1/* 2 * jdarith.c 3 * 4 * This file was part of the Independent JPEG Group's software: 5 * Developed 1997-2015 by Guido Vollbeding. 6 * libjpeg-turbo Modifications: 7 * Copyright (C) 2015-2016, D. R. Commander. 8 * For conditions of distribution and use, see the accompanying README.ijg 9 * file. 10 * 11 * This file contains portable arithmetic entropy decoding routines for JPEG 12 * (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81). 13 * 14 * Both sequential and progressive modes are supported in this single module. 15 * 16 * Suspension is not currently supported in this module. 17 */ 18 19#define JPEG_INTERNALS 20#include "jinclude.h" 21#include "jpeglib.h" 22 23 24/* Expanded entropy decoder object for arithmetic decoding. */ 25 26typedef struct { 27 struct jpeg_entropy_decoder pub; /* public fields */ 28 29 JLONG c; /* C register, base of coding interval + input bit buffer */ 30 JLONG a; /* A register, normalized size of coding interval */ 31 int ct; /* bit shift counter, # of bits left in bit buffer part of C */ 32 /* init: ct = -16 */ 33 /* run: ct = 0..7 */ 34 /* error: ct = -1 */ 35 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 36 int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */ 37 38 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 39 40 /* Pointers to statistics areas (these workspaces have image lifespan) */ 41 unsigned char *dc_stats[NUM_ARITH_TBLS]; 42 unsigned char *ac_stats[NUM_ARITH_TBLS]; 43 44 /* Statistics bin for coding with fixed probability 0.5 */ 45 unsigned char fixed_bin[4]; 46} arith_entropy_decoder; 47 48typedef arith_entropy_decoder *arith_entropy_ptr; 49 50/* The following two definitions specify the allocation chunk size 51 * for the statistics area. 52 * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least 53 * 49 statistics bins for DC, and 245 statistics bins for AC coding. 54 * 55 * We use a compact representation with 1 byte per statistics bin, 56 * thus the numbers directly represent byte sizes. 57 * This 1 byte per statistics bin contains the meaning of the MPS 58 * (more probable symbol) in the highest bit (mask 0x80), and the 59 * index into the probability estimation state machine table 60 * in the lower bits (mask 0x7F). 61 */ 62 63#define DC_STAT_BINS 64 64#define AC_STAT_BINS 256 65 66 67LOCAL(int) 68get_byte (j_decompress_ptr cinfo) 69/* Read next input byte; we do not support suspension in this module. */ 70{ 71 struct jpeg_source_mgr *src = cinfo->src; 72 73 if (src->bytes_in_buffer == 0) 74 if (! (*src->fill_input_buffer) (cinfo)) 75 ERREXIT(cinfo, JERR_CANT_SUSPEND); 76 src->bytes_in_buffer--; 77 return GETJOCTET(*src->next_input_byte++); 78} 79 80 81/* 82 * The core arithmetic decoding routine (common in JPEG and JBIG). 83 * This needs to go as fast as possible. 84 * Machine-dependent optimization facilities 85 * are not utilized in this portable implementation. 86 * However, this code should be fairly efficient and 87 * may be a good base for further optimizations anyway. 88 * 89 * Return value is 0 or 1 (binary decision). 90 * 91 * Note: I've changed the handling of the code base & bit 92 * buffer register C compared to other implementations 93 * based on the standards layout & procedures. 94 * While it also contains both the actual base of the 95 * coding interval (16 bits) and the next-bits buffer, 96 * the cut-point between these two parts is floating 97 * (instead of fixed) with the bit shift counter CT. 98 * Thus, we also need only one (variable instead of 99 * fixed size) shift for the LPS/MPS decision, and 100 * we can do away with any renormalization update 101 * of C (except for new data insertion, of course). 102 * 103 * I've also introduced a new scheme for accessing 104 * the probability estimation state machine table, 105 * derived from Markus Kuhn's JBIG implementation. 