get the bytes and the length for the output */
+                /* MBCS_OUTPUT_2 */
+                value=MBCS_VALUE_2_FROM_STAGE_2(bytes, stage2Entry, c);
+
+                /* is this code point assigned, or do we use fallbacks? */
+                if(!(MBCS_FROM_U_IS_ROUNDTRIP(stage2Entry, c) ||
+                     (UCNV_FROM_U_USE_FALLBACK(cnv, c) && value!=0))
+                ) {
+                    /*
+                     * We allow a 0 byte output if the "assigned" bit is set for this entry.
+                     * There is no way with this data structure for fallback output
+                     * to be a zero byte.
+                     */
+
+unassigned:
+                    /* try an extension mapping */
+                    pArgs->source=source;
+                    c=_extFromU(cnv, cnv->sharedData,
+                                c, &source, sourceLimit,
+                                &target, target+targetCapacity,
+                                &offsets, sourceIndex,
+                                pArgs->flush,
+                                pErrorCode);
+                    nextSourceIndex+=(int32_t)(source-pArgs->source);
+
+                    if(U_FAILURE(*pErrorCode)) {
+                        /* not mappable or buffer overflow */
+                        break;
+                    } else {
+                        /* a mapping was written to the target, continue */
+
+                        /* recalculate the targetCapacity after an extension mapping */
+                        targetCapacity=(int32_t)(pArgs->targetLimit-(char *)target);
+
+                        /* normal end of conversion: prepare for a new character */
+                        sourceIndex=nextSourceIndex;
+                        continue;
+                    }
+                }
+            }
+
+            /* write the output character bytes from value and length */
+            /* from the first if in the loop we know that targetCapacity>0 */
+            if(value<=0xff) {
+                /* this is easy because we know that there is enough space */
+                *target++=(uint8_t)value;
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+                --targetCapacity;
+            } else /* length==2 */ {
+                *target++=(uint8_t)(value>>8);
+                if(2<=targetCapacity) {
+                    *target++=(uint8_t)value;
+                    if(offsets!=NULL) {
+                        *offsets++=sourceIndex;
+                        *offsets++=sourceIndex;
+                    }
+                    targetCapacity-=2;
+                } else {
+                    if(offsets!=NULL) {
+                        *offsets++=sourceIndex;
+                    }
+                    cnv->charErrorBuffer[0]=(char)value;
+                    cnv->charErrorBufferLength=1;
+
+                    /* target overflow */
+                    targetCapacity=0;
+                    *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+                    c=0;
+                    break;
+                }
+            }
+
+            /* normal end of conversion: prepare for a new character */
+            c=0;
+            sourceIndex=nextSourceIndex;
+            continue;
+        } else {
+            /* target is full */
+            *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+            break;
+        }
+    }
+
+    /* set the converter state back into UConverter */
+    cnv->fromUChar32=c;
+
+    /* write back the updated pointers */
+    pArgs->source=source;
+    pArgs->target=(char *)target;
+    pArgs->offsets=offsets;
+}
+
+/* This version of ucnv_MBCSFromUnicodeWithOffsets() is optimized for single-byte codepages. */
+static void
+ucnv_MBCSSingleFromUnicodeWithOffsets(UConverterFromUnicodeArgs *pArgs,
+                                  UErrorCode *pErrorCode) {
+    UConverter *cnv;
+    const UChar *source, *sourceLimit;
+    uint8_t *target;
+    int32_t targetCapacity;
+    int32_t *offsets;
+
+    const uint16_t *table;
+    const uint16_t *results;
+
+    UChar32 c;
+
+    int32_t sourceIndex, nextSourceIndex;
+
+    uint16_t value, minValue;
+    UBool hasSupplementary;
+
+    /* set up the local pointers */
+    cnv=pArgs->converter;
+    source=pArgs->source;
+    sourceLimit=pArgs->sourceLimit;
+    target=(uint8_t *)pArgs->target;
+    targetCapacity=(int32_t)(pArgs->targetLimit-pArgs->target);
+    offsets=pArgs->offsets;
+
+    table=cnv->sharedData->mbcs.fromUnicodeTable;
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        results=(uint16_t *)cnv->sharedData->mbcs.swapLFNLFromUnicodeBytes;
+    } else {
+        results=(uint16_t *)cnv->sharedData->mbcs.fromUnicodeBytes;
+    }
+
+    if(cnv->useFallback) {
+        /* use all roundtrip and fallback results */
+        minValue=0x800;
+    } else {
+        /* use only roundtrips and fallbacks from private-use characters */
+        minValue=0xc00;
+    }
+    hasSupplementary=(UBool)(cnv->sharedData->mbcs.unicodeMask&UCNV_HAS_SUPPLEMENTARY);
+
+    /* get the converter state from UConverter */
+    c=cnv->fromUChar32;
+
+    /* sourceIndex=-1 if the current character began in the previous buffer */
+    sourceIndex= c==0 ? 0 : -1;
+    nextSourceIndex=0;
+
+    /* conversion loop */
+    if(c!=0 && targetCapacity>0) {
+        goto getTrail;
+    }
+
+    while(source<sourceLimit) {
+        /*
+         * This following test is to see if available input would overflow the output.
+         * It does not catch output of more than one byte that
+         * overflows as a result of a multi-byte character or callback output
+         * from the last source character.
+         * Therefore, those situations also test for overflows and will
+         * then break the loop, too.
+         */
+        if(targetCapacity>0) {
+            /*
+             * Get a correct Unicode code point:
+             * a single UChar for a BMP code point or
+             * a matched surrogate pair for a "supplementary code point".
+             */
+            c=*source++;
+            ++nextSourceIndex;
+            if(UTF_IS_SURROGATE(c)) {
+                if(UTF_IS_SURROGATE_FIRST(c)) {
+getTrail:
+                    if(source<sourceLimit) {
+                        /* test the following code unit */
+                        UChar trail=*source;
+                        if(UTF_IS_SECOND_SURROGATE(trail)) {
+                            ++source;
+                            ++nextSourceIndex;
+                            c=UTF16_GET_PAIR_VALUE(c, trail);
+                            if(!hasSupplementary) {
+                                /* BMP-only codepages are stored without stage 1 entries for supplementary code points */
+                                /* callback(unassigned) */
+                                goto unassigned;
+                            }
+                            /* convert this supplementary code point */
+                            /* exit this condition tree */
+                        } else {
+                            /* this is an unmatched lead code unit (1st surrogate) */
+                            /* callback(illegal) */
+                            *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                            break;
+                        }
+                    } else {
+                        /* no more input */
+                        break;
+                    }
+                } else {
+                    /* this is an unmatched trail code unit (2nd surrogate) */
+                    /* callback(illegal) */
+                    *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                    break;
+                }
+            }
+
+            /* convert the Unicode code point in c into codepage bytes */
+            value=MBCS_SINGLE_RESULT_FROM_U(table, results, c);
+
+            /* is this code point assigned, or do we use fallbacks? */
+            if(value>=minValue) {
+                /* assigned, write the output character bytes from value and length */
+                /* length==1 */
+                /* this is easy because we know that there is enough space */
+                *target++=(uint8_t)value;
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                }
+                --targetCapacity;
+
+                /* normal end of conversion: prepare for a new character */
+                c=0;
+                sourceIndex=nextSourceIndex;
+            } else { /* unassigned */
+unassigned:
+                /* try an extension mapping */
+                pArgs->source=source;
+                c=_extFromU(cnv, cnv->sharedData,
+                            c, &source, sourceLimit,
+                            &target, target+targetCapacity,
+                            &offsets, sourceIndex,
+                            pArgs->flush,
+                            pErrorCode);
+                nextSourceIndex+=(int32_t)(source-pArgs->source);
+
+                if(U_FAILURE(*pErrorCode)) {
+                    /* not mappable or buffer overflow */
+                    break;
+                } else {
+                    /* a mapping was written to the target, continue */
+
+                    /* recalculate the targetCapacity after an extension mapping */
+                    targetCapacity=(int32_t)(pArgs->targetLimit-(char *)target);
+
+                    /* normal end of conversion: prepare for a new character */
+                    sourceIndex=nextSourceIndex;
+                }
+            }
+        } else {
+            /* target is full */
+            *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+            break;
+        }
+    }
+
+    /* set the converter state back into UConverter */
+    cnv->fromUChar32=c;
+
+    /* write back the updated pointers */
+    pArgs->source=source;
+    pArgs->target=(char *)target;
+    pArgs->offsets=offsets;
+}
+
+/*
+ * This version of ucnv_MBCSFromUnicode() is optimized for single-byte codepages
+ * that map only to and from the BMP.
+ * In addition to single-byte/state optimizations, the offset calculations
+ * become much easier.
+ * It would be possible to use the sbcsIndex for UTF-8-friendly tables,
+ * but measurements have shown that this diminishes performance
+ * in more cases than it improves it.
+ * See SVN revision 21013 (2007-feb-06) for the last version with #if switches
+ * for various MBCS and SBCS optimizations.
