jdhuff.c (20866B)
1 /* 2 * jdhuff.c 3 * 4 * Copyright (C) 1991-1997, Thomas G. Lane. 5 * This file is part of the Independent JPEG Group's software. 6 * For conditions of distribution and use, see the accompanying README file. 7 * 8 * This file contains Huffman entropy decoding routines. 9 * 10 * Much of the complexity here has to do with supporting input suspension. 11 * If the data source module demands suspension, we want to be able to back 12 * up to the start of the current MCU. To do this, we copy state variables 13 * into local working storage, and update them back to the permanent 14 * storage only upon successful completion of an MCU. 15 */ 16 17 #define JPEG_INTERNALS 18 #include "jinclude.h" 19 #include "jpeglib.h" 20 #include "jdhuff.h" /* Declarations shared with jdphuff.c */ 21 22 23 /* 24 * Expanded entropy decoder object for Huffman decoding. 25 * 26 * The savable_state subrecord contains fields that change within an MCU, 27 * but must not be updated permanently until we complete the MCU. 28 */ 29 30 typedef struct { 31 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 32 } savable_state; 33 34 /* This macro is to work around compilers with missing or broken 35 * structure assignment. You'll need to fix this code if you have 36 * such a compiler and you change MAX_COMPS_IN_SCAN. 37 */ 38 39 #ifndef NO_STRUCT_ASSIGN 40 #define ASSIGN_STATE(dest,src) ((dest) = (src)) 41 #else 42 #if MAX_COMPS_IN_SCAN == 4 43 #define ASSIGN_STATE(dest,src) \ 44 ((dest).last_dc_val[0] = (src).last_dc_val[0], \ 45 (dest).last_dc_val[1] = (src).last_dc_val[1], \ 46 (dest).last_dc_val[2] = (src).last_dc_val[2], \ 47 (dest).last_dc_val[3] = (src).last_dc_val[3]) 48 #endif 49 #endif 50 51 52 typedef struct { 53 struct jpeg_entropy_decoder pub; /* public fields */ 54 55 /* These fields are loaded into local variables at start of each MCU. 56 * In case of suspension, we exit WITHOUT updating them. 57 */ 58 bitread_perm_state bitstate; /* Bit buffer at start of MCU */ 59 savable_state saved; /* Other state at start of MCU */ 60 61 /* These fields are NOT loaded into local working state. */ 62 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 63 64 /* Pointers to derived tables (these workspaces have image lifespan) */ 65 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS]; 66 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS]; 67 68 /* Precalculated info set up by start_pass for use in decode_mcu: */ 69 70 /* Pointers to derived tables to be used for each block within an MCU */ 71 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 72 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU]; 73 /* Whether we care about the DC and AC coefficient values for each block */ 74 boolean dc_needed[D_MAX_BLOCKS_IN_MCU]; 75 boolean ac_needed[D_MAX_BLOCKS_IN_MCU]; 76 } huff_entropy_decoder; 77 78 typedef huff_entropy_decoder * huff_entropy_ptr; 79 80 81 /* 82 * Initialize for a Huffman-compressed scan. 83 */ 84 85 METHODDEF(void) 86 start_pass_huff_decoder (j_decompress_ptr cinfo) 87 { 88 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 89 int ci, blkn, dctbl, actbl; 90 jpeg_component_info * compptr; 91 92 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 93 * This ought to be an error condition, but we make it a warning because 94 * there are some baseline files out there with all zeroes in these bytes. 95 */ 96 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 || 97 cinfo->Ah != 0 || cinfo->Al != 0) 98 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 99 100 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 101 compptr = cinfo->cur_comp_info[ci]; 102 dctbl = compptr->dc_tbl_no; 103 actbl = compptr->ac_tbl_no; 104 /* Compute derived values for Huffman tables */ 105 /* We may do this more than once for a table, but it's not expensive */ 106 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl, 107 & entropy->dc_derived_tbls[dctbl]); 108 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl, 109 & entropy->ac_derived_tbls[actbl]); 110 /* Initialize DC predictions to 0 */ 111 entropy->saved.last_dc_val[ci] = 0; 112 } 113 114 /* Precalculate decoding info for each block in an MCU of this scan */ 115 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 116 ci = cinfo->MCU_membership[blkn]; 117 compptr = cinfo->cur_comp_info[ci]; 