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/src/FreeImage/Source/LibJPEG/jdarith.c

https://bitbucket.org/cabalistic/ogredeps/
C | 776 lines | 497 code | 101 blank | 178 comment | 189 complexity | d17d1f9dfb57b0cfbc2419a302a21cc6 MD5 | raw file
  1/*
  2 * jdarith.c
  3 *
  4 * Developed 1997-2011 by Guido Vollbeding.
  5 * This file is part of the Independent JPEG Group's software.
  6 * For conditions of distribution and use, see the accompanying README file.
  7 *
  8 * This file contains portable arithmetic entropy decoding routines for JPEG
  9 * (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81).
 10 *
 11 * Both sequential and progressive modes are supported in this single module.
 12 *
 13 * Suspension is not currently supported in this module.
 14 */
 15
 16#define JPEG_INTERNALS
 17#include "jinclude.h"
 18#include "jpeglib.h"
 19
 20
 21/* Expanded entropy decoder object for arithmetic decoding. */
 22
 23typedef struct {
 24  struct jpeg_entropy_decoder pub; /* public fields */
 25
 26  INT32 c;       /* C register, base of coding interval + input bit buffer */
 27  INT32 a;               /* A register, normalized size of coding interval */
 28  int ct;     /* bit shift counter, # of bits left in bit buffer part of C */
 29                                                         /* init: ct = -16 */
 30                                                         /* run: ct = 0..7 */
 31                                                         /* error: ct = -1 */
 32  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
 33  int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */
 34
 35  unsigned int restarts_to_go;	/* MCUs left in this restart interval */
 36
 37  /* Pointers to statistics areas (these workspaces have image lifespan) */
 38  unsigned char * dc_stats[NUM_ARITH_TBLS];
 39  unsigned char * ac_stats[NUM_ARITH_TBLS];
 40
 41  /* Statistics bin for coding with fixed probability 0.5 */
 42  unsigned char fixed_bin[4];
 43} arith_entropy_decoder;
 44
 45typedef arith_entropy_decoder * arith_entropy_ptr;
 46
 47/* The following two definitions specify the allocation chunk size
 48 * for the statistics area.
 49 * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least
 50 * 49 statistics bins for DC, and 245 statistics bins for AC coding.
 51 *
 52 * We use a compact representation with 1 byte per statistics bin,
 53 * thus the numbers directly represent byte sizes.
 54 * This 1 byte per statistics bin contains the meaning of the MPS
 55 * (more probable symbol) in the highest bit (mask 0x80), and the
 56 * index into the probability estimation state machine table
 57 * in the lower bits (mask 0x7F).
 58 */
 59
 60#define DC_STAT_BINS 64
 61#define AC_STAT_BINS 256
 62
 63
 64LOCAL(int)
 65get_byte (j_decompress_ptr cinfo)
 66/* Read next input byte; we do not support suspension in this module. */
 67{
 68  struct jpeg_source_mgr * src = cinfo->src;
 69
 70  if (src->bytes_in_buffer == 0)
 71    if (! (*src->fill_input_buffer) (cinfo))
 72      ERREXIT(cinfo, JERR_CANT_SUSPEND);
 73  src->bytes_in_buffer--;
 74  return GETJOCTET(*src->next_input_byte++);
 75}
 76
 77
 78/*
 79 * The core arithmetic decoding routine (common in JPEG and JBIG).
 80 * This needs to go as fast as possible.
 81 * Machine-dependent optimization facilities
 82 * are not utilized in this portable implementation.
 83 * However, this code should be fairly efficient and
 84 * may be a good base for further optimizations anyway.
 85 *
 86 * Return value is 0 or 1 (binary decision).
 87 *
 88 * Note: I've changed the handling of the code base & bit
 89 * buffer register C compared to other implementations
 90 * based on the standards layout & procedures.
 91 * While it also contains both the actual base of the
 92 * coding interval (16 bits) and the next-bits buffer,
 93 * the cut-point between these two parts is floating
 94 * (instead of fixed) with the bit shift counter CT.
 95 * Thus, we also need only one (variable instead of
 96 * fixed size) shift for the LPS/MPS decision, and
 97 * we can get away with any renormalization update
 98 * of C (except for new data insertion, of course).
 99 *
100 * I've also introduced a new scheme for accessing
101 * the probability estimation state machine table,
102 * derived from Markus Kuhn's JBIG implementation.
