Skip to content
This repository

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
branch: ics
Fetching contributors…

Octocat-spinner-32-eaf2f5

Cannot retrieve contributors at this time

file 762 lines (663 sloc) 23.598 kb
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761
/*
* jdarith.c
*
* Developed 1997-2009 by Guido Vollbeding.
* This file is part of the Independent JPEG Group's software.
* For conditions of distribution and use, see the accompanying README file.
*
* This file contains portable arithmetic entropy decoding routines for JPEG
* (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81).
*
* Both sequential and progressive modes are supported in this single module.
*
* Suspension is not currently supported in this module.
*/

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"


/* Expanded entropy decoder object for arithmetic decoding. */

typedef struct {
  struct jpeg_entropy_decoder pub; /* public fields */

  INT32 c; /* C register, base of coding interval + input bit buffer */
  INT32 a; /* A register, normalized size of coding interval */
  int ct; /* bit shift counter, # of bits left in bit buffer part of C */
                                                         /* init: ct = -16 */
                                                         /* run: ct = 0..7 */
                                                         /* error: ct = -1 */
  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
  int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */

  unsigned int restarts_to_go; /* MCUs left in this restart interval */

  /* Pointers to statistics areas (these workspaces have image lifespan) */
  unsigned char * dc_stats[NUM_ARITH_TBLS];
  unsigned char * ac_stats[NUM_ARITH_TBLS];

  /* Statistics bin for coding with fixed probability 0.5 */
  unsigned char fixed_bin[4];
} arith_entropy_decoder;

typedef arith_entropy_decoder * arith_entropy_ptr;

/* The following two definitions specify the allocation chunk size
* for the statistics area.
* According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least
* 49 statistics bins for DC, and 245 statistics bins for AC coding.
*
* We use a compact representation with 1 byte per statistics bin,
* thus the numbers directly represent byte sizes.
* This 1 byte per statistics bin contains the meaning of the MPS
* (more probable symbol) in the highest bit (mask 0x80), and the
* index into the probability estimation state machine table
* in the lower bits (mask 0x7F).
*/

#define DC_STAT_BINS 64
#define AC_STAT_BINS 256


LOCAL(int)
get_byte (j_decompress_ptr cinfo)
/* Read next input byte; we do not support suspension in this module. */
{
  struct jpeg_source_mgr * src = cinfo->src;

  if (src->bytes_in_buffer == 0)
    if (! (*src->fill_input_buffer) (cinfo))
      ERREXIT(cinfo, JERR_CANT_SUSPEND);
  src->bytes_in_buffer--;
  return GETJOCTET(*src->next_input_byte++);
}


/*
* The core arithmetic decoding routine (common in JPEG and JBIG).
* This needs to go as fast as possible.
* Machine-dependent optimization facilities
* are not utilized in this portable implementation.
* However, this code should be fairly efficient and
* may be a good base for further optimizations anyway.
*
* Return value is 0 or 1 (binary decision).
*
* Note: I've changed the handling of the code base & bit
* buffer register C compared to other implementations
* based on the standards layout & procedures.
* While it also contains both the actual base of the
* coding interval (16 bits) and the next-bits buffer,
* the cut-point between these two parts is floating
* (instead of fixed) with the bit shift counter CT.
* Thus, we also need only one (variable instead of
* fixed size) shift for the LPS/MPS decision, and
* we can get away with any renormalization update
* of C (except for new data insertion, of course).
*
* I've also introduced a new scheme for accessing
* the probability estimation state machine table,
* derived from Markus Kuhn's JBIG implementation.
*/

LOCAL(int)
arith_decode (j_decompress_ptr cinfo, unsigned char *st)
{
  register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;
  register unsigned char nl, nm;
  register INT32 qe, temp;
  register int sv, data;

  /* Renormalization & data input per section D.2.6 */
  while (e->a < 0x8000L) {
    if (--e->ct < 0) {
      /* Need to fetch next data byte */
      if (cinfo->unread_marker)
data = 0; /* stuff zero data */
      else {
data = get_byte(cinfo); /* read next input byte */
if (data == 0xFF) { /* zero stuff or marker code */
do data = get_byte(cinfo);
while (data == 0xFF); /* swallow extra 0xFF bytes */
if (data == 0)
data = 0xFF; /* discard stuffed zero byte */
else {
/* Note: Different from the Huffman decoder, hitting
* a marker while processing the compressed data
* segment is legal in arithmetic coding.
* The convention is to supply zero data
* then until decoding is complete.
*/
cinfo->unread_marker = data;
data = 0;
}
}
      }
      e->c = (e->c << 8) | data; /* insert data into C register */
      if ((e->ct += 8) < 0) /* update bit shift counter */
/* Need more initial bytes */
if (++e->ct == 0)
/* Got 2 initial bytes -> re-init A and exit loop */
e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */
    }
    e->a <<= 1;
  }