118 /* Precalculate which table to use for each block */ 119 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no]; 120 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no]; 121 /* Decide whether we really care about the coefficient values */ 122 if (compptr->component_needed) { 123 entropy->dc_needed[blkn] = TRUE; 124 /* we don't need the ACs if producing a 1/8th-size image */ 125 entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1); 126 } else { 127 entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE; 128 } 129 } 130 131 /* Initialize bitread state variables */ 132 entropy->bitstate.bits_left = 0; 133 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */ 134 entropy->pub.insufficient_data = FALSE; 135 136 /* Initialize restart counter */ 137 entropy->restarts_to_go = cinfo->restart_interval; 138 } 139 140 141 /* 142 * Compute the derived values for a Huffman table. 143 * This routine also performs some validation checks on the table. 144 * 145 * Note this is also used by jdphuff.c. 146 */ 147 148 GLOBAL(void) 149 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno, 150 d_derived_tbl ** pdtbl) 151 { 152 JHUFF_TBL *htbl; 153 d_derived_tbl *dtbl; 154 int p, i, l, si, numsymbols; 155 int lookbits, ctr; 156 char huffsize[257]; 157 unsigned int huffcode[257]; 158 unsigned int code; 159 160 /* Note that huffsize[] and huffcode[] are filled in code-length order, 161 * paralleling the order of the symbols themselves in htbl->huffval[]. 162 */ 163 164 /* Find the input Huffman table */ 165 if (tblno < 0 || tblno >= NUM_HUFF_TBLS) 166 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 167 htbl = 168 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno]; 169 if (htbl == NULL) 170 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno); 171 172 /* Allocate a workspace if we haven't already done so. */ 173 if (*pdtbl == NULL) 174 *pdtbl = (d_derived_tbl *) 175 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 176 SIZEOF(d_derived_tbl)); 177 dtbl = *pdtbl; 178 dtbl->pub = htbl; /* fill in back link */ 179 180 /* Figure C.1: make table of Huffman code length for each symbol */ 181 182 p = 0; 183 for (l = 1; l <= 16; l++) { 184 i = (int) htbl->bits[l]; 185 if (i < 0 || p + i > 256) /* protect against table overrun */ 186 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 187 while (i--) 188 huffsize[p++] = (char) l; 189 } 190 huffsize[p] = 0; 191 numsymbols = p; 192 193 /* Figure C.2: generate the codes themselves */ 194 /* We also validate that the counts represent a legal Huffman code tree. */ 195 196 code = 0; 197 si = huffsize[0]; 198 p = 0; 199 while (huffsize[p]) { 200 while (((int) huffsize[p]) == si) { 201 huffcode[p++] = code; 202 code++; 203 } 204 /* code is now 1 more than the last code used for codelength si; but 205 * it must still fit in si bits, since no code is allowed to be all ones. 206 */ 207 if (((INT32) code) >= (((INT32) 1) << si)) 208 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 209 code <<= 1; 210 si++; 211 } 212 213 /* Figure F.15: generate decoding tables for bit-sequential decoding */ 214 215 p = 0; 216 for (l = 1; l <= 16; l++) { 217 if (htbl->bits[l]) { 218 /* valoffset[l] = huffval[] index of 1st symbol of code length l, 219 * minus the minimum code of length l 220 */ 221 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p]; 222 p += htbl->bits[l]; 223 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */ 224 } else { 225 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */ 226 } 227 } 228 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */ 229 230 /* Compute lookahead tables to speed up decoding. 231 * First we set all the table entries to 0, indicating "too long"; 232 * then we iterate through the Huffman codes that are short enough and 233 * fill in all the entries that correspond to bit sequences starting 234 * with that code. 235 */ 236 237 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits)); 238 239 p = 0; 240 for (l = 1; l <= HUFF_LOOKAHEAD; l++) { 241 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) { 242 /* l = current code's length, p = its index in huffcode[] & huffval[]. */ 243 /* Generate left-justified code followed by all possible bit sequences */ 244 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l); 245 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) { 246 dtbl->look_nbits[lookbits] = l; 247 dtbl->look_sym[lookbits] = htbl->huffval[p]; 248 lookbits++; 249 } 250 } 251 } 252 253 /* Validate symbols as being reasonable. 