1/* 2 * jdhuff.c 3 * 4 * Copyright (C) 1991-1997, Thomas G. Lane. 5 * Modified 2006-2009 by Guido Vollbeding. 6 * This file is part of the Independent JPEG Group's software. 7 * For conditions of distribution and use, see the accompanying README file. 8 * 9 * This file contains Huffman entropy decoding routines. 10 * Both sequential and progressive modes are supported in this single module. 11 * 12 * Much of the complexity here has to do with supporting input suspension. 13 * If the data source module demands suspension, we want to be able to back 14 * up to the start of the current MCU. To do this, we copy state variables 15 * into local working storage, and update them back to the permanent 16 * storage only upon successful completion of an MCU. 17 */ 18 19#define JPEG_INTERNALS 20#include "jinclude.h" 21#include "jpeglib.h" 22 23 24/* Derived data constructed for each Huffman table */ 25 26#define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */ 27 28typedef 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[17]; /* 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 tables: 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 these tables. 45 */ 46 int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */ 47 UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */ 48} d_derived_tbl; 49 50 51/* 52 * Fetching the next N bits from the input stream is a time-critical operation 53 * for the Huffman decoders. We implement it with a combination of inline 54 * macros and out-of-line subroutines. Note that N (the number of bits 55 * demanded at one time) never exceeds 15 for JPEG use. 56 * 57 * We read source bytes into get_buffer and dole out bits as needed. 58 * If get_buffer already contains enough bits, they are fetched in-line 59 * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough 60 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer 61 * as full as possible (not just to the number of bits needed; this 62 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer). 63 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension. 64 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains 65 * at least the requested number of bits --- dummy zeroes are inserted if 66 * necessary. 67 */ 68 69typedef INT32 bit_buf_type; /* type of bit-extraction buffer */ 70#define BIT_BUF_SIZE 32 /* size of buffer in bits */ 71 72/* If long is > 32 bits on your machine, and shifting/masking longs is 73 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE 74 * appropriately should be a win. Unfortunately we can't define the size 75 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8) 76 * because not all machines measure sizeof in 8-bit bytes. 77 */ 78 79typedef struct { /* Bitreading state saved across MCUs */ 80 bit_buf_type get_buffer; /* current bit-extraction buffer */ 81 int bits_left; /* # of unused bits in it */ 82} bitread_perm_state; 83 84typedef struct { /* Bitreading working state within an MCU */ 85 /* Current data source location */ 86 /* We need a copy, rather than munging the original, in case of suspension */ 87 const JOCTET * next_input_byte; /* => next byte to read from source */ 88 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */ 89 /* Bit input buffer --- note these values are kept in register variables, 90 * not in this struct, inside the inner loops. 91 */ 92 bit_buf_type get_buffer; /* current bit-extraction buffer */ 93 int bits_left; /* # of unused bits in it */ 94 /* Pointer needed by jpeg_fill_bit_buffer. */ 95 j_decompress_ptr cinfo; /* back link to decompress master record */ 96} bitread_working_state; 97 98/* Macros to declare and load/save bitread local variables. */ 99#define BITREAD_STATE_VARS \ 100 register bit_buf_type get_buffer; \ 101 register int bits_left; \ 102 bitread_working_state br_state 103 104#define BITREAD_LOAD_STATE(cinfop,permstate) \ 105 br_state.cinfo = cinfop; \ 106 br_state.next_input_byte = cinfop->src->next_input_byte; \ 107 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \ 108 get_buffer = permstate.get_buffer; \ 109 bits_left = permstate.bits_left; 110 111#define BITREAD_SAVE_STATE(cinfop,permstate) \ 112 cinfop->src->next_input_byte = br_state.next_input_byte; \ 113 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \ 114 permstate.get_buffer = get_buffer; \ 115 permstate.bits_left = bits_left 116 117/* 118 * These macros provide the in-line portion of bit fetching. 119 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer 120 * before using GET_BITS, PEEK_BITS, or DROP_BITS. 121 * The variables get_buffer and bits_left are assumed to be locals, 122 * but the state struct might not be (jpeg_huff_decode needs this). 123 * CHECK_BIT_BUFFER(state,n,action); 124 * Ensure there are N bits in get_buffer; if suspend, take action. 125 * val = GET_BITS(n); 126 * Fetch next N bits. 127 * val = PEEK_BITS(n); 128 * Fetch next N bits without removing them from the buffer. 129 * DROP_BITS(n); 130 * Discard next N bits. 131 * The value N should be a simple variable, not an expression, because it 132 * is evaluated multiple times. 133 */ 134 135#define CHECK_BIT_BUFFER(state,nbits,action) \ 136 { if (bits_left < (nbits)) { \ 137 if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \ 138 { action; } \ 139 get_buffer = (state).get_buffer; bits_left = (state).bits_left; } } 140 141#define GET_BITS(nbits) \ 142 (((int) (get_buffer >> (bits_left -= (nbits)))) & BIT_MASK(nbits)) 143 144#define PEEK_BITS(nbits) \ 145 (((int) (get_buffer >> (bits_left - (nbits)))) & BIT_MASK(nbits)) 146 147#define DROP_BITS(nbits) \ 148 (bits_left -= (nbits)) 149 150 151/* 152 * Code for extracting next Huffman-coded symbol from input bit stream. 