+ */
+static void
+ucnv_MBCSSingleFromBMPWithOffsets(UConverterFromUnicodeArgs *pArgs,
+                              UErrorCode *pErrorCode) {
+    UConverter *cnv;
+    const UChar *source, *sourceLimit, *lastSource;
+    uint8_t *target;
+    int32_t targetCapacity, length;
+    int32_t *offsets;
+
+    const uint16_t *table;
+    const uint16_t *results;
+
+    UChar32 c;
+
+    int32_t sourceIndex;
+
+    uint32_t asciiRoundtrips;
+    uint16_t value, minValue;
+
+    /* set up the local pointers */
+    cnv=pArgs->converter;
+    source=pArgs->source;
+    sourceLimit=pArgs->sourceLimit;
+    target=(uint8_t *)pArgs->target;
+    targetCapacity=(int32_t)(pArgs->targetLimit-pArgs->target);
+    offsets=pArgs->offsets;
+
+    table=cnv->sharedData->mbcs.fromUnicodeTable;
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        results=(uint16_t *)cnv->sharedData->mbcs.swapLFNLFromUnicodeBytes;
+    } else {
+        results=(uint16_t *)cnv->sharedData->mbcs.fromUnicodeBytes;
+    }
+    asciiRoundtrips=cnv->sharedData->mbcs.asciiRoundtrips;
+
+    if(cnv->useFallback) {
+        /* use all roundtrip and fallback results */
+        minValue=0x800;
+    } else {
+        /* use only roundtrips and fallbacks from private-use characters */
+        minValue=0xc00;
+    }
+
+    /* get the converter state from UConverter */
+    c=cnv->fromUChar32;
+
+    /* sourceIndex=-1 if the current character began in the previous buffer */
+    sourceIndex= c==0 ? 0 : -1;
+    lastSource=source;
+
+    /*
+     * since the conversion here is 1:1 UChar:uint8_t, we need only one counter
+     * for the minimum of the sourceLength and targetCapacity
+     */
+    length=(int32_t)(sourceLimit-source);
+    if(length<targetCapacity) {
+        targetCapacity=length;
+    }
+
+    /* conversion loop */
+    if(c!=0 && targetCapacity>0) {
+        goto getTrail;
+    }
+
+#if MBCS_UNROLL_SINGLE_FROM_BMP
+    /* unrolling makes it slower on Pentium III/Windows 2000?! */
+    /* unroll the loop with the most common case */
+unrolled:
+    if(targetCapacity>=4) {
+        int32_t count, loops;
+        uint16_t andedValues;
+
+        loops=count=targetCapacity>>2;
+        do {
+            c=*source++;
+            andedValues=value=MBCS_SINGLE_RESULT_FROM_U(table, results, c);
+            *target++=(uint8_t)value;
+            c=*source++;
+            andedValues&=value=MBCS_SINGLE_RESULT_FROM_U(table, results, c);
+            *target++=(uint8_t)value;
+            c=*source++;
+            andedValues&=value=MBCS_SINGLE_RESULT_FROM_U(table, results, c);
+            *target++=(uint8_t)value;
+            c=*source++;
+            andedValues&=value=MBCS_SINGLE_RESULT_FROM_U(table, results, c);
+            *target++=(uint8_t)value;
+
+            /* were all 4 entries really valid? */
+            if(andedValues<minValue) {
+                /* no, return to the first of these 4 */
+                source-=4;
+                target-=4;
+                break;
+            }
+        } while(--count>0);
+        count=loops-count;
+        targetCapacity-=4*count;
+
+        if(offsets!=NULL) {
+            lastSource+=4*count;
+            while(count>0) {
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                *offsets++=sourceIndex++;
+                --count;
+            }
+        }
+
+        c=0;
+    }
+#endif
+
+    while(targetCapacity>0) {
+        /*
+         * Get a correct Unicode code point:
+         * a single UChar for a BMP code point or
+         * a matched surrogate pair for a "supplementary code point".
+         */
+        c=*source++;
+        /*
+         * Do not immediately check for single surrogates:
+         * Assume that they are unassigned and check for them in that case.
+         * This speeds up the conversion of assigned characters.
+         */
+        /* convert the Unicode code point in c into codepage bytes */
+        if(c<=0x7f && IS_ASCII_ROUNDTRIP(c, asciiRoundtrips)) {
+            *target++=(uint8_t)c;
+            --targetCapacity;
+            c=0;
+            continue;
+        }
+        value=MBCS_SINGLE_RESULT_FROM_U(table, results, c);
+        /* is this code point assigned, or do we use fallbacks? */
+        if(value>=minValue) {
+            /* assigned, write the output character bytes from value and length */
+            /* length==1 */
+            /* this is easy because we know that there is enough space */
+            *target++=(uint8_t)value;
+            --targetCapacity;
+
+            /* normal end of conversion: prepare for a new character */
+            c=0;
+            continue;
+        } else if(!UTF_IS_SURROGATE(c)) {
+            /* normal, unassigned BMP character */
+        } else if(UTF_IS_SURROGATE_FIRST(c)) {
+getTrail:
+            if(source<sourceLimit) {
+                /* test the following code unit */
+                UChar trail=*source;
+                if(UTF_IS_SECOND_SURROGATE(trail)) {
+                    ++source;
+                    c=UTF16_GET_PAIR_VALUE(c, trail);
+                    /* this codepage does not map supplementary code points */
+                    /* callback(unassigned) */
+                } else {
+                    /* this is an unmatched lead code unit (1st surrogate) */
+                    /* callback(illegal) */
+                    *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                    break;
+                }
+            } else {
+                /* no more input */
+                if (pArgs->flush) {
+                    *pErrorCode=U_TRUNCATED_CHAR_FOUND;
+                }
+                break;
+            }
+        } else {
+            /* this is an unmatched trail code unit (2nd surrogate) */
+            /* callback(illegal) */
+            *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+            break;
+        }
+
+        /* c does not have a mapping */
+
+        /* get the number of code units for c to correctly advance sourceIndex */
+        length=U16_LENGTH(c);
+
+        /* set offsets since the start or the last extension */
+        if(offsets!=NULL) {
+            int32_t count=(int32_t)(source-lastSource);
+
+            /* do not set the offset for this character */
+            count-=length;
+
+            while(count>0) {
+                *offsets++=sourceIndex++;
+                --count;
+            }
+            /* offsets and sourceIndex are now set for the current character */
+        }
+
+        /* try an extension mapping */
+        lastSource=source;
+        c=_extFromU(cnv, cnv->sharedData,
+                    c, &source, sourceLimit,
+                    &target, (const uint8_t *)(pArgs->targetLimit),
+                    &offsets, sourceIndex,
+                    pArgs->flush,
+                    pErrorCode);
+        sourceIndex+=length+(int32_t)(source-lastSource);
+        lastSource=source;
+
+        if(U_FAILURE(*pErrorCode)) {
+            /* not mappable or buffer overflow */
+            break;
+        } else {
+            /* a mapping was written to the target, continue */
+
+            /* recalculate the targetCapacity after an extension mapping */
+            targetCapacity=(int32_t)(pArgs->targetLimit-(char *)target);
+            length=(int32_t)(sourceLimit-source);
+            if(length<targetCapacity) {
+                targetCapacity=length;
+            }
+        }
+
+#if MBCS_UNROLL_SINGLE_FROM_BMP
+        /* unrolling makes it slower on Pentium III/Windows 2000?! */
+        goto unrolled;
+#endif
+    }
+
+    if(U_SUCCESS(*pErrorCode) && source<sourceLimit && target>=(uint8_t *)pArgs->targetLimit) {
+        /* target is full */
+        *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+    }
+
+    /* set offsets since the start or the last callback */
+    if(offsets!=NULL) {
+        size_t count=source-lastSource;
+        if (count > 0 && *pErrorCode == U_TRUNCATED_CHAR_FOUND) {
+            /*
+            Caller gave us a partial supplementary character,
+            which this function couldn't convert in any case.
+            The callback will handle the offset.
+            */
+            count--;
+        }
+        while(count>0) {
+            *offsets++=sourceIndex++;
+            --count;
+        }
+    }
+
+    /* set the converter state back into UConverter */
+    cnv->fromUChar32=c;
+
+    /* write back the updated pointers */
+    pArgs->source=source;
+    pArgs->target=(char *)target;
+    pArgs->offsets=offsets;
+}
+
+U_CFUNC void
+ucnv_MBCSFromUnicodeWithOffsets(UConverterFromUnicodeArgs *pArgs,
+                            UErrorCode *pErrorCode) {
+    UConverter *cnv;
+    const UChar *source, *sourceLimit;
+    uint8_t *target;
+    int32_t targetCapacity;
+    int32_t *offsets;
+
+    const uint16_t *table;
+    const uint16_t *mbcsIndex;
+    const uint8_t *p, *bytes;
+    uint8_t outputType;
+
+    UChar32 c;
+
+    int32_t prevSourceIndex, sourceIndex, nextSourceIndex;
+
+    uint32_t stage2Entry;
+    uint32_t asciiRoundtrips;
+    uint32_t value;
+    uint8_t si_value[2] = {0, 0}; 
+    uint8_t so_value[2] = {0, 0}; 
+    uint8_t si_value_length, so_value_length;
+    int32_t length = 0, prevLength;
+    uint8_t unicodeMask;
+
+    cnv=pArgs->converter;
+
+    if(cnv->preFromUFirstCP>=0) {
+        /*
+         * pass sourceIndex=-1 because we continue from an earlier buffer
+         * in the future, this may change with continuous offsets
+         */
+        ucnv_extContinueMatchFromU(cnv, pArgs, -1, pErrorCode);
+
+        if(U_FAILURE(*pErrorCode) || cnv->preFromULength<0) {
+            return;
+        }
+    }
+
+    /* use optimized function if possible */
+    outputType=cnv->sharedData->mbcs.outputType;
+    unicodeMask=cnv->sharedData->mbcs.unicodeMask;
+    if(outputType==MBCS_OUTPUT_1 && !(unicodeMask&UCNV_HAS_SURROGATES)) {
+        if(!(unicodeMask&UCNV_HAS_SUPPLEMENTARY)) {
+            ucnv_MBCSSingleFromBMPWithOffsets(pArgs, pErrorCode);
+        } else {
+            ucnv_MBCSSingleFromUnicodeWithOffsets(pArgs, pErrorCode);
+        }
+        return;
+    } else if(outputType==MBCS_OUTPUT_2 && cnv->sharedData->mbcs.utf8Friendly) {
+        ucnv_MBCSDoubleFromUnicodeWithOffsets(pArgs, pErrorCode);
+        return;
+    }
+
+    /* set up the local pointers */
+    source=pArgs->source;
+    sourceLimit=pArgs->sourceLimit;
+    target=(uint8_t *)pArgs->target;
+    targetCapacity=(int32_t)(pArgs->targetLimit-pArgs->target);
+    offsets=pArgs->offsets;
+
+    table=cnv->sharedData->mbcs.fromUnicodeTable;
+    if(cnv->sharedData->mbcs.utf8Friendly) {
+        mbcsIndex=cnv->sharedData->mbcs.mbcsIndex;
+    } else {
+        mbcsIndex=NULL;
+    }
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        bytes=cnv->sharedData->mbcs.swapLFNLFromUnicodeBytes;
+    } else {
+        bytes=cnv->sharedData->mbcs.fromUnicodeBytes;
+    }
+    asciiRoundtrips=cnv->sharedData->mbcs.asciiRoundtrips;
+
+    /* get the converter state from UConverter */
+    c=cnv->fromUChar32;
+
+    if(outputType==MBCS_OUTPUT_2_SISO) {
+        prevLength=cnv->fromUnicodeStatus;
+        if(prevLength==0) {
+            /* set the real value */
+            prevLength=1;
+        }
+    } else {
+        /* prevent fromUnicodeStatus from being set to something non-0 */
+        prevLength=0;
+    }
+
+    /* sourceIndex=-1 if the current character began in the previous buffer */
+    prevSourceIndex=-1;
+    sourceIndex= c==0 ? 0 : -1;
+    nextSourceIndex=0;
+
+    /* Get the SI/SO character for the converter */
+    si_value_length = getSISOBytes(SI, cnv->options, si_value);
+    so_value_length = getSISOBytes(SO, cnv->options, so_value);
+
+    /* conversion loop */
+    /*
+     * This is another piece of ugly code:
+     * A goto into the loop if the converter state contains a first surrogate
+     * from the previous function call.