106 */ 107 108LOCAL(int) 109arith_decode (j_decompress_ptr cinfo, unsigned char *st) 110{ 111 register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy; 112 register unsigned char nl, nm; 113 register JLONG qe, temp; 114 register int sv, data; 115 116 /* Renormalization & data input per section D.2.6 */ 117 while (e->a < 0x8000L) { 118 if (--e->ct < 0) { 119 /* Need to fetch next data byte */ 120 if (cinfo->unread_marker) 121 data = 0; /* stuff zero data */ 122 else { 123 data = get_byte(cinfo); /* read next input byte */ 124 if (data == 0xFF) { /* zero stuff or marker code */ 125 do data = get_byte(cinfo); 126 while (data == 0xFF); /* swallow extra 0xFF bytes */ 127 if (data == 0) 128 data = 0xFF; /* discard stuffed zero byte */ 129 else { 130 /* Note: Different from the Huffman decoder, hitting 131 * a marker while processing the compressed data 132 * segment is legal in arithmetic coding. 133 * The convention is to supply zero data 134 * then until decoding is complete. 135 */ 136 cinfo->unread_marker = data; 137 data = 0; 138 } 139 } 140 } 141 e->c = (e->c << 8) | data; /* insert data into C register */ 142 if ((e->ct += 8) < 0) /* update bit shift counter */ 143 /* Need more initial bytes */ 144 if (++e->ct == 0) 145 /* Got 2 initial bytes -> re-init A and exit loop */ 146 e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */ 147 } 148 e->a <<= 1; 149 } 150 151 /* Fetch values from our compact representation of Table D.2: 152 * Qe values and probability estimation state machine 153 */ 154 sv = *st; 155 qe = jpeg_aritab[sv & 0x7F]; /* => Qe_Value */ 156 nl = qe & 0xFF; qe >>= 8; /* Next_Index_LPS + Switch_MPS */ 157 nm = qe & 0xFF; qe >>= 8; /* Next_Index_MPS */ 158 159 /* Decode & estimation procedures per sections D.2.4 & D.2.5 */ 160 temp = e->a - qe; 161 e->a = temp; 162 temp <<= e->ct; 163 if (e->c >= temp) { 164 e->c -= temp; 165 /* Conditional LPS (less probable symbol) exchange */ 166 if (e->a < qe) { 167 e->a = qe; 168 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */ 169 } else { 170 e->a = qe; 171 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */ 172 sv ^= 0x80; /* Exchange LPS/MPS */ 173 } 174 } else if (e->a < 0x8000L) { 175 /* Conditional MPS (more probable symbol) exchange */ 176 if (e->a < qe) { 177 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */ 178 sv ^= 0x80; /* Exchange LPS/MPS */ 179 } else { 180 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */ 181 } 182 } 183 184 return sv >> 7; 185} 186 187 188/* 189 * Check for a restart marker & resynchronize decoder. 190 */ 191 192LOCAL(void) 193process_restart (j_decompress_ptr cinfo) 194{ 195 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 196 int ci; 197 jpeg_component_info *compptr; 198 199 /* Advance past the RSTn marker */ 200 if (! (*cinfo->marker->read_restart_marker) (cinfo)) 201 ERREXIT(cinfo, JERR_CANT_SUSPEND); 202 203 /* Re-initialize statistics areas */ 204 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 205 compptr = cinfo->cur_comp_info[ci]; 206 if (!cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) { 207 MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS); 208 /* Reset DC predictions to 0 */ 209 entropy->last_dc_val[ci] = 0; 210 entropy->dc_context[ci] = 0; 211 } 212 if (!cinfo->progressive_mode || cinfo->Ss) { 213 MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS); 214 } 215 } 216 217 /* Reset arithmetic decoding variables */ 218 entropy->c = 0; 219 entropy->a = 0; 220 entropy->ct = -16; /* force reading 2 initial bytes to fill C */ 221 222 /* Reset restart counter */ 223 entropy->restarts_to_go = cinfo->restart_interval; 224} 225 226 227/* 228 * Arithmetic MCU decoding. 229 * Each of these routines decodes and returns one MCU's worth of 230 * arithmetic-compressed coefficients. 231 * The coefficients are reordered from zigzag order into natural array order, 232 * but are not dequantized. 233 * 234 * The i'th block of the MCU is stored into the block pointed to by 235 * MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER. 236 */ 237 238/* 239 * MCU decoding for DC initial scan (either spectral selection, 240 * or first pass of successive approximation). 