103 */
104
105LOCAL(int)
106arith_decode (j_decompress_ptr cinfo, unsigned char *st)
107{
108  register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;
109  register unsigned char nl, nm;
110  register INT32 qe, temp;
111  register int sv, data;
112
113  /* Renormalization & data input per section D.2.6 */
114  while (e->a < 0x8000L) {
115    if (--e->ct < 0) {
116      /* Need to fetch next data byte */
117      if (cinfo->unread_marker)
118	data = 0;		/* stuff zero data */
119      else {
120	data = get_byte(cinfo);	/* read next input byte */
121	if (data == 0xFF) {	/* zero stuff or marker code */
122	  do data = get_byte(cinfo);
123	  while (data == 0xFF);	/* swallow extra 0xFF bytes */
124	  if (data == 0)
125	    data = 0xFF;	/* discard stuffed zero byte */
126	  else {
127	    /* Note: Different from the Huffman decoder, hitting
128	     * a marker while processing the compressed data
129	     * segment is legal in arithmetic coding.
130	     * The convention is to supply zero data
131	     * then until decoding is complete.
132	     */
133	    cinfo->unread_marker = data;
134	    data = 0;
135	  }
136	}
137      }
138      e->c = (e->c << 8) | data; /* insert data into C register */
139      if ((e->ct += 8) < 0)	 /* update bit shift counter */
140	/* Need more initial bytes */
141	if (++e->ct == 0)
142	  /* Got 2 initial bytes -> re-init A and exit loop */
143	  e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */
144    }
145    e->a <<= 1;
146  }
147
148  /* Fetch values from our compact representation of Table D.3(D.2):
149   * Qe values and probability estimation state machine
150   */
151  sv = *st;
152  qe = jpeg_aritab[sv & 0x7F];	/* => Qe_Value */
153  nl = qe & 0xFF; qe >>= 8;	/* Next_Index_LPS + Switch_MPS */
154  nm = qe & 0xFF; qe >>= 8;	/* Next_Index_MPS */
155
156  /* Decode & estimation procedures per sections D.2.4 & D.2.5 */
157  temp = e->a - qe;
158  e->a = temp;
159  temp <<= e->ct;
160  if (e->c >= temp) {
161    e->c -= temp;
162    /* Conditional LPS (less probable symbol) exchange */
163    if (e->a < qe) {
164      e->a = qe;
165      *st = (sv & 0x80) ^ nm;	/* Estimate_after_MPS */
166    } else {
167      e->a = qe;
168      *st = (sv & 0x80) ^ nl;	/* Estimate_after_LPS */
169      sv ^= 0x80;		/* Exchange LPS/MPS */
170    }
171  } else if (e->a < 0x8000L) {
172    /* Conditional MPS (more probable symbol) exchange */
173    if (e->a < qe) {
174      *st = (sv & 0x80) ^ nl;	/* Estimate_after_LPS */
175      sv ^= 0x80;		/* Exchange LPS/MPS */
176    } else {
177      *st = (sv & 0x80) ^ nm;	/* Estimate_after_MPS */
178    }
179  }
180
181  return sv >> 7;
182}
183
184
185/*
186 * Check for a restart marker & resynchronize decoder.
187 */
188
189LOCAL(void)
190process_restart (j_decompress_ptr cinfo)
191{
192  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
193  int ci;
194  jpeg_component_info * compptr;
195
196  /* Advance past the RSTn marker */
197  if (! (*cinfo->marker->read_restart_marker) (cinfo))
198    ERREXIT(cinfo, JERR_CANT_SUSPEND);
199
200  /* Re-initialize statistics areas */
201  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
202    compptr = cinfo->cur_comp_info[ci];
203    if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
204      MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS);
205      /* Reset DC predictions to 0 */
206      entropy->last_dc_val[ci] = 0;
207      entropy->dc_context[ci] = 0;
208    }
209    if ((! cinfo->progressive_mode && cinfo->lim_Se) ||
210	(cinfo->progressive_mode && cinfo->Ss)) {
211      MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS);
212    }
213  }
214
215  /* Reset arithmetic decoding variables */
216  entropy->c = 0;
217  entropy->a = 0;
218  entropy->ct = -16;	/* force reading 2 initial bytes to fill C */
219
220  /* Reset restart counter */
221  entropy->restarts_to_go = cinfo->restart_interval;
222}
223
224
225/*
226 * Arithmetic MCU decoding.
