1/* 2 * jdarith.c 3 * 4 * Developed 1997-2012 by Guido Vollbeding. 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 portable arithmetic entropy decoding routines for JPEG 9 * (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81). 10 * 11 * Both sequential and progressive modes are supported in this single module. 12 * 13 * Suspension is not currently supported in this module. 14 */ 15 16#define JPEG_INTERNALS 17#include "jinclude.h" 18#include "jpeglib.h" 19 20 21/* Expanded entropy decoder object for arithmetic decoding. */ 22 23typedef struct { 24 struct jpeg_entropy_decoder pub; /* public fields */ 25 26 INT32 c; /* C register, base of coding interval + input bit buffer */ 27 INT32 a; /* A register, normalized size of coding interval */ 28 int ct; /* bit shift counter, # of bits left in bit buffer part of C */ 29 /* init: ct = -16 */ 30 /* run: ct = 0..7 */ 31 /* error: ct = -1 */ 32 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 33 int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */ 34 35 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 36 37 /* Pointers to statistics areas (these workspaces have image lifespan) */ 38 unsigned char * dc_stats[NUM_ARITH_TBLS]; 39 unsigned char * ac_stats[NUM_ARITH_TBLS]; 40 41 /* Statistics bin for coding with fixed probability 0.5 */ 42 unsigned char fixed_bin[4]; 43} arith_entropy_decoder; 44 45typedef arith_entropy_decoder * arith_entropy_ptr; 46 47/* The following two definitions specify the allocation chunk size 48 * for the statistics area. 49 * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least 50 * 49 statistics bins for DC, and 245 statistics bins for AC coding. 51 * 52 * We use a compact representation with 1 byte per statistics bin, 53 * thus the numbers directly represent byte sizes. 54 * This 1 byte per statistics bin contains the meaning of the MPS 55 * (more probable symbol) in the highest bit (mask 0x80), and the 56 * index into the probability estimation state machine table 57 * in the lower bits (mask 0x7F). 58 */ 59 60#define DC_STAT_BINS 64 61#define AC_STAT_BINS 256 62 63 64LOCAL(int) 65get_byte (j_decompress_ptr cinfo) 66/* Read next input byte; we do not support suspension in this module. */ 67{ 68 struct jpeg_source_mgr * src = cinfo->src; 69 70 if (src->bytes_in_buffer == 0) 71 if (! (*src->fill_input_buffer) (cinfo)) 72 ERREXIT(cinfo, JERR_CANT_SUSPEND); 73 src->bytes_in_buffer--; 74 return GETJOCTET(*src->next_input_byte++); 75} 76 77 78/* 79 * The core arithmetic decoding routine (common in JPEG and JBIG). 80 * This needs to go as fast as possible. 81 * Machine-dependent optimization facilities 82 * are not utilized in this portable implementation. 83 * However, this code should be fairly efficient and 84 * may be a good base for further optimizations anyway. 85 * 86 * Return value is 0 or 1 (binary decision). 87 * 88 * Note: I've changed the handling of the code base & bit 89 * buffer register C compared to other implementations 90 * based on the standards layout & procedures. 91 * While it also contains both the actual base of the 92 * coding interval (16 bits) and the next-bits buffer, 93 * the cut-point between these two parts is floating 94 * (instead of fixed) with the bit shift counter CT. 95 * Thus, we also need only one (variable instead of 96 * fixed size) shift for the LPS/MPS decision, and 97 * we can get away with any renormalization update 98 * of C (except for new data insertion, of course). 99 * 100 * I've also introduced a new scheme for accessing 101 * the probability estimation state machine table, 102 * derived from Markus Kuhn's JBIG implementation. 