jdarith.c revision 6eb7d3798b5a79347c62825fc4c16f7ce673bdd0 
1/*
2 * jdarith.c
3 *
4 * This file was part of the Independent JPEG Group's software:
5 * Developed 1997-2015 by Guido Vollbeding.
6 * libjpeg-turbo Modifications:
7 * Copyright (C) 2015-2016, D. R. Commander.
8 * For conditions of distribution and use, see the accompanying README.ijg
9 * file.
10 *
11 * This file contains portable arithmetic entropy decoding routines for JPEG
12 * (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81).
13 *
14 * Both sequential and progressive modes are supported in this single module.
15 *
16 * Suspension is not currently supported in this module.
17 */
18
19#define JPEG_INTERNALS
20#include "jinclude.h"
21#include "jpeglib.h"
22
23
24/* Expanded entropy decoder object for arithmetic decoding. */
25
26typedef struct {
27  struct jpeg_entropy_decoder pub; /* public fields */
28
29  JLONG c;       /* C register, base of coding interval + input bit buffer */
30  JLONG a;               /* A register, normalized size of coding interval */
31  int ct;     /* bit shift counter, # of bits left in bit buffer part of C */
32                                                         /* init: ct = -16 */
33                                                         /* run: ct = 0..7 */
34                                                         /* error: ct = -1 */
35  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
36  int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */
37
38  unsigned int restarts_to_go;  /* MCUs left in this restart interval */
39
40  /* Pointers to statistics areas (these workspaces have image lifespan) */
41  unsigned char *dc_stats[NUM_ARITH_TBLS];
42  unsigned char *ac_stats[NUM_ARITH_TBLS];
43
44  /* Statistics bin for coding with fixed probability 0.5 */
45  unsigned char fixed_bin[4];
46} arith_entropy_decoder;
47
48typedef arith_entropy_decoder *arith_entropy_ptr;
49
50/* The following two definitions specify the allocation chunk size
51 * for the statistics area.
52 * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least
53 * 49 statistics bins for DC, and 245 statistics bins for AC coding.
54 *
55 * We use a compact representation with 1 byte per statistics bin,
56 * thus the numbers directly represent byte sizes.
57 * This 1 byte per statistics bin contains the meaning of the MPS
58 * (more probable symbol) in the highest bit (mask 0x80), and the
59 * index into the probability estimation state machine table
60 * in the lower bits (mask 0x7F).
61 */
62
63#define DC_STAT_BINS 64
64#define AC_STAT_BINS 256
65
66
67LOCAL(int)
68get_byte (j_decompress_ptr cinfo)
69/* Read next input byte; we do not support suspension in this module. */
70{
71  struct jpeg_source_mgr *src = cinfo->src;
72
73  if (src->bytes_in_buffer == 0)
74    if (! (*src->fill_input_buffer) (cinfo))
75      ERREXIT(cinfo, JERR_CANT_SUSPEND);
76  src->bytes_in_buffer--;
77  return GETJOCTET(*src->next_input_byte++);
78}
79
80
81/*
82 * The core arithmetic decoding routine (common in JPEG and JBIG).
83 * This needs to go as fast as possible.
84 * Machine-dependent optimization facilities
85 * are not utilized in this portable implementation.
86 * However, this code should be fairly efficient and
87 * may be a good base for further optimizations anyway.
88 *
89 * Return value is 0 or 1 (binary decision).
90 *
91 * Note: I've changed the handling of the code base & bit
92 * buffer register C compared to other implementations
93 * based on the standards layout & procedures.
94 * While it also contains both the actual base of the
95 * coding interval (16 bits) and the next-bits buffer,
96 * the cut-point between these two parts is floating
97 * (instead of fixed) with the bit shift counter CT.
98 * Thus, we also need only one (variable instead of
99 * fixed size) shift for the LPS/MPS decision, and
100 * we can do away with any renormalization update
101 * of C (except for new data insertion, of course).
102 *
103 * I've also introduced a new scheme for accessing
104 * the probability estimation state machine table,
105 * derived from Markus Kuhn's JBIG implementation.