254 * For AC tables, we make no check, but accept all byte values 0..255. 255 * For DC tables, we require the symbols to be in range 0..15. 256 * (Tighter bounds could be applied depending on the data depth and mode, 257 * but this is sufficient to ensure safe decoding.) 258 */ 259 if (isDC) { 260 for (i = 0; i < numsymbols; i++) { 261 int sym = htbl->huffval[i]; 262 if (sym < 0 || sym > 15) 263 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE); 264 } 265 } 266 } 267 268 269 /* 270 * Out-of-line code for bit fetching (shared with jdphuff.c). 271 * See jdhuff.h for info about usage. 272 * Note: current values of get_buffer and bits_left are passed as parameters, 273 * but are returned in the corresponding fields of the state struct. 274 * 275 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width 276 * of get_buffer to be used. (On machines with wider words, an even larger 277 * buffer could be used.) However, on some machines 32-bit shifts are 278 * quite slow and take time proportional to the number of places shifted. 279 * (This is true with most PC compilers, for instance.) In this case it may 280 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the 281 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer. 282 */ 283 284 #ifdef SLOW_SHIFT_32 285 #define MIN_GET_BITS 15 /* minimum allowable value */ 286 #else 287 #define MIN_GET_BITS (BIT_BUF_SIZE-7) 288 #endif 289 290 291 GLOBAL(boolean) 292 jpeg_fill_bit_buffer (bitread_working_state * state, 293 register bit_buf_type get_buffer, register int bits_left, 294 int nbits) 295 /* Load up the bit buffer to a depth of at least nbits */ 296 { 297 /* Copy heavily used state fields into locals (hopefully registers) */ 298 register const JOCTET * next_input_byte = state->next_input_byte; 299 register size_t bytes_in_buffer = state->bytes_in_buffer; 300 j_decompress_ptr cinfo = state->cinfo; 301 302 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */ 303 /* (It is assumed that no request will be for more than that many bits.) */ 304 /* We fail to do so only if we hit a marker or are forced to suspend. */ 305 306 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */ 307 while (bits_left < MIN_GET_BITS) { 308 register int c; 309 310 /* Attempt to read a byte */ 311 if (bytes_in_buffer == 0) { 312 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 313 return FALSE; 314 next_input_byte = cinfo->src->next_input_byte; 315 bytes_in_buffer = cinfo->src->bytes_in_buffer; 316 } 317 bytes_in_buffer--; 318 c = GETJOCTET(*next_input_byte++); 319 320 /* If it's 0xFF, check and discard stuffed zero byte */ 321 if (c == 0xFF) { 322 /* Loop here to discard any padding FF's on terminating marker, 323 * so that we can save a valid unread_marker value. NOTE: we will 324 * accept multiple FF's followed by a 0 as meaning a single FF data 325 * byte. This data pattern is not valid according to the standard. 326 */ 327 do { 328 if (bytes_in_buffer == 0) { 329 if (! (*cinfo->src->fill_input_buffer) (cinfo)) 330 return FALSE; 331 next_input_byte = cinfo->src->next_input_byte; 332 bytes_in_buffer = cinfo->src->bytes_in_buffer; 333 } 334 bytes_in_buffer--; 335 c = GETJOCTET(*next_input_byte++); 336 } while (c == 0xFF); 337 338 if (c == 0) { 339 /* Found FF/00, which represents an FF data byte */ 340 c = 0xFF; 341 } else { 342 /* Oops, it's actually a marker indicating end of compressed data. 343 * Save the marker code for later use. 344 * Fine point: it might appear that we should save the marker into 345 * bitread working state, not straight into permanent state. But 346 * once we have hit a marker, we cannot need to suspend within the 347 * current MCU, because we will read no more bytes from the data 348 * source. So it is OK to update permanent state right away. 349 */ 350 cinfo->unread_marker = c; 351 /* See if we need to insert some fake zero bits. */ 352 goto no_more_bytes; 353 } 354 } 355 356 /* OK, load c into get_buffer */ 357 get_buffer = (get_buffer << 8) | c; 358 bits_left += 8; 359 } /* end while */ 360 } else { 361 no_more_bytes: 362 /* We get here if we've read the marker that terminates the compressed 363 * data segment. There should be enough bits in the buffer register 364 * to satisfy the request; if so, no problem. 