4 * Developed 1997-2012 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.3(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 */
350 st = entropy->ac_stats[tbl] + 3 * k;
351 if (arith_decode(cinfo, st)) break; /* EOB flag */
354 if (arith_decode(cinfo, st + 1)) break;
356 if (k >= cinfo->Se) {
357 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
358 entropy->ct = -1; /* spectral overflow */
362 /* Figure F.21: Decoding nonzero value v */
363 /* Figure F.22: Decoding the sign of v */
364 sign = arith_decode(cinfo, entropy->fixed_bin);
366 /* Figure F.23: Decoding the magnitude category of v */
367 if ((m = arith_decode(cinfo, st)) != 0) {
368 if (arith_decode(cinfo, st)) {
370 st = entropy->ac_stats[tbl] +
371 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
372 while (arith_decode(cinfo, st)) {
373 if ((m <<= 1) == 0x8000) {
374 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
375 entropy->ct = -1; /* magnitude overflow */
383 /* Figure F.24: Decoding the magnitude bit pattern of v */
386 if (arith_decode(cinfo, st)) v |= m;
387 v += 1; if (sign) v = -v;
388 /* Scale and output coefficient in natural (dezigzagged) order */
389 (*block)[natural_order[k]] = (JCOEF) (v << cinfo->Al);
390 } while (k < cinfo->Se);
397 * MCU decoding for DC successive approximation refinement scan.
401 decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
403 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
407 /* Process restart marker if needed */
408 if (cinfo->restart_interval) {
409 if (entropy->restarts_to_go == 0)
410 process_restart(cinfo);
411 entropy->restarts_to_go--;
414 st = entropy->fixed_bin; /* use fixed probability estimation */
415 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
417 /* Outer loop handles each block in the MCU */
419 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
420 /* Encoded data is simply the next bit of the two's-complement DC value */
421 if (arith_decode(cinfo, st))
422 MCU_data[blkn][0][0] |= p1;
430 * MCU decoding for AC successive approximation refinement scan.
434 decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
436 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
442 const int * natural_order;
444 /* Process restart marker if needed */
445 if (cinfo->restart_interval) {
446 if (entropy->restarts_to_go == 0)
447 process_restart(cinfo);
448 entropy->restarts_to_go--;
451 if (entropy->ct == -1) return TRUE; /* if error do nothing */
453 natural_order = cinfo->natural_order;
455 /* There is always only one block per MCU */
457 tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
459 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
460 m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */
462 /* Establish EOBx (previous stage end-of-block) index */
465 if ((*block)[natural_order[kex]]) break;
470 st = entropy->ac_stats[tbl] + 3 * k;
472 if (arith_decode(cinfo, st)) break; /* EOB flag */
474 thiscoef = *block + natural_order[++k];
475 if (*thiscoef) { /* previously nonzero coef */
476 if (arith_decode(cinfo, st + 2)) {
484 if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */
485 if (arith_decode(cinfo, entropy->fixed_bin))
492 if (k >= cinfo->Se) {
493 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
494 entropy->ct = -1; /* spectral overflow */
498 } while (k < cinfo->Se);
505 * Decode one MCU's worth of arithmetic-compressed coefficients.
509 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
511 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
512 jpeg_component_info * compptr;
515 int blkn, ci, tbl, sign, k;
517 const int * natural_order;
519 /* Process restart marker if needed */
520 if (cinfo->restart_interval) {
521 if (entropy->restarts_to_go == 0)
522 process_restart(cinfo);
523 entropy->restarts_to_go--;
526 if (entropy->ct == -1) return TRUE; /* if error do nothing */
528 natural_order = cinfo->natural_order;
530 /* Outer loop handles each block in the MCU */
532 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
533 block = MCU_data[blkn];
534 ci = cinfo->MCU_membership[blkn];
535 compptr = cinfo->cur_comp_info[ci];
537 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
539 tbl = compptr->dc_tbl_no;
541 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
542 st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
544 /* Figure F.19: Decode_DC_DIFF */
545 if (arith_decode(cinfo, st) == 0)
546 entropy->dc_context[ci] = 0;
548 /* Figure F.21: Decoding nonzero value v */
549 /* Figure F.22: Decoding the sign of v */
550 sign = arith_decode(cinfo, st + 1);
552 /* Figure F.23: Decoding the magnitude category of v */
553 if ((m = arith_decode(cinfo, st)) != 0) {
554 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
555 while (arith_decode(cinfo, st)) {
556 if ((m <<= 1) == 0x8000) {
557 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
558 entropy->ct = -1; /* magnitude overflow */
564 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
565 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
566 entropy->dc_context[ci] = 0; /* zero diff category */
567 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
568 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
570 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
572 /* Figure F.24: Decoding the magnitude bit pattern of v */
575 if (arith_decode(cinfo, st)) v |= m;
576 v += 1; if (sign) v = -v;
577 entropy->last_dc_val[ci] += v;
580 (*block)[0] = (JCOEF) entropy->last_dc_val[ci];
582 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
584 if (cinfo->lim_Se == 0) continue;
585 tbl = compptr->ac_tbl_no;
588 /* Figure F.20: Decode_AC_coefficients */
590 st = entropy->ac_stats[tbl] + 3 * k;
591 if (arith_decode(cinfo, st)) break; /* EOB flag */
594 if (arith_decode(cinfo, st + 1)) break;
596 if (k >= cinfo->lim_Se) {
597 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
598 entropy->ct = -1; /* spectral overflow */
602 /* Figure F.21: Decoding nonzero value v */
603 /* Figure F.22: Decoding the sign of v */
604 sign = arith_decode(cinfo, entropy->fixed_bin);
606 /* Figure F.23: Decoding the magnitude category of v */
607 if ((m = arith_decode(cinfo, st)) != 0) {
608 if (arith_decode(cinfo, st)) {
610 st = entropy->ac_stats[tbl] +
611 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
612 while (arith_decode(cinfo, st)) {
613 if ((m <<= 1) == 0x8000) {
614 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
615 entropy->ct = -1; /* magnitude overflow */
623 /* Figure F.24: Decoding the magnitude bit pattern of v */
626 if (arith_decode(cinfo, st)) v |= m;
627 v += 1; if (sign) v = -v;
628 (*block)[natural_order[k]] = (JCOEF) v;
629 } while (k < cinfo->lim_Se);
637 * Initialize for an arithmetic-compressed scan.