106 */
107
108LOCAL(int)
109arith_decode (j_decompress_ptr cinfo, unsigned char *st)
110{
111  register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;
112  register unsigned char nl, nm;
113  register JLONG qe, temp;
114  register int sv, data;
115
116  /* Renormalization & data input per section D.2.6 */
117  while (e->a < 0x8000L) {
118    if (--e->ct < 0) {
119      /* Need to fetch next data byte */
120      if (cinfo->unread_marker)
121        data = 0;               /* stuff zero data */
122      else {
123        data = get_byte(cinfo); /* read next input byte */
124        if (data == 0xFF) {     /* zero stuff or marker code */
125          do data = get_byte(cinfo);
126          while (data == 0xFF); /* swallow extra 0xFF bytes */
127          if (data == 0)
128            data = 0xFF;        /* discard stuffed zero byte */
129          else {
130            /* Note: Different from the Huffman decoder, hitting
131             * a marker while processing the compressed data
132             * segment is legal in arithmetic coding.
133             * The convention is to supply zero data
134             * then until decoding is complete.
135             */
136            cinfo->unread_marker = data;
137            data = 0;
138          }
139        }
140      }
141      e->c = (e->c << 8) | data; /* insert data into C register */
142      if ((e->ct += 8) < 0)      /* update bit shift counter */
143        /* Need more initial bytes */
144        if (++e->ct == 0)
145          /* Got 2 initial bytes -> re-init A and exit loop */
146          e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */
147    }
148    e->a <<= 1;
149  }
150
151  /* Fetch values from our compact representation of Table D.2:
152   * Qe values and probability estimation state machine
153   */
154  sv = *st;
155  qe = jpeg_aritab[sv & 0x7F];  /* => Qe_Value */
156  nl = qe & 0xFF; qe >>= 8;     /* Next_Index_LPS + Switch_MPS */
157  nm = qe & 0xFF; qe >>= 8;     /* Next_Index_MPS */
158
159  /* Decode & estimation procedures per sections D.2.4 & D.2.5 */
160  temp = e->a - qe;
161  e->a = temp;
162  temp <<= e->ct;
163  if (e->c >= temp) {
164    e->c -= temp;
165    /* Conditional LPS (less probable symbol) exchange */
166    if (e->a < qe) {
167      e->a = qe;
168      *st = (sv & 0x80) ^ nm;   /* Estimate_after_MPS */
169    } else {
170      e->a = qe;
171      *st = (sv & 0x80) ^ nl;   /* Estimate_after_LPS */
172      sv ^= 0x80;               /* Exchange LPS/MPS */
173    }
174  } else if (e->a < 0x8000L) {
175    /* Conditional MPS (more probable symbol) exchange */
176    if (e->a < qe) {
177      *st = (sv & 0x80) ^ nl;   /* Estimate_after_LPS */
178      sv ^= 0x80;               /* Exchange LPS/MPS */
179    } else {
180      *st = (sv & 0x80) ^ nm;   /* Estimate_after_MPS */
181    }
182  }
183
184  return sv >> 7;
185}
186
187
188/*
189 * Check for a restart marker & resynchronize decoder.
190 */
191
192LOCAL(void)
193process_restart (j_decompress_ptr cinfo)
194{
195  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
196  int ci;
197  jpeg_component_info *compptr;
198
199  /* Advance past the RSTn marker */
200  if (! (*cinfo->marker->read_restart_marker) (cinfo))
201    ERREXIT(cinfo, JERR_CANT_SUSPEND);
202
203  /* Re-initialize statistics areas */
204  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
205    compptr = cinfo->cur_comp_info[ci];
206    if (!cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
207      MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS);
208      /* Reset DC predictions to 0 */
209      entropy->last_dc_val[ci] = 0;
210      entropy->dc_context[ci] = 0;
211    }
212    if (!cinfo->progressive_mode || cinfo->Ss) {
213      MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS);
214    }
215  }
216
217  /* Reset arithmetic decoding variables */
218  entropy->c = 0;
219  entropy->a = 0;
220  entropy->ct = -16;    /* force reading 2 initial bytes to fill C */
221
222  /* Reset restart counter */
223  entropy->restarts_to_go = cinfo->restart_interval;
224}
225
226
227/*
228 * Arithmetic MCU decoding.
229 * Each of these routines decodes and returns one MCU's worth of
230 * arithmetic-compressed coefficients.
231 * The coefficients are reordered from zigzag order into natural array order,
232 * but are not dequantized.
