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, D. R. Commander. 8 * For conditions of distribution and use, see the accompanying README file. 9 * 10 * This file contains declarations for Huffman entropy decoding routines 11 * that are shared between the sequential decoder (jdhuff.c) and the 12 * progressive decoder (jdphuff.c). No other modules need to see these. 13 */ 14 15 16 /* Derived data constructed for each Huffman table */ 17 18 #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */ 19 20 typedef struct { 21 /* Basic tables: (element [0] of each array is unused) */ 22 INT32 maxcode[18]; /* largest code of length k (-1 if none) */ 23 /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */ 24 INT32 valoffset[18]; /* huffval[] offset for codes of length k */ 25 /* valoffset[k] = huffval[] index of 1st symbol of code length k, less 26 * the smallest code of length k; so given a code of length k, the 27 * corresponding symbol is huffval[code + valoffset[k]] 28 */ 29 30 /* Link to public Huffman table (needed only in jpeg_huff_decode) */ 31 JHUFF_TBL *pub; 32 33 /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of 34 * the input data stream. If the next Huffman code is no more 35 * than HUFF_LOOKAHEAD bits long, we can obtain its length and 36 * the corresponding symbol directly from this tables. 37 * 38 * The lower 8 bits of each table entry contain the number of 39 * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1 40 * if too long. The next 8 bits of each entry contain the 41 * symbol. 42 */ 43 int lookup[1<<HUFF_LOOKAHEAD]; 44 } d_derived_tbl; 45 46 /* Expand a Huffman table definition into the derived format */ 47 EXTERN(void) jpeg_make_d_derived_tbl 48 (j_decompress_ptr cinfo, boolean isDC, int tblno, 49 d_derived_tbl ** pdtbl); 50 51 52 /* 53 * Fetching the next N bits from the input stream is a time-critical operation 54 * for the Huffman decoders. We implement it with a combination of inline 55 * macros and out-of-line subroutines. Note that N (the number of bits 56 * demanded at one time) never exceeds 15 for JPEG use. 57 * 58 * We read source bytes into get_buffer and dole out bits as needed. 59 * If get_buffer already contains enough bits, they are fetched in-line 60 * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough 61 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer 62 * as full as possible (not just to the number of bits needed; this 63 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer). 64 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension. 65 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains 66 * at least the requested number of bits --- dummy zeroes are inserted if 67 * necessary. 68 */ 69 70 #if !defined(_WIN32) && !defined(SIZEOF_SIZE_T) 71 #error Cannot determine word size 72 #endif 73 74 #if SIZEOF_SIZE_T==8 || defined(_WIN64) 75 76 typedef size_t bit_buf_type; /* type of bit-extraction buffer */ 77 #define BIT_BUF_SIZE 64 /* size of buffer in bits */ 78 79 #else 80 81 typedef INT32 bit_buf_type; /* type of bit-extraction buffer */ 82 #define BIT_BUF_SIZE 32 /* size of buffer in bits */ 83 84 #endif 85 86 /* If long is > 32 bits on your machine, and shifting/masking longs is 87 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE 88 * appropriately should be a win. Unfortunately we can't define the size 89 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) 90 * because not all machines measure sizeof in 8-bit bytes. 91 */ 92 93 typedef struct { /* Bitreading state saved across MCUs */ 94 bit_buf_type get_buffer; /* current bit-extraction buffer */ 95 int bits_left; /* # of unused bits in it */ 96 } bitread_perm_state; 97 98 typedef struct { /* Bitreading working state within an MCU */ 99 /* Current data source location */ 100 /* We need a copy, rather than munging the original, in case of suspension */ 101 const JOCTET * next_input_byte; /* => next byte to read from source */ 102 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ 103 /* Bit input buffer --- note these values are kept in register variables, 104 * not in this struct, inside the inner loops. 