153 * Again, this is time-critical and we make the main paths be macros. 154 * 155 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits 156 * without looping. Usually, more than 95% of the Huffman codes will be 8 157 * or fewer bits long. The few overlength codes are handled with a loop, 158 * which need not be inline code. 159 * 160 * Notes about the HUFF_DECODE macro: 161 * 1. Near the end of the data segment, we may fail to get enough bits 162 * for a lookahead. In that case, we do it the hard way. 163 * 2. If the lookahead table contains no entry, the next code must be 164 * more than HUFF_LOOKAHEAD bits long. 165 * 3. jpeg_huff_decode returns -1 if forced to suspend. 166 */ 167 168#define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \ 169{ register int nb, look; \ 170 if (bits_left < HUFF_LOOKAHEAD) { \ 171 if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \ 172 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 173 if (bits_left < HUFF_LOOKAHEAD) { \ 174 nb = 1; goto slowlabel; \ 175 } \ 176 } \ 177 look = PEEK_BITS(HUFF_LOOKAHEAD); \ 178 if ((nb = htbl->look_nbits[look]) != 0) { \ 179 DROP_BITS(nb); \ 180 result = htbl->look_sym[look]; \ 181 } else { \ 182 nb = HUFF_LOOKAHEAD+1; \ 183slowlabel: \ 184 if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \ 185 { failaction; } \ 186 get_buffer = state.get_buffer; bits_left = state.bits_left; \ 187 } \ 188} 189 190 191/* 192 * Expanded entropy decoder object for Huffman decoding. 193 * 194 * The savable_state subrecord contains fields that change within an MCU, 195 * but must not be updated permanently until we complete the MCU. 196 */ 197 198typedef struct { 199 unsigned int EOBRUN; /* remaining EOBs in EOBRUN */ 200 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 201} savable_state; 202 203/* This macro is to work around compilers with missing or broken 204 * structure assignment. You'll need to fix this code if you have 205 * such a compiler and you change MAX_COMPS_IN_SCAN. 206 */ 207 208#ifndef NO_STRUCT_ASSIGN 209#define ASSIGN_STATE(dest,src) ((dest) = (src)) 210#else 211#if MAX_COMPS_IN_SCAN == 4 212#define ASSIGN_STATE(dest,src) \ 213 ((dest).EOBRUN = (src).EOBRUN, \ 214 (dest).last_dc_val[0] = (src).last_dc_val[0], \ 215 (dest).last_dc_val[1] = (src).last_dc_val[1], \ 216 (dest).last_dc_val[2] = (src).last_dc_val[2], \ 217 (dest).last_dc_val[3] = (src).last_dc_val[3]) 218#endif 219#endif 220 221 222typedef struct { 223 struct jpeg_entropy_decoder pub; /* public fields */ 224 225 /* These fields are loaded into local variables at start of each MCU. 226 * In case of suspension, we exit WITHOUT updating them. 227 */ 228 bitread_perm_state bitstate; /* Bit buffer at start of MCU */ 229 savable_state saved; /* Other state at start of MCU */ 230 231 /* These fields are NOT loaded into local working state. */ 232 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 233 234 /* Following two fields used only in progressive mode */ 235 236 /* Pointers to derived tables (these workspaces have image lifespan) */ 237 d_derived_tbl * derived_tbls[NUM_HUFF_TBLS]; 238 239 d_derived_tbl * ac_derived_tbl; /* active table during an AC scan */ 240 241 /* Following fields used only in sequential mode */ 242 243 /* Pointers to derived tables (these workspaces have image lifespan) */ 244 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; 245 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; 246 247 /* Precalculated info set up by start_pass for use in decode_mcu: */ 248 249 /* Pointers to derived tables to be used for each block within an MCU */ 250 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 251 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 252 /* Whether we care about the DC and AC coefficient values for each block */ 253 int coef_limit[D_MAX_BLOCKS_IN_MCU]; 254} huff_entropy_decoder; 255 256typedef huff_entropy_decoder * huff_entropy_ptr; 257 258 259static const int jpeg_zigzag_order[8][8] = { 260 { 0, 1, 5, 6, 14, 15, 27, 28 }, 261 { 2, 4, 7, 13, 16, 26, 29, 42 }, 262 { 3, 8, 12, 17, 25, 30, 41, 43 }, 263 { 9, 11, 18, 24, 31, 40, 44, 53 }, 264 { 10, 19, 23, 32, 39, 45, 52, 54 }, 265 { 20, 22, 33, 38, 46, 51, 55, 60 }, 266 { 21, 34, 37, 47, 50, 56, 59, 61 }, 267 { 35, 36, 48, 49, 57, 58, 62, 63 } 268}; 269 270 271/* 272 * Compute the derived values for a Huffman table. 273 * This routine also performs some validation checks on the table. 274 */ 275 276LOCAL(void) 277jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno, 278 d_derived_tbl ** pdtbl) 279{ 280 JHUFF_TBL *htbl; 281 d_derived_tbl *dtbl; 282 int p, i, l, si, numsymbols; 283 int lookbits, ctr; 284 char huffsize[257]; 285 unsigned int huffcode[257]; 286 unsigned int code; 287 288 /* Note that huffsize[] and huffcode[] are filled in code-length order, 289 * paralleling the order of the symbols themselves in htbl->huffval[]. 