233 *
234 * The i'th block of the MCU is stored into the block pointed to by
235 * MCU_data[i].  WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
236 */
237
238/*
239 * MCU decoding for DC initial scan (either spectral selection,
240 * or first pass of successive approximation).
241 */
242
243METHODDEF(boolean)
244decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
245{
246  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
247  JBLOCKROW block;
248  unsigned char *st;
249  int blkn, ci, tbl, sign;
250  int v, m;
251
252  /* Process restart marker if needed */
253  if (cinfo->restart_interval) {
254    if (entropy->restarts_to_go == 0)
255      process_restart(cinfo);
256    entropy->restarts_to_go--;
257  }
258
259  if (entropy->ct == -1) return TRUE;   /* if error do nothing */
260
261  /* Outer loop handles each block in the MCU */
262
263  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
264    block = MCU_data[blkn];
265    ci = cinfo->MCU_membership[blkn];
266    tbl = cinfo->cur_comp_info[ci]->dc_tbl_no;
267
268    /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
269
270    /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
271    st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
272
273    /* Figure F.19: Decode_DC_DIFF */
274    if (arith_decode(cinfo, st) == 0)
275      entropy->dc_context[ci] = 0;
276    else {
277      /* Figure F.21: Decoding nonzero value v */
278      /* Figure F.22: Decoding the sign of v */
279      sign = arith_decode(cinfo, st + 1);
280      st += 2; st += sign;
281      /* Figure F.23: Decoding the magnitude category of v */
282      if ((m = arith_decode(cinfo, st)) != 0) {
283        st = entropy->dc_stats[tbl] + 20;       /* Table F.4: X1 = 20 */
284        while (arith_decode(cinfo, st)) {
285          if ((m <<= 1) == 0x8000) {
286            WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
287            entropy->ct = -1;                   /* magnitude overflow */
288            return TRUE;
289          }
290          st += 1;
291        }
292      }
293      /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
294      if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
295        entropy->dc_context[ci] = 0;               /* zero diff category */
296      else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
297        entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
298      else
299        entropy->dc_context[ci] = 4 + (sign * 4);  /* small diff category */
300      v = m;
301      /* Figure F.24: Decoding the magnitude bit pattern of v */
302      st += 14;
303      while (m >>= 1)
304        if (arith_decode(cinfo, st)) v |= m;
305      v += 1; if (sign) v = -v;
306      entropy->last_dc_val[ci] += v;
307    }
308
309    /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */
310    (*block)[0] = (JCOEF) LEFT_SHIFT(entropy->last_dc_val[ci], cinfo->Al);
311  }
312
313  return TRUE;
314}
315
316
317/*
318 * MCU decoding for AC initial scan (either spectral selection,
319 * or first pass of successive approximation).
320 */
321
322METHODDEF(boolean)
323decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
324{
325  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
326  JBLOCKROW block;
327  unsigned char *st;
328  int tbl, sign, k;
329  int v, m;
330
331  /* Process restart marker if needed */
332  if (cinfo->restart_interval) {
333    if (entropy->restarts_to_go == 0)
334      process_restart(cinfo);
335    entropy->restarts_to_go--;
336  }
337
338  if (entropy->ct == -1) return TRUE;   /* if error do nothing */
339
340  /* There is always only one block per MCU */
341  block = MCU_data[0];
342  tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
343
344  /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
345
346  /* Figure F.20: Decode_AC_coefficients */
347  for (k = cinfo->Ss; k <= cinfo->Se; k++) {
348    st = entropy->ac_stats[tbl] + 3 * (k - 1);
349    if (arith_decode(cinfo, st)) break;         /* EOB flag */
350    while (arith_decode(cinfo, st + 1) == 0) {
351      st += 3; k++;
352      if (k > cinfo->Se) {
353        WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
354        entropy->ct = -1;                       /* spectral overflow */
355        return TRUE;
356      }
357    }
358    /* Figure F.21: Decoding nonzero value v */
359    /* Figure F.22: Decoding the sign of v */
360    sign = arith_decode(cinfo, entropy->fixed_bin);
361    st += 2;
362    /* Figure F.23: Decoding the magnitude category of v */
363    if ((m = arith_decode(cinfo, st)) != 0) {
364      if (arith_decode(cinfo, st)) {
365        m <<= 1;
366        st = entropy->ac_stats[tbl] +
367             (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
368        while (arith_decode(cinfo, st)) {
369          if ((m <<= 1) == 0x8000) {
370            WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
371            entropy->ct = -1;                   /* magnitude overflow */
372            return TRUE;
373          }
374          st += 1;
375        }
376      }
377    }
378    v = m;
379    /* Figure F.24: Decoding the magnitude bit pattern of v */
380    st += 14;
381    while (m >>= 1)
382      if (arith_decode(cinfo, st)) v |= m;
383    v += 1; if (sign) v = -v;
384    /* Scale and output coefficient in natural (dezigzagged) order */
385    (*block)[jpeg_natural_order[k]] = (JCOEF) ((unsigned)v << cinfo->Al);
386  }
387
388  return TRUE;
389}
390
391
392/*
393 * MCU decoding for DC successive approximation refinement scan.