365 */ 366 if (nbits > bits_left) { 367 /* Uh-oh. Report corrupted data to user and stuff zeroes into 368 * the data stream, so that we can produce some kind of image. 369 * We use a nonvolatile flag to ensure that only one warning message 370 * appears per data segment. 371 */ 372 if (! cinfo->entropy->insufficient_data) { 373 WARNMS(cinfo, JWRN_HIT_MARKER); 374 cinfo->entropy->insufficient_data = TRUE; 375 } 376 /* Fill the buffer with zero bits */ 377 get_buffer <<= MIN_GET_BITS - bits_left; 378 bits_left = MIN_GET_BITS; 379 } 380 } 381 382 /* Unload the local registers */ 383 state->next_input_byte = next_input_byte; 384 state->bytes_in_buffer = bytes_in_buffer; 385 state->get_buffer = get_buffer; 386 state->bits_left = bits_left; 387 388 return TRUE; 389 } 390 391 392 /* 393 * Out-of-line code for Huffman code decoding. 394 * See jdhuff.h for info about usage. 395 */ 396 397 GLOBAL(int) 398 jpeg_huff_decode (bitread_working_state * state, 399 register bit_buf_type get_buffer, register int bits_left, 400 d_derived_tbl * htbl, int min_bits) 401 { 402 register int l = min_bits; 403 register INT32 code; 404 405 /* HUFF_DECODE has determined that the code is at least min_bits */ 406 /* bits long, so fetch that many bits in one swoop. */ 407 408 CHECK_BIT_BUFFER(*state, l, return -1); 409 code = GET_BITS(l); 410 411 /* Collect the rest of the Huffman code one bit at a time. */ 412 /* This is per Figure F.16 in the JPEG spec. */ 413 414 while (code > htbl->maxcode[l]) { 415 code <<= 1; 416 CHECK_BIT_BUFFER(*state, 1, return -1); 417 code |= GET_BITS(1); 418 l++; 419 } 420 421 /* Unload the local registers */ 422 state->get_buffer = get_buffer; 423 state->bits_left = bits_left; 424 425 /* With garbage input we may reach the sentinel value l = 17. */ 426 427 if (l > 16) { 428 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE); 429 return 0; /* fake a zero as the safest result */ 430 } 431 432 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ]; 433 } 434 435 436 /* 437 * Figure F.12: extend sign bit. 438 * On some machines, a shift and add will be faster than a table lookup. 439 */ 440 441 #ifdef AVOID_TABLES 442 443 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x)) 444 445 #else 446 447 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x)) 448 449 static const int extend_test[16] = /* entry n is 2**(n-1) */ 450 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080, 451 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 }; 452 453 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */ 454 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1, 455 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1, 456 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1, 457 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 }; 458 459 #endif /* AVOID_TABLES */ 460 461 462 /* 463 * Check for a restart marker & resynchronize decoder. 464 * Returns FALSE if must suspend. 465 */ 466 467 LOCAL(boolean) 468 process_restart (j_decompress_ptr cinfo) 469 { 470 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 471 int ci; 472 473 /* Throw away any unused bits remaining in bit buffer; */ 474 /* include any full bytes in next_marker's count of discarded bytes */ 475 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8; 476 entropy->bitstate.bits_left = 0; 477 478 /* Advance past the RSTn marker */ 479 if (! (*cinfo->marker->read_restart_marker) (cinfo)) 480 return FALSE; 481 482 /* Re-initialize DC predictions to 0 */ 483 for (ci = 0; ci < cinfo->comps_in_scan; ci++) 484 entropy->saved.last_dc_val[ci] = 0; 485 486 /* Reset restart counter */ 487 entropy->restarts_to_go = cinfo->restart_interval; 488 489 /* Reset out-of-data flag, unless read_restart_marker left us smack up 490 * against a marker. In that case we will end up treating the next data 491 * segment as empty, and we can avoid producing bogus output pixels by 492 * leaving the flag set. 493 */ 494 if (cinfo->unread_marker == 0) 495 entropy->pub.insufficient_data = FALSE; 496 497 return TRUE; 498 } 499 500 501 /* 502 * Decode and return one MCU's worth of Huffman-compressed coefficients. 