290 */ 291 292 /* Find the input Huffman table */ 293 if (tblno < 0 || tblno >= NUM_HUFF_TBLS) 294 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 295 htbl = 296 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno]; 297 if (htbl == NULL) 298 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 299 300 /* Allocate a workspace if we haven't already done so. */ 301 if (*pdtbl == NULL) 302 *pdtbl = (d_derived_tbl *) 303 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 304 SIZEOF(d_derived_tbl)); 305 dtbl = *pdtbl; 306 dtbl->pub = htbl; /* fill in back link */ 307 308 /* Figure C.1: make table of Huffman code length for each symbol */ 309 310 p = 0; 311 for (l = 1; l <= 16; l++) { 312 i = (int) htbl->bits[l]; 313 if (i < 0 || p + i > 256) /* protect against table overrun */ 314 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 315 while (i--) 316 huffsize[p++] = (char) l; 317 } 318 huffsize[p] = 0; 319 numsymbols = p; 320 321 /* Figure C.2: generate the codes themselves */ 322 /* We also validate that the counts represent a legal Huffman code tree. */ 323 324 code = 0; 325 si = huffsize[0]; 326 p = 0; 327 while (huffsize[p]) { 328 while (((int) huffsize[p]) == si) { 329 huffcode[p++] = code; 330 code++; 331 } 332 /* code is now 1 more than the last code used for codelength si; but 333 * it must still fit in si bits, since no code is allowed to be all ones. 334 */ 335 if (((INT32) code) >= (((INT32) 1) << si)) 336 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 337 code <<= 1; 338 si++; 339 } 340 341 /* Figure F.15: generate decoding tables for bit-sequential decoding */ 342 343 p = 0; 344 for (l = 1; l <= 16; l++) { 345 if (htbl->bits[l]) { 346 /* valoffset[l] = huffval[] index of 1st symbol of code length l, 347 * minus the minimum code of length l 348 */ 349 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p]; 350 p += htbl->bits[l]; 351 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */ 352 } else { 353 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */ 354 } 355 } 356 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */ 357 358 /* Compute lookahead tables to speed up decoding. 359 * First we set all the table entries to 0, indicating "too long"; 360 * then we iterate through the Huffman codes that are short enough and 361 * fill in all the entries that correspond to bit sequences starting 362 * with that code. 363 */ 364 365 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits)); 366 367 p = 0; 368 for (l = 1; l <= HUFF_LOOKAHEAD; l++) { 369 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) { 370 /* l = current code's length, p = its index in huffcode[] & huffval[]. */ 371 /* Generate left-justified code followed by all possible bit sequences */ 372 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l); 373 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) { 374 dtbl->look_nbits[lookbits] = l; 375 dtbl->look_sym[lookbits] = htbl->huffval[p]; 376 lookbits++; 377 } 378 } 379 } 380 381 /* Validate symbols as being reasonable. 382 * For AC tables, we make no check, but accept all byte values 0..255. 383 * For DC tables, we require the symbols to be in range 0..15. 384 * (Tighter bounds could be applied depending on the data depth and mode, 385 * but this is sufficient to ensure safe decoding.) 386 */ 387 if (isDC) { 388 for (i = 0; i < numsymbols; i++) { 389 int sym = htbl->huffval[i]; 390 if (sym < 0 || sym > 15) 391 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 392 } 393 } 394} 395 396 397/* 398 * Out-of-line code for bit fetching. 399 * Note: current values of get_buffer and bits_left are passed as parameters, 400 * but are returned in the corresponding fields of the state struct. 401 * 402 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width 403 * of get_buffer to be used. (On machines with wider words, an even larger 404 * buffer could be used.) However, on some machines 32-bit shifts are 405 * quite slow and take time proportional to the number of places shifted. 406 * (This is true with most PC compilers, for instance.) In this case it may 407 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the 408 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer. 409 */ 410 411#ifdef SLOW_SHIFT_32 412#define MIN_GET_BITS 15 /* minimum allowable value */ 413#else 414#define MIN_GET_BITS (BIT_BUF_SIZE-7) 415#endif 416 417 418LOCAL(boolean) 419jpeg_fill_bit_buffer (bitread_working_state * state, 420 register bit_buf_type get_buffer, register int bits_left, 421 int nbits) 422/* Load up the bit buffer to a depth of at least nbits */ 423{ 424 /* Copy heavily used state fields into locals (hopefully registers) */ 425 register const JOCTET * next_input_byte = state->next_input_byte; 426 register size_t bytes_in_buffer = state->bytes_in_buffer; 427 j_decompress_ptr cinfo = state->cinfo; 428 429 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */ 430 /* (It is assumed that no request will be for more than that many bits.) */ 431 /* We fail to do so only if we hit a marker or are forced to suspend. */ 432 433 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */ 434 while (bits_left < MIN_GET_BITS) { 435 register int c; 436 437 /* Attempt to read a byte */ 438 if (bytes_in_buffer == 0) { 439 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 440 return FALSE; 441 next_input_byte = cinfo->src->next_input_byte; 442 bytes_in_buffer = cinfo->src->bytes_in_buffer; 443 } 444 bytes_in_buffer--; 445 c = GETJOCTET(*next_input_byte++); 446 447 /* If it's 0xFF, check and discard stuffed zero byte */ 448 if (c == 0xFF) { 449 /* Loop here to discard any padding FF's on terminating marker, 450 * so that we can save a valid unread_marker value. NOTE: we will 451 * accept multiple FF's followed by a 0 as meaning a single FF data 452 * byte. This data pattern is not valid according to the standard. 