241 */ 242 243METHODDEF(boolean) 244decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 245{ 246 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 247 JBLOCKROW block; 248 unsigned char *st; 249 int blkn, ci, tbl, sign; 250 int v, m; 251 252 /* Process restart marker if needed */ 253 if (cinfo->restart_interval) { 254 if (entropy->restarts_to_go == 0) 255 process_restart(cinfo); 256 entropy->restarts_to_go--; 257 } 258 259 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 260 261 /* Outer loop handles each block in the MCU */ 262 263 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 264 block = MCU_data[blkn]; 265 ci = cinfo->MCU_membership[blkn]; 266 tbl = cinfo->cur_comp_info[ci]->dc_tbl_no; 267 268 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */ 269 270 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 271 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 272 273 /* Figure F.19: Decode_DC_DIFF */ 274 if (arith_decode(cinfo, st) == 0) 275 entropy->dc_context[ci] = 0; 276 else { 277 /* Figure F.21: Decoding nonzero value v */ 278 /* Figure F.22: Decoding the sign of v */ 279 sign = arith_decode(cinfo, st + 1); 280 st += 2; st += sign; 281 /* Figure F.23: Decoding the magnitude category of v */ 282 if ((m = arith_decode(cinfo, st)) != 0) { 283 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 284 while (arith_decode(cinfo, st)) { 285 if ((m <<= 1) == 0x8000) { 286 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 287 entropy->ct = -1; /* magnitude overflow */ 288 return TRUE; 289 } 290 st += 1; 291 } 292 } 293 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 294 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1)) 295 entropy->dc_context[ci] = 0; /* zero diff category */ 296 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1)) 297 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */ 298 else 299 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */ 300 v = m; 301 /* Figure F.24: Decoding the magnitude bit pattern of v */ 302 st += 14; 303 while (m >>= 1) 304 if (arith_decode(cinfo, st)) v |= m; 305 v += 1; if (sign) v = -v; 306 entropy->last_dc_val[ci] += v; 307 } 308 309 /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */ 310 (*block)[0] = (JCOEF) LEFT_SHIFT(entropy->last_dc_val[ci], cinfo->Al); 311 } 312 313 return TRUE; 314} 315 316 317/* 318 * MCU decoding for AC initial scan (either spectral selection, 319 * or first pass of successive approximation). 320 */ 321 322METHODDEF(boolean) 323decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 324{ 325 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 326 JBLOCKROW block; 327 unsigned char *st; 328 int tbl, sign, k; 329 int v, m; 330 331 /* Process restart marker if needed */ 332 if (cinfo->restart_interval) { 333 if (entropy->restarts_to_go == 0) 334 process_restart(cinfo); 335 entropy->restarts_to_go--; 336 } 337 338 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 339 340 /* There is always only one block per MCU */ 341 block = MCU_data[0]; 342 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 343 344 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */ 345 346 /* Figure F.20: Decode_AC_coefficients */ 347 for (k = cinfo->Ss; k <= cinfo->Se; k++) { 348 st = entropy->ac_stats[tbl] + 3 * (k - 1); 349 if (arith_decode(cinfo, st)) break; /* EOB flag */ 350 while (arith_decode(cinfo, st + 1) == 0) { 351 st += 3; k++; 352 if (k > cinfo->Se) { 353 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 354 entropy->ct = -1; /* spectral overflow */ 355 return TRUE; 356 } 357 } 358 /* Figure F.21: Decoding nonzero value v */ 359 /* Figure F.22: Decoding the sign of v */ 360 sign = arith_decode(cinfo, entropy->fixed_bin); 361 st += 2; 362 /* Figure F.23: Decoding the magnitude category of v */ 363 if ((m = arith_decode(cinfo, st)) != 0) { 364 if (arith_decode(cinfo, st)) { 365 m <<= 1; 366 st = entropy->ac_stats[tbl] + 367 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 368 while (arith_decode(cinfo, st)) { 369 if ((m <<= 1) == 0x8000) { 370 