105 */ 106 bit_buf_type get_buffer; /* current bit-extraction buffer */ 107 int bits_left; /* # of unused bits in it */ 108 /* Pointer needed by jpeg_fill_bit_buffer. */ 109 j_decompress_ptr cinfo; /* back link to decompress master record */ 110 } bitread_working_state; 111 112 /* Macros to declare and load/save bitread local variables. */ 113 #define BITREAD_STATE_VARS \ 114 register bit_buf_type get_buffer; \ 115 register int bits_left; \ 116 bitread_working_state br_state 117 118 #define BITREAD_LOAD_STATE(cinfop,permstate) \ 119 br_state.cinfo = cinfop; \ 120 br_state.next_input_byte = cinfop->src->next_input_byte; \ 121 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ 122 get_buffer = permstate.get_buffer; \ 123 bits_left = permstate.bits_left; 124 125 #define BITREAD_SAVE_STATE(cinfop,permstate) \ 126 cinfop->src->next_input_byte = br_state.next_input_byte; \ 127 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ 128 permstate.get_buffer = get_buffer; \ 129 permstate.bits_left = bits_left 130 131 /* 132 * These macros provide the in-line portion of bit fetching. 133 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer 134 * before using GET_BITS, PEEK_BITS, or DROP_BITS. 135 * The variables get_buffer and bits_left are assumed to be locals, 136 * but the state struct might not be (jpeg_huff_decode needs this). 137 * CHECK_BIT_BUFFER(state,n,action); 138 * Ensure there are N bits in get_buffer; if suspend, take action. 139 * val = GET_BITS(n); 140 * Fetch next N bits. 141 * val = PEEK_BITS(n); 142 * Fetch next N bits without removing them from the buffer. 143 * DROP_BITS(n); 144 * Discard next N bits. 145 * The value N should be a simple variable, not an expression, because it 146 * is evaluated multiple times. 147 */ 148 149 #define CHECK_BIT_BUFFER(state,nbits,action) \ 150 { if (bits_left < (nbits)) { \ 151 if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \ 152 { action; } \ 153 get_buffer = (state).get_buffer; bits_left = (state).bits_left; } } 154 155 #define GET_BITS(nbits) \ 156 (((int) (get_buffer >> (bits_left -= (nbits)))) & ((1<<(nbits))-1)) 157 158 #define PEEK_BITS(nbits) \ 159 (((int) (get_buffer >> (bits_left - (nbits)))) & ((1<<(nbits))-1)) 160 161 #define DROP_BITS(nbits) \ 162 (bits_left -= (nbits)) 163 164 /* Load up the bit buffer to a depth of at least nbits */ 165 EXTERN(boolean) jpeg_fill_bit_buffer 166 (bitread_working_state * state, register bit_buf_type get_buffer, 167 register int bits_left, int nbits); 168 169 170 /* 171 * Code for extracting next Huffman-coded symbol from input bit stream. 172 * Again, this is time-critical and we make the main paths be macros. 173 * 174 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits 175 * without looping. Usually, more than 95% of the Huffman codes will be 8 176 * or fewer bits long. The few overlength codes are handled with a loop, 177 * which need not be inline code. 178 * 179 * Notes about the HUFF_DECODE macro: 180 * 1. Near the end of the data segment, we may fail to get enough bits 181 * for a lookahead. In that case, we do it the hard way. 182 * 2. If the lookahead table contains no entry, the next code must be 183 * more than HUFF_LOOKAHEAD bits long. 184 * 3. jpeg_huff_decode returns -1 if forced to suspend. 185 */ 186 187 #define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \ 188 { register int nb, look; \ 189 if (bits_left < HUFF_LOOKAHEAD) { \ 190 if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \ 191 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 192 if (bits_left < HUFF_LOOKAHEAD) { \ 193 nb = 1; goto slowlabel; \ 194 } \ 195 } \ 196 look = PEEK_BITS(HUFF_LOOKAHEAD); \ 197 if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \ 198 DROP_BITS(nb); \ 199 result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \ 200 } else { \ 201 slowlabel: \ 202 if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \ 203 { failaction; } \ 204 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 205 } \ 206 } 207 208 #define HUFF_DECODE_FAST(s,nb,htbl) \ 209 FILL_BIT_BUFFER_FAST; \ 210 s = PEEK_BITS(HUFF_LOOKAHEAD); \ 211 s = htbl->lookup[s]; \ 212 nb = s >> HUFF_LOOKAHEAD; \ 213 /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \ 214 DROP_BITS(nb); \ 215 s = s & ((1 << HUFF_LOOKAHEAD) - 1); \ 216 if (nb > HUFF_LOOKAHEAD) { \ 217 /* Equivalent of jpeg_huff_decode() */ \ 218 /* Don't use GET_BITS() here because we don't want to modify bits_left */ \ 219 s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \ 220 while (s > htbl->maxcode[nb]) { \ 221 s <<= 1; \ 222 s |= GET_BITS(1); \ 223 nb++; \ 224 } \ 225 s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) & 0xFF ]; \ 226 } 227 228 /* Out-of-line case for Huffman code fetching */ 229 EXTERN(int) jpeg_huff_decode 230 (bitread_working_state * state, register bit_buf_type get_buffer, 231 register int bits_left, d_derived_tbl * htbl, int min_bits); 232