453 */ 454 do { 455 if (bytes_in_buffer == 0) { 456 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 457 return FALSE; 458 next_input_byte = cinfo->src->next_input_byte; 459 bytes_in_buffer = cinfo->src->bytes_in_buffer; 460 } 461 bytes_in_buffer--; 462 c = GETJOCTET(*next_input_byte++); 463 } while (c == 0xFF); 464 465 if (c == 0) { 466 /* Found FF/00, which represents an FF data byte */ 467 c = 0xFF; 468 } else { 469 /* Oops, it's actually a marker indicating end of compressed data. 470 * Save the marker code for later use. 471 * Fine point: it might appear that we should save the marker into 472 * bitread working state, not straight into permanent state. But 473 * once we have hit a marker, we cannot need to suspend within the 474 * current MCU, because we will read no more bytes from the data 475 * source. So it is OK to update permanent state right away. 476 */ 477 cinfo->unread_marker = c; 478 /* See if we need to insert some fake zero bits. */ 479 goto no_more_bytes; 480 } 481 } 482 483 /* OK, load c into get_buffer */ 484 get_buffer = (get_buffer << 8) | c; 485 bits_left += 8; 486 } /* end while */ 487 } else { 488 no_more_bytes: 489 /* We get here if we've read the marker that terminates the compressed 490 * data segment. There should be enough bits in the buffer register 491 * to satisfy the request; if so, no problem. 492 */ 493 if (nbits > bits_left) { 494 /* Uh-oh. Report corrupted data to user and stuff zeroes into 495 * the data stream, so that we can produce some kind of image. 496 * We use a nonvolatile flag to ensure that only one warning message 497 * appears per data segment. 498 */ 499 if (! cinfo->entropy->insufficient_data) { 500 WARNMS(cinfo, JWRN_HIT_MARKER); 501 cinfo->entropy->insufficient_data = TRUE; 502 } 503 /* Fill the buffer with zero bits */ 504 get_buffer <<= MIN_GET_BITS - bits_left; 505 bits_left = MIN_GET_BITS; 506 } 507 } 508 509 /* Unload the local registers */ 510 state->next_input_byte = next_input_byte; 511 state->bytes_in_buffer = bytes_in_buffer; 512 state->get_buffer = get_buffer; 513 state->bits_left = bits_left; 514 515 return TRUE; 516} 517 518 519/* 520 * Figure F.12: extend sign bit. 521 * On some machines, a shift and sub will be faster than a table lookup. 522 */ 523 524#ifdef AVOID_TABLES 525 526#define BIT_MASK(nbits) ((1<<(nbits))-1) 527#define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) - ((1<<(s))-1) : (x)) 528 529#else 530 531#define BIT_MASK(nbits) bmask[nbits] 532#define HUFF_EXTEND(x,s) ((x) <= bmask[(s) - 1] ? (x) - bmask[s] : (x)) 533 534static const int bmask[16] = /* bmask[n] is mask for n rightmost bits */ 535 { 0, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 536 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF }; 537 538#endif /* AVOID_TABLES */ 539 540 541/* 542 * Out-of-line code for Huffman code decoding. 543 */ 544 545LOCAL(int) 546jpeg_huff_decode (bitread_working_state * state, 547 register bit_buf_type get_buffer, register int bits_left, 548 d_derived_tbl * htbl, int min_bits) 549{ 550 register int l = min_bits; 551 register INT32 code; 552 553 /* HUFF_DECODE has determined that the code is at least min_bits */ 554 /* bits long, so fetch that many bits in one swoop. */ 555 556 CHECK_BIT_BUFFER(*state, l, return -1); 557 code = GET_BITS(l); 558 559 /* Collect the rest of the Huffman code one bit at a time. */ 560 /* This is per Figure F.16 in the JPEG spec. */ 561 562 while (code > htbl->maxcode[l]) { 563 code <<= 1; 564 CHECK_BIT_BUFFER(*state, 1, return -1); 565 code |= GET_BITS(1); 566 l++; 567 } 568 569 /* Unload the local registers */ 570 state->get_buffer = get_buffer; 571 state->bits_left = bits_left; 572 573 /* With garbage input we may reach the sentinel value l = 17. */ 574 575 if (l > 16) { 576 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE); 577 return 0; /* fake a zero as the safest result */ 578 } 579 580 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ]; 581} 582 583 584/* 585 * Check for a restart marker & resynchronize decoder. 586 * Returns FALSE if must suspend. 587 */ 588 589LOCAL(boolean) 590process_restart (j_decompress_ptr cinfo) 591{ 592 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 593 int ci; 594 595 /* Throw away any unused bits remaining in bit buffer; */ 596 /* include any full bytes in next_marker's count of discarded bytes */ 597 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8; 598 entropy->bitstate.bits_left = 0; 599 600 /* Advance past the RSTn marker */ 601 if (! (*cinfo->marker->read_restart_marker) (cinfo)) 602 return FALSE; 603 604 /* Re-initialize DC predictions to 0 */ 605 for (ci = 0; ci < cinfo->comps_in_scan; ci++) 606 entropy->saved.last_dc_val[ci] = 0; 607 /* Re-init EOB run count, too */ 608 entropy->saved.EOBRUN = 0; 609 610 /* Reset restart counter */ 611 entropy->restarts_to_go = cinfo->restart_interval; 612 613 /* Reset out-of-data flag, unless read_restart_marker left us smack up 614 * against a marker. In that case we will end up treating the next data 615 * segment as empty, and we can avoid producing bogus output pixels by 616 * leaving the flag set. 617 */ 618 if (cinfo->unread_marker == 0) 619 entropy->pub.insufficient_data = FALSE; 620 621 return TRUE; 622} 623 624 625/* 626 * Huffman MCU decoding. 