103 */ 104 105LOCAL(int) 106arith_decode (j_decompress_ptr cinfo, unsigned char *st) 107{ 108 register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy; 109 register unsigned char nl, nm; 110 register INT32 qe, temp; 111 register int sv, data; 112 113 /* Renormalization & data input per section D.2.6 */ 114 while (e->a < 0x8000L) { 115 if (--e->ct < 0) { 116 /* Need to fetch next data byte */ 117 if (cinfo->unread_marker) 118 data = 0; /* stuff zero data */ 119 else { 120 data = get_byte(cinfo); /* read next input byte */ 121 if (data == 0xFF) { /* zero stuff or marker code */ 122 do data = get_byte(cinfo); 123 while (data == 0xFF); /* swallow extra 0xFF bytes */ 124 if (data == 0) 125 data = 0xFF; /* discard stuffed zero byte */ 126 else { 127 /* Note: Different from the Huffman decoder, hitting 128 * a marker while processing the compressed data 129 * segment is legal in arithmetic coding. 130 * The convention is to supply zero data 131 * then until decoding is complete. 132 */ 133 cinfo->unread_marker = data; 134 data = 0; 135 } 136 } 137 } 138 e->c = (e->c << 8) | data; /* insert data into C register */ 139 if ((e->ct += 8) < 0) /* update bit shift counter */ 140 /* Need more initial bytes */ 141 if (++e->ct == 0) 142 /* Got 2 initial bytes -> re-init A and exit loop */ 143 e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */ 144 } 145 e->a <<= 1; 146 } 147 148 /* Fetch values from our compact representation of Table D.3(D.2): 149 * Qe values and probability estimation state machine 150 */ 151 sv = *st; 152 qe = jpeg_aritab[sv & 0x7F]; /* => Qe_Value */ 153 nl = qe & 0xFF; qe >>= 8; /* Next_Index_LPS + Switch_MPS */ 154 nm = qe & 0xFF; qe >>= 8; /* Next_Index_MPS */ 155 156 /* Decode & estimation procedures per sections D.2.4 & D.2.5 */ 157 temp = e->a - qe; 158 e->a = temp; 159 temp <<= e->ct; 160 if (e->c >= temp) { 161 e->c -= temp; 162 /* Conditional LPS (less probable symbol) exchange */ 163 if (e->a < qe) { 164 e->a = qe; 165 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */ 166 } else { 167 e->a = qe; 168 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */ 169 sv ^= 0x80; /* Exchange LPS/MPS */ 170 } 171 } else if (e->a < 0x8000L) { 172 /* Conditional MPS (more probable symbol) exchange */ 173 if (e->a < qe) { 174 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */ 175 sv ^= 0x80; /* Exchange LPS/MPS */ 176 } else { 177 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */ 178 } 179 } 180 181 return sv >> 7; 182} 183 184 185/* 186 * Check for a restart marker & resynchronize decoder. 187 */ 188 189LOCAL(void) 190process_restart (j_decompress_ptr cinfo) 191{ 192 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 193 int ci; 194 jpeg_component_info * compptr; 195 196 /* Advance past the RSTn marker */ 197 if (! (*cinfo->marker->read_restart_marker) (cinfo)) 198 ERREXIT(cinfo, JERR_CANT_SUSPEND); 199 200 /* Re-initialize statistics areas */ 201 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 202 compptr = cinfo->cur_comp_info[ci]; 203 if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) { 204 MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS); 205 /* Reset DC predictions to 0 */ 206 entropy->last_dc_val[ci] = 0; 207 entropy->dc_context[ci] = 0; 208 } 209 if ((! cinfo->progressive_mode && cinfo->lim_Se) || 210 (cinfo->progressive_mode && cinfo->Ss)) { 211 MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS); 212 } 213 } 214 215 /* Reset arithmetic decoding variables */ 216 entropy->c = 0; 217 entropy->a = 0; 218 entropy->ct = -16; /* force reading 2 initial bytes to fill C */ 219 220 /* Reset restart counter */ 221 entropy->restarts_to_go = cinfo->restart_interval; 222} 223 224 225/* 226 * Arithmetic MCU decoding. 227 * Each of these routines decodes and returns one MCU's worth of 228 * arithmetic-compressed coefficients. 229 * The coefficients are reordered from zigzag order into natural array order, 230 * but are not dequantized. 231 * 232 * The i'th block of the MCU is stored into the block pointed to by 233 * MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER. 234 */ 235 236/* 237 * MCU decoding for DC initial scan (either spectral selection, 238 * or first pass of successive approximation). 