  /* Fetch values from our compact representation of Table D.2:
* Qe values and probability estimation state machine
*/
  sv = *st;
  qe = jpeg_aritab[sv & 0x7F]; /* => Qe_Value */
  nl = qe & 0xFF; qe >>= 8; /* Next_Index_LPS + Switch_MPS */
  nm = qe & 0xFF; qe >>= 8; /* Next_Index_MPS */

  /* Decode & estimation procedures per sections D.2.4 & D.2.5 */
  temp = e->a - qe;
  e->a = temp;
  temp <<= e->ct;
  if (e->c >= temp) {
    e->c -= temp;
    /* Conditional LPS (less probable symbol) exchange */
    if (e->a < qe) {
      e->a = qe;
      *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
    } else {
      e->a = qe;
      *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
      sv ^= 0x80; /* Exchange LPS/MPS */
    }
  } else if (e->a < 0x8000L) {
    /* Conditional MPS (more probable symbol) exchange */
    if (e->a < qe) {
      *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
      sv ^= 0x80; /* Exchange LPS/MPS */
    } else {
      *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
    }
  }

  return sv >> 7;
}


/*
* Check for a restart marker & resynchronize decoder.
*/

LOCAL(void)
process_restart (j_decompress_ptr cinfo)
{
  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
  int ci;
  jpeg_component_info * compptr;

  /* Advance past the RSTn marker */
  if (! (*cinfo->marker->read_restart_marker) (cinfo))
    ERREXIT(cinfo, JERR_CANT_SUSPEND);

  /* Re-initialize statistics areas */
  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
    compptr = cinfo->cur_comp_info[ci];
    if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
      MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS);
      /* Reset DC predictions to 0 */
      entropy->last_dc_val[ci] = 0;
      entropy->dc_context[ci] = 0;
    }
    if (! cinfo->progressive_mode || cinfo->Ss) {
      MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS);
    }
  }

  /* Reset arithmetic decoding variables */
  entropy->c = 0;
  entropy->a = 0;
  entropy->ct = -16; /* force reading 2 initial bytes to fill C */

  /* Reset restart counter */
  entropy->restarts_to_go = cinfo->restart_interval;
}


/*
* Arithmetic MCU decoding.
* Each of these routines decodes and returns one MCU's worth of
* arithmetic-compressed coefficients.
* The coefficients are reordered from zigzag order into natural array order,
* but are not dequantized.
*
* The i'th block of the MCU is stored into the block pointed to by
* MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
*/

/*
* MCU decoding for DC initial scan (either spectral selection,
* or first pass of successive approximation).
*/

METHODDEF(boolean)
decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
  JBLOCKROW block;
  unsigned char *st;
  int blkn, ci, tbl, sign;
  int v, m;

  /* Process restart marker if needed */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      process_restart(cinfo);
    entropy->restarts_to_go--;
  }

  if (entropy->ct == -1) return TRUE; /* if error do nothing */

  /* Outer loop handles each block in the MCU */

  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
    block = MCU_data[blkn];
    ci = cinfo->MCU_membership[blkn];
    tbl = cinfo->cur_comp_info[ci]->dc_tbl_no;

    /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */

    /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
    st = entropy->dc_stats[tbl] + entropy->dc_context[ci];

    /* Figure F.19: Decode_DC_DIFF */
    if (arith_decode(cinfo, st) == 0)
      entropy->dc_context[ci] = 0;
    else {
      /* Figure F.21: Decoding nonzero value v */
      /* Figure F.22: Decoding the sign of v */
      sign = arith_decode(cinfo, st + 1);
      st += 2; st += sign;
      /* Figure F.23: Decoding the magnitude category of v */
      if ((m = arith_decode(cinfo, st)) != 0) {
st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
while (arith_decode(cinfo, st)) {
if ((m <<= 1) == 0x8000) {
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
entropy->ct = -1; /* magnitude overflow */
return TRUE;
}
st += 1;
}
      }
      /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
      if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
entropy->dc_context[ci] = 0; /* zero diff category */
      else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
      else
entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
      v = m;
      /* Figure F.24: Decoding the magnitude bit pattern of v */
      st += 14;
      while (m >>= 1)
if (arith_decode(cinfo, st)) v |= m;
      v += 1; if (sign) v = -v;
      entropy->last_dc_val[ci] += v;
    }