+     * It saves me to check in each loop iteration a check of if(c==0)
+     * and duplicating the trail-surrogate-handling code in the else
+     * branch of that check.
+     * I could not find any other way to get around this other than
+     * using a function call for the conversion and callback, which would
+     * be even more inefficient.
+     *
+     * Markus Scherer 2000-jul-19
+     */
+    if(c!=0 && targetCapacity>0) {
+        goto getTrail;
+    }
+
+    while(source<sourceLimit) {
+        /*
+         * This following test is to see if available input would overflow the output.
+         * It does not catch output of more than one byte that
+         * overflows as a result of a multi-byte character or callback output
+         * from the last source character.
+         * Therefore, those situations also test for overflows and will
+         * then break the loop, too.
+         */
+        if(targetCapacity>0) {
+            /*
+             * Get a correct Unicode code point:
+             * a single UChar for a BMP code point or
+             * a matched surrogate pair for a "supplementary code point".
+             */
+            c=*source++;
+            ++nextSourceIndex;
+            if(c<=0x7f && IS_ASCII_ROUNDTRIP(c, asciiRoundtrips)) {
+                *target++=(uint8_t)c;
+                if(offsets!=NULL) {
+                    *offsets++=sourceIndex;
+                    prevSourceIndex=sourceIndex;
+                    sourceIndex=nextSourceIndex;
+                }
+                --targetCapacity;
+                c=0;
+                continue;
+            }
+            /*
+             * utf8Friendly table: Test for <=0xd7ff rather than <=MBCS_FAST_MAX
+             * to avoid dealing with surrogates.
+             * MBCS_FAST_MAX must be >=0xd7ff.
+             */
+            if(c<=0xd7ff && mbcsIndex!=NULL) {
+                value=mbcsIndex[c>>6];
+
+                /* get the bytes and the length for the output (copied from below and adapted for utf8Friendly data) */
+                /* There are only roundtrips (!=0) and no-mapping (==0) entries. */
+                switch(outputType) {
+                case MBCS_OUTPUT_2:
+                    value=((const uint16_t *)bytes)[value +(c&0x3f)];
+                    if(value<=0xff) {
+                        if(value==0) {
+                            goto unassigned;
+                        } else {
+                            length=1;
+                        }
+                    } else {
+                        length=2;
+                    }
+                    break;
+                case MBCS_OUTPUT_2_SISO:
+                    /* 1/2-byte stateful with Shift-In/Shift-Out */
+                    /*
+                     * Save the old state in the converter object
+                     * right here, then change the local prevLength state variable if necessary.
+                     * Then, if this character turns out to be unassigned or a fallback that
+                     * is not taken, the callback code must not save the new state in the converter
+                     * because the new state is for a character that is not output.
+                     * However, the callback must still restore the state from the converter
+                     * in case the callback function changed it for its output.
+                     */
+                    cnv->fromUnicodeStatus=prevLength; /* save the old state */
+                    value=((const uint16_t *)bytes)[value +(c&0x3f)];
+                    if(value<=0xff) {
+                        if(value==0) {
+                            goto unassigned;
+                        } else if(prevLength<=1) {
+                            length=1;
+                        } else {
+                            /* change from double-byte mode to single-byte */
+                            if (si_value_length == 1) {
+                                value|=(uint32_t)si_value[0]<<8;
+                                length = 2;
+                            } else if (si_value_length == 2) {
+                                value|=(uint32_t)si_value[1]<<8;
+                                value|=(uint32_t)si_value[0]<<16;
+                                length = 3;
+                            }
+                            prevLength=1;
+                        }
+                    } else {
+                        if(prevLength==2) {
+                            length=2;
+                        } else {
+                            /* change from single-byte mode to double-byte */
+                            if (so_value_length == 1) {
+                                value|=(uint32_t)so_value[0]<<16;
+                                length = 3;
+                            } else if (so_value_length == 2) {
+                                value|=(uint32_t)so_value[1]<<16;
+                                value|=(uint32_t)so_value[0]<<24;
+                                length = 4;
+                            }
+                            prevLength=2;
+                        }
+                    }
+                    break;
+                case MBCS_OUTPUT_DBCS_ONLY:
+                    /* table with single-byte results, but only DBCS mappings used */
+                    value=((const uint16_t *)bytes)[value +(c&0x3f)];
+                    if(value<=0xff) {
+                        /* no mapping or SBCS result, not taken for DBCS-only */
+                        goto unassigned;
+                    } else {
+                        length=2;
+                    }
+                    break;
+                case MBCS_OUTPUT_3:
+                    p=bytes+(value+(c&0x3f))*3;
+                    value=((uint32_t)*p<<16)|((uint32_t)p[1]<<8)|p[2];
+                    if(value<=0xff) {
+                        if(value==0) {
+                            goto unassigned;
+                        } else {
+                            length=1;
+                        }
+                    } else if(value<=0xffff) {
+                        length=2;
+                    } else {
+                        length=3;
+                    }
+                    break;
+                case MBCS_OUTPUT_4:
+                    value=((const uint32_t *)bytes)[value +(c&0x3f)];
+                    if(value<=0xff) {
+                        if(value==0) {
+                            goto unassigned;
+                        } else {
+                            length=1;
+                        }
+                    } else if(value<=0xffff) {
+                        length=2;
+                    } else if(value<=0xffffff) {
+                        length=3;
+                    } else {
+                        length=4;
+                    }
+                    break;
+                case MBCS_OUTPUT_3_EUC:
+                    value=((const uint16_t *)bytes)[value +(c&0x3f)];
+                    /* EUC 16-bit fixed-length representation */
+                    if(value<=0xff) {
+                        if(value==0) {
+                            goto unassigned;
+                        } else {
+                            length=1;
+                        }
+                    } else if((value&0x8000)==0) {
+                        value|=0x8e8000;
+                        length=3;
+                    } else if((value&0x80)==0) {
+                        value|=0x8f0080;
+                        length=3;
+                    } else {
+                        length=2;
+                    }
+                    break;
+                case MBCS_OUTPUT_4_EUC:
+                    p=bytes+(value+(c&0x3f))*3;
+                    value=((uint32_t)*p<<16)|((uint32_t)p[1]<<8)|p[2];
+                    /* EUC 16-bit fixed-length representation applied to the first two bytes */
+                    if(value<=0xff) {
+                        if(value==0) {
+                            goto unassigned;
+                        } else {
+                            length=1;
+                        }
+                    } else if(value<=0xffff) {
+                        length=2;
+                    } else if((value&0x800000)==0) {
+                        value|=0x8e800000;
+                        length=4;
+                    } else if((value&0x8000)==0) {
+                        value|=0x8f008000;
+                        length=4;
+                    } else {
+                        length=3;
+                    }
+                    break;
+                default:
+                    /* must not occur */
+                    /*
+                     * To avoid compiler warnings that value & length may be
+                     * used without having been initialized, we set them here.
+                     * In reality, this is unreachable code.
+                     * Not having a default branch also causes warnings with
+                     * some compilers.
+                     */
+                    value=0;
+                    length=0;
+                    break;
+                }
+                /* output the value */
+            } else {
+                /*
+                 * This also tests if the codepage maps single surrogates.
+                 * If it does, then surrogates are not paired but mapped separately.
+                 * Note that in this case unmatched surrogates are not detected.
+                 */
+                if(UTF_IS_SURROGATE(c) && !(unicodeMask&UCNV_HAS_SURROGATES)) {
+                    if(UTF_IS_SURROGATE_FIRST(c)) {
+getTrail:
+                        if(source<sourceLimit) {
+                            /* test the following code unit */
+                            UChar trail=*source;
+                            if(UTF_IS_SECOND_SURROGATE(trail)) {
+                                ++source;
+                                ++nextSourceIndex;
+                                c=UTF16_GET_PAIR_VALUE(c, trail);
+                                if(!(unicodeMask&UCNV_HAS_SUPPLEMENTARY)) {
+                                    /* BMP-only codepages are stored without stage 1 entries for supplementary code points */
+                                    cnv->fromUnicodeStatus=prevLength; /* save the old state */
+                                    /* callback(unassigned) */
+                                    goto unassigned;
+                                }
+                                /* convert this supplementary code point */
+                                /* exit this condition tree */
+                            } else {
+                                /* this is an unmatched lead code unit (1st surrogate) */
+                                /* callback(illegal) */
+                                *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                                break;
+                            }
+                        } else {
+                            /* no more input */
+                            break;
+                        }
+                    } else {
+                        /* this is an unmatched trail code unit (2nd surrogate) */
+                        /* callback(illegal) */
+                        *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                        break;
+                    }
+                }
+
+                /* convert the Unicode code point in c into codepage bytes */
+
+                /*
+                 * The basic lookup is a triple-stage compact array (trie) lookup.
+                 * For details see the beginning of this file.
+                 *
+                 * Single-byte codepages are handled with a different data structure
+                 * by _MBCSSingle... functions.
+                 *
+                 * The result consists of a 32-bit value from stage 2 and
+                 * a pointer to as many bytes as are stored per character.
+                 * The pointer points to the character's bytes in stage 3.