239 */ 240 241METHODDEF(boolean) 242decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 243{ 244 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 245 JBLOCKROW block; 246 unsigned char *st; 247 int blkn, ci, tbl, sign; 248 int v, m; 249 250 /* Process restart marker if needed */ 251 if (cinfo->restart_interval) { 252 if (entropy->restarts_to_go == 0) 253 process_restart(cinfo); 254 entropy->restarts_to_go--; 255 } 256 257 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 258 259 /* Outer loop handles each block in the MCU */ 260 261 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 262 block = MCU_data[blkn]; 263 ci = cinfo->MCU_membership[blkn]; 264 tbl = cinfo->cur_comp_info[ci]->dc_tbl_no; 265 266 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */ 267 268 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 269 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 270 271 /* Figure F.19: Decode_DC_DIFF */ 272 if (arith_decode(cinfo, st) == 0) 273 entropy->dc_context[ci] = 0; 274 else { 275 /* Figure F.21: Decoding nonzero value v */ 276 /* Figure F.22: Decoding the sign of v */ 277 sign = arith_decode(cinfo, st + 1); 278 st += 2; st += sign; 279 /* Figure F.23: Decoding the magnitude category of v */ 280 if ((m = arith_decode(cinfo, st)) != 0) { 281 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 282 while (arith_decode(cinfo, st)) { 283 if ((m <<= 1) == 0x8000) { 284 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 285 entropy->ct = -1; /* magnitude overflow */ 286 return TRUE; 287 } 288 st += 1; 289 } 290 } 291 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 292 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1)) 293 entropy->dc_context[ci] = 0; /* zero diff category */ 294 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1)) 295 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */ 296 else 297 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */ 298 v = m; 299 /* Figure F.24: Decoding the magnitude bit pattern of v */ 300 st += 14; 301 while (m >>= 1) 302 if (arith_decode(cinfo, st)) v |= m; 303 v += 1; if (sign) v = -v; 304 entropy->last_dc_val[ci] += v; 305 } 306 307 /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */ 308 (*block)[0] = (JCOEF) (entropy->last_dc_val[ci] << cinfo->Al); 309 } 310 311 return TRUE; 312} 313 314 315/* 316 * MCU decoding for AC initial scan (either spectral selection, 317 * or first pass of successive approximation). 318 */ 319 320METHODDEF(boolean) 321decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 322{ 323 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 324 JBLOCKROW block; 325 unsigned char *st; 326 int tbl, sign, k; 327 int v, m; 328 const int * natural_order; 329 330 /* Process restart marker if needed */ 331 if (cinfo->restart_interval) { 332 if (entropy->restarts_to_go == 0) 333 process_restart(cinfo); 334 entropy->restarts_to_go--; 335 } 336 337 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 338 339 natural_order = cinfo->natural_order; 340 341 /* There is always only one block per MCU */ 342 block = MCU_data[0]; 343 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 344 345 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */ 346 347 /* Figure F.20: Decode_AC_coefficients */ 348 k = cinfo->Ss - 1; 349 do { 350 st = entropy->ac_stats[tbl] + 3 * k; 351 if (arith_decode(cinfo, st)) break; /* EOB flag */ 352 for (;;) { 353 k++; 354 if (arith_decode(cinfo, st + 1)) break; 355 st += 3; 356 if (k >= cinfo->Se) { 357 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 358 entropy->ct = -1; /* spectral overflow */ 359 return TRUE; 360 } 361 } 362 /* Figure F.21: Decoding nonzero value v */ 363 /* Figure F.22: Decoding the sign of v */ 364 sign = arith_decode(cinfo, entropy->fixed_bin); 365 st += 2; 366 /* Figure F.23: Decoding the magnitude category of v */ 367 if ((m = arith_decode(cinfo, st)) != 0) { 368 if (arith_decode(cinfo, st)) { 369 m <<= 1; 370 st = entropy->ac_stats[tbl] + 371 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 372 while (arith_decode(cinfo, st)) { 373 if ((m <<= 1) == 0x8000) { 374 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 375 entropy->ct = -1; /* magnitude overflow */ 376 return TRUE; 377 } 378 st += 1; 379 } 380 } 381 } 382 