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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1:1d09e1dec1d9 2:b50eed0cc0ef
1 /*
2 * jdarith.c
3 *
4 * Developed 1997-2020 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
23 typedef 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
45 typedef 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
64 LOCAL(int)
65 get_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 do 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
105 LOCAL(int)
106 arith_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 = (unsigned char)(qe & 0xFF); qe >>= 8; /* Next_Index_LPS + Switch_MPS */
154 nm = (unsigned char)(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
189 LOCAL(void)
190 process_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
241 METHODDEF(boolean)
242 decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKARRAY 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) == (int) 0x8000U) {
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
320 METHODDEF(boolean)
321 decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKARRAY 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 k = cinfo->Ss - 1;
349 do {
350 st = entropy->ac_stats[tbl] + 3 * k;
351 if (arith_decode(cinfo, st)) break; /* EOB flag */
352 for (;;) {
353 k++;
354 if (arith_decode(cinfo, st + 1)) break;
355 st += 3;
356 if (k >= cinfo->Se) {
357 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
358 entropy->ct = -1; /* spectral overflow */
359 return TRUE;
360 }
361 }
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);
365 st += 2;
366 /* Figure F.23: Decoding the magnitude category of v */
367 if ((m = arith_decode(cinfo, st)) != 0) {
368 if (arith_decode(cinfo, st)) {
369 m <<= 1;
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) == (int) 0x8000U) {
374 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
375 entropy->ct = -1; /* magnitude overflow */
376 return TRUE;
377 }
378 st += 1;
379 }
380 }
381 }
382 v = m;
383 /* Figure F.24: Decoding the magnitude bit pattern of v */
384 st += 14;
385 while (m >>= 1)
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);
391
392 return TRUE;
393 }
394
395
396 /*
397 * MCU decoding for DC successive approximation refinement scan.
398 * Note: we assume such scans can be multi-component,
399 * although the spec is not very clear on the point.
400 */
401
402 METHODDEF(boolean)
403 decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKARRAY MCU_data)
404 {
405 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
406 unsigned char *st;
407 JCOEF p1;
408 int blkn;
409
410 /* Process restart marker if needed */
411 if (cinfo->restart_interval) {
412 if (entropy->restarts_to_go == 0)
413 process_restart(cinfo);
414 entropy->restarts_to_go--;
415 }
416
417 st = entropy->fixed_bin; /* use fixed probability estimation */
418 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
419
420 /* Outer loop handles each block in the MCU */
421
422 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
423 /* Encoded data is simply the next bit of the two's-complement DC value */
424 if (arith_decode(cinfo, st))
425 MCU_data[blkn][0][0] |= p1;
426 }
427
428 return TRUE;
429 }
430
431
432 /*
433 * MCU decoding for AC successive approximation refinement scan.
434 */
435
436 METHODDEF(boolean)
437 decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKARRAY MCU_data)
438 {
439 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
440 JBLOCKROW block;
441 JCOEFPTR thiscoef;
442 unsigned char *st;
443 int tbl, k, kex;
444 JCOEF p1, m1;
445 const int * natural_order;
446
447 /* Process restart marker if needed */
448 if (cinfo->restart_interval) {
449 if (entropy->restarts_to_go == 0)
450 process_restart(cinfo);
451 entropy->restarts_to_go--;
452 }
453
454 if (entropy->ct == -1) return TRUE; /* if error do nothing */
455
456 natural_order = cinfo->natural_order;
457
458 /* There is always only one block per MCU */
459 block = MCU_data[0];
460 tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
461
462 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
463 m1 = -p1; /* -1 in the bit position being coded */
464
465 /* Establish EOBx (previous stage end-of-block) index */
466 kex = cinfo->Se;
467 do {
468 if ((*block)[natural_order[kex]]) break;
469 } while (--kex);
470
471 k = cinfo->Ss - 1;
472 do {
473 st = entropy->ac_stats[tbl] + 3 * k;
474 if (k >= kex)
475 if (arith_decode(cinfo, st)) break; /* EOB flag */
476 for (;;) {
477 thiscoef = *block + natural_order[++k];
478 if (*thiscoef) { /* previously nonzero coef */
479 if (arith_decode(cinfo, st + 2)) {
480 if (*thiscoef < 0)
481 *thiscoef += m1;
482 else
483 *thiscoef += p1;
484 }
485 break;
486 }
487 if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */
488 if (arith_decode(cinfo, entropy->fixed_bin))
489 *thiscoef = m1;
490 else
491 *thiscoef = p1;
492 break;
493 }
494 st += 3;
495 if (k >= cinfo->Se) {
496 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
497 entropy->ct = -1; /* spectral overflow */
498 return TRUE;
499 }
500 }
501 } while (k < cinfo->Se);
502
503 return TRUE;
504 }
505
506
507 /*
508 * Decode one MCU's worth of arithmetic-compressed coefficients.