227 * Each of these routines decodes and returns one MCU's worth of
228 * arithmetic-compressed coefficients.
229 * The coefficients are reordered from zigzag order into natural array order,
230 * but are not dequantized.
231 *
232 * The i'th block of the MCU is stored into the block pointed to by
233 * MCU_data[i].  WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
234 */
235
236/*
237 * MCU decoding for DC initial scan (either spectral selection,
238 * or first pass of successive approximation).
239 */
240
241METHODDEF(boolean)
242decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
243{
244  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
245  JBLOCKROW block;
246  unsigned char *st;
247  int blkn, ci, tbl, sign;
248  int v, m;
249
250  /* Process restart marker if needed */
251  if (cinfo->restart_interval) {
252    if (entropy->restarts_to_go == 0)
253      process_restart(cinfo);
254    entropy->restarts_to_go--;
255  }
256
257  if (entropy->ct == -1) return TRUE;	/* if error do nothing */
258
259  /* Outer loop handles each block in the MCU */
260
261  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
262    block = MCU_data[blkn];
263    ci = cinfo->MCU_membership[blkn];
264    tbl = cinfo->cur_comp_info[ci]->dc_tbl_no;
265
266    /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
267
268    /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
269    st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
270
271    /* Figure F.19: Decode_DC_DIFF */
272    if (arith_decode(cinfo, st) == 0)
273      entropy->dc_context[ci] = 0;
274    else {
275      /* Figure F.21: Decoding nonzero value v */
276      /* Figure F.22: Decoding the sign of v */
277      sign = arith_decode(cinfo, st + 1);
278      st += 2; st += sign;
279      /* Figure F.23: Decoding the magnitude category of v */
280      if ((m = arith_decode(cinfo, st)) != 0) {
281	st = entropy->dc_stats[tbl] + 20;	/* Table F.4: X1 = 20 */
282	while (arith_decode(cinfo, st)) {
283	  if ((m <<= 1) == 0x8000) {
284	    WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
285	    entropy->ct = -1;			/* magnitude overflow */
286	    return TRUE;
287	  }
288	  st += 1;
289	}
290      }
291      /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
292      if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
293	entropy->dc_context[ci] = 0;		   /* zero diff category */
294      else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
295	entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
296      else
297	entropy->dc_context[ci] = 4 + (sign * 4);  /* small diff category */
298      v = m;
299      /* Figure F.24: Decoding the magnitude bit pattern of v */
300      st += 14;
301      while (m >>= 1)
302	if (arith_decode(cinfo, st)) v |= m;
303      v += 1; if (sign) v = -v;
304      entropy->last_dc_val[ci] += v;
305    }
306
307    /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */
308    (*block)[0] = (JCOEF) (entropy->last_dc_val[ci] << cinfo->Al);
309  }
310
311  return TRUE;
312}
313
314
315/*
316 * MCU decoding for AC initial scan (either spectral selection,
317 * or first pass of successive approximation).
318 */
319
320METHODDEF(boolean)
321decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
322{
323  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
324  JBLOCKROW block;
325  unsigned char *st;
326  int tbl, sign, k;
327  int v, m;
328  const int * natural_order;
329
330  /* Process restart marker if needed */
331  if (cinfo->restart_interval) {
332    if (entropy->restarts_to_go == 0)
333      process_restart(cinfo);
334    entropy->restarts_to_go--;
335  }
336
337  if (entropy->ct == -1) return TRUE;	/* if error do nothing */
338
339  natural_order = cinfo->natural_order;
340
341  /* There is always only one block per MCU */
342  block = MCU_data[0];
343  tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
344
345  /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
346
347  /* Figure F.20: Decode_AC_coefficients */
348  for (k = cinfo->Ss; k <= cinfo->Se; k++) {
349    st = entropy->ac_stats[tbl] + 3 * (k - 1);
350    if (arith_decode(cinfo, st)) break;		/* EOB flag */
351    while (arith_decode(cinfo, st + 1) == 0) {
352      st += 3; k++;
353      if (k > cinfo->Se) {
354	WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
355	entropy->ct = -1;			/* spectral overflow */
356	return TRUE;
357      }
358    }
359    /* Figure F.21: Decoding nonzero value v */
360    /* Figure F.22: Decoding the sign of v */
361    sign = arith_decode(cinfo, entropy->fixed_bin);
362    st += 2;
363    /* Figure F.23: Decoding the magnitude category of v */
364    if ((m = arith_decode(cinfo, st)) != 0) {
365      if (arith_decode(cinfo, st)) {
366	m <<= 1;
367	st = entropy->ac_stats[tbl] +
368	     (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
369	while (arith_decode(cinfo, st)) {
370	  if ((m <<= 1) == 0x8000) {
371	    WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
372	    entropy->ct = -1;			/* magnitude overflow */
373	    return TRUE;
374	  }
375	  st += 1;
376	}
377      }
378    }
379    v = m;
380    /* Figure F.24: Decoding the magnitude bit pattern of v */
381    st += 14;
382    while (m >>= 1)
383      if (arith_decode(cinfo, st)) v |= m;
384    v += 1; if (sign) v = -v;
385    /* Scale and output coefficient in natural (dezigzagged) order */
386    (*block)[natural_order[k]] = (JCOEF) (v << cinfo->Al);
387  }
388
389  return TRUE;
390}
391
392
393/*
394 * MCU decoding for DC successive approximation refinement scan.
