jdarith.c (25539B)
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) 2015-2020, 2022, 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 encoding routines for JPEG 12 * (implementing Recommendation ITU-T T.81 | ISO/IEC 10918-1). 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 * NOTE: All referenced figures are from 19 * Recommendation ITU-T T.81 (1992) | ISO/IEC 10918-1:1994. 20 */ 21 22 #define JPEG_INTERNALS 23 #include "jinclude.h" 24 #include "jpeglib.h" 25 26 27 #define NEG_1 ((unsigned int)-1) 28 29 30 /* Expanded entropy decoder object for arithmetic decoding. */ 31 32 typedef struct { 33 struct jpeg_entropy_decoder pub; /* public fields */ 34 35 JLONG c; /* C register, base of coding interval + input bit buffer */ 36 JLONG a; /* A register, normalized size of coding interval */ 37 int ct; /* bit shift counter, # of bits left in bit buffer part of C */ 38 /* init: ct = -16 */ 39 /* run: ct = 0..7 */ 40 /* error: ct = -1 */ 41 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */ 42 int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */ 43 44 unsigned int restarts_to_go; /* MCUs left in this restart interval */ 45 46 /* Pointers to statistics areas (these workspaces have image lifespan) */ 47 unsigned char *dc_stats[NUM_ARITH_TBLS]; 48 unsigned char *ac_stats[NUM_ARITH_TBLS]; 49 50 /* Statistics bin for coding with fixed probability 0.5 */ 51 unsigned char fixed_bin[4]; 52 } arith_entropy_decoder; 53 54 typedef arith_entropy_decoder *arith_entropy_ptr; 55 56 /* The following two definitions specify the allocation chunk size 57 * for the statistics area. 58 * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least 59 * 49 statistics bins for DC, and 245 statistics bins for AC coding. 60 * 61 * We use a compact representation with 1 byte per statistics bin, 62 * thus the numbers directly represent byte sizes. 63 * This 1 byte per statistics bin contains the meaning of the MPS 64 * (more probable symbol) in the highest bit (mask 0x80), and the 65 * index into the probability estimation state machine table 66 * in the lower bits (mask 0x7F). 67 */ 68 69 #define DC_STAT_BINS 64 70 #define AC_STAT_BINS 256 71 72 73 LOCAL(int) 74 get_byte(j_decompress_ptr cinfo) 75 /* Read next input byte; we do not support suspension in this module. */ 76 { 77 struct jpeg_source_mgr *src = cinfo->src; 78 79 if (src->bytes_in_buffer == 0) 80 if (!(*src->fill_input_buffer) (cinfo)) 81 ERREXIT(cinfo, JERR_CANT_SUSPEND); 82 src->bytes_in_buffer--; 83 return *src->next_input_byte++; 84 } 85 86 87 /* 88 * The core arithmetic decoding routine (common in JPEG and JBIG). 89 * This needs to go as fast as possible. 90 * Machine-dependent optimization facilities 91 * are not utilized in this portable implementation. 92 * However, this code should be fairly efficient and 93 * may be a good base for further optimizations anyway. 94 * 95 * Return value is 0 or 1 (binary decision). 96 * 97 * Note: I've changed the handling of the code base & bit 98 * buffer register C compared to other implementations 99 * based on the standards layout & procedures. 100 * While it also contains both the actual base of the 101 * coding interval (16 bits) and the next-bits buffer, 102 * the cut-point between these two parts is floating 103 * (instead of fixed) with the bit shift counter CT. 104 * Thus, we also need only one (variable instead of 105 * fixed size) shift for the LPS/MPS decision, and 106 * we can do away with any renormalization update 107 * of C (except for new data insertion, of course). 