4
* Developed 1997-2009 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.
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).
11
* Both sequential and progressive modes are supported in this single module.
13
* Suspension is not currently supported in this module.
16
#define JPEG_INTERNALS
21
/* Expanded entropy decoder object for arithmetic decoding. */
24
struct jpeg_entropy_decoder pub; /* public fields */
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 */
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 */
35
unsigned int restarts_to_go; /* MCUs left in this restart interval */
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];
41
/* Statistics bin for coding with fixed probability 0.5 */
42
unsigned char fixed_bin[4];
43
} arith_entropy_decoder;
45
typedef arith_entropy_decoder * arith_entropy_ptr;
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.
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).
60
#define DC_STAT_BINS 64
61
#define AC_STAT_BINS 256
65
get_byte (j_decompress_ptr cinfo)
66
/* Read next input byte; we do not support suspension in this module. */
68
struct jpeg_source_mgr * src = cinfo->src;
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++);
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.
86
* Return value is 0 or 1 (binary decision).
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).
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.
106
arith_decode (j_decompress_ptr cinfo, unsigned char *st)
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;
113
/* Renormalization & data input per section D.2.6 */
114
while (e->a < 0x8000L) {
116
/* Need to fetch next data byte */
117
if (cinfo->unread_marker)
118
data = 0; /* stuff zero data */
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 */
125
data = 0xFF; /* discard stuffed zero byte */
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.
133
cinfo->unread_marker = data;
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 */
142
/* Got 2 initial bytes -> re-init A and exit loop */
143
e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */
148
/* Fetch values from our compact representation of Table D.2:
149
* Qe values and probability estimation state machine
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 */
156
/* Decode & estimation procedures per sections D.2.4 & D.2.5 */
162
/* Conditional LPS (less probable symbol) exchange */
165
*st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
168
*st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
169
sv ^= 0x80; /* Exchange LPS/MPS */
171
} else if (e->a < 0x8000L) {
172
/* Conditional MPS (more probable symbol) exchange */
174
*st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
175
sv ^= 0x80; /* Exchange LPS/MPS */
177
*st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
186
* Check for a restart marker & resynchronize decoder.
190
process_restart (j_decompress_ptr cinfo)
192
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
194
jpeg_component_info * compptr;
196
/* Advance past the RSTn marker */
197
if (! (*cinfo->marker->read_restart_marker) (cinfo))
198
ERREXIT(cinfo, JERR_CANT_SUSPEND);
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;
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);
215
/* Reset arithmetic decoding variables */
218
entropy->ct = -16; /* force reading 2 initial bytes to fill C */
220
/* Reset restart counter */
221
entropy->restarts_to_go = cinfo->restart_interval;
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.
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.
237
* MCU decoding for DC initial scan (either spectral selection,
238
* or first pass of successive approximation).
242
decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
244
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
247
int blkn, ci, tbl, sign;
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--;
257
if (entropy->ct == -1) return TRUE; /* if error do nothing */
259
/* Outer loop handles each block in the MCU */
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;
266
/* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
268
/* Table F.4: Point to statistics bin S0 for DC coefficient coding */
269
st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
271
/* Figure F.19: Decode_DC_DIFF */
272
if (arith_decode(cinfo, st) == 0)
273
entropy->dc_context[ci] = 0;
275
/* Figure F.21: Decoding nonzero value v */
276
/* Figure F.22: Decoding the sign of v */
277
sign = arith_decode(cinfo, st + 1);
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 */
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 */
297
entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
299
/* Figure F.24: Decoding the magnitude bit pattern of v */
302
if (arith_decode(cinfo, st)) v |= m;
303
v += 1; if (sign) v = -v;
304
entropy->last_dc_val[ci] += v;
307
/* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */
308
(*block)[0] = (JCOEF) (entropy->last_dc_val[ci] << cinfo->Al);
316
* MCU decoding for AC initial scan (either spectral selection,
317
* or first pass of successive approximation).