627 * Each of these routines decodes and returns one MCU's worth of 628 * Huffman-compressed coefficients. 629 * The coefficients are reordered from zigzag order into natural array order, 630 * but are not dequantized. 631 * 632 * The i'th block of the MCU is stored into the block pointed to by 633 * MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER. 634 * (Wholesale zeroing is usually a little faster than retail...) 635 * 636 * We return FALSE if data source requested suspension. In that case no 637 * changes have been made to permanent state. (Exception: some output 638 * coefficients may already have been assigned. This is harmless for 639 * spectral selection, since we'll just re-assign them on the next call. 640 * Successive approximation AC refinement has to be more careful, however.) 641 */ 642 643/* 644 * MCU decoding for DC initial scan (either spectral selection, 645 * or first pass of successive approximation). 646 */ 647 648METHODDEF(boolean) 649decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 650{ 651 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 652 int Al = cinfo->Al; 653 register int s, r; 654 int blkn, ci; 655 JBLOCKROW block; 656 BITREAD_STATE_VARS; 657 savable_state state; 658 d_derived_tbl * tbl; 659 jpeg_component_info * compptr; 660 661 /* Process restart marker if needed; may have to suspend */ 662 if (cinfo->restart_interval) { 663 if (entropy->restarts_to_go == 0) 664 if (! process_restart(cinfo)) 665 return FALSE; 666 } 667 668 /* If we've run out of data, just leave the MCU set to zeroes. 669 * This way, we return uniform gray for the remainder of the segment. 670 */ 671 if (! entropy->pub.insufficient_data) { 672 673 /* Load up working state */ 674 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 675 ASSIGN_STATE(state, entropy->saved); 676 677 /* Outer loop handles each block in the MCU */ 678 679 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 680 block = MCU_data[blkn]; 681 ci = cinfo->MCU_membership[blkn]; 682 compptr = cinfo->cur_comp_info[ci]; 683 tbl = entropy->derived_tbls[compptr->dc_tbl_no]; 684 685 /* Decode a single block's worth of coefficients */ 686 687 /* Section F.2.2.1: decode the DC coefficient difference */ 688 HUFF_DECODE(s, br_state, tbl, return FALSE, label1); 689 if (s) { 690 CHECK_BIT_BUFFER(br_state, s, return FALSE); 691 r = GET_BITS(s); 692 s = HUFF_EXTEND(r, s); 693 } 694 695 /* Convert DC difference to actual value, update last_dc_val */ 696 s += state.last_dc_val[ci]; 697 state.last_dc_val[ci] = s; 698 /* Scale and output the coefficient (assumes jpeg_natural_order[0]=0) */ 699 (*block)[0] = (JCOEF) (s << Al); 700 } 701 702 /* Completed MCU, so update state */ 703 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 704 ASSIGN_STATE(entropy->saved, state); 705 } 706 707 /* Account for restart interval (no-op if not using restarts) */ 708 entropy->restarts_to_go--; 709 710 return TRUE; 711} 712 713 714/* 715 * MCU decoding for AC initial scan (either spectral selection, 716 * or first pass of successive approximation). 717 */ 718 719METHODDEF(boolean) 720decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 721{ 722 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 723 int Se = cinfo->Se; 724 int Al = cinfo->Al; 725 register int s, k, r; 726 unsigned int EOBRUN; 727 JBLOCKROW block; 728 BITREAD_STATE_VARS; 729 d_derived_tbl * tbl; 730 731 /* Process restart marker if needed; may have to suspend */ 732 if (cinfo->restart_interval) { 733 if (entropy->restarts_to_go == 0) 734 if (! process_restart(cinfo)) 735 return FALSE; 736 } 737 738 /* If we've run out of data, just leave the MCU set to zeroes. 739 * This way, we return uniform gray for the remainder of the segment. 740 */ 741 if (! entropy->pub.insufficient_data) { 742 743 /* Load up working state. 744 * We can avoid loading/saving bitread state if in an EOB run. 745 */ 746 EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */ 747 748 /* There is always only one block per MCU */ 749 750 if (EOBRUN > 0) /* if it's a band of zeroes... */ 751 EOBRUN--; /* ...process it now (we do nothing) */ 752 else { 753 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 754 block = MCU_data[0]; 755 tbl = entropy->ac_derived_tbl; 756 757 for (k = cinfo->Ss; k <= Se; k++) { 758 HUFF_DECODE(s, br_state, tbl, return FALSE, label2); 759 r = s >> 4; 760 s &= 15; 761 if (s) { 762 k += r; 763 CHECK_BIT_BUFFER(br_state, s, return FALSE); 764 r = GET_BITS(s); 765 s = HUFF_EXTEND(r, s); 766 /* Scale and output coefficient in natural (dezigzagged) order */ 767 (*block)[jpeg_natural_order[k]] = (JCOEF) (s << Al); 768 } else { 769 if (r == 15) { /* ZRL */ 770 k += 15; /* skip 15 zeroes in band */ 771 } else { /* EOBr, run length is 2^r + appended bits */ 772 EOBRUN = 1 << r; 773 if (r) { /* EOBr, r > 0 */ 774 CHECK_BIT_BUFFER(br_state, r, return FALSE); 775 r = GET_BITS(r); 776 EOBRUN += r; 777 } 778 EOBRUN--; /* this band is processed at this moment */ 779 break; /* force end-of-band */ 780 } 781 } 782 } 783 784 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 785 } 786 787 /* Completed MCU, so update state */ 788 entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */ 789 } 790 791 /* Account for restart interval (no-op if not using restarts) */ 792 entropy->restarts_to_go--; 793 794 return TRUE; 795} 796 797 798/* 799 * MCU decoding for DC successive approximation refinement scan. 800 * Note: we assume such scans can be multi-component, although the spec 801 * is not very clear on the point. 