jdhuff.h (9903B)
1 /* 2 * jdhuff.h 3 * 4 * This file was part of the Independent JPEG Group's software: 5 * Copyright (C) 1991-1997, Thomas G. Lane. 6 * Lossless JPEG Modifications: 7 * Copyright (C) 1999, Ken Murchison. 8 * libjpeg-turbo Modifications: 9 * Copyright (C) 2010-2011, 2015-2016, 2021, D. R. Commander. 10 * Copyright (C) 2018, Matthias Räncker. 11 * For conditions of distribution and use, see the accompanying README.ijg 12 * file. 13 * 14 * This file contains declarations for Huffman entropy decoding routines 15 * that are shared between the sequential decoder (jdhuff.c), the progressive 16 * decoder (jdphuff.c), and the lossless decoder (jdlhuff.c). No other modules 17 * need to see these. 18 */ 19 20 #include "jconfigint.h" 21 22 23 /* Derived data constructed for each Huffman table */ 24 25 #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */ 26 27 typedef struct { 28 /* Basic tables: (element [0] of each array is unused) */ 29 JLONG maxcode[18]; /* largest code of length k (-1 if none) */ 30 /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */ 31 JLONG valoffset[18]; /* huffval[] offset for codes of length k */ 32 /* valoffset[k] = huffval[] index of 1st symbol of code length k, less 33 * the smallest code of length k; so given a code of length k, the 34 * corresponding symbol is huffval[code + valoffset[k]] 35 */ 36 37 /* Link to public Huffman table (needed only in jpeg_huff_decode) */ 38 JHUFF_TBL *pub; 39 40 /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of 41 * the input data stream. If the next Huffman code is no more 42 * than HUFF_LOOKAHEAD bits long, we can obtain its length and 43 * the corresponding symbol directly from this tables. 44 * 45 * The lower 8 bits of each table entry contain the number of 46 * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1 47 * if too long. The next 8 bits of each entry contain the 48 * symbol. 49 */ 50 int lookup[1 << HUFF_LOOKAHEAD]; 51 } d_derived_tbl; 52 53 /* Expand a Huffman table definition into the derived format */ 54 EXTERN(void) jpeg_make_d_derived_tbl(j_decompress_ptr cinfo, boolean isDC, 55 int tblno, d_derived_tbl **pdtbl); 56 57 58 /* 59 * Fetching the next N bits from the input stream is a time-critical operation 60 * for the Huffman decoders. We implement it with a combination of inline 61 * macros and out-of-line subroutines. Note that N (the number of bits 62 * demanded at one time) never exceeds 15 for JPEG use. 63 * 64 * We read source bytes into get_buffer and dole out bits as needed. 65 * If get_buffer already contains enough bits, they are fetched in-line 66 * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough 67 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer 68 * as full as possible (not just to the number of bits needed; this 69 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer). 70 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension. 71 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains 72 * at least the requested number of bits --- dummy zeroes are inserted if 73 * necessary. 74 */ 75 76 #if !defined(_WIN32) && !defined(SIZEOF_SIZE_T) 77 #error Cannot determine word size 78 #endif 79 80 #if SIZEOF_SIZE_T == 8 || defined(_WIN64) 81 82 typedef size_t bit_buf_type; /* type of bit-extraction buffer */ 83 #define BIT_BUF_SIZE 64 /* size of buffer in bits */ 84 85 #elif defined(__x86_64__) && defined(__ILP32__) 86 87 typedef unsigned long long bit_buf_type; /* type of bit-extraction buffer */ 88 #define BIT_BUF_SIZE 64 /* size of buffer in bits */ 89 90 #else 91 92 typedef unsigned long bit_buf_type; /* type of bit-extraction buffer */ 93 #define BIT_BUF_SIZE 32 /* size of buffer in bits */ 94 95 #endif 96 97 /* If long is > 32 bits on your machine, and shifting/masking longs is 98 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE 99 * appropriately should be a win. Unfortunately we can't define the size 100 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) 101 * because not all machines measure sizeof in 8-bit bytes. 102 */ 103 104 typedef struct { /* Bitreading state saved across MCUs */ 105 bit_buf_type get_buffer; /* current bit-extraction buffer */ 106 int bits_left; /* # of unused bits in it */ 107 } bitread_perm_state; 108 109 typedef struct { /* Bitreading working state within an MCU */ 110 /* Current data source location */ 111 /* We need a copy, rather than munging the original, in case of suspension */ 112 const JOCTET *next_input_byte; /* => next byte to read from source */ 113 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ 114 /* Bit input buffer --- note these values are kept in register variables, 115 * not in this struct, inside the inner loops. 