394 */
395
396METHODDEF(boolean)
397decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
398{
399  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
400  unsigned char *st;
401  int p1, blkn;
402
403  /* Process restart marker if needed */
404  if (cinfo->restart_interval) {
405    if (entropy->restarts_to_go == 0)
406      process_restart(cinfo);
407    entropy->restarts_to_go--;
408  }
409
410  st = entropy->fixed_bin;      /* use fixed probability estimation */
411  p1 = 1 << cinfo->Al;          /* 1 in the bit position being coded */
412
413  /* Outer loop handles each block in the MCU */
414
415  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
416    /* Encoded data is simply the next bit of the two's-complement DC value */
417    if (arith_decode(cinfo, st))
418      MCU_data[blkn][0][0] |= p1;
419  }
420
421  return TRUE;
422}
423
424
425/*
426 * MCU decoding for AC successive approximation refinement scan.
427 */
428
429METHODDEF(boolean)
430decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
431{
432  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
433  JBLOCKROW block;
434  JCOEFPTR thiscoef;
435  unsigned char *st;
436  int tbl, k, kex;
437  int p1, m1;
438
439  /* Process restart marker if needed */
440  if (cinfo->restart_interval) {
441    if (entropy->restarts_to_go == 0)
442      process_restart(cinfo);
443    entropy->restarts_to_go--;
444  }
445
446  if (entropy->ct == -1) return TRUE;   /* if error do nothing */
447
448  /* There is always only one block per MCU */
449  block = MCU_data[0];
450  tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
451
452  p1 = 1 << cinfo->Al;          /* 1 in the bit position being coded */
453  m1 = (-1) << cinfo->Al;       /* -1 in the bit position being coded */
454
455  /* Establish EOBx (previous stage end-of-block) index */
456  for (kex = cinfo->Se; kex > 0; kex--)
457    if ((*block)[jpeg_natural_order[kex]]) break;
458
459  for (k = cinfo->Ss; k <= cinfo->Se; k++) {
460    st = entropy->ac_stats[tbl] + 3 * (k - 1);
461    if (k > kex)
462      if (arith_decode(cinfo, st)) break;       /* EOB flag */
463    for (;;) {
464      thiscoef = *block + jpeg_natural_order[k];
465      if (*thiscoef) {                          /* previously nonzero coef */
466        if (arith_decode(cinfo, st + 2)) {
467          if (*thiscoef < 0)
468            *thiscoef += m1;
469          else
470            *thiscoef += p1;
471        }
472        break;
473      }
474      if (arith_decode(cinfo, st + 1)) {        /* newly nonzero coef */
475        if (arith_decode(cinfo, entropy->fixed_bin))
476          *thiscoef = m1;
477        else
478          *thiscoef = p1;
479        break;
480      }
481      st += 3; k++;
482      if (k > cinfo->Se) {
483        WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
484        entropy->ct = -1;                       /* spectral overflow */
485        return TRUE;
486      }
487    }
488  }
489
490  return TRUE;
491}
492
493
494/*
495 * Decode one MCU's worth of arithmetic-compressed coefficients.