v = m; 383 /* Figure F.24: Decoding the magnitude bit pattern of v */ 384 st += 14; 385 while (m >>= 1) 386 if (arith_decode(cinfo, st)) v |= m; 387 v += 1; if (sign) v = -v; 388 /* Scale and output coefficient in natural (dezigzagged) order */ 389 (*block)[natural_order[k]] = (JCOEF) (v << cinfo->Al); 390 } while (k < cinfo->Se); 391 392 return TRUE; 393} 394 395 396/* 397 * MCU decoding for DC successive approximation refinement scan. 398 */ 399 400METHODDEF(boolean) 401decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 402{ 403 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 404 unsigned char *st; 405 int p1, blkn; 406 407 /* Process restart marker if needed */ 408 if (cinfo->restart_interval) { 409 if (entropy->restarts_to_go == 0) 410 process_restart(cinfo); 411 entropy->restarts_to_go--; 412 } 413 414 st = entropy->fixed_bin; /* use fixed probability estimation */ 415 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 416 417 /* Outer loop handles each block in the MCU */ 418 419 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 420 /* Encoded data is simply the next bit of the two's-complement DC value */ 421 if (arith_decode(cinfo, st)) 422 MCU_data[blkn][0][0] |= p1; 423 } 424 425 return TRUE; 426} 427 428 429/* 430 * MCU decoding for AC successive approximation refinement scan. 431 */ 432 433METHODDEF(boolean) 434decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 435{ 436 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 437 JBLOCKROW block; 438 JCOEFPTR thiscoef; 439 unsigned char *st; 440 int tbl, k, kex; 441 int p1, m1; 442 const int * natural_order; 443 444 /* Process restart marker if needed */ 445 if (cinfo->restart_interval) { 446 if (entropy->restarts_to_go == 0) 447 process_restart(cinfo); 448 entropy->restarts_to_go--; 449 } 450 451 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 452 453 natural_order = cinfo->natural_order; 454 455 /* There is always only one block per MCU */ 456 block = MCU_data[0]; 457 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 458 459 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 460 m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */ 461 462 /* Establish EOBx (previous stage end-of-block) index */ 463 kex = cinfo->Se; 464 do { 465 if ((*block)[natural_order[kex]]) break; 466 } while (--kex); 467 468 k = cinfo->Ss - 1; 469 do { 470 st = entropy->ac_stats[tbl] + 3 * k; 471 if (k >= kex) 472 if (arith_decode(cinfo, st)) break; /* EOB flag */ 473 for (;;) { 474 thiscoef = *block + natural_order[++k]; 475 if (*thiscoef) { /* previously nonzero coef */ 476 if (arith_decode(cinfo, st + 2)) { 477 if (*thiscoef < 0) 478 *thiscoef += m1; 479 else 480 *thiscoef += p1; 481 } 482 break; 483 } 484 if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */ 485 if (arith_decode(cinfo, entropy->fixed_bin)) 486 *thiscoef = m1; 487 else 488 *thiscoef = p1; 489 break; 490 } 491 st += 3; 492 if (k >= cinfo->Se) { 493 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 494 entropy->ct = -1; /* spectral overflow */ 495 return TRUE; 496 } 497 } 498 } while (k < cinfo->Se); 499 500 return TRUE; 501} 502 503 504/* 505 * Decode one MCU's worth of arithmetic-compressed coefficients. 506 */ 507 508METHODDEF(boolean) 509decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 510{ 511 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 512 jpeg_component_info * compptr; 513 JBLOCKROW block; 514 unsigned char *st; 515 int blkn, ci, tbl, sign, k; 516 int v, m; 517 const int * natural_order; 518 519 /* Process restart marker if needed */ 520 if (cinfo->restart_interval) { 521 if (entropy->restarts_to_go == 0) 522 process_restart(cinfo); 523 entropy->restarts_to_go--; 524 } 525 526 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 527 528 natural_order = cinfo->natural_order; 529 530 /* Outer loop handles each block in the MCU */ 531 532 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 533 block = MCU_data[blkn]; 534 ci = cinfo->MCU_membership[blkn]; 535 compptr = cinfo->cur_comp_info[ci]; 536 