    /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */
    (*block)[0] = (JCOEF) (entropy->last_dc_val[ci] << cinfo->Al);
  }

  return TRUE;
}


/*
* MCU decoding for AC initial scan (either spectral selection,
* or first pass of successive approximation).
*/

METHODDEF(boolean)
decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
  JBLOCKROW block;
  unsigned char *st;
  int tbl, sign, k;
  int v, m;

  /* Process restart marker if needed */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      process_restart(cinfo);
    entropy->restarts_to_go--;
  }

  if (entropy->ct == -1) return TRUE; /* if error do nothing */

  /* There is always only one block per MCU */
  block = MCU_data[0];
  tbl = cinfo->cur_comp_info[0]->ac_tbl_no;

  /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */

  /* Figure F.20: Decode_AC_coefficients */
  for (k = cinfo->Ss; k <= cinfo->Se; k++) {
    st = entropy->ac_stats[tbl] + 3 * (k - 1);
    if (arith_decode(cinfo, st)) break; /* EOB flag */
    while (arith_decode(cinfo, st + 1) == 0) {
      st += 3; k++;
      if (k > cinfo->Se) {
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
entropy->ct = -1; /* spectral overflow */
return TRUE;
      }
    }
    /* Figure F.21: Decoding nonzero value v */
    /* Figure F.22: Decoding the sign of v */
    sign = arith_decode(cinfo, entropy->fixed_bin);
    st += 2;
    /* Figure F.23: Decoding the magnitude category of v */
    if ((m = arith_decode(cinfo, st)) != 0) {
      if (arith_decode(cinfo, st)) {
m <<= 1;
st = entropy->ac_stats[tbl] +
(k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
while (arith_decode(cinfo, st)) {
if ((m <<= 1) == 0x8000) {
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
entropy->ct = -1; /* magnitude overflow */
return TRUE;
}
st += 1;
}
      }
    }
    v = m;
    /* Figure F.24: Decoding the magnitude bit pattern of v */
    st += 14;
    while (m >>= 1)
      if (arith_decode(cinfo, st)) v |= m;
    v += 1; if (sign) v = -v;
    /* Scale and output coefficient in natural (dezigzagged) order */
    (*block)[jpeg_natural_order[k]] = (JCOEF) (v << cinfo->Al);
  }

  return TRUE;
}


/*
* MCU decoding for DC successive approximation refinement scan.
*/

METHODDEF(boolean)
decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
  unsigned char *st;
  int p1, blkn;

  /* Process restart marker if needed */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      process_restart(cinfo);
    entropy->restarts_to_go--;
  }

  st = entropy->fixed_bin; /* use fixed probability estimation */
  p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */

  /* Outer loop handles each block in the MCU */

  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
    /* Encoded data is simply the next bit of the two's-complement DC value */
    if (arith_decode(cinfo, st))
      MCU_data[blkn][0][0] |= p1;
  }

  return TRUE;
}


/*
* MCU decoding for AC successive approximation refinement scan.
*/

METHODDEF(boolean)
decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
  JBLOCKROW block;
  JCOEFPTR thiscoef;
  unsigned char *st;
  int tbl, k, kex;
  int p1, m1;

  /* Process restart marker if needed */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      process_restart(cinfo);
    entropy->restarts_to_go--;
  }

  if (entropy->ct == -1) return TRUE; /* if error do nothing */

  /* There is always only one block per MCU */
  block = MCU_data[0];
  tbl = cinfo->cur_comp_info[0]->ac_tbl_no;

  p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
  m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */

  /* Establish EOBx (previous stage end-of-block) index */
  for (kex = cinfo->Se; kex > 0; kex--)
    if ((*block)[jpeg_natural_order[kex]]) break;

  for (k = cinfo->Ss; k <= cinfo->Se; k++) {
    st = entropy->ac_stats[tbl] + 3 * (k - 1);
    if (k > kex)
      if (arith_decode(cinfo, st)) break; /* EOB flag */
    for (;;) {
      thiscoef = *block + jpeg_natural_order[k];
      if (*thiscoef) { /* previously nonzero coef */
if (arith_decode(cinfo, st + 2)) {
if (*thiscoef < 0)
*thiscoef += m1;
else
*thiscoef += p1;
}
break;
      }
      if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */
if (arith_decode(cinfo, entropy->fixed_bin))
*thiscoef = m1;
else
*thiscoef = p1;
break;
      }
      st += 3; k++;
      if (k > cinfo->Se) {
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
entropy->ct = -1; /* spectral overflow */
return TRUE;
      }
    }
  }

  return TRUE;
}


/*
* Decode one MCU's worth of arithmetic-compressed coefficients.
*/

METHODDEF(boolean)
decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
{
  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
  jpeg_component_info * compptr;
  JBLOCKROW block;
  unsigned char *st;
  int blkn, ci, tbl, sign, k;
  int v, m;

  /* Process restart marker if needed */
  if (cinfo->restart_interval) {
    if (entropy->restarts_to_go == 0)
      process_restart(cinfo);
    entropy->restarts_to_go--;
  }

  if (entropy->ct == -1) return TRUE; /* if error do nothing */

  /* Outer loop handles each block in the MCU */

  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
    block = MCU_data[blkn];
    ci = cinfo->MCU_membership[blkn];
    compptr = cinfo->cur_comp_info[ci];

    /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */

    tbl = compptr->dc_tbl_no;

    /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
    st = entropy->dc_stats[tbl] + entropy->dc_context[ci];

    /* Figure F.19: Decode_DC_DIFF */
    if (arith_decode(cinfo, st) == 0)
      entropy->dc_context[ci] = 0;
    else {
      /* Figure F.21: Decoding nonzero value v */
      /* Figure F.22: Decoding the sign of v */
      sign = arith_decode(cinfo, st + 1);
      st += 2; st += sign;
      /* Figure F.23: Decoding the magnitude category of v */
      if ((m = arith_decode(cinfo, st)) != 0) {
st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
while (arith_decode(cinfo, st)) {
if ((m <<= 1) == 0x8000) {
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
entropy->ct = -1; /* magnitude overflow */
return TRUE;
}
st += 1;
}
      }
      /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
      if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
entropy->dc_context[ci] = 0; /* zero diff category */
      else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
      else
entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
      v = m;
      /* Figure F.24: Decoding the magnitude bit pattern of v */
      st += 14;
      while (m >>= 1)
if (arith_decode(cinfo, st)) v |= m;
      v += 1; if (sign) v = -v;
      entropy->last_dc_val[ci] += v;
    }

    (*block)[0] = (JCOEF) entropy->last_dc_val[ci];

    /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */

    tbl = compptr->ac_tbl_no;

    /* Figure F.20: Decode_AC_coefficients */
    for (k = 1; k <= DCTSIZE2 - 1; k++) {
      st = entropy->ac_stats[tbl] + 3 * (k - 1);
      if (arith_decode(cinfo, st)) break; /* EOB flag */
      while (arith_decode(cinfo, st + 1) == 0) {
st += 3; k++;
if (k > DCTSIZE2 - 1) {
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
entropy->ct = -1; /* spectral overflow */
return TRUE;
}
      }
      /* Figure F.21: Decoding nonzero value v */
      /* Figure F.22: Decoding the sign of v */
      sign = arith_decode(cinfo, entropy->fixed_bin);
      st += 2;
      /* Figure F.23: Decoding the magnitude category of v */
      if ((m = arith_decode(cinfo, st)) != 0) {
if (arith_decode(cinfo, st)) {
m <<= 1;
st = entropy->ac_stats[tbl] +
(k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
while (arith_decode(cinfo, st)) {
if ((m <<= 1) == 0x8000) {
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
entropy->ct = -1; /* magnitude overflow */
return TRUE;
}
st += 1;
}
}
      }
      v = m;
      /* Figure F.24: Decoding the magnitude bit pattern of v */
      st += 14;
      while (m >>= 1)
if (arith_decode(cinfo, st)) v |= m;
      v += 1; if (sign) v = -v;
      (*block)[jpeg_natural_order[k]] = (JCOEF) v;
    }
  }