395 */
396
397METHODDEF(boolean)
398decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
399{
400  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
401  unsigned char *st;
402  int p1, blkn;
403
404  /* Process restart marker if needed */
405  if (cinfo->restart_interval) {
406    if (entropy->restarts_to_go == 0)
407      process_restart(cinfo);
408    entropy->restarts_to_go--;
409  }
410
411  st = entropy->fixed_bin;	/* use fixed probability estimation */
412  p1 = 1 << cinfo->Al;		/* 1 in the bit position being coded */
413
414  /* Outer loop handles each block in the MCU */
415
416  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
417    /* Encoded data is simply the next bit of the two's-complement DC value */
418    if (arith_decode(cinfo, st))
419      MCU_data[blkn][0][0] |= p1;
420  }
421
422  return TRUE;
423}
424
425
426/*
427 * MCU decoding for AC successive approximation refinement scan.
428 */
429
430METHODDEF(boolean)
431decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
432{
433  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
434  JBLOCKROW block;
435  JCOEFPTR thiscoef;
436  unsigned char *st;
437  int tbl, k, kex;
438  int p1, m1;
439  const int * natural_order;
440
441  /* Process restart marker if needed */
442  if (cinfo->restart_interval) {
443    if (entropy->restarts_to_go == 0)
444      process_restart(cinfo);
445    entropy->restarts_to_go--;
446  }
447
448  if (entropy->ct == -1) return TRUE;	/* if error do nothing */
449
450  natural_order = cinfo->natural_order;
451
452  /* There is always only one block per MCU */
453  block = MCU_data[0];
454  tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
455
456  p1 = 1 << cinfo->Al;		/* 1 in the bit position being coded */
457  m1 = (-1) << cinfo->Al;	/* -1 in the bit position being coded */
458
459  /* Establish EOBx (previous stage end-of-block) index */
460  for (kex = cinfo->Se; kex > 0; kex--)
461    if ((*block)[natural_order[kex]]) break;
462
463  for (k = cinfo->Ss; k <= cinfo->Se; k++) {
464    st = entropy->ac_stats[tbl] + 3 * (k - 1);
465    if (k > kex)
466      if (arith_decode(cinfo, st)) break;	/* EOB flag */
467    for (;;) {
468      thiscoef = *block + natural_order[k];
469      if (*thiscoef) {				/* previously nonzero coef */
470	if (arith_decode(cinfo, st + 2)) {
471	  if (*thiscoef < 0)
472	    *thiscoef += m1;
473	  else
474	    *thiscoef += p1;
475	}
476	break;
477      }
478      if (arith_decode(cinfo, st + 1)) {	/* newly nonzero coef */
479	if (arith_decode(cinfo, entropy->fixed_bin))
480	  *thiscoef = m1;
481	else
482	  *thiscoef = p1;
483	break;
484      }
485      st += 3; k++;
486      if (k > cinfo->Se) {
487	WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
488	entropy->ct = -1;			/* spectral overflow */
489	return TRUE;
490      }
491    }
492  }
493
494  return TRUE;
495}
496
497
498/*
499 * Decode one MCU's worth of arithmetic-compressed coefficients.