+                 * Bits 15..0 of the stage 2 entry contain the stage 3 index
+                 * for that pointer, while bits 31..16 are flags for which of
+                 * the 16 characters in the block are roundtrip-assigned.
+                 *
+                 * For 2-byte and 4-byte codepages, the bytes are stored as uint16_t
+                 * respectively as uint32_t, in the platform encoding.
+                 * For 3-byte codepages, the bytes are always stored in big-endian order.
+                 *
+                 * For EUC encodings that use only either 0x8e or 0x8f as the first
+                 * byte of their longest byte sequences, the first two bytes in
+                 * this third stage indicate with their 7th bits whether these bytes
+                 * are to be written directly or actually need to be preceeded by
+                 * one of the two Single-Shift codes. With this, the third stage
+                 * stores one byte fewer per character than the actual maximum length of
+                 * EUC byte sequences.
+                 *
+                 * Other than that, leading zero bytes are removed and the other
+                 * bytes output. A single zero byte may be output if the "assigned"
+                 * bit in stage 2 was on.
+                 * The data structure does not support zero byte output as a fallback,
+                 * and also does not allow output of leading zeros.
+                 */
+                stage2Entry=MBCS_STAGE_2_FROM_U(table, c);
+
+                /* get the bytes and the length for the output */
+                switch(outputType) {
+                case MBCS_OUTPUT_2:
+                    value=MBCS_VALUE_2_FROM_STAGE_2(bytes, stage2Entry, c);
+                    if(value<=0xff) {
+                        length=1;
+                    } else {
+                        length=2;
+                    }
+                    break;
+                case MBCS_OUTPUT_2_SISO:
+                    /* 1/2-byte stateful with Shift-In/Shift-Out */
+                    /*
+                     * Save the old state in the converter object
+                     * right here, then change the local prevLength state variable if necessary.
+                     * Then, if this character turns out to be unassigned or a fallback that
+                     * is not taken, the callback code must not save the new state in the converter
+                     * because the new state is for a character that is not output.
+                     * However, the callback must still restore the state from the converter
+                     * in case the callback function changed it for its output.
+                     */
+                    cnv->fromUnicodeStatus=prevLength; /* save the old state */
+                    value=MBCS_VALUE_2_FROM_STAGE_2(bytes, stage2Entry, c);
+                    if(value<=0xff) {
+                        if(value==0 && MBCS_FROM_U_IS_ROUNDTRIP(stage2Entry, c)==0) {
+                            /* no mapping, leave value==0 */
+                            length=0;
+                        } else if(prevLength<=1) {
+                            length=1;
+                        } else {
+                            /* change from double-byte mode to single-byte */
+                            if (si_value_length == 1) {
+                                value|=(uint32_t)si_value[0]<<8;
+                                length = 2;
+                            } else if (si_value_length == 2) {
+                                value|=(uint32_t)si_value[1]<<8;
+                                value|=(uint32_t)si_value[0]<<16;
+                                length = 3;
+                            }
+                            prevLength=1;
+                        }
+                    } else {
+                        if(prevLength==2) {
+                            length=2;
+                        } else {
+                            /* change from single-byte mode to double-byte */
+                            if (so_value_length == 1) {
+                                value|=(uint32_t)so_value[0]<<16;
+                                length = 3;
+                            } else if (so_value_length == 2) {
+                                value|=(uint32_t)so_value[1]<<16;
+                                value|=(uint32_t)so_value[0]<<24;
+                                length = 4;
+                            }
+                            prevLength=2;
+                        }
+                    }
+                    break;
+                case MBCS_OUTPUT_DBCS_ONLY:
+                    /* table with single-byte results, but only DBCS mappings used */
+                    value=MBCS_VALUE_2_FROM_STAGE_2(bytes, stage2Entry, c);
+                    if(value<=0xff) {
+                        /* no mapping or SBCS result, not taken for DBCS-only */
+                        value=stage2Entry=0; /* stage2Entry=0 to reset roundtrip flags */
+                        length=0;
+                    } else {
+                        length=2;
+                    }
+                    break;
+                case MBCS_OUTPUT_3:
+                    p=MBCS_POINTER_3_FROM_STAGE_2(bytes, stage2Entry, c);
+                    value=((uint32_t)*p<<16)|((uint32_t)p[1]<<8)|p[2];
+                    if(value<=0xff) {
+                        length=1;
+                    } else if(value<=0xffff) {
+                        length=2;
+                    } else {
+                        length=3;
+                    }
+                    break;
+                case MBCS_OUTPUT_4:
+                    value=MBCS_VALUE_4_FROM_STAGE_2(bytes, stage2Entry, c);
+                    if(value<=0xff) {
+                        length=1;
+                    } else if(value<=0xffff) {
+                        length=2;
+                    } else if(value<=0xffffff) {
+                        length=3;
+                    } else {
+                        length=4;
+                    }
+                    break;
+                case MBCS_OUTPUT_3_EUC:
+                    value=MBCS_VALUE_2_FROM_STAGE_2(bytes, stage2Entry, c);
+                    /* EUC 16-bit fixed-length representation */
+                    if(value<=0xff) {
+                        length=1;
+                    } else if((value&0x8000)==0) {
+                        value|=0x8e8000;
+                        length=3;
+                    } else if((value&0x80)==0) {
+                        value|=0x8f0080;
+                        length=3;
+                    } else {
+                        length=2;
+                    }
+                    break;
+                case MBCS_OUTPUT_4_EUC:
+                    p=MBCS_POINTER_3_FROM_STAGE_2(bytes, stage2Entry, c);
+                    value=((uint32_t)*p<<16)|((uint32_t)p[1]<<8)|p[2];
+                    /* EUC 16-bit fixed-length representation applied to the first two bytes */
+                    if(value<=0xff) {
+                        length=1;
+                    } else if(value<=0xffff) {
+                        length=2;
+                    } else if((value&0x800000)==0) {
+                        value|=0x8e800000;
+                        length=4;
+                    } else if((value&0x8000)==0) {
+                        value|=0x8f008000;
+                        length=4;
+                    } else {
+                        length=3;
+                    }
+                    break;
+                default:
+                    /* must not occur */
+                    /*
+                     * To avoid compiler warnings that value & length may be
+                     * used without having been initialized, we set them here.
+                     * In reality, this is unreachable code.
+                     * Not having a default branch also causes warnings with
+                     * some compilers.
+                     */
+                    value=stage2Entry=0; /* stage2Entry=0 to reset roundtrip flags */
+                    length=0;
+                    break;
+                }
+
+                /* is this code point assigned, or do we use fallbacks? */
+                if(!(MBCS_FROM_U_IS_ROUNDTRIP(stage2Entry, c)!=0 ||
+                     (UCNV_FROM_U_USE_FALLBACK(cnv, c) && value!=0))
+                ) {
+                    /*
+                     * We allow a 0 byte output if the "assigned" bit is set for this entry.
+                     * There is no way with this data structure for fallback output
+                     * to be a zero byte.
+                     */
+
+unassigned:
+                    /* try an extension mapping */
+                    pArgs->source=source;
+                    c=_extFromU(cnv, cnv->sharedData,
+                                c, &source, sourceLimit,
+                                &target, target+targetCapacity,
+                                &offsets, sourceIndex,
+                                pArgs->flush,
+                                pErrorCode);
+                    nextSourceIndex+=(int32_t)(source-pArgs->source);
+                    prevLength=cnv->fromUnicodeStatus; /* restore SISO state */
+
+                    if(U_FAILURE(*pErrorCode)) {
+                        /* not mappable or buffer overflow */
+                        break;
+                    } else {
+                        /* a mapping was written to the target, continue */
+
+                        /* recalculate the targetCapacity after an extension mapping */
+                        targetCapacity=(int32_t)(pArgs->targetLimit-(char *)target);
+
+                        /* normal end of conversion: prepare for a new character */
+                        if(offsets!=NULL) {
+                            prevSourceIndex=sourceIndex;
+                            sourceIndex=nextSourceIndex;
+                        }
+                        continue;
+                    }
+                }
+            }
+
+            /* write the output character bytes from value and length */
+            /* from the first if in the loop we know that targetCapacity>0 */
+            if(length<=targetCapacity) {
+                if(offsets==NULL) {
+                    switch(length) {
+                        /* each branch falls through to the next one */
+                    case 4:
+                        *target++=(uint8_t)(value>>24);
+                    case 3:
+                        *target++=(uint8_t)(value>>16);
+                    case 2:
+                        *target++=(uint8_t)(value>>8);
+                    case 1:
+                        *target++=(uint8_t)value;
+                    default:
+                        /* will never occur */
+                        break;
+                    }
+                } else {
+                    switch(length) {
+                        /* each branch falls through to the next one */
+                    case 4:
+                        *target++=(uint8_t)(value>>24);
+                        *offsets++=sourceIndex;
+                    case 3:
+                        *target++=(uint8_t)(value>>16);
+                        *offsets++=sourceIndex;
+                    case 2:
+                        *target++=(uint8_t)(value>>8);
+                        *offsets++=sourceIndex;
+                    case 1:
+                        *target++=(uint8_t)value;
+                        *offsets++=sourceIndex;
+                    default:
+                        /* will never occur */
+                        break;
+                    }
+                }
+                targetCapacity-=length;
+            } else {
+                uint8_t *charErrorBuffer;
+
+                /*
+                 * We actually do this backwards here:
+                 * In order to save an intermediate variable, we output
+                 * first to the overflow buffer what does not fit into the
+                 * regular target.