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 371 entropy->ct = -1; /* magnitude overflow */ 372 return TRUE; 373 } 374 st += 1; 375 } 376 } 377 } 378 v = m; 379 /* Figure F.24: Decoding the magnitude bit pattern of v */ 380 st += 14; 381 while (m >>= 1) 382 if (arith_decode(cinfo, st)) v |= m; 383 v += 1; if (sign) v = -v; 384 /* Scale and output coefficient in natural (dezigzagged) order */ 385 (*block)[jpeg_natural_order[k]] = (JCOEF) ((unsigned)v << cinfo->Al); 386 } 387 388 return TRUE; 389} 390 391 392/* 393 * MCU decoding for DC successive approximation refinement scan. 394 */ 395 396METHODDEF(boolean) 397decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 398{ 399 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 400 unsigned char *st; 401 int p1, blkn; 402 403 /* Process restart marker if needed */ 404 if (cinfo->restart_interval) { 405 if (entropy->restarts_to_go == 0) 406 process_restart(cinfo); 407 entropy->restarts_to_go--; 408 } 409 410 st = entropy->fixed_bin; /* use fixed probability estimation */ 411 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 412 413 /* Outer loop handles each block in the MCU */ 414 415 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 416 /* Encoded data is simply the next bit of the two's-complement DC value */ 417 if (arith_decode(cinfo, st)) 418 MCU_data[blkn][0][0] |= p1; 419 } 420 421 return TRUE; 422} 423 424 425/* 426 * MCU decoding for AC successive approximation refinement scan. 427 */ 428 429METHODDEF(boolean) 430decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 431{ 432 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 433 JBLOCKROW block; 434 JCOEFPTR thiscoef; 435 unsigned char *st; 436 int tbl, k, kex; 437 int p1, m1; 438 439 /* Process restart marker if needed */ 440 if (cinfo->restart_interval) { 441 if (entropy->restarts_to_go == 0) 442 process_restart(cinfo); 443 entropy->restarts_to_go--; 444 } 445 446 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 447 448 /* There is always only one block per MCU */ 449 block = MCU_data[0]; 450 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 451 452 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 453 m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */ 454 455 /* Establish EOBx (previous stage end-of-block) index */ 456 for (kex = cinfo->Se; kex > 0; kex--) 457 if ((*block)[jpeg_natural_order[kex]]) break; 458 459 for (k = cinfo->Ss; k <= cinfo->Se; k++) { 460 st = entropy->ac_stats[tbl] + 3 * (k - 1); 461 if (k > kex) 462 if (arith_decode(cinfo, st)) break; /* EOB flag */ 463 for (;;) { 464 thiscoef = *block + jpeg_natural_order[k]; 465 if (*thiscoef) { /* previously nonzero coef */ 466 if (arith_decode(cinfo, st + 2)) { 467 if (*thiscoef < 0) 468 *thiscoef += m1; 469 else 470 *thiscoef += p1; 471 } 472 break; 473 } 474 if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */ 475 if (arith_decode(cinfo, entropy->fixed_bin)) 476 *thiscoef = m1; 477 else 478 *thiscoef = p1; 479 break; 480 } 481 st += 3; k++; 482 if (k > cinfo->Se) { 483 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 484 entropy->ct = -1; /* spectral overflow */ 485 return TRUE; 486 } 487 } 488 } 489 490 return TRUE; 491} 492 493 494/* 495 * Decode one MCU's worth of arithmetic-compressed coefficients. 496 */ 497 498METHODDEF(boolean) 499decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 500{ 501 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 502 jpeg_component_info *compptr; 503 JBLOCKROW block; 504 unsigned char *st; 505 int blkn, ci, tbl, sign, k; 506 int v, m; 507 508 /* Process restart marker if needed */ 509 if (cinfo->restart_interval) { 510 if (entropy->restarts_to_go == 0) 511 process_restart(cinfo); 512 entropy->restarts_to_go--; 513 } 514 515 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 516 517 /* Outer loop handles each block in the MCU */ 518 519 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 520 block = MCU_data ? MCU_data[blkn] : NULL; 521 ci = cinfo->MCU_membership[blkn]; 522 compptr = cinfo->cur_comp_info[ci]; 