500 */
501
502METHODDEF(boolean)
503decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
504{
505  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
506  jpeg_component_info * compptr;
507  JBLOCKROW block;
508  unsigned char *st;
509  int blkn, ci, tbl, sign, k;
510  int v, m;
511  const int * natural_order;
512
513  /* Process restart marker if needed */
514  if (cinfo->restart_interval) {
515    if (entropy->restarts_to_go == 0)
516      process_restart(cinfo);
517    entropy->restarts_to_go--;
518  }
519
520  if (entropy->ct == -1) return TRUE;	/* if error do nothing */
521
522  natural_order = cinfo->natural_order;
523
524  /* Outer loop handles each block in the MCU */
525
526  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
527    block = MCU_data[blkn];
528    ci = cinfo->MCU_membership[blkn];
529    compptr = cinfo->cur_comp_info[ci];
530
531    /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
532
533    tbl = compptr->dc_tbl_no;
534
535    /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
536    st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
537
538    /* Figure F.19: Decode_DC_DIFF */
539    if (arith_decode(cinfo, st) == 0)
540      entropy->dc_context[ci] = 0;
541    else {
542      /* Figure F.21: Decoding nonzero value v */
543      /* Figure F.22: Decoding the sign of v */
544      sign = arith_decode(cinfo, st + 1);
545      st += 2; st += sign;
546      /* Figure F.23: Decoding the magnitude category of v */
547      if ((m = arith_decode(cinfo, st)) != 0) {
548	st = entropy->dc_stats[tbl] + 20;	/* Table F.4: X1 = 20 */
549	while (arith_decode(cinfo, st)) {
550	  if ((m <<= 1) == 0x8000) {
551	    WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
552	    entropy->ct = -1;			/* magnitude overflow */
553	    return TRUE;
554	  }
555	  st += 1;
556	}
557      }
558      /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
559      if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
560	entropy->dc_context[ci] = 0;		   /* zero diff category */
561      else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
562	entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
563      else
564	entropy->dc_context[ci] = 4 + (sign * 4);  /* small diff category */
565      v = m;
566      /* Figure F.24: Decoding the magnitude bit pattern of v */
567      st += 14;
568      while (m >>= 1)
569	if (arith_decode(cinfo, st)) v |= m;
570      v += 1; if (sign) v = -v;
571      entropy->last_dc_val[ci] += v;
572    }
573
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    if (cinfo->lim_Se == 0) continue;
579    tbl = compptr->ac_tbl_no;
580    k = 0;
581
582    /* Figure F.20: Decode_AC_coefficients */
583    do {
584      st = entropy->ac_stats[tbl] + 3 * k;
585      if (arith_decode(cinfo, st)) break;	/* EOB flag */
586      for (;;) {
587	k++;
588	if (arith_decode(cinfo, st + 1)) break;
589	st += 3;
590	if (k >= cinfo->lim_Se) {
591	  WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
592	  entropy->ct = -1;			/* spectral overflow */
593	  return TRUE;
594	}
595      }
596      /* Figure F.21: Decoding nonzero value v */
597      /* Figure F.22: Decoding the sign of v */
598      sign = arith_decode(cinfo, entropy->fixed_bin);
599      st += 2;
600      /* Figure F.23: Decoding the magnitude category of v */
601      if ((m = arith_decode(cinfo, st)) != 0) {
602	if (arith_decode(cinfo, st)) {
603	  m <<= 1;
604	  st = entropy->ac_stats[tbl] +
605	       (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
606	  while (arith_decode(cinfo, st)) {
607	    if ((m <<= 1) == 0x8000) {
608	      WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
609	      entropy->ct = -1;			/* magnitude overflow */
610	      return TRUE;
611	    }
612	    st += 1;
613	  }
614	}
615      }
616      v = m;
617      /* Figure F.24: Decoding the magnitude bit pattern of v */
618      st += 14;
619      while (m >>= 1)
620	if (arith_decode(cinfo, st)) v |= m;
621      v += 1; if (sign) v = -v;
622      (*block)[natural_order[k]] = (JCOEF) v;
623    } while (k < cinfo->lim_Se);
624  }
625
626  return TRUE;
627}
628
629
630/*
631 * Initialize for an arithmetic-compressed scan.
