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icu46/source/i18n/csr2022.cpp

+/*
+ **********************************************************************
+ *   Copyright (C) 2005-2009, International Business Machines
+ *   Corporation and others.  All Rights Reserved.
+ **********************************************************************
+ */
+
+#include "unicode/utypes.h"
+
+#if !UCONFIG_NO_CONVERSION
+
+#include "cstring.h"
+
+#include "csr2022.h"
+
+U_NAMESPACE_BEGIN
+
+#define ARRAY_SIZE(array) (sizeof array / sizeof array[0])
+
+/**
+ * Matching function shared among the 2022 detectors JP, CN and KR
+ * Counts up the number of legal an unrecognized escape sequences in
+ * the sample of text, and computes a score based on the total number &
+ * the proportion that fit the encoding.
+ * 
+ * 
+ * @param text the byte buffer containing text to analyse
+ * @param textLen  the size of the text in the byte.
+ * @param escapeSequences the byte escape sequences to test for.
+ * @return match quality, in the range of 0-100.
+ */
+int32_t CharsetRecog_2022::match_2022(const uint8_t *text, int32_t textLen, const uint8_t escapeSequences[][5], int32_t escapeSequences_length)
+{
+    int32_t i, j;
+    int32_t escN;
+    int32_t hits   = 0;
+    int32_t misses = 0;
+    int32_t shifts = 0;
+    int32_t quality;
+
+    i = 0;
+    while(i < textLen) {
+        if(text[i] == 0x1B) {
+            escN = 0;
+            while(escN < escapeSequences_length) {
+                const uint8_t *seq = escapeSequences[escN];
+                int32_t seq_length = (int32_t)uprv_strlen((const char *) seq);
+
+                if (textLen-i >= seq_length) {
+                    j = 1;
+                    while(j < seq_length) {
+                        if(seq[j] != text[i+j]) {
+                            goto checkEscapes;
+                        }
+
+                        j += 1;
+                    }
+
+                    hits += 1;
+                    i += seq_length-1;
+                    goto scanInput;
+                }
+                // else we ran out of string to compare this time.
+checkEscapes:
+                escN += 1;
+            }
+
+            misses += 1;
+        }
+
+        if( text[i]== 0x0e || text[i] == 0x0f){
+            shifts += 1;
+        }
+
+scanInput:
+        i += 1;
+    }
+
+    if (hits == 0) {
+        return 0;
+    }
+
+    //
+    // Initial quality is based on relative proportion of recongized vs.
+    //   unrecognized escape sequences. 
+    //   All good:  quality = 100;
+    //   half or less good: quality = 0;
+    //   linear inbetween.
+    quality = (100*hits - 100*misses) / (hits + misses);
+
+    // Back off quality if there were too few escape sequences seen.
+    //   Include shifts in this computation, so that KR does not get penalized
+    //   for having only a single Escape sequence, but many shifts.
+    if (hits+shifts < 5) {
+        quality -= (5-(hits+shifts))*10;
+    }
+
+    if (quality < 0) {
+        quality = 0;
+    }
+
+    return quality;
+}
+
+
+static const uint8_t escapeSequences_2022JP[][5] = {
+    {0x1b, 0x24, 0x28, 0x43, 0x00},   // KS X 1001:1992
+    {0x1b, 0x24, 0x28, 0x44, 0x00},   // JIS X 212-1990
+    {0x1b, 0x24, 0x40, 0x00, 0x00},   // JIS C 6226-1978
+    {0x1b, 0x24, 0x41, 0x00, 0x00},   // GB 2312-80
+    {0x1b, 0x24, 0x42, 0x00, 0x00},   // JIS X 208-1983
+    {0x1b, 0x26, 0x40, 0x00, 0x00},   // JIS X 208 1990, 1997
+    {0x1b, 0x28, 0x42, 0x00, 0x00},   // ASCII
+    {0x1b, 0x28, 0x48, 0x00, 0x00},   // JIS-Roman
+    {0x1b, 0x28, 0x49, 0x00, 0x00},   // Half-width katakana
+    {0x1b, 0x28, 0x4a, 0x00, 0x00},   // JIS-Roman
+    {0x1b, 0x2e, 0x41, 0x00, 0x00},   // ISO 8859-1
+    {0x1b, 0x2e, 0x46, 0x00, 0x00}    // ISO 8859-7
+};
+
+static const uint8_t escapeSequences_2022KR[][5] = {
+    {0x1b, 0x24, 0x29, 0x43, 0x00}   
+};
+
+static const uint8_t escapeSequences_2022CN[][5] = {
+    {0x1b, 0x24, 0x29, 0x41, 0x00},   // GB 2312-80
+    {0x1b, 0x24, 0x29, 0x47, 0x00},   // CNS 11643-1992 Plane 1
+    {0x1b, 0x24, 0x2A, 0x48, 0x00},   // CNS 11643-1992 Plane 2
+    {0x1b, 0x24, 0x29, 0x45, 0x00},   // ISO-IR-165
+    {0x1b, 0x24, 0x2B, 0x49, 0x00},   // CNS 11643-1992 Plane 3
+    {0x1b, 0x24, 0x2B, 0x4A, 0x00},   // CNS 11643-1992 Plane 4
+    {0x1b, 0x24, 0x2B, 0x4B, 0x00},   // CNS 11643-1992 Plane 5
+    {0x1b, 0x24, 0x2B, 0x4C, 0x00},   // CNS 11643-1992 Plane 6
+    {0x1b, 0x24, 0x2B, 0x4D, 0x00},   // CNS 11643-1992 Plane 7
+    {0x1b, 0x4e, 0x00, 0x00, 0x00},   // SS2
+    {0x1b, 0x4f, 0x00, 0x00, 0x00},   // SS3
+};
+
+const char *CharsetRecog_2022JP::getName() const
+{
+    return "ISO-2022-JP";
+}
+
+int32_t CharsetRecog_2022JP::match(InputText *textIn)
+{
+    return match_2022(textIn->fInputBytes, textIn->fInputLen, escapeSequences_2022JP, ARRAY_SIZE(escapeSequences_2022JP));
+}
+
+const char *CharsetRecog_2022KR::getName() const
+{
+    return "ISO-2022-KR";
+}
+
+int32_t CharsetRecog_2022KR::match(InputText *textIn)
+{
+    return match_2022(textIn->fInputBytes, textIn->fInputLen, escapeSequences_2022KR, ARRAY_SIZE(escapeSequences_2022KR));
+}
+
+const char *CharsetRecog_2022CN::getName() const
+{
+    return "ISO-2022-CN";
+}
+
+int32_t CharsetRecog_2022CN::match(InputText *textIn)
+{
+    return match_2022(textIn->fInputBytes, textIn->fInputLen, escapeSequences_2022CN, ARRAY_SIZE(escapeSequences_2022CN));
+}
+
+CharsetRecog_2022::~CharsetRecog_2022()
+{
+    // nothing to do
+}
+
+U_NAMESPACE_END
+#endif