641 start_pass (j_decompress_ptr cinfo)
643 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
645 jpeg_component_info * compptr;
647 if (cinfo->progressive_mode) {
648 /* Validate progressive scan parameters */
649 if (cinfo->Ss == 0) {
653 /* need not check Ss/Se < 0 since they came from unsigned bytes */
654 if (cinfo->Se < cinfo->Ss || cinfo->Se > cinfo->lim_Se)
656 /* AC scans may have only one component */
657 if (cinfo->comps_in_scan != 1)
660 if (cinfo->Ah != 0) {
661 /* Successive approximation refinement scan: must have Al = Ah-1. */
662 if (cinfo->Ah-1 != cinfo->Al)
665 if (cinfo->Al > 13) { /* need not check for < 0 */
667 ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
668 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
670 /* Update progression status, and verify that scan order is legal.
671 * Note that inter-scan inconsistencies are treated as warnings
672 * not fatal errors ... not clear if this is right way to behave.
674 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
675 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
676 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
677 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
678 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
679 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
680 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
681 if (cinfo->Ah != expected)
682 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
683 coef_bit_ptr[coefi] = cinfo->Al;
686 /* Select MCU decoding routine */
687 if (cinfo->Ah == 0) {
689 entropy->pub.decode_mcu = decode_mcu_DC_first;
691 entropy->pub.decode_mcu = decode_mcu_AC_first;
694 entropy->pub.decode_mcu = decode_mcu_DC_refine;
696 entropy->pub.decode_mcu = decode_mcu_AC_refine;
699 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
700 * This ought to be an error condition, but we make it a warning.
702 if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
703 (cinfo->Se < DCTSIZE2 && cinfo->Se != cinfo->lim_Se))
704 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
705 /* Select MCU decoding routine */
706 entropy->pub.decode_mcu = decode_mcu;
709 /* Allocate & initialize requested statistics areas */
710 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
711 compptr = cinfo->cur_comp_info[ci];
712 if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
713 tbl = compptr->dc_tbl_no;
714 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
715 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
716 if (entropy->dc_stats[tbl] == NULL)
717 entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
718 ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
719 MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
720 /* Initialize DC predictions to 0 */
721 entropy->last_dc_val[ci] = 0;
722 entropy->dc_context[ci] = 0;
724 if ((! cinfo->progressive_mode && cinfo->lim_Se) ||
725 (cinfo->progressive_mode && cinfo->Ss)) {
726 tbl = compptr->ac_tbl_no;
727 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
728 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
729 if (entropy->ac_stats[tbl] == NULL)
730 entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
731 ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
732 MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
736 /* Initialize arithmetic decoding variables */
739 entropy->ct = -16; /* force reading 2 initial bytes to fill C */
741 /* Initialize restart counter */
742 entropy->restarts_to_go = cinfo->restart_interval;
747 * Module initialization routine for arithmetic entropy decoding.
751 jinit_arith_decoder (j_decompress_ptr cinfo)
753 arith_entropy_ptr entropy;
756 entropy = (arith_entropy_ptr)
757 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
758 SIZEOF(arith_entropy_decoder));
759 cinfo->entropy = &entropy->pub;
760 entropy->pub.start_pass = start_pass;
762 /* Mark tables unallocated */
763 for (i = 0; i < NUM_ARITH_TBLS; i++) {
764 entropy->dc_stats[i] = NULL;
765 entropy->ac_stats[i] = NULL;
768 /* Initialize index for fixed probability estimation */
769 entropy->fixed_bin[0] = 113;
771 if (cinfo->progressive_mode) {
772 /* Create progression status table */
773 int *coef_bit_ptr, ci;
774 cinfo->coef_bits = (int (*)[DCTSIZE2])
775 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
776 cinfo->num_components*DCTSIZE2*SIZEOF(int));
777 coef_bit_ptr = & cinfo->coef_bits[0][0];
778 for (ci = 0; ci < cinfo->num_components; ci++)
779 for (i = 0; i < DCTSIZE2; i++)
780 *coef_bit_ptr++ = -1;