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