503 * The coefficients are reordered from zigzag order into natural array order, 504 * but are not dequantized. 505 * 506 * The i'th block of the MCU is stored into the block pointed to by 507 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER. 508 * (Wholesale zeroing is usually a little faster than retail...) 509 * 510 * Returns FALSE if data source requested suspension. In that case no 511 * changes have been made to permanent state. (Exception: some output 512 * coefficients may already have been assigned. This is harmless for 513 * this module, since we'll just re-assign them on the next call.) 514 */ 515 516 METHODDEF(boolean) 517 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 518 { 519 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy; 520 int blkn; 521 BITREAD_STATE_VARS; 522 savable_state state; 523 524 /* Process restart marker if needed; may have to suspend */ 525 if (cinfo->restart_interval) { 526 if (entropy->restarts_to_go == 0) 527 if (! process_restart(cinfo)) 528 return FALSE; 529 } 530 531 /* If we've run out of data, just leave the MCU set to zeroes. 532 * This way, we return uniform gray for the remainder of the segment. 533 */ 534 if (! entropy->pub.insufficient_data) { 535 536 /* Load up working state */ 537 BITREAD_LOAD_STATE(cinfo,entropy->bitstate); 538 ASSIGN_STATE(state, entropy->saved); 539 540 /* Outer loop handles each block in the MCU */ 541 542 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 543 JBLOCKROW block = MCU_data[blkn]; 544 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn]; 545 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn]; 546 register int s, k, r; 547 548 /* Decode a single block's worth of coefficients */ 549 550 /* Section F.2.2.1: decode the DC coefficient difference */ 551 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1); 552 if (s) { 553 CHECK_BIT_BUFFER(br_state, s, return FALSE); 554 r = GET_BITS(s); 555 s = HUFF_EXTEND(r, s); 556 } 557 558 if (entropy->dc_needed[blkn]) { 559 /* Convert DC difference to actual value, update last_dc_val */ 560 int ci = cinfo->MCU_membership[blkn]; 561 s += state.last_dc_val[ci]; 562 state.last_dc_val[ci] = s; 563 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */ 564 (*block)[0] = (JCOEF) s; 565 } 566 567 if (entropy->ac_needed[blkn]) { 568 569 /* Section F.2.2.2: decode the AC coefficients */ 570 /* Since zeroes are skipped, output area must be cleared beforehand */ 571 for (k = 1; k < DCTSIZE2; k++) { 572 HUFF_DECODE(s, br_state, actbl, return FALSE, label2); 573 574 r = s >> 4; 575 s &= 15; 576 577 if (s) { 578 k += r; 579 CHECK_BIT_BUFFER(br_state, s, return FALSE); 580 r = GET_BITS(s); 581 s = HUFF_EXTEND(r, s); 582 /* Output coefficient in natural (dezigzagged) order. 583 * Note: the extra entries in jpeg_natural_order[] will save us 584 * if k >= DCTSIZE2, which could happen if the data is corrupted. 585 */ 586 (*block)[jpeg_natural_order[k]] = (JCOEF) s; 587 } else { 588 if (r != 15) 589 break; 590 k += 15; 591 } 592 } 593 594 } else { 595 596 /* Section F.2.2.2: decode the AC coefficients */ 597 /* In this path we just discard the values */ 598 for (k = 1; k < DCTSIZE2; k++) { 599 HUFF_DECODE(s, br_state, actbl, return FALSE, label3); 600 601 r = s >> 4; 602 s &= 15; 603 604 if (s) { 605 k += r; 606 CHECK_BIT_BUFFER(br_state, s, return FALSE); 607 DROP_BITS(s); 608 } else { 609 if (r != 15) 610 break; 611 k += 15; 612 } 613 } 614 615 } 616 } 617 618 /* Completed MCU, so update state */ 619 BITREAD_SAVE_STATE(cinfo,entropy->bitstate); 620 ASSIGN_STATE(entropy->saved, state); 621 } 622 623 /* Account for restart interval (no-op if not using restarts) */ 624 entropy->restarts_to_go--; 625 626 return TRUE; 627 } 628 629 630 /* 631 * Module initialization routine for Huffman entropy decoding. 632 */ 633 634 GLOBAL(void) 635 jinit_huff_decoder (j_decompress_ptr cinfo) 636 { 637 huff_entropy_ptr entropy; 638 int i; 639 640 entropy = (huff_entropy_ptr) 641 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 642 SIZEOF(huff_entropy_decoder)); 643 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy; 644 entropy->pub.start_pass = start_pass_huff_decoder; 645 entropy->pub.decode_mcu = decode_mcu; 646 647 /* Mark tables unallocated */ 648 for (i = 0; i < NUM_HUFF_TBLS; i++) { 649 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL; 650 } 651 }