802 */ 803 804METHODDEF(boolean) 805decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 806{ 807 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 808 int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 809 int blkn; 810 JBLOCKROW block; 811 BITREAD_STATE_VARS; 812 813 /* Process restart marker if needed; may have to suspend */ 814 if (cinfo->restart_interval) { 815 if (entropy->restarts_to_go == 0) 816 if (! process_restart(cinfo)) 817 return FALSE; 818 } 819 820 /* Not worth the cycles to check insufficient_data here, 821 * since we will not change the data anyway if we read zeroes. 822 */ 823 824 /* Load up working state */ 825 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 826 827 /* Outer loop handles each block in the MCU */ 828 829 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 830 block = MCU_data[blkn]; 831 832 /* Encoded data is simply the next bit of the two's-complement DC value */ 833 CHECK_BIT_BUFFER(br_state, 1, return FALSE); 834 if (GET_BITS(1)) 835 (*block)[0] |= p1; 836 /* Note: since we use |=, repeating the assignment later is safe */ 837 } 838 839 /* Completed MCU, so update state */ 840 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 841 842 /* Account for restart interval (no-op if not using restarts) */ 843 entropy->restarts_to_go--; 844 845 return TRUE; 846} 847 848 849/* 850 * MCU decoding for AC successive approximation refinement scan. 851 */ 852 853METHODDEF(boolean) 854decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 855{ 856 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 857 int Se = cinfo->Se; 858 int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 859 int m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */ 860 register int s, k, r; 861 unsigned int EOBRUN; 862 JBLOCKROW block; 863 JCOEFPTR thiscoef; 864 BITREAD_STATE_VARS; 865 d_derived_tbl * tbl; 866 int num_newnz; 867 int newnz_pos[DCTSIZE2]; 868 869 /* Process restart marker if needed; may have to suspend */ 870 if (cinfo->restart_interval) { 871 if (entropy->restarts_to_go == 0) 872 if (! process_restart(cinfo)) 873 return FALSE; 874 } 875 876 /* If we've run out of data, don't modify the MCU. 877 */ 878 if (! entropy->pub.insufficient_data) { 879 880 /* Load up working state */ 881 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 882 EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */ 883 884 /* There is always only one block per MCU */ 885 block = MCU_data[0]; 886 tbl = entropy->ac_derived_tbl; 887 888 /* If we are forced to suspend, we must undo the assignments to any newly 889 * nonzero coefficients in the block, because otherwise we'd get confused 890 * next time about which coefficients were already nonzero. 891 * But we need not undo addition of bits to already-nonzero coefficients; 892 * instead, we can test the current bit to see if we already did it. 893 */ 894 num_newnz = 0; 895 896 /* initialize coefficient loop counter to start of band */ 897 k = cinfo->Ss; 898 899 if (EOBRUN == 0) { 900 for (; k <= Se; k++) { 901 HUFF_DECODE(s, br_state, tbl, goto undoit, label3); 902 r = s >> 4; 903 s &= 15; 904 if (s) { 905 if (s != 1) /* size of new coef should always be 1 */ 906 WARNMS(cinfo, JWRN_HUFF_BAD_CODE); 907 CHECK_BIT_BUFFER(br_state, 1, goto undoit); 908 if (GET_BITS(1)) 909 s = p1; /* newly nonzero coef is positive */ 910 else 911 s = m1; /* newly nonzero coef is negative */ 912 } else { 913 if (r != 15) { 914 EOBRUN = 1 << r; /* EOBr, run length is 2^r + appended bits */ 915 if (r) { 916 CHECK_BIT_BUFFER(br_state, r, goto undoit); 917 r = GET_BITS(r); 918 EOBRUN += r; 919 } 920 break; /* rest of block is handled by EOB logic */ 921 } 922 /* note s = 0 for processing ZRL */ 923 } 924 /* Advance over already-nonzero coefs and r still-zero coefs, 925 * appending correction bits to the nonzeroes. A correction bit is 1 926 * if the absolute value of the coefficient must be increased. 927 */ 928 do { 929 thiscoef = *block + jpeg_natural_order[k]; 930 if (*thiscoef != 0) { 931 CHECK_BIT_BUFFER(br_state, 1, goto undoit); 932 if (GET_BITS(1)) { 933 if ((*thiscoef & p1) == 0) { /* do nothing if already set it */ 934 if (*thiscoef >= 0) 935 *thiscoef += p1; 936 else 937 *thiscoef += m1; 938 } 939 } 940 } else { 941 if (--r < 0) 942 break; /* reached target zero coefficient */ 943 } 944 k++; 945 } while (k <= Se); 946 if (s) { 947 int pos = jpeg_natural_order[k]; 948 /* Output newly nonzero coefficient */ 949 (*block)[pos] = (JCOEF) s; 950 /* Remember its position in case we have to suspend */ 951 newnz_pos[num_newnz++] = pos; 952 } 953 } 954 } 955 956 if (EOBRUN > 0) { 957 /* Scan any remaining coefficient positions after the end-of-band 958 * (the last newly nonzero coefficient, if any). Append a correction 959 * bit to each already-nonzero coefficient. A correction bit is 1 960 * if the absolute value of the coefficient must be increased. 