+                 */
+                /* we know that 1<=targetCapacity<length<=4 */
+                length-=targetCapacity;
+                charErrorBuffer=(uint8_t *)cnv->charErrorBuffer;
+                switch(length) {
+                    /* each branch falls through to the next one */
+                case 3:
+                    *charErrorBuffer++=(uint8_t)(value>>16);
+                case 2:
+                    *charErrorBuffer++=(uint8_t)(value>>8);
+                case 1:
+                    *charErrorBuffer=(uint8_t)value;
+                default:
+                    /* will never occur */
+                    break;
+                }
+                cnv->charErrorBufferLength=(int8_t)length;
+
+                /* now output what fits into the regular target */
+                value>>=8*length; /* length was reduced by targetCapacity */
+                switch(targetCapacity) {
+                    /* each branch falls through to the next one */
+                case 3:
+                    *target++=(uint8_t)(value>>16);
+                    if(offsets!=NULL) {
+                        *offsets++=sourceIndex;
+                    }
+                case 2:
+                    *target++=(uint8_t)(value>>8);
+                    if(offsets!=NULL) {
+                        *offsets++=sourceIndex;
+                    }
+                case 1:
+                    *target++=(uint8_t)value;
+                    if(offsets!=NULL) {
+                        *offsets++=sourceIndex;
+                    }
+                default:
+                    /* will never occur */
+                    break;
+                }
+
+                /* target overflow */
+                targetCapacity=0;
+                *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+                c=0;
+                break;
+            }
+
+            /* normal end of conversion: prepare for a new character */
+            c=0;
+            if(offsets!=NULL) {
+                prevSourceIndex=sourceIndex;
+                sourceIndex=nextSourceIndex;
+            }
+            continue;
+        } else {
+            /* target is full */
+            *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+            break;
+        }
+    }
+
+    /*
+     * the end of the input stream and detection of truncated input
+     * are handled by the framework, but for EBCDIC_STATEFUL conversion
+     * we need to emit an SI at the very end
+     *
+     * conditions:
+     *   successful
+     *   EBCDIC_STATEFUL in DBCS mode
+     *   end of input and no truncated input
+     */
+    if( U_SUCCESS(*pErrorCode) &&
+        outputType==MBCS_OUTPUT_2_SISO && prevLength==2 &&
+        pArgs->flush && source>=sourceLimit && c==0
+    ) {
+        /* EBCDIC_STATEFUL ending with DBCS: emit an SI to return the output stream to SBCS */
+        if(targetCapacity>0) {
+            *target++=(uint8_t)si_value[0];
+            if (si_value_length == 2) {
+                if (targetCapacity<2) {
+                    cnv->charErrorBuffer[0]=(uint8_t)si_value[1];
+                    cnv->charErrorBufferLength=1;
+                    *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+                } else {
+                    *target++=(uint8_t)si_value[1];
+                }
+            }
+            if(offsets!=NULL) {
+                /* set the last source character's index (sourceIndex points at sourceLimit now) */
+                *offsets++=prevSourceIndex;
+            }
+        } else {
+            /* target is full */
+            cnv->charErrorBuffer[0]=(uint8_t)si_value[0];
+            if (si_value_length == 2) {
+                cnv->charErrorBuffer[1]=(uint8_t)si_value[1];
+            }
+            cnv->charErrorBufferLength=si_value_length;
+            *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+        }
+        prevLength=1; /* we switched into SBCS */
+    }
+
+    /* set the converter state back into UConverter */
+    cnv->fromUChar32=c;
+    cnv->fromUnicodeStatus=prevLength;
+
+    /* write back the updated pointers */
+    pArgs->source=source;
+    pArgs->target=(char *)target;
+    pArgs->offsets=offsets;
+}
+
+/*
+ * This is another simple conversion function for internal use by other
+ * conversion implementations.
+ * It does not use the converter state nor call callbacks.
+ * It does not handle the EBCDIC swaplfnl option (set in UConverter).
+ * It handles conversion extensions but not GB 18030.
+ *
+ * It converts one single Unicode code point into codepage bytes, encoded
+ * as one 32-bit value. The function returns the number of bytes in *pValue:
+ * 1..4 the number of bytes in *pValue
+ * 0    unassigned (*pValue undefined)
+ * -1   illegal (currently not used, *pValue undefined)
+ *
+ * *pValue will contain the resulting bytes with the last byte in bits 7..0,
+ * the second to last byte in bits 15..8, etc.
+ * Currently, the function assumes but does not check that 0<=c<=0x10ffff.
+ */
+U_CFUNC int32_t
+ucnv_MBCSFromUChar32(UConverterSharedData *sharedData,
+                 UChar32 c, uint32_t *pValue,
+                 UBool useFallback) {
+    const int32_t *cx;
+    const uint16_t *table;
+#if 0
+/* #if 0 because this is not currently used in ICU - reduce code, increase code coverage */
+    const uint8_t *p;
+#endif
+    uint32_t stage2Entry;
+    uint32_t value;
+    int32_t length;
+
+    /* BMP-only codepages are stored without stage 1 entries for supplementary code points */
+    if(c<=0xffff || (sharedData->mbcs.unicodeMask&UCNV_HAS_SUPPLEMENTARY)) {
+        table=sharedData->mbcs.fromUnicodeTable;
+
+        /* convert the Unicode code point in c into codepage bytes (same as in _MBCSFromUnicodeWithOffsets) */
+        if(sharedData->mbcs.outputType==MBCS_OUTPUT_1) {
+            value=MBCS_SINGLE_RESULT_FROM_U(table, (uint16_t *)sharedData->mbcs.fromUnicodeBytes, c);
+            /* is this code point assigned, or do we use fallbacks? */
+            if(useFallback ? value>=0x800 : value>=0xc00) {
+                *pValue=value&0xff;
+                return 1;
+            }
+        } else /* outputType!=MBCS_OUTPUT_1 */ {
+            stage2Entry=MBCS_STAGE_2_FROM_U(table, c);
+
+            /* get the bytes and the length for the output */
+            switch(sharedData->mbcs.outputType) {
+            case MBCS_OUTPUT_2:
+                value=MBCS_VALUE_2_FROM_STAGE_2(sharedData->mbcs.fromUnicodeBytes, stage2Entry, c);
+                if(value<=0xff) {
+                    length=1;
+                } else {
+                    length=2;
+                }
+                break;
+#if 0
+/* #if 0 because this is not currently used in ICU - reduce code, increase code coverage */
+            case MBCS_OUTPUT_DBCS_ONLY:
+                /* table with single-byte results, but only DBCS mappings used */
+                value=MBCS_VALUE_2_FROM_STAGE_2(sharedData->mbcs.fromUnicodeBytes, stage2Entry, c);
+                if(value<=0xff) {
+                    /* no mapping or SBCS result, not taken for DBCS-only */
+                    value=stage2Entry=0; /* stage2Entry=0 to reset roundtrip flags */
+                    length=0;
+                } else {
+                    length=2;
+                }
+                break;
+            case MBCS_OUTPUT_3:
+                p=MBCS_POINTER_3_FROM_STAGE_2(sharedData->mbcs.fromUnicodeBytes, stage2Entry, c);
+                value=((uint32_t)*p<<16)|((uint32_t)p[1]<<8)|p[2];
+                if(value<=0xff) {
+                    length=1;
+                } else if(value<=0xffff) {
+                    length=2;
+                } else {
+                    length=3;
+                }
+                break;
+            case MBCS_OUTPUT_4:
+                value=MBCS_VALUE_4_FROM_STAGE_2(sharedData->mbcs.fromUnicodeBytes, stage2Entry, c);
+                if(value<=0xff) {
+                    length=1;
+                } else if(value<=0xffff) {
+                    length=2;
+                } else if(value<=0xffffff) {
+                    length=3;
+                } else {
+                    length=4;
+                }
+                break;
+            case MBCS_OUTPUT_3_EUC:
+                value=MBCS_VALUE_2_FROM_STAGE_2(sharedData->mbcs.fromUnicodeBytes, stage2Entry, c);
+                /* EUC 16-bit fixed-length representation */
+                if(value<=0xff) {
+                    length=1;
+                } else if((value&0x8000)==0) {
+                    value|=0x8e8000;
+                    length=3;
+                } else if((value&0x80)==0) {
+                    value|=0x8f0080;
+                    length=3;
+                } else {
+                    length=2;
+                }
+                break;
+            case MBCS_OUTPUT_4_EUC:
+                p=MBCS_POINTER_3_FROM_STAGE_2(sharedData->mbcs.fromUnicodeBytes, stage2Entry, c);
+                value=((uint32_t)*p<<16)|((uint32_t)p[1]<<8)|p[2];
+                /* EUC 16-bit fixed-length representation applied to the first two bytes */
+                if(value<=0xff) {
+                    length=1;
+                } else if(value<=0xffff) {
+                    length=2;
+                } else if((value&0x800000)==0) {
+                    value|=0x8e800000;
+                    length=4;
+                } else if((value&0x8000)==0) {
+                    value|=0x8f008000;
+                    length=4;
+                } else {
+                    length=3;
+                }
+                break;
+#endif
+            default:
+                /* must not occur */
+                return -1;
+            }
+
+            /* is this code point assigned, or do we use fallbacks? */
+            if( MBCS_FROM_U_IS_ROUNDTRIP(stage2Entry, c) ||
+                (FROM_U_USE_FALLBACK(useFallback, c) && value!=0)
+            ) {
+                /*
+                 * We allow a 0 byte output if the "assigned" bit is set for this entry.
+                 * There is no way with this data structure for fallback output
+                 * to be a zero byte.
+                 */
+                /* assigned */
+                *pValue=value;
+                return length;
+            }
+        }
+    }
+
+    cx=sharedData->mbcs.extIndexes;
+    if(cx!=NULL) {
+        length=ucnv_extSimpleMatchFromU(cx, c, pValue, useFallback);
+        return length>=0 ? length : -length;  /* return abs(length); */
+    }
+
+    /* unassigned */
+    return 0;
+}
+
+
+#if 0
+/*
+ * This function has been moved to ucnv2022.c for inlining.
+ * This implementation is here only for documentation purposes
+ */
+
+/**
+ * This version of ucnv_MBCSFromUChar32() is optimized for single-byte codepages.
+ * It does not handle the EBCDIC swaplfnl option (set in UConverter).
+ * It does not handle conversion extensions (_extFromU()).
+ *
+ * It returns the codepage byte for the code point, or -1 if it is unassigned.