321
decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
323
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
328
const int * natural_order;
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--;
337
if (entropy->ct == -1) return TRUE; /* if error do nothing */
339
natural_order = cinfo->natural_order;
341
/* There is always only one block per MCU */
343
tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
345
/* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
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) {
354
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
355
entropy->ct = -1; /* spectral overflow */
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);
363
/* Figure F.23: Decoding the magnitude category of v */
364
if ((m = arith_decode(cinfo, st)) != 0) {
365
if (arith_decode(cinfo, st)) {
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 */
380
/* Figure F.24: Decoding the magnitude bit pattern of v */
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);
394
* MCU decoding for DC successive approximation refinement scan.
398
decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
400
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
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--;
411
st = entropy->fixed_bin; /* use fixed probability estimation */
412
p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
414
/* Outer loop handles each block in the MCU */
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;
427
* MCU decoding for AC successive approximation refinement scan.
431
decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
433
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
439
const int * natural_order;
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--;
448
if (entropy->ct == -1) return TRUE; /* if error do nothing */
450
natural_order = cinfo->natural_order;
452
/* There is always only one block per MCU */
454
tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
456
p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
457
m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */
459
/* Establish EOBx (previous stage end-of-block) index */
460
for (kex = cinfo->Se; kex > 0; kex--)
461
if ((*block)[natural_order[kex]]) break;
463
for (k = cinfo->Ss; k <= cinfo->Se; k++) {
464
st = entropy->ac_stats[tbl] + 3 * (k - 1);
466
if (arith_decode(cinfo, st)) break; /* EOB flag */
468
thiscoef = *block + natural_order[k];
469
if (*thiscoef) { /* previously nonzero coef */
470
if (arith_decode(cinfo, st + 2)) {
478
if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */
479
if (arith_decode(cinfo, entropy->fixed_bin))
487
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
488
entropy->ct = -1; /* spectral overflow */
499
* Decode one MCU's worth of arithmetic-compressed coefficients.
503
decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
505
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
506
jpeg_component_info * compptr;
509
int blkn, ci, tbl, sign, k;
511
const int * natural_order;
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--;
520
if (entropy->ct == -1) return TRUE; /* if error do nothing */
522
natural_order = cinfo->natural_order;
524
/* Outer loop handles each block in the MCU */
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];
531
/* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
533
tbl = compptr->dc_tbl_no;
535
/* Table F.4: Point to statistics bin S0 for DC coefficient coding */
536
st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
538
/* Figure F.19: Decode_DC_DIFF */
539
if (arith_decode(cinfo, st) == 0)
540
entropy->dc_context[ci] = 0;
542
/* Figure F.21: Decoding nonzero value v */
543
/* Figure F.22: Decoding the sign of v */
544
sign = arith_decode(cinfo, st + 1);
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 */
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 */
564
entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
566
/* Figure F.24: Decoding the magnitude bit pattern of v */
569
if (arith_decode(cinfo, st)) v |= m;
570
v += 1; if (sign) v = -v;
571
entropy->last_dc_val[ci] += v;
574
(*block)[0] = (JCOEF) entropy->last_dc_val[ci];
576
/* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
578
tbl = compptr->ac_tbl_no;
580
/* Figure F.20: Decode_AC_coefficients */
581
for (k = 1; k <= cinfo->lim_Se; 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) {
586
if (k > cinfo->lim_Se) {
587
WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
588
entropy->ct = -1; /* spectral overflow */
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);
596
/* Figure F.23: Decoding the magnitude category of v */
597
if ((m = arith_decode(cinfo, st)) != 0) {
598
if (arith_decode(cinfo, st)) {
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 */
613
/* Figure F.24: Decoding the magnitude bit pattern of v */
616
if (arith_decode(cinfo, st)) v |= m;
617
v += 1; if (sign) v = -v;
618
(*block)[natural_order[k]] = (JCOEF) v;
627
* Initialize for an arithmetic-compressed scan.