523 524 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */ 525 526 tbl = compptr->dc_tbl_no; 527 528 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 529 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 530 531 /* Figure F.19: Decode_DC_DIFF */ 532 if (arith_decode(cinfo, st) == 0) 533 entropy->dc_context[ci] = 0; 534 else { 535 /* Figure F.21: Decoding nonzero value v */ 536 /* Figure F.22: Decoding the sign of v */ 537 sign = arith_decode(cinfo, st + 1); 538 st += 2; st += sign; 539 /* Figure F.23: Decoding the magnitude category of v */ 540 if ((m = arith_decode(cinfo, st)) != 0) { 541 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 542 while (arith_decode(cinfo, st)) { 543 if ((m <<= 1) == 0x8000) { 544 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 545 entropy->ct = -1; /* magnitude overflow */ 546 return TRUE; 547 } 548 st += 1; 549 } 550 } 551 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 552 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1)) 553 entropy->dc_context[ci] = 0; /* zero diff category */ 554 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1)) 555 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */ 556 else 557 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */ 558 v = m; 559 /* Figure F.24: Decoding the magnitude bit pattern of v */ 560 st += 14; 561 while (m >>= 1) 562 if (arith_decode(cinfo, st)) v |= m; 563 v += 1; if (sign) v = -v; 564 entropy->last_dc_val[ci] += v; 565 } 566 567 if (block) 568 (*block)[0] = (JCOEF) entropy->last_dc_val[ci]; 569 570 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */ 571 572 tbl = compptr->ac_tbl_no; 573 574 /* Figure F.20: Decode_AC_coefficients */ 575 for (k = 1; k <= DCTSIZE2 - 1; k++) { 576 st = entropy->ac_stats[tbl] + 3 * (k - 1); 577 if (arith_decode(cinfo, st)) break; /* EOB flag */ 578 while (arith_decode(cinfo, st + 1) == 0) { 579 st += 3; k++; 580 if (k > DCTSIZE2 - 1) { 581 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 582 entropy->ct = -1; /* spectral overflow */ 583 return TRUE; 584 } 585 } 586 /* Figure F.21: Decoding nonzero value v */ 587 /* Figure F.22: Decoding the sign of v */ 588 sign = arith_decode(cinfo, entropy->fixed_bin); 589 st += 2; 590 /* Figure F.23: Decoding the magnitude category of v */ 591 if ((m = arith_decode(cinfo, st)) != 0) { 592 if (arith_decode(cinfo, st)) { 593 m <<= 1; 594 st = entropy->ac_stats[tbl] + 595 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 596 while (arith_decode(cinfo, st)) { 597 if ((m <<= 1) == 0x8000) { 598 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 599 entropy->ct = -1; /* magnitude overflow */ 600 return TRUE; 601 } 602 st += 1; 603 } 604 } 605 } 606 v = m; 607 /* Figure F.24: Decoding the magnitude bit pattern of v */ 608 st += 14; 609 while (m >>= 1) 610 if (arith_decode(cinfo, st)) v |= m; 611 v += 1; if (sign) v = -v; 612 if (block) 613 (*block)[jpeg_natural_order[k]] = (JCOEF) v; 614 } 615 } 616 617 return TRUE; 618} 619 620 621/* 622 * Initialize for an arithmetic-compressed scan. 623 */ 624 625METHODDEF(void) 626start_pass (j_decompress_ptr cinfo) 627{ 628 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy; 629 int ci, tbl; 630 jpeg_component_info *compptr; 631 632 if (cinfo->progressive_mode) { 633 /* Validate progressive scan parameters */ 634 if (cinfo->Ss == 0) { 635 if (cinfo->Se != 0) 636 goto bad; 637 } else { 638 /* need not check Ss/Se < 0 since they came from unsigned bytes */ 639 if (cinfo->Se < cinfo->Ss || cinfo->Se > DCTSIZE2 - 1) 640 goto bad; 641 /* AC scans may have only one component */ 642 if (cinfo->comps_in_scan != 1) 643 goto bad; 644 } 645 if (cinfo->Ah != 0) { 646 /* Successive approximation refinement scan: must have Al = Ah-1. */ 647 if (cinfo->Ah-1 != cinfo->Al) 648 goto bad; 649 } 650 if (cinfo->Al > 13) { /* need not check for < 0 */ 651 bad: 652 ERREXIT4(cinfo, JERR_BAD_PROGRESSION, 653 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al); 654 } 655 /* Update progression status, and verify that scan order is legal. 