  return TRUE;
}


/*
* Initialize for an arithmetic-compressed scan.
*/

METHODDEF(void)
start_pass (j_decompress_ptr cinfo)
{
  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
  int ci, tbl;
  jpeg_component_info * compptr;

  if (cinfo->progressive_mode) {
    /* Validate progressive scan parameters */
    if (cinfo->Ss == 0) {
      if (cinfo->Se != 0)
goto bad;
    } else {
      /* need not check Ss/Se < 0 since they came from unsigned bytes */
      if (cinfo->Se < cinfo->Ss || cinfo->Se > DCTSIZE2 - 1)
goto bad;
      /* AC scans may have only one component */
      if (cinfo->comps_in_scan != 1)
goto bad;
    }
    if (cinfo->Ah != 0) {
      /* Successive approximation refinement scan: must have Al = Ah-1. */
      if (cinfo->Ah-1 != cinfo->Al)
goto bad;
    }
    if (cinfo->Al > 13) { /* need not check for < 0 */
      bad:
      ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
    }
    /* Update progression status, and verify that scan order is legal.
* Note that inter-scan inconsistencies are treated as warnings
* not fatal errors ... not clear if this is right way to behave.
*/
    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
      int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
      int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
      if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
      for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
if (cinfo->Ah != expected)
WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
coef_bit_ptr[coefi] = cinfo->Al;
      }
    }
    /* Select MCU decoding routine */
    if (cinfo->Ah == 0) {
      if (cinfo->Ss == 0)
entropy->pub.decode_mcu = decode_mcu_DC_first;
      else
entropy->pub.decode_mcu = decode_mcu_AC_first;
    } else {
      if (cinfo->Ss == 0)
entropy->pub.decode_mcu = decode_mcu_DC_refine;
      else
entropy->pub.decode_mcu = decode_mcu_AC_refine;
    }
  } else {
    /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
* This ought to be an error condition, but we make it a warning.
*/
    if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
(cinfo->Se < DCTSIZE2 && cinfo->Se != DCTSIZE2 - 1))
      WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
    /* Select MCU decoding routine */
    entropy->pub.decode_mcu = decode_mcu;
  }

  /* Allocate & initialize requested statistics areas */
  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
    compptr = cinfo->cur_comp_info[ci];
    if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
      tbl = compptr->dc_tbl_no;
      if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
      if (entropy->dc_stats[tbl] == NULL)
entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
      MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
      /* Initialize DC predictions to 0 */
      entropy->last_dc_val[ci] = 0;
      entropy->dc_context[ci] = 0;
    }
    if (! cinfo->progressive_mode || cinfo->Ss) {
      tbl = compptr->ac_tbl_no;
      if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
      if (entropy->ac_stats[tbl] == NULL)
entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
      MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
    }
  }

  /* Initialize arithmetic decoding variables */
  entropy->c = 0;
  entropy->a = 0;
  entropy->ct = -16; /* force reading 2 initial bytes to fill C */

  /* Initialize restart counter */
  entropy->restarts_to_go = cinfo->restart_interval;
}


/*
* Module initialization routine for arithmetic entropy decoding.
*/

GLOBAL(void)
jinit_arith_decoder (j_decompress_ptr cinfo)
{
  arith_entropy_ptr entropy;
  int i;

  entropy = (arith_entropy_ptr)
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
SIZEOF(arith_entropy_decoder));
  cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
  entropy->pub.start_pass = start_pass;

  /* Mark tables unallocated */
  for (i = 0; i < NUM_ARITH_TBLS; i++) {
    entropy->dc_stats[i] = NULL;
    entropy->ac_stats[i] = NULL;
  }

  /* Initialize index for fixed probability estimation */
  entropy->fixed_bin[0] = 113;

  if (cinfo->progressive_mode) {
    /* Create progression status table */
    int *coef_bit_ptr, ci;
    cinfo->coef_bits = (int (*)[DCTSIZE2])
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
cinfo->num_components*DCTSIZE2*SIZEOF(int));
    coef_bit_ptr = & cinfo->coef_bits[0][0];
    for (ci = 0; ci < cinfo->num_components; ci++)
      for (i = 0; i < DCTSIZE2; i++)
*coef_bit_ptr++ = -1;
  }
}
Something went wrong with that request. Please try again.