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| 1 /* | |
| 2 * jdhuff.h | |
| 3 * | |
| 4 * Copyright (C) 1991-1997, Thomas G. Lane. | |
| 5 * This file is part of the Independent JPEG Group's software. | |
| 6 * For conditions of distribution and use, see the accompanying README file. | |
| 7 * | |
| 8 * This file contains declarations for Huffman entropy decoding routines | |
| 9 * that are shared between the sequential decoder (jdhuff.c) and the | |
| 10 * progressive decoder (jdphuff.c). No other modules need to see these. | |
| 11 */ | |
| 12 | |
| 13 /* Short forms of external names for systems with brain-damaged linkers. */ | |
| 14 | |
| 15 #ifdef NEED_SHORT_EXTERNAL_NAMES | |
| 16 #define jpeg_make_d_derived_tbl jMkDDerived | |
| 17 #define jpeg_fill_bit_buffer jFilBitBuf | |
| 18 #define jpeg_huff_decode jHufDecode | |
| 19 #endif /* NEED_SHORT_EXTERNAL_NAMES */ | |
| 20 | |
| 21 | |
| 22 /* Derived data constructed for each Huffman table */ | |
| 23 | |
| 24 #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */ | |
| 25 | |
| 26 typedef struct { | |
| 27 /* Basic tables: (element [0] of each array is unused) */ | |
| 28 INT32 maxcode[18]; /* largest code of length k (-1 if none) */ | |
| 29 /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */ | |
| 30 INT32 valoffset[17]; /* huffval[] offset for codes of length k */ | |
| 31 /* valoffset[k] = huffval[] index of 1st symbol of code length k, less | |
| 32 * the smallest code of length k; so given a code of length k, the | |
| 33 * corresponding symbol is huffval[code + valoffset[k]] | |
| 34 */ | |
| 35 | |
| 36 /* Link to public Huffman table (needed only in jpeg_huff_decode) */ | |
| 37 JHUFF_TBL *pub; | |
| 38 | |
| 39 /* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of | |
| 40 * the input data stream. If the next Huffman code is no more | |
| 41 * than HUFF_LOOKAHEAD bits long, we can obtain its length and | |
| 42 * the corresponding symbol directly from these tables. | |
| 43 */ | |
| 44 int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */ | |
| 45 UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */ | |
| 46 } d_derived_tbl; | |
| 47 | |
| 48 /* Expand a Huffman table definition into the derived format */ | |
| 49 EXTERN(void) jpeg_make_d_derived_tbl | |
| 50 JPP((j_decompress_ptr cinfo, boolean isDC, int tblno, | |
| 51 d_derived_tbl ** pdtbl)); | |
| 52 | |
| 53 | |
| 54 /* | |
| 55 * Fetching the next N bits from the input stream is a time-critical operation | |
| 56 * for the Huffman decoders. We implement it with a combination of inline | |
| 57 * macros and out-of-line subroutines. Note that N (the number of bits | |
| 58 * demanded at one time) never exceeds 15 for JPEG use. | |
| 59 * | |
| 60 * We read source bytes into get_buffer and dole out bits as needed. | |
| 61 * If get_buffer already contains enough bits, they are fetched in-line | |
| 62 * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough | |
| 63 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer | |
| 64 * as full as possible (not just to the number of bits needed; this | |
| 65 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer). | |
| 66 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension. | |
| 67 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains | |
| 68 * at least the requested number of bits --- dummy zeroes are inserted if | |
| 69 * necessary. | |
| 70 */ | |
| 71 | |
| 72 typedef INT32 bit_buf_type; /* type of bit-extraction buffer */ | |
| 73 #define BIT_BUF_SIZE 32 /* size of buffer in bits */ | |
| 74 | |
| 75 /* If long is > 32 bits on your machine, and shifting/masking longs is | |
| 76 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE | |
| 77 * appropriately should be a win. Unfortunately we can't define the size | |
| 78 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) | |
| 79 * because not all machines measure sizeof in 8-bit bytes. | |
| 80 */ | |
| 81 | |
| 82 typedef struct { /* Bitreading state saved across MCUs */ | |
| 83 bit_buf_type get_buffer; /* current bit-extraction buffer */ | |
| 84 int bits_left; /* # of unused bits in it */ | |
| 85 } bitread_perm_state; | |
| 86 | |
| 87 typedef struct { /* Bitreading working state within an MCU */ | |
| 88 /* Current data source location */ | |
| 89 /* We need a copy, rather than munging the original, in case of suspension */ | |
| 90 const JOCTET * next_input_byte; /* => next byte to read from source */ | |
| 91 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ | |
| 92 /* Bit input buffer --- note these values are kept in register variables, | |
| 93 * not in this struct, inside the inner loops. | |
| 94 */ | |
| 95 bit_buf_type get_buffer; /* current bit-extraction buffer */ | |
| 96 int bits_left; /* # of unused bits in it */ | |
| 97 /* Pointer needed by jpeg_fill_bit_buffer. */ | |