496 */
497
498METHODDEF(boolean)
499decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
500{
501  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
502  jpeg_component_info *compptr;
503  JBLOCKROW block;
504  unsigned char *st;
505  int blkn, ci, tbl, sign, k;
506  int v, m;
507
508  /* Process restart marker if needed */
509  if (cinfo->restart_interval) {
510    if (entropy->restarts_to_go == 0)
511      process_restart(cinfo);
512    entropy->restarts_to_go--;
513  }
514
515  if (entropy->ct == -1) return TRUE;   /* if error do nothing */
516
517  /* Outer loop handles each block in the MCU */
518
519  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
520    block = MCU_data ? MCU_data[blkn] : NULL;
521    ci = cinfo->MCU_membership[blkn];
522    compptr = cinfo->cur_comp_info[ci];
523
524    /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
525
526    tbl = compptr->dc_tbl_no;
527
528    /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
529    st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
530
531    /* Figure F.19: Decode_DC_DIFF */
532    if (arith_decode(cinfo, st) == 0)
533      entropy->dc_context[ci] = 0;
534    else {
535      /* Figure F.21: Decoding nonzero value v */
536      /* Figure F.22: Decoding the sign of v */
537      sign = arith_decode(cinfo, st + 1);
538      st += 2; st += sign;
539      /* Figure F.23: Decoding the magnitude category of v */
540      if ((m = arith_decode(cinfo, st)) != 0) {
541        st = entropy->dc_stats[tbl] + 20;       /* Table F.4: X1 = 20 */
542        while (arith_decode(cinfo, st)) {
543          if ((m <<= 1) == 0x8000) {
544            WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
545            entropy->ct = -1;                   /* magnitude overflow */
546            return TRUE;
547          }
548          st += 1;
549        }
550      }
551      /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
552      if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
553        entropy->dc_context[ci] = 0;               /* zero diff category */
554      else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
555        entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
556      else
557        entropy->dc_context[ci] = 4 + (sign * 4);  /* small diff category */
558      v = m;
559      /* Figure F.24: Decoding the magnitude bit pattern of v */
560      st += 14;
561      while (m >>= 1)
562        if (arith_decode(cinfo, st)) v |= m;
563      v += 1; if (sign) v = -v;
564      entropy->last_dc_val[ci] += v;
565    }
566
567    if (block)
568      (*block)[0] = (JCOEF) entropy->last_dc_val[ci];
569
570    /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
571
572    tbl = compptr->ac_tbl_no;
573
574    /* Figure F.20: Decode_AC_coefficients */
575    for (k = 1; k <= DCTSIZE2 - 1; k++) {
576      st = entropy->ac_stats[tbl] + 3 * (k - 1);
577      if (arith_decode(cinfo, st)) break;       /* EOB flag */
578      while (arith_decode(cinfo, st + 1) == 0) {
579        st += 3; k++;
580        if (k > DCTSIZE2 - 1) {
581          WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
582          entropy->ct = -1;                     /* spectral overflow */
583          return TRUE;
584        }
585      }
586      /* Figure F.21: Decoding nonzero value v */
587      /* Figure F.22: Decoding the sign of v */
588      sign = arith_decode(cinfo, entropy->fixed_bin);
589      st += 2;
590      /* Figure F.23: Decoding the magnitude category of v */
591      if ((m = arith_decode(cinfo, st)) != 0) {
592        if (arith_decode(cinfo, st)) {
593          m <<= 1;
594          st = entropy->ac_stats[tbl] +
595               (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
596          while (arith_decode(cinfo, st)) {
597            if ((m <<= 1) == 0x8000) {
598              WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
599              entropy->ct = -1;                 /* magnitude overflow */
600              return TRUE;
601            }
602            st += 1;
603          }
604        }
605      }
606      v = m;
607      /* Figure F.24: Decoding the magnitude bit pattern of v */
608      st += 14;
609      while (m >>= 1)
610        if (arith_decode(cinfo, st)) v |= m;
611      v += 1; if (sign) v = -v;
612      if (block)
613        (*block)[jpeg_natural_order[k]] = (JCOEF) v;
614    }
615  }
616
617  return TRUE;
618}
619
620
621/*
622 * Initialize for an arithmetic-compressed scan.
