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 51 (j_decompress_ptr cinfo, boolean isDC, int tblno, 52 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 #else 83 84 typedef unsigned long bit_buf_type; /* type of bit-extraction buffer */ 85 #define BIT_BUF_SIZE 32 /* size of buffer in bits */ 86 87 #endif 88 89 /* If long is > 32 bits on your machine, and shifting/masking longs is 90 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE 91 * appropriately should be a win. Unfortunately we can't define the size 92 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) 93 * because not all machines measure sizeof in 8-bit bytes. 94 */ 95 96 typedef struct { /* Bitreading state saved across MCUs */ 97 bit_buf_type get_buffer; /* current bit-extraction buffer */ 98 int bits_left; /* # of unused bits in it */ 99 } bitread_perm_state; 100 101 typedef struct { /* Bitreading working state within an MCU */ 102 /* Current data source location */ 103 /* We need a copy, rather than munging the original, in case of suspension */ 104 const JOCTET *next_input_byte; /* => next byte to read from source */ 105 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ 106 /* Bit input buffer --- note these values are kept in register variables, 107 * not in this struct, inside the inner loops. 108 */ 109 bit_buf_type get_buffer; /* current bit-extraction buffer */ 110 int bits_left; /* # of unused bits in it */ 111 /* Pointer needed by jpeg_fill_bit_buffer. */ 112 j_decompress_ptr cinfo; /* back link to decompress master record */ 113 } bitread_working_state; 114 115 /* Macros to declare and load/save bitread local variables. */ 116 #define BITREAD_STATE_VARS \ 117 register bit_buf_type get_buffer; \ 118 register int bits_left; \ 119 bitread_working_state br_state 120 121 #define BITREAD_LOAD_STATE(cinfop,permstate) \ 122 br_state.cinfo = cinfop; \ 123 br_state.next_input_byte = cinfop->src->next_input_byte; \ 124 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ 125 get_buffer = permstate.get_buffer; \ 126 bits_left = permstate.bits_left; 127 128 #define BITREAD_SAVE_STATE(cinfop,permstate) \ 129 cinfop->src->next_input_byte = br_state.next_input_byte; \ 130 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ 131 permstate.get_buffer = get_buffer; \ 132 permstate.bits_left = bits_left 133 134 /* 135 * These macros provide the in-line portion of bit fetching. 136 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer 137 * before using GET_BITS, PEEK_BITS, or DROP_BITS. 138 * The variables get_buffer and bits_left are assumed to be locals, 139 * but the state struct might not be (jpeg_huff_decode needs this). 140 * CHECK_BIT_BUFFER(state,n,action); 141 * Ensure there are N bits in get_buffer; if suspend, take action. 142 * val = GET_BITS(n); 143 * Fetch next N bits. 144 * val = PEEK_BITS(n); 145 * Fetch next N bits without removing them from the buffer. 146 * DROP_BITS(n); 147 * Discard next N bits. 148 * The value N should be a simple variable, not an expression, because it 149 * is evaluated multiple times. 150 */ 151 152 #define CHECK_BIT_BUFFER(state,nbits,action) \ 153 { if (bits_left < (nbits)) { \ 154 if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \ 155 { action; } \ 156 get_buffer = (state).get_buffer; bits_left = (state).bits_left; } } 157 158 #define GET_BITS(nbits) \ 159 (((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1)) 160 161 #define PEEK_BITS(nbits) \ 162 (((int) (get_buffer >> (bits_left - (nbits)))) & ((1<<(nbits))-1)) 163 164 #define DROP_BITS(nbits) \ 165 (bits_left -= (nbits)) 166 167 /* Load up the bit buffer to a depth of at least nbits */ 168 EXTERN(boolean) jpeg_fill_bit_buffer 169 (bitread_working_state *state, register bit_buf_type get_buffer, 170 register int bits_left, int nbits); 171 172 173 /* 174 * Code for extracting next Huffman-coded symbol from input bit stream. 175 * Again, this is time-critical and we make the main paths be macros. 176 * 177 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits 178 * without looping. Usually, more than 95% of the Huffman codes will be 8 179 * or fewer bits long. The few overlength codes are handled with a loop, 180 * which need not be inline code. 181 * 182 * Notes about the HUFF_DECODE macro: 183 * 1. Near the end of the data segment, we may fail to get enough bits 184 * for a lookahead. In that case, we do it the hard way. 185 * 2. If the lookahead table contains no entry, the next code must be 186 * more than HUFF_LOOKAHEAD bits long. 187 * 3. jpeg_huff_decode returns -1 if forced to suspend. 188 */ 189 190 #define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \ 191 { register int nb, look; \ 192 if (bits_left < HUFF_LOOKAHEAD) { \ 193 if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \ 194 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 195 if (bits_left < HUFF_LOOKAHEAD) { \ 196 nb = 1; goto slowlabel; \ 197 } \ 198 } \ 199 look = PEEK_BITS(HUFF_LOOKAHEAD); \ 200 if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \ 201 DROP_BITS(nb); \ 202 result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \ 203 } else { \ 204 slowlabel: \ 205 if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \ 206 { failaction; } \ 207 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 208 } \ 209 } 210 211 #define HUFF_DECODE_FAST(s,nb,htbl) \ 212 FILL_BIT_BUFFER_FAST; \ 213 s = PEEK_BITS(HUFF_LOOKAHEAD); \ 214 s = htbl->lookup[s]; \ 215 nb = s >> HUFF_LOOKAHEAD; \ 216 /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \ 217 DROP_BITS(nb); \ 218 s = s & ((1 << HUFF_LOOKAHEAD) - 1); \ 219 if (nb > HUFF_LOOKAHEAD) { \ 220 /* Equivalent of jpeg_huff_decode() */ \ 221 /* Don't use GET_BITS() here because we don't want to modify bits_left */ \ 222 s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \ 223 while (s > htbl->maxcode[nb]) { \ 224 s <<= 1; \ 225 s |= GET_BITS(1); \ 226 nb++; \ 227 } \ 228 s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) & 0xFF ]; \ 229 } 230 231 /* Out-of-line case for Huffman code fetching */ 232 EXTERN(int) jpeg_huff_decode 233 (bitread_working_state *state, register bit_buf_type get_buffer, 234 register int bits_left, d_derived_tbl *htbl, int min_bits); 235
