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 * 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 /* Short forms of external names for systems with brain-damaged linkers. */ 16 17 #ifdef NEED_SHORT_EXTERNAL_NAMES 18 #define jpeg_make_d_derived_tbl jMkDDerived 19 #define jpeg_fill_bit_buffer jFilBitBuf 20 #define jpeg_huff_decode jHufDecode 21 #endif /* NEED_SHORT_EXTERNAL_NAMES */ 22 23 24 /* Derived data constructed for each Huffman table */ 25 26 #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */ 27 28 typedef struct { 29 /* Basic tables: (element [0] of each array is unused) */ 30 INT32 maxcode[18]; /* largest code of length k (-1 if none) */ 31 /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */ 32 INT32 valoffset[18]; /* huffval[] offset for codes of length k */ 33 /* valoffset[k] = huffval[] index of 1st symbol of code length k, less 34 * the smallest code of length k; so given a code of length k, the 35 * corresponding symbol is huffval[code + valoffset[k]] 36 */ 37 38 /* Link to public Huffman table (needed only in jpeg_huff_decode) */ 39 JHUFF_TBL *pub; 40 41 /* Lookahead table: indexed by the next HUFF_LOOKAHEAD bits of 42 * the input data stream. If the next Huffman code is no more 43 * than HUFF_LOOKAHEAD bits long, we can obtain its length and 44 * the corresponding symbol directly from this tables. 45 * 46 * The lower 8 bits of each table entry contain the number of 47 * bits in the corresponding Huffman code, or HUFF_LOOKAHEAD + 1 48 * if too long. The next 8 bits of each entry contain the 49 * symbol. 50 */ 51 int lookup[1<<HUFF_LOOKAHEAD]; 52 } d_derived_tbl; 53 54 /* Expand a Huffman table definition into the derived format */ 55 EXTERN(void) jpeg_make_d_derived_tbl 56 JPP((j_decompress_ptr cinfo, boolean isDC, int tblno, 57 d_derived_tbl ** pdtbl)); 58 59 60 /* 61 * Fetching the next N bits from the input stream is a time-critical operation 62 * for the Huffman decoders. We implement it with a combination of inline 63 * macros and out-of-line subroutines. Note that N (the number of bits 64 * demanded at one time) never exceeds 15 for JPEG use. 65 * 66 * We read source bytes into get_buffer and dole out bits as needed. 67 * If get_buffer already contains enough bits, they are fetched in-line 68 * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough 69 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer 70 * as full as possible (not just to the number of bits needed; this 71 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer). 72 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension. 73 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains 74 * at least the requested number of bits --- dummy zeroes are inserted if 75 * necessary. 76 */ 77 78 #if __WORDSIZE == 64 || defined(_WIN64) 79 80 typedef size_t bit_buf_type; /* type of bit-extraction buffer */ 81 #define BIT_BUF_SIZE 64 /* size of buffer in bits */ 82 83 #else 84 85 typedef INT32 bit_buf_type; /* type of bit-extraction buffer */ 86 #define BIT_BUF_SIZE 32 /* size of buffer in bits */ 87 88 #endif 89 90 /* If long is > 32 bits on your machine, and shifting/masking longs is 91 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE 92 * appropriately should be a win. Unfortunately we can't define the size 93 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) 94 * because not all machines measure sizeof in 8-bit bytes. 95 */ 96 97 typedef struct { /* Bitreading state saved across MCUs */ 98 bit_buf_type get_buffer; /* current bit-extraction buffer */ 99 int bits_left; /* # of unused bits in it */ 100 } bitread_perm_state; 101 102 typedef struct { /* Bitreading working state within an MCU */ 103 /* Current data source location */ 104 /* We need a copy, rather than munging the original, in case of suspension */ 105 const JOCTET * next_input_byte; /* => next byte to read from source */ 106 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ 107 /* Bit input buffer --- note these values are kept in register variables, 108 * not in this struct, inside the inner loops. 