+ */
+U_CFUNC int32_t
+ucnv_MBCSSingleFromUChar32(UConverterSharedData *sharedData,
+                       UChar32 c,
+                       UBool useFallback) {
+    const uint16_t *table;
+    int32_t value;
+
+    /* BMP-only codepages are stored without stage 1 entries for supplementary code points */
+    if(c>=0x10000 && !(sharedData->mbcs.unicodeMask&UCNV_HAS_SUPPLEMENTARY)) {
+        return -1;
+    }
+
+    /* convert the Unicode code point in c into codepage bytes (same as in _MBCSFromUnicodeWithOffsets) */
+    table=sharedData->mbcs.fromUnicodeTable;
+
+    /* get the byte for the output */
+    value=MBCS_SINGLE_RESULT_FROM_U(table, (uint16_t *)sharedData->mbcs.fromUnicodeBytes, c);
+    /* is this code point assigned, or do we use fallbacks? */
+    if(useFallback ? value>=0x800 : value>=0xc00) {
+        return value&0xff;
+    } else {
+        return -1;
+    }
+}
+#endif
+
+/* MBCS-from-UTF-8 conversion functions ------------------------------------- */
+
+/* minimum code point values for n-byte UTF-8 sequences, n=0..4 */
+static const UChar32
+utf8_minLegal[5]={ 0, 0, 0x80, 0x800, 0x10000 };
+
+/* offsets for n-byte UTF-8 sequences that were calculated with ((lead<<6)+trail)<<6+trail... */
+static const UChar32
+utf8_offsets[7]={ 0, 0, 0x3080, 0xE2080, 0x3C82080 };
+
+static void
+ucnv_SBCSFromUTF8(UConverterFromUnicodeArgs *pFromUArgs,
+                  UConverterToUnicodeArgs *pToUArgs,
+                  UErrorCode *pErrorCode) {
+    UConverter *utf8, *cnv;
+    const uint8_t *source, *sourceLimit;
+    uint8_t *target;
+    int32_t targetCapacity;
+
+    const uint16_t *table, *sbcsIndex;
+    const uint16_t *results;
+
+    int8_t oldToULength, toULength, toULimit;
+
+    UChar32 c;
+    uint8_t b, t1, t2;
+
+    uint32_t asciiRoundtrips;
+    uint16_t value, minValue;
+    UBool hasSupplementary;
+
+    /* set up the local pointers */
+    utf8=pToUArgs->converter;
+    cnv=pFromUArgs->converter;
+    source=(uint8_t *)pToUArgs->source;
+    sourceLimit=(uint8_t *)pToUArgs->sourceLimit;
+    target=(uint8_t *)pFromUArgs->target;
+    targetCapacity=(int32_t)(pFromUArgs->targetLimit-pFromUArgs->target);
+
+    table=cnv->sharedData->mbcs.fromUnicodeTable;
+    sbcsIndex=cnv->sharedData->mbcs.sbcsIndex;
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        results=(uint16_t *)cnv->sharedData->mbcs.swapLFNLFromUnicodeBytes;
+    } else {
+        results=(uint16_t *)cnv->sharedData->mbcs.fromUnicodeBytes;
+    }
+    asciiRoundtrips=cnv->sharedData->mbcs.asciiRoundtrips;
+
+    if(cnv->useFallback) {
+        /* use all roundtrip and fallback results */
+        minValue=0x800;
+    } else {
+        /* use only roundtrips and fallbacks from private-use characters */
+        minValue=0xc00;
+    }
+    hasSupplementary=(UBool)(cnv->sharedData->mbcs.unicodeMask&UCNV_HAS_SUPPLEMENTARY);
+
+    /* get the converter state from the UTF-8 UConverter */
+    c=(UChar32)utf8->toUnicodeStatus;
+    if(c!=0) {
+        toULength=oldToULength=utf8->toULength;
+        toULimit=(int8_t)utf8->mode;
+    } else {
+        toULength=oldToULength=toULimit=0;
+    }
+
+    /*
+     * Make sure that the last byte sequence before sourceLimit is complete
+     * or runs into a lead byte.
+     * Do not go back into the bytes that will be read for finishing a partial
+     * sequence from the previous buffer.
+     * In the conversion loop compare source with sourceLimit only once
+     * per multi-byte character.
+     */
+    {
+        int32_t i, length;
+
+        length=(int32_t)(sourceLimit-source) - (toULimit-oldToULength);
+        for(i=0; i<3 && i<length;) {
+            b=*(sourceLimit-i-1);
+            if(U8_IS_TRAIL(b)) {
+                ++i;
+            } else {
+                if(i<utf8_countTrailBytes[b]) {
+                    /* exit the conversion loop before the lead byte if there are not enough trail bytes for it */
+                    sourceLimit-=i+1;
+                }
+                break;
+            }
+        }
+    }
+
+    if(c!=0 && targetCapacity>0) {
+        utf8->toUnicodeStatus=0;
+        utf8->toULength=0;
+        goto moreBytes;
+        /*
+         * Note: We could avoid the goto by duplicating some of the moreBytes
+         * code, but only up to the point of collecting a complete UTF-8
+         * sequence; then recurse for the toUBytes[toULength]
+         * and then continue with normal conversion.
+         *
+         * If so, move this code to just after initializing the minimum
+         * set of local variables for reading the UTF-8 input
+         * (utf8, source, target, limits but not cnv, table, minValue, etc.).
+         *
+         * Potential advantages:
+         * - avoid the goto
+         * - oldToULength could become a local variable in just those code blocks
+         *   that deal with buffer boundaries
+         * - possibly faster if the goto prevents some compiler optimizations
+         *   (this would need measuring to confirm)
+         * Disadvantage:
+         * - code duplication
+         */
+    }
+
+    /* conversion loop */
+    while(source<sourceLimit) {
+        if(targetCapacity>0) {
+            b=*source++;
+            if((int8_t)b>=0) {
+                /* convert ASCII */
+                if(IS_ASCII_ROUNDTRIP(b, asciiRoundtrips)) {
+                    *target++=(uint8_t)b;
+                    --targetCapacity;
+                    continue;
+                } else {
+                    c=b;
+                    value=SBCS_RESULT_FROM_UTF8(sbcsIndex, results, 0, c);
+                }
+            } else {
+                if(b<0xe0) {
+                    if( /* handle U+0080..U+07FF inline */
+                        b>=0xc2 &&
+                        (t1=(uint8_t)(*source-0x80)) <= 0x3f
+                    ) {
+                        c=b&0x1f;
+                        ++source;
+                        value=SBCS_RESULT_FROM_UTF8(sbcsIndex, results, c, t1);
+                        if(value>=minValue) {
+                            *target++=(uint8_t)value;
+                            --targetCapacity;
+                            continue;
+                        } else {
+                            c=(c<<6)|t1;
+                        }
+                    } else {
+                        c=-1;
+                    }
+                } else if(b==0xe0) {
+                    if( /* handle U+0800..U+0FFF inline */
+                        (t1=(uint8_t)(source[0]-0x80)) <= 0x3f && t1 >= 0x20 &&
+                        (t2=(uint8_t)(source[1]-0x80)) <= 0x3f
+                    ) {
+                        c=t1;
+                        source+=2;
+                        value=SBCS_RESULT_FROM_UTF8(sbcsIndex, results, c, t2);
+                        if(value>=minValue) {
+                            *target++=(uint8_t)value;
+                            --targetCapacity;
+                            continue;
+                        } else {
+                            c=(c<<6)|t2;
+                        }
+                    } else {
+                        c=-1;
+                    }
+                } else {
+                    c=-1;
+                }
+
+                if(c<0) {
+                    /* handle "complicated" and error cases, and continuing partial characters */
+                    oldToULength=0;
+                    toULength=1;
+                    toULimit=utf8_countTrailBytes[b]+1;
+                    c=b;
+moreBytes:
+                    while(toULength<toULimit) {
+                        /*
+                         * The sourceLimit may have been adjusted before the conversion loop
+                         * to stop before a truncated sequence.
+                         * Here we need to use the real limit in case we have two truncated
+                         * sequences at the end.
+                         * See ticket #7492.
+                         */
+                        if(source<(uint8_t *)pToUArgs->sourceLimit) {
+                            b=*source;
+                            if(U8_IS_TRAIL(b)) {
+                                ++source;
+                                ++toULength;
+                                c=(c<<6)+b;
+                            } else {
+                                break; /* sequence too short, stop with toULength<toULimit */
+                            }
+                        } else {
+                            /* store the partial UTF-8 character, compatible with the regular UTF-8 converter */
+                            source-=(toULength-oldToULength);
+                            while(oldToULength<toULength) {
+                                utf8->toUBytes[oldToULength++]=*source++;
+                            }
+                            utf8->toUnicodeStatus=c;
+                            utf8->toULength=toULength;
+                            utf8->mode=toULimit;
+                            pToUArgs->source=(char *)source;
+                            pFromUArgs->target=(char *)target;
+                            return;
+                        }
+                    }
+
+                    if( toULength==toULimit &&      /* consumed all trail bytes */
+                        (toULength==3 || toULength==2) &&             /* BMP */
+                        (c-=utf8_offsets[toULength])>=utf8_minLegal[toULength] &&
+                        (c<=0xd7ff || 0xe000<=c)    /* not a surrogate */
+                    ) {
+                        value=MBCS_SINGLE_RESULT_FROM_U(table, results, c);
+                    } else if(
+                        toULength==toULimit && toULength==4 &&
+                        (0x10000<=(c-=utf8_offsets[4]) && c<=0x10ffff)
+                    ) {
+                        /* supplementary code point */
+                        if(!hasSupplementary) {
+                            /* BMP-only codepages are stored without stage 1 entries for supplementary code points */
+                            value=0;
+                        } else {
+                            value=MBCS_SINGLE_RESULT_FROM_U(table, results, c);
+                        }
+                    } else {
+                        /* error handling: illegal UTF-8 byte sequence */
+                        source-=(toULength-oldToULength);
+                        while(oldToULength<toULength) {
+                            utf8->toUBytes[oldToULength++]=*source++;
+                        }
+                        utf8->toULength=toULength;
+                        pToUArgs->source=(char *)source;
+                        pFromUArgs->target=(char *)target;
+                        *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                        return;
+                    }
+                }
+            }
+
+            if(value>=minValue) {
+                /* output the mapping for c */
+                *target++=(uint8_t)value;
+                --targetCapacity;
+            } else {
+                /* value<minValue means c is unassigned (unmappable) */
+                /*
+                 * Try an extension mapping.
+                 * Pass in no source because we don't have UTF-16 input.
+                 * If we have a partial match on c, we will return and revert
+                 * to UTF-8->UTF-16->charset conversion.