961 */ 962 for (; k <= Se; k++) { 963 thiscoef = *block + jpeg_natural_order[k]; 964 if (*thiscoef != 0) { 965 CHECK_BIT_BUFFER(br_state, 1, goto undoit); 966 if (GET_BITS(1)) { 967 if ((*thiscoef & p1) == 0) { /* do nothing if already changed it */ 968 if (*thiscoef >= 0) 969 *thiscoef += p1; 970 else 971 *thiscoef += m1; 972 } 973 } 974 } 975 } 976 /* Count one block completed in EOB run */ 977 EOBRUN--; 978 } 979 980 /* Completed MCU, so update state */ 981 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 982 entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */ 983 } 984 985 /* Account for restart interval (no-op if not using restarts) */ 986 entropy->restarts_to_go--; 987 988 return TRUE; 989 990undoit: 991 /* Re-zero any output coefficients that we made newly nonzero */ 992 while (num_newnz > 0) 993 (*block)[newnz_pos[--num_newnz]] = 0; 994 995 return FALSE; 996} 997 998 999/* 1000 * Decode one MCU's worth of Huffman-compressed coefficients. 1001 */ 1002 1003METHODDEF(boolean) 1004decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 1005{ 1006 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 1007 int blkn; 1008 BITREAD_STATE_VARS; 1009 savable_state state; 1010 1011 /* Process restart marker if needed; may have to suspend */ 1012 if (cinfo->restart_interval) { 1013 if (entropy->restarts_to_go == 0) 1014 if (! process_restart(cinfo)) 1015 return FALSE; 1016 } 1017 1018 /* If we've run out of data, just leave the MCU set to zeroes. 1019 * This way, we return uniform gray for the remainder of the segment. 1020 */ 1021 if (! entropy->pub.insufficient_data) { 1022 1023 /* Load up working state */ 1024 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 1025 ASSIGN_STATE(state, entropy->saved); 1026 1027 /* Outer loop handles each block in the MCU */ 1028 1029 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 1030 JBLOCKROW block = MCU_data[blkn]; 1031 d_derived_tbl * htbl; 1032 register int s, k, r; 1033 int coef_limit, ci; 1034 1035 /* Decode a single block's worth of coefficients */ 1036 1037 /* Section F.2.2.1: decode the DC coefficient difference */ 1038 htbl = entropy->dc_cur_tbls[blkn]; 1039 HUFF_DECODE(s, br_state, htbl, return FALSE, label1); 1040 1041 htbl = entropy->ac_cur_tbls[blkn]; 1042 k = 1; 1043 coef_limit = entropy->coef_limit[blkn]; 1044 if (coef_limit) { 1045 /* Convert DC difference to actual value, update last_dc_val */ 1046 if (s) { 1047 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1048 r = GET_BITS(s); 1049 s = HUFF_EXTEND(r, s); 1050 } 1051 ci = cinfo->MCU_membership[blkn]; 1052 s += state.last_dc_val[ci]; 1053 state.last_dc_val[ci] = s; 1054 /* Output the DC coefficient */ 1055 (*block)[0] = (JCOEF) s; 1056 1057 /* Section F.2.2.2: decode the AC coefficients */ 1058 /* Since zeroes are skipped, output area must be cleared beforehand */ 1059 for (; k < coef_limit; k++) { 1060 HUFF_DECODE(s, br_state, htbl, return FALSE, label2); 1061 1062 r = s >> 4; 1063 s &= 15; 1064 1065 if (s) { 1066 k += r; 1067 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1068 r = GET_BITS(s); 1069 s = HUFF_EXTEND(r, s); 1070 /* Output coefficient in natural (dezigzagged) order. 1071 * Note: the extra entries in jpeg_natural_order[] will save us 1072 * if k >= DCTSIZE2, which could happen if the data is corrupted. 1073 */ 1074 (*block)[jpeg_natural_order[k]] = (JCOEF) s; 1075 } else { 1076 if (r != 15) 1077 goto EndOfBlock; 1078 k += 15; 1079 } 1080 } 1081 } else { 1082 if (s) { 1083 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1084 DROP_BITS(s); 1085 } 1086 } 1087 1088 /* Section F.2.2.2: decode the AC coefficients */ 1089 /* In this path we just discard the values */ 1090 for (; k < DCTSIZE2; k++) { 1091 HUFF_DECODE(s, br_state, htbl, return FALSE, label3); 1092 1093 r = s >> 4; 1094 s &= 15; 1095 1096 if (s) { 1097 k += r; 1098 CHECK_BIT_BUFFER(br_state, s, return FALSE); 1099 DROP_BITS(s); 1100 } else { 1101 if (r != 15) 1102 break; 1103 k += 15; 1104 } 1105 } 1106 1107 EndOfBlock: ; 1108 } 1109 1110 /* Completed MCU, so update state */ 1111 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 1112 ASSIGN_STATE(entropy->saved, state); 1113 } 1114 1115 /* Account for restart interval (no-op if not using restarts) */ 1116 entropy->restarts_to_go--; 1117 1118 return TRUE; 1119} 1120 1121 1122/* 1123 * Initialize for a Huffman-compressed scan. 1124 */ 1125 1126METHODDEF(void) 1127start_pass_huff_decoder (j_decompress_ptr cinfo) 1128{ 1129 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 1130 int ci, blkn, dctbl, actbl, i; 1131 jpeg_component_info * compptr; 1132 1133 if (cinfo->progressive_mode) { 1134 /* Validate progressive scan parameters */ 1135 if (cinfo->Ss == 0) { 1136 if (cinfo->Se != 0) 1137 goto bad; 1138 } else { 1139 /* need not check Ss/Se < 0 since they came from unsigned bytes */ 1140 if (cinfo->Se < cinfo->Ss || cinfo->Se >= DCTSIZE2) 1141 goto bad; 1142 /* AC scans may have only one component */ 1143 if (cinfo->comps_in_scan != 1) 1144 goto bad; 1145 } 1146 if (cinfo->Ah != 0) { 1147 /* Successive approximation refinement scan: must have Al = Ah-1. */ 1148 if (cinfo->Ah-1 != cinfo->Al) 1149 goto bad; 1150 } 1151 if (cinfo->Al > 13) { /* need not check for < 0 */ 1152 /* Arguably the maximum Al value should be less than 13 for 8-bit precision, 1153 * but the spec doesn't say so, and we try to be liberal about what we 1154 * accept. Note: large Al values could result in out-of-range DC 1155 * coefficients during early scans, leading to bizarre displays due to 1156 * overflows in the IDCT math. But we won't crash. 1157 */ 1158 bad: 1159 ERREXIT4(cinfo, JERR_BAD_PROGRESSION, 1160 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al); 1161 } 1162 /* Update progression status, and verify that scan order is legal. 