509 */
510
511 METHODDEF(boolean)
512 decode_mcu (j_decompress_ptr cinfo, JBLOCKARRAY MCU_data)
513 {
514 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
515 jpeg_component_info * compptr;
516 JBLOCKROW block;
517 unsigned char *st;
518 int blkn, ci, tbl, sign, k;
519 int v, m;
520 const int * natural_order;
521
522 /* Process restart marker if needed */
523 if (cinfo->restart_interval) {
524 if (entropy->restarts_to_go == 0)
525 process_restart(cinfo);
526 entropy->restarts_to_go--;
527 }
528
529 if (entropy->ct == -1) return TRUE; /* if error do nothing */
530
531 natural_order = cinfo->natural_order;
532
533 /* Outer loop handles each block in the MCU */
534
535 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
536 block = MCU_data[blkn];
537 ci = cinfo->MCU_membership[blkn];
538 compptr = cinfo->cur_comp_info[ci];
539
540 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
541
542 tbl = compptr->dc_tbl_no;
543
544 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
545 st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
546
547 /* Figure F.19: Decode_DC_DIFF */
548 if (arith_decode(cinfo, st) == 0)
549 entropy->dc_context[ci] = 0;
550 else {
551 /* Figure F.21: Decoding nonzero value v */
552 /* Figure F.22: Decoding the sign of v */
553 sign = arith_decode(cinfo, st + 1);
554 st += 2; st += sign;
555 /* Figure F.23: Decoding the magnitude category of v */
556 if ((m = arith_decode(cinfo, st)) != 0) {
557 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
558 while (arith_decode(cinfo, st)) {
559 if ((m <<= 1) == (int) 0x8000U) {
560 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
561 entropy->ct = -1; /* magnitude overflow */
562 return TRUE;
563 }
564 st += 1;
565 }
566 }
567 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
568 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
569 entropy->dc_context[ci] = 0; /* zero diff category */
570 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
571 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
572 else
573 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
574 v = m;
575 /* Figure F.24: Decoding the magnitude bit pattern of v */
576 st += 14;
577 while (m >>= 1)
578 if (arith_decode(cinfo, st)) v |= m;
579 v += 1; if (sign) v = -v;
580 entropy->last_dc_val[ci] += v;
581 }
582
583 (*block)[0] = (JCOEF) entropy->last_dc_val[ci];
584
585 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
586
587 if (cinfo->lim_Se == 0) continue;
588 tbl = compptr->ac_tbl_no;
589 k = 0;
590
591 /* Figure F.20: Decode_AC_coefficients */
592 do {
593 st = entropy->ac_stats[tbl] + 3 * k;
594 if (arith_decode(cinfo, st)) break; /* EOB flag */
595 for (;;) {
596 k++;
597 if (arith_decode(cinfo, st + 1)) break;
598 st += 3;
599 if (k >= cinfo->lim_Se) {
600 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
601 entropy->ct = -1; /* spectral overflow */
602 return TRUE;
603 }
604 }
605 /* Figure F.21: Decoding nonzero value v */
606 /* Figure F.22: Decoding the sign of v */
607 sign = arith_decode(cinfo, entropy->fixed_bin);
608 st += 2;
609 /* Figure F.23: Decoding the magnitude category of v */
610 if ((m = arith_decode(cinfo, st)) != 0) {
611 if (arith_decode(cinfo, st)) {
612 m <<= 1;
613 st = entropy->ac_stats[tbl] +
614 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
615 while (arith_decode(cinfo, st)) {
616 if ((m <<= 1) == (int) 0x8000U) {
617 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
618 entropy->ct = -1; /* magnitude overflow */
619 return TRUE;
620 }
621 st += 1;
622 }
623 }
624 }
625 v = m;
626 /* Figure F.24: Decoding the magnitude bit pattern of v */
627 st += 14;
628 while (m >>= 1)
629 if (arith_decode(cinfo, st)) v |= m;
630 v += 1; if (sign) v = -v;
631 (*block)[natural_order[k]] = (JCOEF) v;
632 } while (k < cinfo->lim_Se);
633 }
634
635 return TRUE;
636 }
637
638
639 /*
640 * Initialize for an arithmetic-compressed scan.