656 * Note that inter-scan inconsistencies are treated as warnings 657 * not fatal errors ... not clear if this is right way to behave. 658 */ 659 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 660 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index; 661 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0]; 662 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */ 663 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0); 664 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) { 665 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi]; 666 if (cinfo->Ah != expected) 667 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi); 668 coef_bit_ptr[coefi] = cinfo->Al; 669 } 670 } 671 /* Select MCU decoding routine */ 672 if (cinfo->Ah == 0) { 673 if (cinfo->Ss == 0) 674 entropy->pub.decode_mcu = decode_mcu_DC_first; 675 else 676 entropy->pub.decode_mcu = decode_mcu_AC_first; 677 } else { 678 if (cinfo->Ss == 0) 679 entropy->pub.decode_mcu = decode_mcu_DC_refine; 680 else 681 entropy->pub.decode_mcu = decode_mcu_AC_refine; 682 } 683 } else { 684 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 685 * This ought to be an error condition, but we make it a warning. 686 */ 687 if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 || 688 (cinfo->Se < DCTSIZE2 && cinfo->Se != DCTSIZE2 - 1)) 689 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 690 /* Select MCU decoding routine */ 691 entropy->pub.decode_mcu = decode_mcu; 692 } 693 694 /* Allocate & initialize requested statistics areas */ 695 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 696 compptr = cinfo->cur_comp_info[ci]; 697 if (!cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) { 698 tbl = compptr->dc_tbl_no; 699 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 700 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 701 if (entropy->dc_stats[tbl] == NULL) 702 entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small) 703 ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS); 704 MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS); 705 /* Initialize DC predictions to 0 */ 706 entropy->last_dc_val[ci] = 0; 707 entropy->dc_context[ci] = 0; 708 } 709 if (!cinfo->progressive_mode || cinfo->Ss) { 710 tbl = compptr->ac_tbl_no; 711 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 712 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 713 if (entropy->ac_stats[tbl] == NULL) 714 entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small) 715 ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS); 716 MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS); 717 } 718 } 719 720 /* Initialize arithmetic decoding variables */ 721 entropy->c = 0; 722 entropy->a = 0; 723 entropy->ct = -16; /* force reading 2 initial bytes to fill C */ 724 725 /* Initialize restart counter */ 726 entropy->restarts_to_go = cinfo->restart_interval; 727} 728 729 730/* 731 * Module initialization routine for arithmetic entropy decoding. 732 */ 733 734GLOBAL(void) 735jinit_arith_decoder (j_decompress_ptr cinfo) 736{ 737 arith_entropy_ptr entropy; 738 int i; 739 740 entropy = (arith_entropy_ptr) 741 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 742 sizeof(arith_entropy_decoder)); 743 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy; 744 entropy->pub.start_pass = start_pass; 745 746 /* Mark tables unallocated */ 747 for (i = 0; i < NUM_ARITH_TBLS; i++) { 748 entropy->dc_stats[i] = NULL; 749 entropy->ac_stats[i] = NULL; 750 } 751 752 /* Initialize index for fixed probability estimation */ 753 entropy->fixed_bin[0] = 113; 754 755 if (cinfo->progressive_mode) { 756 /* Create progression status table */ 757 int *coef_bit_ptr, ci; 758 cinfo->coef_bits = (int (*)[DCTSIZE2]) 759 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE, 760 cinfo->num_components*DCTSIZE2*sizeof(int)); 761 coef_bit_ptr = & cinfo->coef_bits[0][0]; 762 for (ci = 0; ci < cinfo->num_components; ci++) 763 for (i = 0; i < DCTSIZE2; i++) 764 *coef_bit_ptr++ = -1; 765 } 766} 767