116 */ 117 bit_buf_type get_buffer; /* current bit-extraction buffer */ 118 int bits_left; /* # of unused bits in it */ 119 /* Pointer needed by jpeg_fill_bit_buffer. */ 120 j_decompress_ptr cinfo; /* back link to decompress master record */ 121 } bitread_working_state; 122 123 /* Macros to declare and load/save bitread local variables. */ 124 #define BITREAD_STATE_VARS \ 125 register bit_buf_type get_buffer; \ 126 register int bits_left; \ 127 bitread_working_state br_state 128 129 #define BITREAD_LOAD_STATE(cinfop, permstate) \ 130 br_state.cinfo = cinfop; \ 131 br_state.next_input_byte = cinfop->src->next_input_byte; \ 132 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ 133 get_buffer = permstate.get_buffer; \ 134 bits_left = permstate.bits_left; 135 136 #define BITREAD_SAVE_STATE(cinfop, permstate) \ 137 cinfop->src->next_input_byte = br_state.next_input_byte; \ 138 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ 139 permstate.get_buffer = get_buffer; \ 140 permstate.bits_left = bits_left 141 142 /* 143 * These macros provide the in-line portion of bit fetching. 144 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer 145 * before using GET_BITS, PEEK_BITS, or DROP_BITS. 146 * The variables get_buffer and bits_left are assumed to be locals, 147 * but the state struct might not be (jpeg_huff_decode needs this). 148 * CHECK_BIT_BUFFER(state, n, action); 149 * Ensure there are N bits in get_buffer; if suspend, take action. 150 * val = GET_BITS(n); 151 * Fetch next N bits. 152 * val = PEEK_BITS(n); 153 * Fetch next N bits without removing them from the buffer. 154 * DROP_BITS(n); 155 * Discard next N bits. 156 * The value N should be a simple variable, not an expression, because it 157 * is evaluated multiple times. 158 */ 159 160 #define CHECK_BIT_BUFFER(state, nbits, action) { \ 161 if (bits_left < (nbits)) { \ 162 if (!jpeg_fill_bit_buffer(&(state), get_buffer, bits_left, nbits)) \ 163 { action; } \ 164 get_buffer = (state).get_buffer; bits_left = (state).bits_left; \ 165 } \ 166 } 167 168 #define GET_BITS(nbits) \ 169 (((int)(get_buffer >> (bits_left -= (nbits)))) & ((1 << (nbits)) - 1)) 170 171 #define PEEK_BITS(nbits) \ 172 (((int)(get_buffer >> (bits_left - (nbits)))) & ((1 << (nbits)) - 1)) 173 174 #define DROP_BITS(nbits) \ 175 (bits_left -= (nbits)) 176 177 /* Load up the bit buffer to a depth of at least nbits */ 178 EXTERN(boolean) jpeg_fill_bit_buffer(bitread_working_state *state, 179 register bit_buf_type get_buffer, 180 register int bits_left, int nbits); 181 182 183 /* 184 * Code for extracting next Huffman-coded symbol from input bit stream. 185 * Again, this is time-critical and we make the main paths be macros. 186 * 187 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits 188 * without looping. Usually, more than 95% of the Huffman codes will be 8 189 * or fewer bits long. The few overlength codes are handled with a loop, 190 * which need not be inline code. 191 * 192 * Notes about the HUFF_DECODE macro: 193 * 1. Near the end of the data segment, we may fail to get enough bits 194 * for a lookahead. In that case, we do it the hard way. 195 * 2. If the lookahead table contains no entry, the next code must be 196 * more than HUFF_LOOKAHEAD bits long. 197 * 3. jpeg_huff_decode returns -1 if forced to suspend. 198 */ 199 200 #define HUFF_DECODE(result, state, htbl, failaction, slowlabel) { \ 201 register int nb, look; \ 202 if (bits_left < HUFF_LOOKAHEAD) { \ 203 if (!jpeg_fill_bit_buffer(&state, get_buffer, bits_left, 0)) \ 204 { failaction; } \ 205 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 206 if (bits_left < HUFF_LOOKAHEAD) { \ 207 nb = 1; goto slowlabel; \ 208 } \ 209 } \ 210 look = PEEK_BITS(HUFF_LOOKAHEAD); \ 211 if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \ 212 DROP_BITS(nb); \ 213 result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \ 214 } else { \ 215 slowlabel: \ 216 if ((result = \ 217 jpeg_huff_decode(&state, get_buffer, bits_left, htbl, nb)) < 0) \ 218 { failaction; } \ 219 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 220 } \ 221 } 222 223 #define HUFF_DECODE_FAST(s, nb, htbl) \ 224 FILL_BIT_BUFFER_FAST; \ 225 s = PEEK_BITS(HUFF_LOOKAHEAD); \ 226 s = htbl->lookup[s]; \ 227 nb = s >> HUFF_LOOKAHEAD; \ 228 /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \ 229 DROP_BITS(nb); \ 230 s = s & ((1 << HUFF_LOOKAHEAD) - 1); \ 231 if (nb > HUFF_LOOKAHEAD) { \ 232 /* Equivalent of jpeg_huff_decode() */ \ 233 /* Don't use GET_BITS() here because we don't want to modify bits_left */ \ 234 s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \ 235 while (s > htbl->maxcode[nb]) { \ 236 s <<= 1; \ 237 s |= GET_BITS(1); \ 238 nb++; \ 239 } \ 240 if (nb > 16) \ 241 s = 0; \ 242 else \ 243 s = htbl->pub->huffval[(int)(s + htbl->valoffset[nb]) & 0xFF]; \ 244 } 245 246 /* Out-of-line case for Huffman code fetching */ 247 EXTERN(int) jpeg_huff_decode(bitread_working_state *state, 248 register bit_buf_type get_buffer, 249 register int bits_left, d_derived_tbl *htbl, 250 int min_bits);