641 */
642
643 METHODDEF(void)
644 start_pass (j_decompress_ptr cinfo)
645 {
646 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
647 int ci, tbl;
648 jpeg_component_info * compptr;
649
650 if (cinfo->progressive_mode) {
651 /* Validate progressive scan parameters */
652 if (cinfo->Ss == 0) {
653 if (cinfo->Se != 0)
654 goto bad;
655 } else {
656 /* need not check Ss/Se < 0 since they came from unsigned bytes */
657 if (cinfo->Se < cinfo->Ss || cinfo->Se > cinfo->lim_Se)
658 goto bad;
659 /* AC scans may have only one component */
660 if (cinfo->comps_in_scan != 1)
661 goto bad;
662 }
663 if (cinfo->Ah != 0) {
664 /* Successive approximation refinement scan: must have Al = Ah-1. */
665 if (cinfo->Ah-1 != cinfo->Al)
666 goto bad;
667 }
668 if (cinfo->Al > 13) { /* need not check for < 0 */
669 bad:
670 ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
671 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
672 }
673 /* Update progression status, and verify that scan order is legal.
674 * Note that inter-scan inconsistencies are treated as warnings
675 * not fatal errors ... not clear if this is right way to behave.
676 */
677 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
678 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
679 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
680 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
681 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
682 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
683 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
684 if (cinfo->Ah != expected)
685 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
686 coef_bit_ptr[coefi] = cinfo->Al;
687 }
688 }
689 /* Select MCU decoding routine */
690 if (cinfo->Ah == 0) {
691 if (cinfo->Ss == 0)
692 entropy->pub.decode_mcu = decode_mcu_DC_first;
693 else
694 entropy->pub.decode_mcu = decode_mcu_AC_first;
695 } else {
696 if (cinfo->Ss == 0)
697 entropy->pub.decode_mcu = decode_mcu_DC_refine;
698 else
699 entropy->pub.decode_mcu = decode_mcu_AC_refine;
700 }
701 } else {
702 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
703 * This ought to be an error condition, but we make it a warning.
704 */
705 if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
706 (cinfo->Se < DCTSIZE2 && cinfo->Se != cinfo->lim_Se))
707 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
708 /* Select MCU decoding routine */
709 entropy->pub.decode_mcu = decode_mcu;
710 }
711
712 /* Allocate & initialize requested statistics areas */
713 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
714 compptr = cinfo->cur_comp_info[ci];
715 if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
716 tbl = compptr->dc_tbl_no;
717 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
718 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
719 if (entropy->dc_stats[tbl] == NULL)
720 entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
721 ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
722 MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
723 /* Initialize DC predictions to 0 */
724 entropy->last_dc_val[ci] = 0;
725 entropy->dc_context[ci] = 0;
726 }
727 if ((! cinfo->progressive_mode && cinfo->lim_Se) ||
728 (cinfo->progressive_mode && cinfo->Ss)) {
729 tbl = compptr->ac_tbl_no;
730 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
731 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
732 if (entropy->ac_stats[tbl] == NULL)
733 entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
734 ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
735 MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
736 }
737 }
738
739 /* Initialize arithmetic decoding variables */
740 entropy->c = 0;
741 entropy->a = 0;
742 entropy->ct = -16; /* force reading 2 initial bytes to fill C */
743
744 /* Initialize restart counter */
745 entropy->restarts_to_go = cinfo->restart_interval;
746 }
747
748
749 /*
750 * Finish up at the end of an arithmetic-compressed scan.
751 */
752
753 METHODDEF(void)
754 finish_pass (j_decompress_ptr cinfo)
755 {
756 /* no work necessary here */
757 }
758
759
760 /*
761 * Module initialization routine for arithmetic entropy decoding.
762 */
763
764 GLOBAL(void)
765 jinit_arith_decoder (j_decompress_ptr cinfo)
766 {
767 arith_entropy_ptr entropy;
768 int i;
769
770 entropy = (arith_entropy_ptr) (*cinfo->mem->alloc_small)
771 ((j_common_ptr) cinfo, JPOOL_IMAGE, SIZEOF(arith_entropy_decoder));
772 cinfo->entropy = &entropy->pub;
773 entropy->pub.start_pass = start_pass;
774 entropy->pub.finish_pass = finish_pass;
775
776 /* Mark tables unallocated */
777 for (i = 0; i < NUM_ARITH_TBLS; i++) {
778 entropy->dc_stats[i] = NULL;
779 entropy->ac_stats[i] = NULL;
780 }
781
782 /* Initialize index for fixed probability estimation */
783 entropy->fixed_bin[0] = 113;
784
785 if (cinfo->progressive_mode) {
786 /* Create progression status table */
787 int *coef_bit_ptr, ci;
788 cinfo->coef_bits = (int (*)[DCTSIZE2]) (*cinfo->mem->alloc_small)
789 ((j_common_ptr) cinfo, JPOOL_IMAGE,
790 cinfo->num_components * DCTSIZE2 * SIZEOF(int));
791 coef_bit_ptr = & cinfo->coef_bits[0][0];
792 for (ci = 0; ci < cinfo->num_components; ci++)
793 for (i = 0; i < DCTSIZE2; i++)
794 *coef_bit_ptr++ = -1;
795 }
796 }