537 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */ 538 539 tbl = compptr->dc_tbl_no; 540 541 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 542 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 543 544 /* Figure F.19: Decode_DC_DIFF */ 545 if (arith_decode(cinfo, st) == 0) 546 entropy->dc_context[ci] = 0; 547 else { 548 /* Figure F.21: Decoding nonzero value v */ 549 /* Figure F.22: Decoding the sign of v */ 550 sign = arith_decode(cinfo, st + 1); 551 st += 2; st += sign; 552 /* Figure F.23: Decoding the magnitude category of v */ 553 if ((m = arith_decode(cinfo, st)) != 0) { 554 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 555 while (arith_decode(cinfo, st)) { 556 if ((m <<= 1) == 0x8000) { 557 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 558 entropy->ct = -1; /* magnitude overflow */ 559 return TRUE; 560 } 561 st += 1; 562 } 563 } 564 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 565 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1)) 566 entropy->dc_context[ci] = 0; /* zero diff category */ 567 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1)) 568 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */ 569 else 570 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */ 571 v = m; 572 /* Figure F.24: Decoding the magnitude bit pattern of v */ 573 st += 14; 574 while (m >>= 1) 575 if (arith_decode(cinfo, st)) v |= m; 576 v += 1; if (sign) v = -v; 577 entropy->last_dc_val[ci] += v; 578 } 579 580 (*block)[0] = (JCOEF) entropy->last_dc_val[ci]; 581 582 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */ 583 584 if (cinfo->lim_Se == 0) continue; 585 tbl = compptr->ac_tbl_no; 586 k = 0; 587 588 /* Figure F.20: Decode_AC_coefficients */ 589 do { 590 st = entropy->ac_stats[tbl] + 3 * k; 591 if (arith_decode(cinfo, st)) break; /* EOB flag */ 592 for (;;) { 593 k++; 594 if (arith_decode(cinfo, st + 1)) break; 595 st += 3; 596 if (k >= cinfo->lim_Se) { 597 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 598 entropy->ct = -1; /* spectral overflow */ 599 return TRUE; 600 } 601 } 602 /* Figure F.21: Decoding nonzero value v */ 603 /* Figure F.22: Decoding the sign of v */ 604 sign = arith_decode(cinfo, entropy->fixed_bin); 605 st += 2; 606 /* Figure F.23: Decoding the magnitude category of v */ 607 if ((m = arith_decode(cinfo, st)) != 0) { 608 if (arith_decode(cinfo, st)) { 609 m <<= 1; 610 st = entropy->ac_stats[tbl] + 611 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 612 while (arith_decode(cinfo, st)) { 613 if ((m <<= 1) == 0x8000) { 614 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 615 entropy->ct = -1; /* magnitude overflow */ 616 return TRUE; 617 } 618 st += 1; 619 } 620 } 621 } 622 v = m; 623 /* Figure F.24: Decoding the magnitude bit pattern of v */ 624 st += 14; 625 while (m >>= 1) 626 if (arith_decode(cinfo, st)) v |= m; 627 v += 1; if (sign) v = -v; 628 (*block)[natural_order[k]] = (JCOEF) v; 629 } while (k < cinfo->lim_Se); 630 } 631 632 return TRUE; 633} 634 635 636/* 637 * Initialize for an arithmetic-compressed scan. 638 */ 639 640METHODDEF(void) 641start_pass (j_decompress_ptr cinfo) 642{ 643 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 644 int ci, tbl; 645 jpeg_component_info * compptr; 646 647 if (cinfo->progressive_mode) { 648 /* Validate progressive scan parameters */ 649 if (cinfo->Ss == 0) { 650 if (cinfo->Se != 0) 651 goto bad; 652 } else { 653 /* need not check Ss/Se < 0 since they came from unsigned bytes */ 654 if (cinfo->Se < cinfo->Ss || cinfo->Se > cinfo->lim_Se) 655 goto bad; 656 /* AC scans may have only one component */ 657 if (cinfo->comps_in_scan != 1) 658 goto bad; 659 } 660 if (cinfo->Ah != 0) { 661 /* Successive approximation refinement scan: must have Al = Ah-1. */ 662 if (cinfo->Ah-1 != cinfo->Al) 663 goto bad; 664 } 665 if (cinfo->Al > 13) { /* need not check for < 0 */ 666 bad: 667 ERREXIT4(cinfo, JERR_BAD_PROGRESSION, 668 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al); 669 } 670 /* Update progression status, and verify that scan order is legal. 