108 * 109 * I've also introduced a new scheme for accessing 110 * the probability estimation state machine table, 111 * derived from Markus Kuhn's JBIG implementation. 112 */ 113 114 LOCAL(int) 115 arith_decode(j_decompress_ptr cinfo, unsigned char *st) 116 { 117 register arith_entropy_ptr e = (arith_entropy_ptr)cinfo->entropy; 118 register unsigned char nl, nm; 119 register JLONG qe, temp; 120 register int sv, data; 121 122 /* Renormalization & data input per section D.2.6 */ 123 while (e->a < 0x8000L) { 124 if (--e->ct < 0) { 125 /* Need to fetch next data byte */ 126 if (cinfo->unread_marker) 127 data = 0; /* stuff zero data */ 128 else { 129 data = get_byte(cinfo); /* read next input byte */ 130 if (data == 0xFF) { /* zero stuff or marker code */ 131 do data = get_byte(cinfo); 132 while (data == 0xFF); /* swallow extra 0xFF bytes */ 133 if (data == 0) 134 data = 0xFF; /* discard stuffed zero byte */ 135 else { 136 /* Note: Different from the Huffman decoder, hitting 137 * a marker while processing the compressed data 138 * segment is legal in arithmetic coding. 139 * The convention is to supply zero data 140 * then until decoding is complete. 141 */ 142 cinfo->unread_marker = data; 143 data = 0; 144 } 145 } 146 } 147 e->c = (e->c << 8) | data; /* insert data into C register */ 148 if ((e->ct += 8) < 0) /* update bit shift counter */ 149 /* Need more initial bytes */ 150 if (++e->ct == 0) 151 /* Got 2 initial bytes -> re-init A and exit loop */ 152 e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */ 153 } 154 e->a <<= 1; 155 } 156 157 /* Fetch values from our compact representation of Table D.2: 158 * Qe values and probability estimation state machine 159 */ 160 sv = *st; 161 qe = jpeg_aritab[sv & 0x7F]; /* => Qe_Value */ 162 nl = qe & 0xFF; qe >>= 8; /* Next_Index_LPS + Switch_MPS */ 163 nm = qe & 0xFF; qe >>= 8; /* Next_Index_MPS */ 164 165 /* Decode & estimation procedures per sections D.2.4 & D.2.5 */ 166 temp = e->a - qe; 167 e->a = temp; 168 temp <<= e->ct; 169 if (e->c >= temp) { 170 e->c -= temp; 171 /* Conditional LPS (less probable symbol) exchange */ 172 if (e->a < qe) { 173 e->a = qe; 174 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */ 175 } else { 176 e->a = qe; 177 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */ 178 sv ^= 0x80; /* Exchange LPS/MPS */ 179 } 180 } else if (e->a < 0x8000L) { 181 /* Conditional MPS (more probable symbol) exchange */ 182 if (e->a < qe) { 183 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */ 184 sv ^= 0x80; /* Exchange LPS/MPS */ 185 } else { 186 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */ 187 } 188 } 189 190 return sv >> 7; 191 } 192 193 194 /* 195 * Check for a restart marker & resynchronize decoder. 196 */ 197 198 LOCAL(void) 199 process_restart(j_decompress_ptr cinfo) 200 { 201 arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; 202 int ci; 203 jpeg_component_info *compptr; 204 205 /* Advance past the RSTn marker */ 206 if (!(*cinfo->marker->read_restart_marker) (cinfo)) 207 ERREXIT(cinfo, JERR_CANT_SUSPEND); 208 209 /* Re-initialize statistics areas */ 210 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 211 compptr = cinfo->cur_comp_info[ci]; 212 if (!cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) { 213 memset(entropy->dc_stats[compptr->dc_tbl_no], 0, DC_STAT_BINS); 214 /* Reset DC predictions to 0 */ 215 entropy->last_dc_val[ci] = 0; 216 entropy->dc_context[ci] = 0; 217 } 218 if (!cinfo->progressive_mode || cinfo->Ss) { 219 memset(entropy->ac_stats[compptr->ac_tbl_no], 0, AC_STAT_BINS); 220 } 221 } 222 223 /* Reset arithmetic decoding variables */ 224 entropy->c = 0; 225 entropy->a = 0; 226 entropy->ct = -16; /* force reading 2 initial bytes to fill C */ 227 228 /* Reset restart counter */ 229 entropy->restarts_to_go = cinfo->restart_interval; 230 } 231 232 233 /* 234 * Arithmetic MCU decoding. 