| 98 j_decompress_ptr cinfo; /* back link to decompress master record */ | |
| 99 } bitread_working_state; | |
| 100 | |
| 101 /* Macros to declare and load/save bitread local variables. */ | |
| 102 #define BITREAD_STATE_VARS \ | |
| 103 register bit_buf_type get_buffer; \ | |
| 104 register int bits_left; \ | |
| 105 bitread_working_state br_state | |
| 106 | |
| 107 #define BITREAD_LOAD_STATE(cinfop,permstate) \ | |
| 108 br_state.cinfo = cinfop; \ | |
| 109 br_state.next_input_byte = cinfop->src->next_input_byte; \ | |
| 110 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ | |
| 111 get_buffer = permstate.get_buffer; \ | |
| 112 bits_left = permstate.bits_left; | |
| 113 | |
| 114 #define BITREAD_SAVE_STATE(cinfop,permstate) \ | |
| 115 cinfop->src->next_input_byte = br_state.next_input_byte; \ | |
| 116 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ | |
| 117 permstate.get_buffer = get_buffer; \ | |
| 118 permstate.bits_left = bits_left | |
| 119 | |
| 120 /* | |
| 121 * These macros provide the in-line portion of bit fetching. | |
| 122 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer | |
| 123 * before using GET_BITS, PEEK_BITS, or DROP_BITS. | |
| 124 * The variables get_buffer and bits_left are assumed to be locals, | |
| 125 * but the state struct might not be (jpeg_huff_decode needs this). | |
| 126 * CHECK_BIT_BUFFER(state,n,action); | |
| 127 * Ensure there are N bits in get_buffer; if suspend, take action. | |
| 128 * val = GET_BITS(n); | |
| 129 * Fetch next N bits. | |
| 130 * val = PEEK_BITS(n); | |
| 131 * Fetch next N bits without removing them from the buffer. | |
| 132 * DROP_BITS(n); | |
| 133 * Discard next N bits. | |
| 134 * The value N should be a simple variable, not an expression, because it | |
| 135 * is evaluated multiple times. | |
| 136 */ | |
| 137 | |
| 138 #define CHECK_BIT_BUFFER(state,nbits,action) \ | |
| 139 { if (bits_left < (nbits)) { \ | |
| 140 if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \ | |
| 141 { action; } \ | |
| 142 get_buffer = (state).get_buffer; bits_left = (state).bits_left; } } | |
| 143 | |
| 144 #define GET_BITS(nbits) \ | |
| 145 (((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1)) | |
| 146 | |
| 147 #define PEEK_BITS(nbits) \ | |
| 148 (((int) (get_buffer >> (bits_left - (nbits)))) & ((1<<(nbits))-1)) | |
| 149 | |
| 150 #define DROP_BITS(nbits) \ | |
| 151 (bits_left -= (nbits)) | |
| 152 | |
| 153 /* Load up the bit buffer to a depth of at least nbits */ | |
| 154 EXTERN(boolean) jpeg_fill_bit_buffer | |
| 155 JPP((bitread_working_state * state, register bit_buf_type get_buffer, | |
| 156 register int bits_left, int nbits)); | |
| 157 | |
| 158 | |
| 159 /* | |
| 160 * Code for extracting next Huffman-coded symbol from input bit stream. | |
| 161 * Again, this is time-critical and we make the main paths be macros. | |
| 162 * | |
| 163 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits | |
| 164 * without looping. Usually, more than 95% of the Huffman codes will be 8 | |
| 165 * or fewer bits long. The few overlength codes are handled with a loop, | |
| 166 * which need not be inline code. | |
| 167 * | |
| 168 * Notes about the HUFF_DECODE macro: | |
| 169 * 1. Near the end of the data segment, we may fail to get enough bits | |
| 170 * for a lookahead. In that case, we do it the hard way. | |
| 171 * 2. If the lookahead table contains no entry, the next code must be | |
| 172 * more than HUFF_LOOKAHEAD bits long. | |
| 173 * 3. jpeg_huff_decode returns -1 if forced to suspend. | |
| 174 */ | |
| 175 | |
| 176 #define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \ | |
| 177 { register int nb, look; \ | |
| 178 if (bits_left < HUFF_LOOKAHEAD) { \ | |
| 179 if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \ | |
| 180 get_buffer = state.get_buffer; bits_left = state.bits_left; \ | |
| 181 if (bits_left < HUFF_LOOKAHEAD) { \ | |
| 182 nb = 1; goto slowlabel; \ | |
| 183 } \ | |
| 184 } \ | |
| 185 look = PEEK_BITS(HUFF_LOOKAHEAD); \ | |
| 186 if ((nb = htbl->look_nbits[look]) != 0) { \ | |
| 187 DROP_BITS(nb); \ | |
| 188 result = htbl->look_sym[look]; \ | |
| 189 } else { \ | |
| 190 nb = HUFF_LOOKAHEAD+1; \ | |
| 191 slowlabel: \ | |
| 192 if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \ | |
| 193 { failaction; } \ | |
| 194 get_buffer = state.get_buffer; bits_left = state.bits_left; \ | |
| 195 } \ | |
| 196 } | |
| 197 | |
| 198 /* Out-of-line case for Huffman code fetching */ | |
| 199 EXTERN(int) jpeg_huff_decode | |
| 200 JPP((bitread_working_state * state, register bit_buf_type get_buffer, | |
| 201 register int bits_left, d_derived_tbl * htbl, int min_bits)); | |
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Chromium Code Reviews
Issue 1705523002:
Remove libjpeg and libjpeg_turbo. (Closed)
Base URL: https://github.com/domokit/mojo.git@master