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, D. R. Commander. 8 * For conditions of distribution and use, see the accompanying README.ijg 9 * file. 10 * 11 * This file contains declarations for Huffman entropy decoding routines 12 * that are shared between the sequential decoder (jdhuff.c) and the 13 * progressive decoder (jdphuff.c). No other modules need to see these. 14 */ 15 16 #include "jconfigint.h" 17 18 19 /* Derived data constructed for each Huffman table */ 20 21 #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */ 22 23 typedef struct { 24 /* Basic tables: (element [0] of each array is unused) */ 25 JLONG maxcode[18]; /* largest code of length k (-1 if none) */ 26 /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */ 27 JLONG valoffset[18]; /* huffval[] offset for codes of length k */ 28 /* valoffset[k] = huffval[] index of 1st symbol of code length k, less 29 * the smallest code of length k; so given a code of length k, the 30 * corresponding symbol is huffval[code + valoffset[k]] 31 */ 32 33 /* Link to public Huffman table (needed only in jpeg_huff_decode) */ 34 JHUFF_TBL *pub; 35 36 /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of 37 * the input data stream. If the next Huffman code is no more 38 * than HUFF_LOOKAHEAD bits long, we can obtain its length and 39 * the corresponding symbol directly from this tables. 40 * 41 * The lower 8 bits of each table entry contain the number of 42 * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1 43 * if too long. The next 8 bits of each entry contain the 44 * symbol. 45 */ 46 int lookup[1 << HUFF_LOOKAHEAD]; 47 } d_derived_tbl; 48 49 /* Expand a Huffman table definition into the derived format */ 50 EXTERN(void) jpeg_make_d_derived_tbl(j_decompress_ptr cinfo, boolean isDC, 51 int tblno, 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 #if !defined(_WIN32) && !defined(SIZEOF_SIZE_T) 73 #error Cannot determine word size 74 #endif 75 76 #if SIZEOF_SIZE_T == 8 || defined(_WIN64) 77 78 typedef size_t bit_buf_type; /* type of bit-extraction buffer */ 79 #define BIT_BUF_SIZE 64 /* size of buffer in bits */ 80 81 #else 82 83 typedef unsigned long bit_buf_type; /* type of bit-extraction buffer */ 84 #define BIT_BUF_SIZE 32 /* size of buffer in bits */ 85 86 #endif 87 88 /* If long is > 32 bits on your machine, and shifting/masking longs is 89 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE 90 * appropriately should be a win. Unfortunately we can't define the size 91 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) 92 * because not all machines measure sizeof in 8-bit bytes. 93 */ 94 95 typedef struct { /* Bitreading state saved across MCUs */ 96 bit_buf_type get_buffer; /* current bit-extraction buffer */ 97 int bits_left; /* # of unused bits in it */ 98 } bitread_perm_state; 99 100 typedef struct { /* Bitreading working state within an MCU */ 101 /* Current data source location */ 102 /* We need a copy, rather than munging the original, in case of suspension */ 103 const JOCTET *next_input_byte; /* => next byte to read from source */ 104 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ 105 /* Bit input buffer --- note these values are kept in register variables, 106 * not in this struct, inside the inner loops. 107 */ 108 bit_buf_type get_buffer; /* current bit-extraction buffer */ 109 int bits_left; /* # of unused bits in it */ 110 /* Pointer needed by jpeg_fill_bit_buffer. */ 111 j_decompress_ptr cinfo; /* back link to decompress master record */ 112 } bitread_working_state; 113 114 /* Macros to declare and load/save bitread local variables. */ 115 #define BITREAD_STATE_VARS \ 116 register bit_buf_type get_buffer; \ 117 register int bits_left; \ 118 bitread_working_state br_state 119 120 #define BITREAD_LOAD_STATE(cinfop, permstate) \ 121 br_state.cinfo = cinfop; \ 122 br_state.next_input_byte = cinfop->src->next_input_byte; \ 123 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ 124 get_buffer = permstate.get_buffer; \ 125 bits_left = permstate.bits_left; 126 127 #define BITREAD_SAVE_STATE(cinfop, permstate) \ 128 cinfop->src->next_input_byte = br_state.next_input_byte; \ 129 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ 130 permstate.get_buffer = get_buffer; \ 131 permstate.bits_left = bits_left 132 133 /* 134 * These macros provide the in-line portion of bit fetching. 