235 * Each of these routines decodes and returns one MCU's worth of 236 * arithmetic-compressed coefficients. 237 * The coefficients are reordered from zigzag order into natural array order, 238 * but are not dequantized. 239 * 240 * The i'th block of the MCU is stored into the block pointed to by 241 * MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER. 242 */ 243 244 /* 245 * MCU decoding for DC initial scan (either spectral selection, 246 * or first pass of successive approximation). 247 */ 248 249 METHODDEF(boolean) 250 decode_mcu_DC_first(j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 251 { 252 arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; 253 JBLOCKROW block; 254 unsigned char *st; 255 int blkn, ci, tbl, sign; 256 int v, m; 257 258 /* Process restart marker if needed */ 259 if (cinfo->restart_interval) { 260 if (entropy->restarts_to_go == 0) 261 process_restart(cinfo); 262 entropy->restarts_to_go--; 263 } 264 265 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 266 267 /* Outer loop handles each block in the MCU */ 268 269 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 270 block = MCU_data[blkn]; 271 ci = cinfo->MCU_membership[blkn]; 272 tbl = cinfo->cur_comp_info[ci]->dc_tbl_no; 273 274 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */ 275 276 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 277 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 278 279 /* Figure F.19: Decode_DC_DIFF */ 280 if (arith_decode(cinfo, st) == 0) 281 entropy->dc_context[ci] = 0; 282 else { 283 /* Figure F.21: Decoding nonzero value v */ 284 /* Figure F.22: Decoding the sign of v */ 285 sign = arith_decode(cinfo, st + 1); 286 st += 2; st += sign; 287 /* Figure F.23: Decoding the magnitude category of v */ 288 if ((m = arith_decode(cinfo, st)) != 0) { 289 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 290 while (arith_decode(cinfo, st)) { 291 if ((m <<= 1) == 0x8000) { 292 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 293 entropy->ct = -1; /* magnitude overflow */ 294 return TRUE; 295 } 296 st += 1; 297 } 298 } 299 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 300 if (m < (int)((1L << cinfo->arith_dc_L[tbl]) >> 1)) 301 entropy->dc_context[ci] = 0; /* zero diff category */ 302 else if (m > (int)((1L << cinfo->arith_dc_U[tbl]) >> 1)) 303 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */ 304 else 305 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */ 306 v = m; 307 /* Figure F.24: Decoding the magnitude bit pattern of v */ 308 st += 14; 309 while (m >>= 1) 310 if (arith_decode(cinfo, st)) v |= m; 311 v += 1; if (sign) v = -v; 312 entropy->last_dc_val[ci] = (entropy->last_dc_val[ci] + v) & 0xffff; 313 } 314 315 /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */ 316 (*block)[0] = (JCOEF)LEFT_SHIFT(entropy->last_dc_val[ci], cinfo->Al); 317 } 318 319 return TRUE; 320 } 321 322 323 /* 324 * MCU decoding for AC initial scan (either spectral selection, 325 * or first pass of successive approximation). 