+                 */
+                static const UChar nul=0;
+                const UChar *noSource=&nul;
+                c=_extFromU(cnv, cnv->sharedData,
+                            c, &noSource, noSource,
+                            &target, target+targetCapacity,
+                            NULL, -1,
+                            pFromUArgs->flush,
+                            pErrorCode);
+
+                if(U_FAILURE(*pErrorCode)) {
+                    /* not mappable or buffer overflow */
+                    cnv->fromUChar32=c;
+                    break;
+                } else if(cnv->preFromUFirstCP>=0) {
+                    /*
+                     * Partial match, return and revert to pivoting.
+                     * In normal from-UTF-16 conversion, we would just continue
+                     * but then exit the loop because the extension match would
+                     * have consumed the source.
+                     */
+                    break;
+                } else {
+                    /* a mapping was written to the target, continue */
+
+                    /* recalculate the targetCapacity after an extension mapping */
+                    targetCapacity=(int32_t)(pFromUArgs->targetLimit-(char *)target);
+                }
+            }
+        } else {
+            /* target is full */
+            *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+            break;
+        }
+    }
+
+    /*
+     * The sourceLimit may have been adjusted before the conversion loop
+     * to stop before a truncated sequence.
+     * If so, then collect the truncated sequence now.
+     */
+    if(U_SUCCESS(*pErrorCode) && source<(sourceLimit=(uint8_t *)pToUArgs->sourceLimit)) {
+        c=utf8->toUBytes[0]=b=*source++;
+        toULength=1;
+        toULimit=utf8_countTrailBytes[b]+1;
+        while(source<sourceLimit) {
+            utf8->toUBytes[toULength++]=b=*source++;
+            c=(c<<6)+b;
+        }
+        utf8->toUnicodeStatus=c;
+        utf8->toULength=toULength;
+        utf8->mode=toULimit;
+    }
+
+    /* write back the updated pointers */
+    pToUArgs->source=(char *)source;
+    pFromUArgs->target=(char *)target;
+}
+
+static void
+ucnv_DBCSFromUTF8(UConverterFromUnicodeArgs *pFromUArgs,
+                  UConverterToUnicodeArgs *pToUArgs,
+                  UErrorCode *pErrorCode) {
+    UConverter *utf8, *cnv;
+    const uint8_t *source, *sourceLimit;
+    uint8_t *target;
+    int32_t targetCapacity;
+
+    const uint16_t *table, *mbcsIndex;
+    const uint16_t *results;
+
+    int8_t oldToULength, toULength, toULimit;
+
+    UChar32 c;
+    uint8_t b, t1, t2;
+
+    uint32_t stage2Entry;
+    uint32_t asciiRoundtrips;
+    uint16_t value, minValue;
+    UBool hasSupplementary;
+
+    /* set up the local pointers */
+    utf8=pToUArgs->converter;
+    cnv=pFromUArgs->converter;
+    source=(uint8_t *)pToUArgs->source;
+    sourceLimit=(uint8_t *)pToUArgs->sourceLimit;
+    target=(uint8_t *)pFromUArgs->target;
+    targetCapacity=(int32_t)(pFromUArgs->targetLimit-pFromUArgs->target);
+
+    table=cnv->sharedData->mbcs.fromUnicodeTable;
+    mbcsIndex=cnv->sharedData->mbcs.mbcsIndex;
+    if((cnv->options&UCNV_OPTION_SWAP_LFNL)!=0) {
+        results=(uint16_t *)cnv->sharedData->mbcs.swapLFNLFromUnicodeBytes;
+    } else {
+        results=(uint16_t *)cnv->sharedData->mbcs.fromUnicodeBytes;
+    }
+    asciiRoundtrips=cnv->sharedData->mbcs.asciiRoundtrips;
+
+    if(cnv->useFallback) {
+        /* use all roundtrip and fallback results */
+        minValue=0x800;
+    } else {
+        /* use only roundtrips and fallbacks from private-use characters */
+        minValue=0xc00;
+    }
+    hasSupplementary=(UBool)(cnv->sharedData->mbcs.unicodeMask&UCNV_HAS_SUPPLEMENTARY);
+
+    /* get the converter state from the UTF-8 UConverter */
+    c=(UChar32)utf8->toUnicodeStatus;
+    if(c!=0) {
+        toULength=oldToULength=utf8->toULength;
+        toULimit=(int8_t)utf8->mode;
+    } else {
+        toULength=oldToULength=toULimit=0;
+    }
+
+    /*
+     * Make sure that the last byte sequence before sourceLimit is complete
+     * or runs into a lead byte.
+     * Do not go back into the bytes that will be read for finishing a partial
+     * sequence from the previous buffer.
+     * In the conversion loop compare source with sourceLimit only once
+     * per multi-byte character.
+     */
+    {
+        int32_t i, length;
+
+        length=(int32_t)(sourceLimit-source) - (toULimit-oldToULength);
+        for(i=0; i<3 && i<length;) {
+            b=*(sourceLimit-i-1);
+            if(U8_IS_TRAIL(b)) {
+                ++i;
+            } else {
+                if(i<utf8_countTrailBytes[b]) {
+                    /* exit the conversion loop before the lead byte if there are not enough trail bytes for it */
+                    sourceLimit-=i+1;
+                }
+                break;
+            }
+        }
+    }
+
+    if(c!=0 && targetCapacity>0) {
+        utf8->toUnicodeStatus=0;
+        utf8->toULength=0;
+        goto moreBytes;
+        /* See note in ucnv_SBCSFromUTF8() about this goto. */
+    }
+
+    /* conversion loop */
+    while(source<sourceLimit) {
+        if(targetCapacity>0) {
+            b=*source++;
+            if((int8_t)b>=0) {
+                /* convert ASCII */
+                if(IS_ASCII_ROUNDTRIP(b, asciiRoundtrips)) {
+                    *target++=b;
+                    --targetCapacity;
+                    continue;
+                } else {
+                    value=DBCS_RESULT_FROM_UTF8(mbcsIndex, results, 0, b);
+                    if(value==0) {
+                        c=b;
+                        goto unassigned;
+                    }
+                }
+            } else {
+                if(b>0xe0) {
+                    if( /* handle U+1000..U+D7FF inline */
+                        (((t1=(uint8_t)(source[0]-0x80), b<0xed) && (t1 <= 0x3f)) ||
+                                                        (b==0xed && (t1 <= 0x1f))) &&
+                        (t2=(uint8_t)(source[1]-0x80)) <= 0x3f
+                    ) {
+                        c=((b&0xf)<<6)|t1;
+                        source+=2;
+                        value=DBCS_RESULT_FROM_UTF8(mbcsIndex, results, c, t2);
+                        if(value==0) {
+                            c=(c<<6)|t2;
+                            goto unassigned;
+                        }
+                    } else {
+                        c=-1;
+                    }
+                } else if(b<0xe0) {
+                    if( /* handle U+0080..U+07FF inline */
+                        b>=0xc2 &&
+                        (t1=(uint8_t)(*source-0x80)) <= 0x3f
+                    ) {
+                        c=b&0x1f;
+                        ++source;
+                        value=DBCS_RESULT_FROM_UTF8(mbcsIndex, results, c, t1);
+                        if(value==0) {
+                            c=(c<<6)|t1;
+                            goto unassigned;
+                        }
+                    } else {
+                        c=-1;
+                    }
+                } else {
+                    c=-1;
+                }
+
+                if(c<0) {
+                    /* handle "complicated" and error cases, and continuing partial characters */
+                    oldToULength=0;
+                    toULength=1;
+                    toULimit=utf8_countTrailBytes[b]+1;
+                    c=b;
+moreBytes:
+                    while(toULength<toULimit) {
+                        /*
+                         * The sourceLimit may have been adjusted before the conversion loop
+                         * to stop before a truncated sequence.
+                         * Here we need to use the real limit in case we have two truncated
+                         * sequences at the end.
+                         * See ticket #7492.
+                         */
+                        if(source<(uint8_t *)pToUArgs->sourceLimit) {
+                            b=*source;
+                            if(U8_IS_TRAIL(b)) {
+                                ++source;
+                                ++toULength;
+                                c=(c<<6)+b;
+                            } else {
+                                break; /* sequence too short, stop with toULength<toULimit */
+                            }
+                        } else {
+                            /* store the partial UTF-8 character, compatible with the regular UTF-8 converter */
+                            source-=(toULength-oldToULength);
+                            while(oldToULength<toULength) {
+                                utf8->toUBytes[oldToULength++]=*source++;
+                            }
+                            utf8->toUnicodeStatus=c;
+                            utf8->toULength=toULength;
+                            utf8->mode=toULimit;
+                            pToUArgs->source=(char *)source;
+                            pFromUArgs->target=(char *)target;
+                            return;
+                        }
+                    }
+
+                    if( toULength==toULimit &&      /* consumed all trail bytes */
+                        (toULength==3 || toULength==2) &&             /* BMP */
+                        (c-=utf8_offsets[toULength])>=utf8_minLegal[toULength] &&
+                        (c<=0xd7ff || 0xe000<=c)    /* not a surrogate */
+                    ) {
+                        stage2Entry=MBCS_STAGE_2_FROM_U(table, c);
+                    } else if(
+                        toULength==toULimit && toULength==4 &&
+                        (0x10000<=(c-=utf8_offsets[4]) && c<=0x10ffff)
+                    ) {
+                        /* supplementary code point */
+                        if(!hasSupplementary) {
+                            /* BMP-only codepages are stored without stage 1 entries for supplementary code points */
+                            stage2Entry=0;
+                        } else {
+                            stage2Entry=MBCS_STAGE_2_FROM_U(table, c);
+                        }
+                    } else {
+                        /* error handling: illegal UTF-8 byte sequence */
+                        source-=(toULength-oldToULength);
+                        while(oldToULength<toULength) {
+                            utf8->toUBytes[oldToULength++]=*source++;
+                        }
+                        utf8->toULength=toULength;
+                        pToUArgs->source=(char *)source;
+                        pFromUArgs->target=(char *)target;
+                        *pErrorCode=U_ILLEGAL_CHAR_FOUND;
+                        return;
+                    }
+
+                    /* get the bytes and the length for the output */
+                    /* MBCS_OUTPUT_2 */
+                    value=MBCS_VALUE_2_FROM_STAGE_2(results, stage2Entry, c);
+
+                    /* is this code point assigned, or do we use fallbacks? */
+                    if(!(MBCS_FROM_U_IS_ROUNDTRIP(stage2Entry, c) ||
+                         (UCNV_FROM_U_USE_FALLBACK(cnv, c) && value!=0))
+                    ) {
+                        goto unassigned;
+                    }
+                }
+            }
+
+            /* write the output character bytes from value and length */
+            /* from the first if in the loop we know that targetCapacity>0 */
+            if(value<=0xff) {
+                /* this is easy because we know that there is enough space */
+                *target++=(uint8_t)value;
+                --targetCapacity;
+            } else /* length==2 */ {
+                *target++=(uint8_t)(value>>8);
+                if(2<=targetCapacity) {
+                    *target++=(uint8_t)value;
+                    targetCapacity-=2;
+                } else {
+                    cnv->charErrorBuffer[0]=(char)value;
+                    cnv->charErrorBufferLength=1;
+
+                    /* target overflow */
+                    *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+                    break;
+                }
+            }
+            continue;
+
+unassigned:
+            {
+                /*
+                 * Try an extension mapping.
