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