326 */ 327 328 METHODDEF(boolean) 329 decode_mcu_AC_first(j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 330 { 331 arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; 332 JBLOCKROW block; 333 unsigned char *st; 334 int tbl, sign, k; 335 int v, m; 336 337 /* Process restart marker if needed */ 338 if (cinfo->restart_interval) { 339 if (entropy->restarts_to_go == 0) 340 process_restart(cinfo); 341 entropy->restarts_to_go--; 342 } 343 344 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 345 346 /* There is always only one block per MCU */ 347 block = MCU_data[0]; 348 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 349 350 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */ 351 352 /* Figure F.20: Decode_AC_coefficients */ 353 for (k = cinfo->Ss; k <= cinfo->Se; k++) { 354 st = entropy->ac_stats[tbl] + 3 * (k - 1); 355 if (arith_decode(cinfo, st)) break; /* EOB flag */ 356 while (arith_decode(cinfo, st + 1) == 0) { 357 st += 3; k++; 358 if (k > cinfo->Se) { 359 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 360 entropy->ct = -1; /* spectral overflow */ 361 return TRUE; 362 } 363 } 364 /* Figure F.21: Decoding nonzero value v */ 365 /* Figure F.22: Decoding the sign of v */ 366 sign = arith_decode(cinfo, entropy->fixed_bin); 367 st += 2; 368 /* Figure F.23: Decoding the magnitude category of v */ 369 if ((m = arith_decode(cinfo, st)) != 0) { 370 if (arith_decode(cinfo, st)) { 371 m <<= 1; 372 st = entropy->ac_stats[tbl] + 373 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 374 while (arith_decode(cinfo, st)) { 375 if ((m <<= 1) == 0x8000) { 376 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 377 entropy->ct = -1; /* magnitude overflow */ 378 return TRUE; 379 } 380 st += 1; 381 } 382 } 383 } 384 v = m; 385 /* Figure F.24: Decoding the magnitude bit pattern of v */ 386 st += 14; 387 while (m >>= 1) 388 if (arith_decode(cinfo, st)) v |= m; 389 v += 1; if (sign) v = -v; 390 /* Scale and output coefficient in natural (dezigzagged) order */ 391 (*block)[jpeg_natural_order[k]] = (JCOEF)((unsigned)v << cinfo->Al); 392 } 393 394 return TRUE; 395 } 396 397 398 /* 399 * MCU decoding for DC successive approximation refinement scan. 400 */ 401 402 METHODDEF(boolean) 403 decode_mcu_DC_refine(j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 404 { 405 arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; 406 unsigned char *st; 407 int p1, blkn; 408 409 /* Process restart marker if needed */ 410 if (cinfo->restart_interval) { 411 if (entropy->restarts_to_go == 0) 412 process_restart(cinfo); 413 entropy->restarts_to_go--; 414 } 415 416 st = entropy->fixed_bin; /* use fixed probability estimation */ 417 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 418 419 /* Outer loop handles each block in the MCU */ 420 421 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 422 /* Encoded data is simply the next bit of the two's-complement DC value */ 423 if (arith_decode(cinfo, st)) 424 MCU_data[blkn][0][0] |= p1; 425 } 426 427 return TRUE; 428 } 429 430 431 /* 432 * MCU decoding for AC successive approximation refinement scan. 433 */ 434 435 METHODDEF(boolean) 436 decode_mcu_AC_refine(j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 437 { 438 arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; 439 JBLOCKROW block; 440 JCOEFPTR thiscoef; 441 unsigned char *st; 442 int tbl, k, kex; 443 int p1, m1; 444 445 /* Process restart marker if needed */ 446 if (cinfo->restart_interval) { 447 if (entropy->restarts_to_go == 0) 448 process_restart(cinfo); 