1163 * Note that inter-scan inconsistencies are treated as warnings 1164 * not fatal errors ... not clear if this is right way to behave. 1165 */ 1166 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 1167 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index; 1168 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0]; 1169 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */ 1170 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0); 1171 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) { 1172 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi]; 1173 if (cinfo->Ah != expected) 1174 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi); 1175 coef_bit_ptr[coefi] = cinfo->Al; 1176 } 1177 } 1178 1179 /* Select MCU decoding routine */ 1180 if (cinfo->Ah == 0) { 1181 if (cinfo->Ss == 0) 1182 entropy->pub.decode_mcu = decode_mcu_DC_first; 1183 else 1184 entropy->pub.decode_mcu = decode_mcu_AC_first; 1185 } else { 1186 if (cinfo->Ss == 0) 1187 entropy->pub.decode_mcu = decode_mcu_DC_refine; 1188 else 1189 entropy->pub.decode_mcu = decode_mcu_AC_refine; 1190 } 1191 1192 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 1193 compptr = cinfo->cur_comp_info[ci]; 1194 /* Make sure requested tables are present, and compute derived tables. 1195 * We may build same derived table more than once, but it's not expensive. 1196 */ 1197 if (cinfo->Ss == 0) { 1198 if (cinfo->Ah == 0) { /* DC refinement needs no table */ 1199 i = compptr->dc_tbl_no; 1200 jpeg_make_d_derived_tbl(cinfo, TRUE, i, 1201 & entropy->derived_tbls[i]); 1202 } 1203 } else { 1204 i = compptr->ac_tbl_no; 1205 jpeg_make_d_derived_tbl(cinfo, FALSE, i, 1206 & entropy->derived_tbls[i]); 1207 /* remember the single active table */ 1208 entropy->ac_derived_tbl = entropy->derived_tbls[i]; 1209 } 1210 /* Initialize DC predictions to 0 */ 1211 entropy->saved.last_dc_val[ci] = 0; 1212 } 1213 1214 /* Initialize private state variables */ 1215 entropy->saved.EOBRUN = 0; 1216 } else { 1217 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 1218 * This ought to be an error condition, but we make it a warning because 1219 * there are some baseline files out there with all zeroes in these bytes. 1220 */ 1221 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 || 1222 cinfo->Ah != 0 || cinfo->Al != 0) 1223 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 1224 1225 /* Select MCU decoding routine */ 1226 entropy->pub.decode_mcu = decode_mcu; 1227 1228 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 1229 compptr = cinfo->cur_comp_info[ci]; 1230 dctbl = compptr->dc_tbl_no; 1231 actbl = compptr->ac_tbl_no; 1232 /* Compute derived values for Huffman tables */ 1233 /* We may do this more than once for a table, but it's not expensive */ 1234 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl, 1235 & entropy->dc_derived_tbls[dctbl]); 1236 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl, 1237 & entropy->ac_derived_tbls[actbl]); 1238 /* Initialize DC predictions to 0 */ 1239 entropy->saved.last_dc_val[ci] = 0; 1240 } 1241 1242 /* Precalculate decoding info for each block in an MCU of this scan */ 1243 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 1244 ci = cinfo->MCU_membership[blkn]; 1245 compptr = cinfo->cur_comp_info[ci]; 1246 /* Precalculate which table to use for each block */ 1247 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no]; 1248 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no]; 1249 /* Decide whether we really care about the coefficient values */ 1250 if (compptr->component_needed) { 1251 ci = compptr->DCT_v_scaled_size; 1252 if (ci <= 0 || ci > 8) ci = 8; 1253 i = compptr->DCT_h_scaled_size; 1254 if (i <= 0 || i > 8) i = 8; 1255 entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order[ci - 1][i - 1]; 1256 } else { 1257 entropy->coef_limit[blkn] = 0; 1258 } 1259 } 1260 } 1261 1262 /* Initialize bitread state variables */ 1263 entropy->bitstate.bits_left = 0; 1264 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */ 1265 entropy->pub.insufficient_data = FALSE; 1266 1267 /* Initialize restart counter */ 1268 entropy->restarts_to_go = cinfo->restart_interval; 1269} 1270 1271 1272/* 1273 * Module initialization routine for Huffman entropy decoding. 1274 */ 1275 1276GLOBAL(void) 1277jinit_huff_decoder (j_decompress_ptr cinfo) 1278{ 1279 huff_entropy_ptr entropy; 1280 int i; 1281 1282 entropy = (huff_entropy_ptr) 1283 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 1284 SIZEOF(huff_entropy_decoder)); 1285 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy; 1286 entropy->pub.start_pass = start_pass_huff_decoder; 1287 1288 if (cinfo->progressive_mode) { 1289 /* Create progression status table */ 1290 int *coef_bit_ptr, ci; 1291 cinfo->coef_bits = (int (*)[DCTSIZE2]) 1292 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 1293 cinfo->num_components*DCTSIZE2*SIZEOF(int)); 1294 coef_bit_ptr = & cinfo->coef_bits[0][0]; 1295 for (ci = 0; ci < cinfo->num_components; ci++) 1296 for (i = 0; i < DCTSIZE2; i++) 1297 *coef_bit_ptr++ = -1; 1298 1299 /* Mark derived tables unallocated */ 1300 for (i = 0; i < NUM_HUFF_TBLS; i++) { 1301 entropy->derived_tbls[i] = NULL; 1302 } 1303 } else { 1304 /* Mark tables unallocated */ 1305 for (i = 0; i < NUM_HUFF_TBLS; i++) { 1306 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; 1307 } 1308 } 1309} 1310