671 * Note that inter-scan inconsistencies are treated as warnings 672 * not fatal errors ... not clear if this is right way to behave. 673 */ 674 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 675 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index; 676 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0]; 677 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */ 678 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0); 679 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) { 680 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi]; 681 if (cinfo->Ah != expected) 682 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi); 683 coef_bit_ptr[coefi] = cinfo->Al; 684 } 685 } 686 /* Select MCU decoding routine */ 687 if (cinfo->Ah == 0) { 688 if (cinfo->Ss == 0) 689 entropy->pub.decode_mcu = decode_mcu_DC_first; 690 else 691 entropy->pub.decode_mcu = decode_mcu_AC_first; 692 } else { 693 if (cinfo->Ss == 0) 694 entropy->pub.decode_mcu = decode_mcu_DC_refine; 695 else 696 entropy->pub.decode_mcu = decode_mcu_AC_refine; 697 } 698 } else { 699 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 700 * This ought to be an error condition, but we make it a warning. 701 */ 702 if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 || 703 (cinfo->Se < DCTSIZE2 && cinfo->Se != cinfo->lim_Se)) 704 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 705 /* Select MCU decoding routine */ 706 entropy->pub.decode_mcu = decode_mcu; 707 } 708 709 /* Allocate & initialize requested statistics areas */ 710 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 711 compptr = cinfo->cur_comp_info[ci]; 712 if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) { 713 tbl = compptr->dc_tbl_no; 714 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 715 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 716 if (entropy->dc_stats[tbl] == NULL) 717 entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small) 718 ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS); 719 MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS); 720 /* Initialize DC predictions to 0 */ 721 entropy->last_dc_val[ci] = 0; 722 entropy->dc_context[ci] = 0; 723 } 724 if ((! cinfo->progressive_mode && cinfo->lim_Se) || 725 (cinfo->progressive_mode && cinfo->Ss)) { 726 tbl = compptr->ac_tbl_no; 727 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 728 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 729 if (entropy->ac_stats[tbl] == NULL) 730 entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small) 731 ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS); 732 MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS); 733 } 734 } 735 736 /* Initialize arithmetic decoding variables */ 737 entropy->c = 0; 738 entropy->a = 0; 739 entropy->ct = -16; /* force reading 2 initial bytes to fill C */ 740 741 /* Initialize restart counter */ 742 entropy->restarts_to_go = cinfo->restart_interval; 743} 744 745 746/* 747 * Module initialization routine for arithmetic entropy decoding. 748 */ 749 750GLOBAL(void) 751jinit_arith_decoder (j_decompress_ptr cinfo) 752{ 753 arith_entropy_ptr entropy; 754 int i; 755 756 entropy = (arith_entropy_ptr) 757 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 758 SIZEOF(arith_entropy_decoder)); 759 cinfo->entropy = &entropy->pub; 760 entropy->pub.start_pass = start_pass; 761 762 /* Mark tables unallocated */ 763 for (i = 0; i < NUM_ARITH_TBLS; i++) { 764 entropy->dc_stats[i] = NULL; 765 entropy->ac_stats[i] = NULL; 766 } 767 768 /* Initialize index for fixed probability estimation */ 769 entropy->fixed_bin[0] = 113; 770 771 if (cinfo->progressive_mode) { 772 /* Create progression status table */ 773 int *coef_bit_ptr, ci; 774 cinfo->coef_bits = (int (*)[DCTSIZE2]) 775 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 776 cinfo->num_components*DCTSIZE2*SIZEOF(int)); 777 coef_bit_ptr = & cinfo->coef_bits[0][0]; 778 for (ci = 0; ci < cinfo->num_components; ci++) 779 for (i = 0; i < DCTSIZE2; i++) 780 *coef_bit_ptr++ = -1; 781 } 782} 783