+                 * Pass in no source because we don't have UTF-16 input.
+                 * If we have a partial match on c, we will return and revert
+                 * to UTF-8->UTF-16->charset conversion.
+                 */
+                static const UChar nul=0;
+                const UChar *noSource=&nul;
+                c=_extFromU(cnv, cnv->sharedData,
+                            c, &noSource, noSource,
+                            &target, target+targetCapacity,
+                            NULL, -1,
+                            pFromUArgs->flush,
+                            pErrorCode);
+
+                if(U_FAILURE(*pErrorCode)) {
+                    /* not mappable or buffer overflow */
+                    cnv->fromUChar32=c;
+                    break;
+                } else if(cnv->preFromUFirstCP>=0) {
+                    /*
+                     * Partial match, return and revert to pivoting.
+                     * In normal from-UTF-16 conversion, we would just continue
+                     * but then exit the loop because the extension match would
+                     * have consumed the source.
+                     */
+                    break;
+                } else {
+                    /* a mapping was written to the target, continue */
+
+                    /* recalculate the targetCapacity after an extension mapping */
+                    targetCapacity=(int32_t)(pFromUArgs->targetLimit-(char *)target);
+                    continue;
+                }
+            }
+        } else {
+            /* target is full */
+            *pErrorCode=U_BUFFER_OVERFLOW_ERROR;
+            break;
+        }
+    }
+
+    /*
+     * The sourceLimit may have been adjusted before the conversion loop
+     * to stop before a truncated sequence.
+     * If so, then collect the truncated sequence now.
+     */
+    if(U_SUCCESS(*pErrorCode) && source<(sourceLimit=(uint8_t *)pToUArgs->sourceLimit)) {
+        c=utf8->toUBytes[0]=b=*source++;
+        toULength=1;
+        toULimit=utf8_countTrailBytes[b]+1;
+        while(source<sourceLimit) {
+            utf8->toUBytes[toULength++]=b=*source++;
+            c=(c<<6)+b;
+        }
+        utf8->toUnicodeStatus=c;
+        utf8->toULength=toULength;
+        utf8->mode=toULimit;
+    }
+
+    /* write back the updated pointers */
+    pToUArgs->source=(char *)source;
+    pFromUArgs->target=(char *)target;
+}
+
+/* miscellaneous ------------------------------------------------------------ */
+
+static void
+ucnv_MBCSGetStarters(const UConverter* cnv,
+                 UBool starters[256],
+                 UErrorCode *pErrorCode) {
+    const int32_t *state0;
+    int i;
+
+    state0=cnv->sharedData->mbcs.stateTable[cnv->sharedData->mbcs.dbcsOnlyState];
+    for(i=0; i<256; ++i) {
+        /* all bytes that cause a state transition from state 0 are lead bytes */
+        starters[i]= (UBool)MBCS_ENTRY_IS_TRANSITION(state0[i]);
+    }
+}
+
+/*
+ * This is an internal function that allows other converter implementations
+ * to check whether a byte is a lead byte.
+ */
+U_CFUNC UBool
+ucnv_MBCSIsLeadByte(UConverterSharedData *sharedData, char byte) {
+    return (UBool)MBCS_ENTRY_IS_TRANSITION(sharedData->mbcs.stateTable[0][(uint8_t)byte]);
+}
+
+static void
+ucnv_MBCSWriteSub(UConverterFromUnicodeArgs *pArgs,
+              int32_t offsetIndex,
+              UErrorCode *pErrorCode) {
+    UConverter *cnv=pArgs->converter;
+    char *p, *subchar;
+    char buffer[4];
+    int32_t length;
+
+    /* first, select between subChar and subChar1 */
+    if( cnv->subChar1!=0 &&
+        (cnv->sharedData->mbcs.extIndexes!=NULL ?
+            cnv->useSubChar1 :
+            (cnv->invalidUCharBuffer[0]<=0xff))
+    ) {
+        /* select subChar1 if it is set (not 0) and the unmappable Unicode code point is up to U+00ff (IBM MBCS behavior) */
+        subchar=(char *)&cnv->subChar1;
+        length=1;
+    } else {
+        /* select subChar in all other cases */
+        subchar=(char *)cnv->subChars;
+        length=cnv->subCharLen;
+    }
+
+    /* reset the selector for the next code point */
+    cnv->useSubChar1=FALSE;
+
+    if (cnv->sharedData->mbcs.outputType == MBCS_OUTPUT_2_SISO) {
+        p=buffer;
+
+        /* fromUnicodeStatus contains prevLength */
+        switch(length) {
+        case 1:
+            if(cnv->fromUnicodeStatus==2) {
+                /* DBCS mode and SBCS sub char: change to SBCS */
+                cnv->fromUnicodeStatus=1;
+                *p++=UCNV_SI;
+            }
+            *p++=subchar[0];
+            break;
+        case 2:
+            if(cnv->fromUnicodeStatus<=1) {
+                /* SBCS mode and DBCS sub char: change to DBCS */
+                cnv->fromUnicodeStatus=2;
+                *p++=UCNV_SO;
+            }
+            *p++=subchar[0];
+            *p++=subchar[1];
+            break;
+        default:
+            *pErrorCode=U_ILLEGAL_ARGUMENT_ERROR;
+            return;
+        }
+        subchar=buffer;
+        length=(int32_t)(p-buffer);
+    }
+
+    ucnv_cbFromUWriteBytes(pArgs, subchar, length, offsetIndex, pErrorCode);
+}
+
+U_CFUNC UConverterType
+ucnv_MBCSGetType(const UConverter* converter) {
+    /* SBCS, DBCS, and EBCDIC_STATEFUL are replaced by MBCS, but here we cheat a little */
+    if(converter->sharedData->mbcs.countStates==1) {
+        return (UConverterType)UCNV_SBCS;
+    } else if((converter->sharedData->mbcs.outputType&0xff)==MBCS_OUTPUT_2_SISO) {
+        return (UConverterType)UCNV_EBCDIC_STATEFUL;
+    } else if(converter->sharedData->staticData->minBytesPerChar==2 && converter->sharedData->staticData->maxBytesPerChar==2) {
+        return (UConverterType)UCNV_DBCS;
+    }
+    return (UConverterType)UCNV_MBCS;
+}
+
+static const UConverterImpl _SBCSUTF8Impl={
+    UCNV_MBCS,
+
+    ucnv_MBCSLoad,
+    ucnv_MBCSUnload,
+
+    ucnv_MBCSOpen,
+    NULL,
+    NULL,
+
+    ucnv_MBCSToUnicodeWithOffsets,
+    ucnv_MBCSToUnicodeWithOffsets,
+    ucnv_MBCSFromUnicodeWithOffsets,
+    ucnv_MBCSFromUnicodeWithOffsets,
+    ucnv_MBCSGetNextUChar,
+
+    ucnv_MBCSGetStarters,
+    ucnv_MBCSGetName,
+    ucnv_MBCSWriteSub,
+    NULL,
+    ucnv_MBCSGetUnicodeSet,
+
+    NULL,
+    ucnv_SBCSFromUTF8
+};
+
+static const UConverterImpl _DBCSUTF8Impl={
+    UCNV_MBCS,
+
+    ucnv_MBCSLoad,
+    ucnv_MBCSUnload,
+
+    ucnv_MBCSOpen,
+    NULL,
+    NULL,
+
+    ucnv_MBCSToUnicodeWithOffsets,
+    ucnv_MBCSToUnicodeWithOffsets,
+    ucnv_MBCSFromUnicodeWithOffsets,
+    ucnv_MBCSFromUnicodeWithOffsets,
+    ucnv_MBCSGetNextUChar,
+
+    ucnv_MBCSGetStarters,
+    ucnv_MBCSGetName,
+    ucnv_MBCSWriteSub,
+    NULL,
+    ucnv_MBCSGetUnicodeSet,
+
+    NULL,
+    ucnv_DBCSFromUTF8
+};
+
+static const UConverterImpl _MBCSImpl={
+    UCNV_MBCS,
+
+    ucnv_MBCSLoad,
+    ucnv_MBCSUnload,
+
+    ucnv_MBCSOpen,
+    NULL,
+    NULL,
+
+    ucnv_MBCSToUnicodeWithOffsets,
+    ucnv_MBCSToUnicodeWithOffsets,
+    ucnv_MBCSFromUnicodeWithOffsets,
+    ucnv_MBCSFromUnicodeWithOffsets,
+    ucnv_MBCSGetNextUChar,
+
+    ucnv_MBCSGetStarters,
+    ucnv_MBCSGetName,
+    ucnv_MBCSWriteSub,
+    NULL,
+    ucnv_MBCSGetUnicodeSet
+};
+
+
+/* Static data is in tools/makeconv/ucnvstat.c for data-based
+ * converters. Be sure to update it as well.
+ */
+
+const UConverterSharedData _MBCSData={
+    sizeof(UConverterSharedData), 1,
+    NULL, NULL, NULL, FALSE, &_MBCSImpl, 
+    0
+};
+
+#endif /* #if !UCONFIG_NO_LEGACY_CONVERSION */