135 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer 136 * before using GET_BITS, PEEK_BITS, or DROP_BITS. 137 * The variables get_buffer and bits_left are assumed to be locals, 138 * but the state struct might not be (jpeg_huff_decode needs this). 139 * CHECK_BIT_BUFFER(state, n, action); 140 * Ensure there are N bits in get_buffer; if suspend, take action. 141 * val = GET_BITS(n); 142 * Fetch next N bits. 143 * val = PEEK_BITS(n); 144 * Fetch next N bits without removing them from the buffer. 145 * DROP_BITS(n); 146 * Discard next N bits. 147 * The value N should be a simple variable, not an expression, because it 148 * is evaluated multiple times. 149 */ 150 151 #define CHECK_BIT_BUFFER(state, nbits, action) { \ 152 if (bits_left < (nbits)) { \ 153 if (!jpeg_fill_bit_buffer(&(state), get_buffer, bits_left, nbits)) \ 154 { action; } \ 155 get_buffer = (state).get_buffer; bits_left = (state).bits_left; \ 156 } \ 157 } 158 159 #define GET_BITS(nbits) \ 160 (((int)(get_buffer >> (bits_left -= (nbits)))) & ((1 << (nbits)) - 1)) 161 162 #define PEEK_BITS(nbits) \ 163 (((int)(get_buffer >> (bits_left - (nbits)))) & ((1 << (nbits)) - 1)) 164 165 #define DROP_BITS(nbits) \ 166 (bits_left -= (nbits)) 167 168 /* Load up the bit buffer to a depth of at least nbits */ 169 EXTERN(boolean) jpeg_fill_bit_buffer(bitread_working_state *state, 170 register bit_buf_type get_buffer, 171 register int bits_left, int nbits); 172 173 174 /* 175 * Code for extracting next Huffman-coded symbol from input bit stream. 176 * Again, this is time-critical and we make the main paths be macros. 177 * 178 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits 179 * without looping. Usually, more than 95% of the Huffman codes will be 8 180 * or fewer bits long. The few overlength codes are handled with a loop, 181 * which need not be inline code. 182 * 183 * Notes about the HUFF_DECODE macro: 184 * 1. Near the end of the data segment, we may fail to get enough bits 185 * for a lookahead. In that case, we do it the hard way. 186 * 2. If the lookahead table contains no entry, the next code must be 187 * more than HUFF_LOOKAHEAD bits long. 188 * 3. jpeg_huff_decode returns -1 if forced to suspend. 189 */ 190 191 #define HUFF_DECODE(result, state, htbl, failaction, slowlabel) { \ 192 register int nb, look; \ 193 if (bits_left < HUFF_LOOKAHEAD) { \ 194 if (!jpeg_fill_bit_buffer(&state, get_buffer, bits_left, 0)) \ 195 { failaction; } \ 196 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 197 if (bits_left < HUFF_LOOKAHEAD) { \ 198 nb = 1; goto slowlabel; \ 199 } \ 200 } \ 201 look = PEEK_BITS(HUFF_LOOKAHEAD); \ 202 if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \ 203 DROP_BITS(nb); \ 204 result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \ 205 } else { \ 206 slowlabel: \ 207 if ((result = \ 208 jpeg_huff_decode(&state, get_buffer, bits_left, htbl, nb)) < 0) \ 209 { failaction; } \ 210 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 211 } \ 212 } 213 214 #define HUFF_DECODE_FAST(s, nb, htbl) \ 215 FILL_BIT_BUFFER_FAST; \ 216 s = PEEK_BITS(HUFF_LOOKAHEAD); \ 217 s = htbl->lookup[s]; \ 218 nb = s >> HUFF_LOOKAHEAD; \ 219 /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \ 220 DROP_BITS(nb); \ 221 s = s & ((1 << HUFF_LOOKAHEAD) - 1); \ 222 if (nb > HUFF_LOOKAHEAD) { \ 223 /* Equivalent of jpeg_huff_decode() */ \ 224 /* Don't use GET_BITS() here because we don't want to modify bits_left */ \ 225 s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \ 226 while (s > htbl->maxcode[nb]) { \ 227 s <<= 1; \ 228 s |= GET_BITS(1); \ 229 nb++; \ 230 } \ 231 s = htbl->pub->huffval[(int)(s + htbl->valoffset[nb]) & 0xFF]; \ 232 } 233 234 /* Out-of-line case for Huffman code fetching */ 235 EXTERN(int) jpeg_huff_decode(bitread_working_state *state, 236 register bit_buf_type get_buffer, 237 register int bits_left, d_derived_tbl *htbl, 238 int min_bits); 239