449 entropy->restarts_to_go--; 450 } 451 452 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 453 454 /* There is always only one block per MCU */ 455 block = MCU_data[0]; 456 tbl = cinfo->cur_comp_info[0]->ac_tbl_no; 457 458 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */ 459 m1 = (NEG_1) << cinfo->Al; /* -1 in the bit position being coded */ 460 461 /* Establish EOBx (previous stage end-of-block) index */ 462 for (kex = cinfo->Se; kex > 0; kex--) 463 if ((*block)[jpeg_natural_order[kex]]) break; 464 465 for (k = cinfo->Ss; k <= cinfo->Se; k++) { 466 st = entropy->ac_stats[tbl] + 3 * (k - 1); 467 if (k > kex) 468 if (arith_decode(cinfo, st)) break; /* EOB flag */ 469 for (;;) { 470 thiscoef = *block + jpeg_natural_order[k]; 471 if (*thiscoef) { /* previously nonzero coef */ 472 if (arith_decode(cinfo, st + 2)) { 473 if (*thiscoef < 0) 474 *thiscoef += (JCOEF)m1; 475 else 476 *thiscoef += (JCOEF)p1; 477 } 478 break; 479 } 480 if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */ 481 if (arith_decode(cinfo, entropy->fixed_bin)) 482 *thiscoef = (JCOEF)m1; 483 else 484 *thiscoef = (JCOEF)p1; 485 break; 486 } 487 st += 3; k++; 488 if (k > cinfo->Se) { 489 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 490 entropy->ct = -1; /* spectral overflow */ 491 return TRUE; 492 } 493 } 494 } 495 496 return TRUE; 497 } 498 499 500 /* 501 * Decode one MCU's worth of arithmetic-compressed coefficients. 502 */ 503 504 METHODDEF(boolean) 505 decode_mcu(j_decompress_ptr cinfo, JBLOCKROW *MCU_data) 506 { 507 arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; 508 jpeg_component_info *compptr; 509 JBLOCKROW block; 510 unsigned char *st; 511 int blkn, ci, tbl, sign, k; 512 int v, m; 513 514 /* Process restart marker if needed */ 515 if (cinfo->restart_interval) { 516 if (entropy->restarts_to_go == 0) 517 process_restart(cinfo); 518 entropy->restarts_to_go--; 519 } 520 521 if (entropy->ct == -1) return TRUE; /* if error do nothing */ 522 523 /* Outer loop handles each block in the MCU */ 524 525 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) { 526 block = MCU_data ? MCU_data[blkn] : NULL; 527 ci = cinfo->MCU_membership[blkn]; 528 compptr = cinfo->cur_comp_info[ci]; 529 530 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */ 531 532 tbl = compptr->dc_tbl_no; 533 534 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */ 535 st = entropy->dc_stats[tbl] + entropy->dc_context[ci]; 536 537 /* Figure F.19: Decode_DC_DIFF */ 538 if (arith_decode(cinfo, st) == 0) 539 entropy->dc_context[ci] = 0; 540 else { 541 /* Figure F.21: Decoding nonzero value v */ 542 /* Figure F.22: Decoding the sign of v */ 543 sign = arith_decode(cinfo, st + 1); 544 st += 2; st += sign; 545 /* Figure F.23: Decoding the magnitude category of v */ 546 if ((m = arith_decode(cinfo, st)) != 0) { 547 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */ 548 while (arith_decode(cinfo, st)) { 549 if ((m <<= 1) == 0x8000) { 550 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 551 entropy->ct = -1; /* magnitude overflow */ 552 return TRUE; 553 } 554 st += 1; 555 } 556 } 557 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */ 558 if (m < (int)((1L << cinfo->arith_dc_L[tbl]) >> 1)) 559 entropy->dc_context[ci] = 0; /* zero diff category */ 560 else if (m > (int)((1L << cinfo->arith_dc_U[tbl]) >> 1)) 561 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */ 562 else 563 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */ 564 v = m; 565 /* Figure F.24: Decoding the magnitude bit pattern of v */ 566 st += 14; 567 while (m >>= 1) 568 if (arith_decode(cinfo, st)) v |= m; 569 v += 1; if (sign) v = -v; 570 entropy->last_dc_val[ci] = (entropy->last_dc_val[ci] + v) & 0xffff; 571 } 572 573 if (block) 574 (*block)[0] = (JCOEF)entropy->last_dc_val[ci]; 575 576 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */ 577 578 tbl = compptr->ac_tbl_no; 579 580 /* Figure F.20: Decode_AC_coefficients */ 581 for (k = 1; k <= DCTSIZE2 - 1; k++) { 582 st = entropy->ac_stats[tbl] + 3 * (k - 1); 583 if (arith_decode(cinfo, st)) break; /* EOB flag */ 584 while (arith_decode(cinfo, st + 1) == 0) { 585 st += 3; k++; 586 if (k > DCTSIZE2 - 1) { 587 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 588 entropy->ct = -1; /* spectral overflow */ 589 return TRUE; 590 } 591 } 592 /* Figure F.21: Decoding nonzero value v */ 593 /* Figure F.22: Decoding the sign of v */ 594 sign = arith_decode(cinfo, entropy->fixed_bin); 595 st += 2; 596 /* Figure F.23: Decoding the magnitude category of v */ 597 if ((m = arith_decode(cinfo, st)) != 0) { 598 if (arith_decode(cinfo, st)) { 599 m <<= 1; 600 st = entropy->ac_stats[tbl] + 601 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217); 602 while (arith_decode(cinfo, st)) { 603 if ((m <<= 1) == 0x8000) { 604 WARNMS(cinfo, JWRN_ARITH_BAD_CODE); 605 entropy->ct = -1; /* magnitude overflow */ 606 return TRUE; 607 } 608 st += 1; 609 } 610 } 611 } 612 v = m; 613 /* Figure F.24: Decoding the magnitude bit pattern of v */ 614 st += 14; 615 while (m >>= 1) 616 if (arith_decode(cinfo, st)) v |= m; 617 v += 1; if (sign) v = -v; 618 if (block) 619 (*block)[jpeg_natural_order[k]] = (JCOEF)v; 620 } 621 } 622 623 return TRUE; 624 } 625 626 627 /* 628 * Initialize for an arithmetic-compressed scan. 629 */ 630 631 METHODDEF(void) 632 start_pass(j_decompress_ptr cinfo) 633 { 634 arith_entropy_ptr entropy = (arith_entropy_ptr)cinfo->entropy; 635 int ci, tbl; 636 jpeg_component_info *compptr; 637 638 if (cinfo->progressive_mode) { 639 /* Validate progressive scan parameters */ 640 if (cinfo->Ss == 0) { 641 if (cinfo->Se != 0) 642 goto bad; 643 } else { 644 /* need not check Ss/Se < 0 since they came from unsigned bytes */ 645 if (cinfo->Se < cinfo->Ss || cinfo->Se > DCTSIZE2 - 1) 646 goto bad; 647 /* AC scans may have only one component */ 648 if (cinfo->comps_in_scan != 1) 649 goto bad; 650 } 651 if (cinfo->Ah != 0) { 652 /* Successive approximation refinement scan: must have Al = Ah-1. */ 653 if (cinfo->Ah - 1 != cinfo->Al) 654 goto bad; 655 } 656 if (cinfo->Al > 13) { /* need not check for < 0 */ 657 bad: 658 ERREXIT4(cinfo, JERR_BAD_PROGRESSION, 659 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al); 660 } 661 /* Update progression status, and verify that scan order is legal. 662 * Note that inter-scan inconsistencies are treated as warnings 663 * not fatal errors ... not clear if this is right way to behave. 664 */ 665 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 666 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index; 667 int *coef_bit_ptr = &cinfo->coef_bits[cindex][0]; 668 int *prev_coef_bit_ptr = 669 &cinfo->coef_bits[cindex + cinfo->num_components][0]; 670 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */ 671 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0); 672 for (coefi = MIN(cinfo->Ss, 1); coefi <= MAX(cinfo->Se, 9); coefi++) { 673 if (cinfo->input_scan_number > 1) 674 prev_coef_bit_ptr[coefi] = coef_bit_ptr[coefi]; 675 