109 */ 110 bit_buf_type get_buffer; /* current bit-extraction buffer */ 111 int bits_left; /* # of unused bits in it */ 112 /* Pointer needed by jpeg_fill_bit_buffer. */ 113 j_decompress_ptr cinfo; /* back link to decompress master record */ 114 } bitread_working_state; 115 116 /* Macros to declare and load/save bitread local variables. */ 117 #define BITREAD_STATE_VARS \ 118 register bit_buf_type get_buffer; \ 119 register int bits_left; \ 120 bitread_working_state br_state 121 122 #define BITREAD_LOAD_STATE(cinfop,permstate) \ 123 br_state.cinfo = cinfop; \ 124 br_state.next_input_byte = cinfop->src->next_input_byte; \ 125 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ 126 get_buffer = permstate.get_buffer; \ 127 bits_left = permstate.bits_left; 128 129 #define BITREAD_SAVE_STATE(cinfop,permstate) \ 130 cinfop->src->next_input_byte = br_state.next_input_byte; \ 131 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ 132 permstate.get_buffer = get_buffer; \ 133 permstate.bits_left = bits_left 134 135 /* 136 * These macros provide the in-line portion of bit fetching. 137 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer 138 * before using GET_BITS, PEEK_BITS, or DROP_BITS. 139 * The variables get_buffer and bits_left are assumed to be locals, 140 * but the state struct might not be (jpeg_huff_decode needs this). 141 * CHECK_BIT_BUFFER(state,n,action); 142 * Ensure there are N bits in get_buffer; if suspend, take action. 143 * val = GET_BITS(n); 144 * Fetch next N bits. 145 * val = PEEK_BITS(n); 146 * Fetch next N bits without removing them from the buffer. 147 * DROP_BITS(n); 148 * Discard next N bits. 149 * The value N should be a simple variable, not an expression, because it 150 * is evaluated multiple times. 151 */ 152 153 #define CHECK_BIT_BUFFER(state,nbits,action) \ 154 { if (bits_left < (nbits)) { \ 155 if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \ 156 { action; } \ 157 get_buffer = (state).get_buffer; bits_left = (state).bits_left; } } 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 170 JPP((bitread_working_state * state, 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)) {failaction;} \ 195 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 196 if (bits_left < HUFF_LOOKAHEAD) { \ 197 nb = 1; goto slowlabel; \ 198 } \ 199 } \ 200 look = PEEK_BITS(HUFF_LOOKAHEAD); \ 201 if ((nb = (htbl->lookup[look] >> HUFF_LOOKAHEAD)) <= HUFF_LOOKAHEAD) { \ 202 DROP_BITS(nb); \ 203 result = htbl->lookup[look] & ((1 << HUFF_LOOKAHEAD) - 1); \ 204 } else { \ 205 slowlabel: \ 206 if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \ 207 { failaction; } \ 208 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 209 } \ 210 } 211 212 #define HUFF_DECODE_FAST(s,nb,htbl) \ 213 FILL_BIT_BUFFER_FAST; \ 214 s = PEEK_BITS(HUFF_LOOKAHEAD); \ 215 s = htbl->lookup[s]; \ 216 nb = s >> HUFF_LOOKAHEAD; \ 217 /* Pre-execute the common case of nb <= HUFF_LOOKAHEAD */ \ 218 DROP_BITS(nb); \ 219 s = s & ((1 << HUFF_LOOKAHEAD) - 1); \ 220 if (nb > HUFF_LOOKAHEAD) { \ 221 /* Equivalent of jpeg_huff_decode() */ \ 222 /* Don't use GET_BITS() here because we don't want to modify bits_left */ \ 223 s = (get_buffer >> bits_left) & ((1 << (nb)) - 1); \ 224 while (s > htbl->maxcode[nb]) { \ 225 s <<= 1; \ 226 s |= GET_BITS(1); \ 227 nb++; \ 228 } \ 229 s = htbl->pub->huffval[ (int) (s + htbl->valoffset[nb]) & 0xFF ]; \ 230 } 231 232 /* Out-of-line case for Huffman code fetching */ 233 EXTERN(int) jpeg_huff_decode 234 JPP((bitread_working_state * state, register bit_buf_type get_buffer, 235 register int bits_left, d_derived_tbl * htbl, int min_bits)); 236