623 */
624
625METHODDEF(void)
626start_pass (j_decompress_ptr cinfo)
627{
628  arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
629  int ci, tbl;
630  jpeg_component_info *compptr;
631
632  if (cinfo->progressive_mode) {
633    /* Validate progressive scan parameters */
634    if (cinfo->Ss == 0) {
635      if (cinfo->Se != 0)
636        goto bad;
637    } else {
638      /* need not check Ss/Se < 0 since they came from unsigned bytes */
639      if (cinfo->Se < cinfo->Ss || cinfo->Se > DCTSIZE2 - 1)
640        goto bad;
641      /* AC scans may have only one component */
642      if (cinfo->comps_in_scan != 1)
643        goto bad;
644    }
645    if (cinfo->Ah != 0) {
646      /* Successive approximation refinement scan: must have Al = Ah-1. */
647      if (cinfo->Ah-1 != cinfo->Al)
648        goto bad;
649    }
650    if (cinfo->Al > 13) {       /* need not check for < 0 */
651      bad:
652      ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
653               cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
654    }
655    /* Update progression status, and verify that scan order is legal.
656     * Note that inter-scan inconsistencies are treated as warnings
657     * not fatal errors ... not clear if this is right way to behave.
658     */
659    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
660      int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
661      int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
662      if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
663        WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
664      for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
665        int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
666        if (cinfo->Ah != expected)
667          WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
668        coef_bit_ptr[coefi] = cinfo->Al;
669      }
670    }
671    /* Select MCU decoding routine */
672    if (cinfo->Ah == 0) {
673      if (cinfo->Ss == 0)
674        entropy->pub.decode_mcu = decode_mcu_DC_first;
675      else
676        entropy->pub.decode_mcu = decode_mcu_AC_first;
677    } else {
678      if (cinfo->Ss == 0)
679        entropy->pub.decode_mcu = decode_mcu_DC_refine;
680      else
681        entropy->pub.decode_mcu = decode_mcu_AC_refine;
682    }
683  } else {
684    /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
685     * This ought to be an error condition, but we make it a warning.
686     */
687    if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
688        (cinfo->Se < DCTSIZE2 && cinfo->Se != DCTSIZE2 - 1))
689      WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
690    /* Select MCU decoding routine */
691    entropy->pub.decode_mcu = decode_mcu;
692  }
693
694  /* Allocate & initialize requested statistics areas */
695  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
696    compptr = cinfo->cur_comp_info[ci];
697    if (!cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
698      tbl = compptr->dc_tbl_no;
699      if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
700        ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
701      if (entropy->dc_stats[tbl] == NULL)
702        entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
703          ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
704      MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
705      /* Initialize DC predictions to 0 */
706      entropy->last_dc_val[ci] = 0;
707      entropy->dc_context[ci] = 0;
708    }
709    if (!cinfo->progressive_mode || cinfo->Ss) {
710      tbl = compptr->ac_tbl_no;
711      if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
712        ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
713      if (entropy->ac_stats[tbl] == NULL)
714        entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
715          ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
716      MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
717    }
718  }
719
720  /* Initialize arithmetic decoding variables */
721  entropy->c = 0;
722  entropy->a = 0;
723  entropy->ct = -16;    /* force reading 2 initial bytes to fill C */
724
725  /* Initialize restart counter */
726  entropy->restarts_to_go = cinfo->restart_interval;
727}
728
729
730/*
731 * Module initialization routine for arithmetic entropy decoding.
732 */
733
734GLOBAL(void)
735jinit_arith_decoder (j_decompress_ptr cinfo)
736{
737  arith_entropy_ptr entropy;
738  int i;
739
740  entropy = (arith_entropy_ptr)
741    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
742                                sizeof(arith_entropy_decoder));
743  cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
744  entropy->pub.start_pass = start_pass;
745
746  /* Mark tables unallocated */
747  for (i = 0; i < NUM_ARITH_TBLS; i++) {
748    entropy->dc_stats[i] = NULL;
749    entropy->ac_stats[i] = NULL;
750  }
751
752  /* Initialize index for fixed probability estimation */
753  entropy->fixed_bin[0] = 113;
754
755  if (cinfo->progressive_mode) {
756    /* Create progression status table */
757    int *coef_bit_ptr, ci;
758    cinfo->coef_bits = (int (*)[DCTSIZE2])
759      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
760                                  cinfo->num_components*DCTSIZE2*sizeof(int));
761    coef_bit_ptr = & cinfo->coef_bits[0][0];
762    for (ci = 0; ci < cinfo->num_components; ci++)
763      for (i = 0; i < DCTSIZE2; i++)
764        *coef_bit_ptr++ = -1;
765  }
766}
767