else 676 prev_coef_bit_ptr[coefi] = 0; 677 } 678 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) { 679 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi]; 680 if (cinfo->Ah != expected) 681 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi); 682 coef_bit_ptr[coefi] = cinfo->Al; 683 } 684 } 685 /* Select MCU decoding routine */ 686 if (cinfo->Ah == 0) { 687 if (cinfo->Ss == 0) 688 entropy->pub.decode_mcu = decode_mcu_DC_first; 689 else 690 entropy->pub.decode_mcu = decode_mcu_AC_first; 691 } else { 692 if (cinfo->Ss == 0) 693 entropy->pub.decode_mcu = decode_mcu_DC_refine; 694 else 695 entropy->pub.decode_mcu = decode_mcu_AC_refine; 696 } 697 } else { 698 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG. 699 * This ought to be an error condition, but we make it a warning. 700 */ 701 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2 - 1 || 702 cinfo->Ah != 0 || cinfo->Al != 0) 703 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL); 704 /* Select MCU decoding routine */ 705 entropy->pub.decode_mcu = decode_mcu; 706 } 707 708 /* Allocate & initialize requested statistics areas */ 709 for (ci = 0; ci < cinfo->comps_in_scan; ci++) { 710 compptr = cinfo->cur_comp_info[ci]; 711 if (!cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) { 712 tbl = compptr->dc_tbl_no; 713 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 714 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 715 if (entropy->dc_stats[tbl] == NULL) 716 entropy->dc_stats[tbl] = (unsigned char *)(*cinfo->mem->alloc_small) 717 ((j_common_ptr)cinfo, JPOOL_IMAGE, DC_STAT_BINS); 718 memset(entropy->dc_stats[tbl], 0, DC_STAT_BINS); 719 /* Initialize DC predictions to 0 */ 720 entropy->last_dc_val[ci] = 0; 721 entropy->dc_context[ci] = 0; 722 } 723 if (!cinfo->progressive_mode || cinfo->Ss) { 724 tbl = compptr->ac_tbl_no; 725 if (tbl < 0 || tbl >= NUM_ARITH_TBLS) 726 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl); 727 if (entropy->ac_stats[tbl] == NULL) 728 entropy->ac_stats[tbl] = (unsigned char *)(*cinfo->mem->alloc_small) 729 ((j_common_ptr)cinfo, JPOOL_IMAGE, AC_STAT_BINS); 730 memset(entropy->ac_stats[tbl], 0, AC_STAT_BINS); 731 } 732 } 733 734 /* Initialize arithmetic decoding variables */ 735 entropy->c = 0; 736 entropy->a = 0; 737 entropy->ct = -16; /* force reading 2 initial bytes to fill C */ 738 entropy->pub.insufficient_data = FALSE; 739 740 /* Initialize restart counter */ 741 entropy->restarts_to_go = cinfo->restart_interval; 742 } 743 744 745 /* 746 * Module initialization routine for arithmetic entropy decoding. 747 */ 748 749 GLOBAL(void) 750 jinit_arith_decoder(j_decompress_ptr cinfo) 751 { 752 arith_entropy_ptr entropy; 753 int i; 754 755 entropy = (arith_entropy_ptr) 756 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 757 sizeof(arith_entropy_decoder)); 758 cinfo->entropy = (struct jpeg_entropy_decoder *)entropy; 759 entropy->pub.start_pass = start_pass; 760 761 /* Mark tables unallocated */ 762 for (i = 0; i < NUM_ARITH_TBLS; i++) { 763 entropy->dc_stats[i] = NULL; 764 entropy->ac_stats[i] = NULL; 765 } 766 767 /* Initialize index for fixed probability estimation */ 768 entropy->fixed_bin[0] = 113; 769 770 if (cinfo->progressive_mode) { 771 /* Create progression status table */ 772 int *coef_bit_ptr, ci; 773 cinfo->coef_bits = (int (*)[DCTSIZE2]) 774 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE, 775 cinfo->num_components * 2 * DCTSIZE2 * 776 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 }