631
start_pass (j_decompress_ptr cinfo)
633
arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
635
jpeg_component_info * compptr;
637
if (cinfo->progressive_mode) {
638
/* Validate progressive scan parameters */
639
if (cinfo->Ss == 0) {
643
/* need not check Ss/Se < 0 since they came from unsigned bytes */
644
if (cinfo->Se < cinfo->Ss || cinfo->Se > cinfo->lim_Se)
646
/* AC scans may have only one component */
647
if (cinfo->comps_in_scan != 1)
650
if (cinfo->Ah != 0) {
651
/* Successive approximation refinement scan: must have Al = Ah-1. */
652
if (cinfo->Ah-1 != cinfo->Al)
655
if (cinfo->Al > 13) { /* need not check for < 0 */
657
ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
658
cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
660
/* Update progression status, and verify that scan order is legal.
661
* Note that inter-scan inconsistencies are treated as warnings
662
* not fatal errors ... not clear if this is right way to behave.
664
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
665
int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
666
int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
667
if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
668
WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
669
for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
670
int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
671
if (cinfo->Ah != expected)
672
WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
673
coef_bit_ptr[coefi] = cinfo->Al;
676
/* Select MCU decoding routine */
677
if (cinfo->Ah == 0) {
679
entropy->pub.decode_mcu = decode_mcu_DC_first;
681
entropy->pub.decode_mcu = decode_mcu_AC_first;
684
entropy->pub.decode_mcu = decode_mcu_DC_refine;
686
entropy->pub.decode_mcu = decode_mcu_AC_refine;
689
/* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
690
* This ought to be an error condition, but we make it a warning.
692
if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
693
(cinfo->Se < DCTSIZE2 && cinfo->Se != cinfo->lim_Se))
694
WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
695
/* Select MCU decoding routine */
696
entropy->pub.decode_mcu = decode_mcu;
699
/* Allocate & initialize requested statistics areas */
700
for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
701
compptr = cinfo->cur_comp_info[ci];
702
if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
703
tbl = compptr->dc_tbl_no;
704
if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
705
ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
706
if (entropy->dc_stats[tbl] == NULL)
707
entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
708
((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
709
MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
710
/* Initialize DC predictions to 0 */
711
entropy->last_dc_val[ci] = 0;
712
entropy->dc_context[ci] = 0;
714
if ((! cinfo->progressive_mode && cinfo->lim_Se) ||
715
(cinfo->progressive_mode && cinfo->Ss)) {
716
tbl = compptr->ac_tbl_no;
717
if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
718
ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
719
if (entropy->ac_stats[tbl] == NULL)
720
entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
721
((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
722
MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
726
/* Initialize arithmetic decoding variables */
729
entropy->ct = -16; /* force reading 2 initial bytes to fill C */
731
/* Initialize restart counter */
732
entropy->restarts_to_go = cinfo->restart_interval;
737
* Module initialization routine for arithmetic entropy decoding.
741
jinit_arith_decoder (j_decompress_ptr cinfo)
743
arith_entropy_ptr entropy;
746
entropy = (arith_entropy_ptr)
747
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
748
SIZEOF(arith_entropy_decoder));
749
cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
750
entropy->pub.start_pass = start_pass;
752
/* Mark tables unallocated */
753
for (i = 0; i < NUM_ARITH_TBLS; i++) {
754
entropy->dc_stats[i] = NULL;
755
entropy->ac_stats[i] = NULL;
758
/* Initialize index for fixed probability estimation */
759
entropy->fixed_bin[0] = 113;
761
if (cinfo->progressive_mode) {
762
/* Create progression status table */
763
int *coef_bit_ptr, ci;
764
cinfo->coef_bits = (int (*)[DCTSIZE2])
765
(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
766
cinfo->num_components*DCTSIZE2*SIZEOF(int));
767
coef_bit_ptr = & cinfo->coef_bits[0][0];
768
for (ci = 0; ci < cinfo->num_components; ci++)
769
for (i = 0; i < DCTSIZE2; i++)
770
*coef_bit_ptr++ = -1;