632 */
633
634METHODDEF(void)
635start_pass (j_decompress_ptr cinfo)
636{
637  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
638  int ci, tbl;
639  jpeg_component_info * compptr;
640
641  if (cinfo->progressive_mode) {
642    /* Validate progressive scan parameters */
643    if (cinfo->Ss == 0) {
644      if (cinfo->Se != 0)
645	goto bad;
646    } else {
647      /* need not check Ss/Se < 0 since they came from unsigned bytes */
648      if (cinfo->Se < cinfo->Ss || cinfo->Se > cinfo->lim_Se)
649	goto bad;
650      /* AC scans may have only one component */
651      if (cinfo->comps_in_scan != 1)
652	goto bad;
653    }
654    if (cinfo->Ah != 0) {
655      /* Successive approximation refinement scan: must have Al = Ah-1. */
656      if (cinfo->Ah-1 != cinfo->Al)
657	goto bad;
658    }
659    if (cinfo->Al > 13) {	/* need not check for < 0 */
660      bad:
661      ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
662	       cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
663    }
664    /* Update progression status, and verify that scan order is legal.
665     * Note that inter-scan inconsistencies are treated as warnings
666     * not fatal errors ... not clear if this is right way to behave.
667     */
668    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
669      int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
670      int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
671      if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
672	WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
673      for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
674	int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
675	if (cinfo->Ah != expected)
676	  WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
677	coef_bit_ptr[coefi] = cinfo->Al;
678      }
679    }
680    /* Select MCU decoding routine */
681    if (cinfo->Ah == 0) {
682      if (cinfo->Ss == 0)
683	entropy->pub.decode_mcu = decode_mcu_DC_first;
684      else
685	entropy->pub.decode_mcu = decode_mcu_AC_first;
686    } else {
687      if (cinfo->Ss == 0)
688	entropy->pub.decode_mcu = decode_mcu_DC_refine;
689      else
690	entropy->pub.decode_mcu = decode_mcu_AC_refine;
691    }
692  } else {
693    /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
694     * This ought to be an error condition, but we make it a warning.
695     */
696    if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
697	(cinfo->Se < DCTSIZE2 && cinfo->Se != cinfo->lim_Se))
698      WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
699    /* Select MCU decoding routine */
700    entropy->pub.decode_mcu = decode_mcu;
701  }
702
703  /* Allocate & initialize requested statistics areas */
704  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
705    compptr = cinfo->cur_comp_info[ci];
706    if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
707      tbl = compptr->dc_tbl_no;
708      if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
709	ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
710      if (entropy->dc_stats[tbl] == NULL)
711	entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
712	  ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
713      MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
714      /* Initialize DC predictions to 0 */
715      entropy->last_dc_val[ci] = 0;
716      entropy->dc_context[ci] = 0;
717    }
718    if ((! cinfo->progressive_mode && cinfo->lim_Se) ||
719	(cinfo->progressive_mode && cinfo->Ss)) {
720      tbl = compptr->ac_tbl_no;
721      if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
722	ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
723      if (entropy->ac_stats[tbl] == NULL)
724	entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
725	  ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
726      MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
727    }
728  }
729
730  /* Initialize arithmetic decoding variables */
731  entropy->c = 0;
732  entropy->a = 0;
733  entropy->ct = -16;	/* force reading 2 initial bytes to fill C */
734
735  /* Initialize restart counter */
736  entropy->restarts_to_go = cinfo->restart_interval;
737}
738
739
740/*
741 * Module initialization routine for arithmetic entropy decoding.
742 */
743
744GLOBAL(void)
745jinit_arith_decoder (j_decompress_ptr cinfo)
746{
747  arith_entropy_ptr entropy;
748  int i;
749
750  entropy = (arith_entropy_ptr)
751    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
752				SIZEOF(arith_entropy_decoder));
753  cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
754  entropy->pub.start_pass = start_pass;
755
756  /* Mark tables unallocated */
757  for (i = 0; i < NUM_ARITH_TBLS; i++) {
758    entropy->dc_stats[i] = NULL;
759    entropy->ac_stats[i] = NULL;
760  }
761
762  /* Initialize index for fixed probability estimation */
763  entropy->fixed_bin[0] = 113;
764
765  if (cinfo->progressive_mode) {
766    /* Create progression status table */
767    int *coef_bit_ptr, ci;
768    cinfo->coef_bits = (int (*)[DCTSIZE2])
769      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
770				  cinfo->num_components*DCTSIZE2*SIZEOF(int));
771    coef_bit_ptr = & cinfo->coef_bits[0][0];
772    for (ci = 0; ci < cinfo->num_components; ci++) 
773      for (i = 0; i < DCTSIZE2; i++)
774	*coef_bit_ptr++ = -1;
775  }
776}