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Revision 31 - (show annotations) (download)
Tue Sep 7 03:24:11 2010 UTC (9 years, 11 months ago) by william
File MIME type: text/plain
File size: 23794 byte(s)
committing r3113 initial commit again...
1 /*
2 * jdarith.c
3 *
4 * Developed 1997 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 } arith_entropy_decoder;
41
42 typedef arith_entropy_decoder * arith_entropy_ptr;
43
44 /* The following two definitions specify the allocation chunk size
45 * for the statistics area.
46 * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least
47 * 49 statistics bins for DC, and 245 statistics bins for AC coding.
48 * Note that we use one additional AC bin for codings with fixed
49 * probability (0.5), thus the minimum number for AC is 246.
50 *
51 * We use a compact representation with 1 byte per statistics bin,
52 * thus the numbers directly represent byte sizes.
53 * This 1 byte per statistics bin contains the meaning of the MPS
54 * (more probable symbol) in the highest bit (mask 0x80), and the
55 * index into the probability estimation state machine table
56 * in the lower bits (mask 0x7F).
57 */
58
59 #define DC_STAT_BINS 64
60 #define AC_STAT_BINS 256
61
62
63 LOCAL(int)
64 get_byte (j_decompress_ptr cinfo)
65 /* Read next input byte; we do not support suspension in this module. */
66 {
67 struct jpeg_source_mgr * src = cinfo->src;
68
69 if (src->bytes_in_buffer == 0)
70 if (! (*src->fill_input_buffer) (cinfo))
71 ERREXIT(cinfo, JERR_CANT_SUSPEND);
72 src->bytes_in_buffer--;
73 return GETJOCTET(*src->next_input_byte++);
74 }
75
76
77 /*
78 * The core arithmetic decoding routine (common in JPEG and JBIG).
79 * This needs to go as fast as possible.
80 * Machine-dependent optimization facilities
81 * are not utilized in this portable implementation.
82 * However, this code should be fairly efficient and
83 * may be a good base for further optimizations anyway.
84 *
85 * Return value is 0 or 1 (binary decision).
86 *
87 * Note: I've changed the handling of the code base & bit
88 * buffer register C compared to other implementations
89 * based on the standards layout & procedures.
90 * While it also contains both the actual base of the
91 * coding interval (16 bits) and the next-bits buffer,
92 * the cut-point between these two parts is floating
93 * (instead of fixed) with the bit shift counter CT.
94 * Thus, we also need only one (variable instead of
95 * fixed size) shift for the LPS/MPS decision, and
96 * we can get away with any renormalization update
97 * of C (except for new data insertion, of course).
98 *
99 * I've also introduced a new scheme for accessing
100 * the probability estimation state machine table,
101 * derived from Markus Kuhn's JBIG implementation.
102 */
103
104 LOCAL(int)
105 arith_decode (j_decompress_ptr cinfo, unsigned char *st)
106 {
107 extern const INT32 jaritab[];
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.2:
149 * Qe values and probability estimation state machine
150 */
151 sv = *st;
152 qe = jaritab[sv & 0x7F]; /* => Qe_Value */
153 nl = qe & 0xFF; qe >>= 8; /* Next_Index_LPS + Switch_MPS */
154 nm = qe & 0xFF; qe >>= 8; /* Next_Index_MPS */
155
156 /* Decode & estimation procedures per sections D.2.4 & D.2.5 */
157 temp = e->a - qe;
158 e->a = temp;
159 temp <<= e->ct;
160 if (e->c >= temp) {
161 e->c -= temp;
162 /* Conditional LPS (less probable symbol) exchange */
163 if (e->a < qe) {
164 e->a = qe;
165 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
166 } else {
167 e->a = qe;
168 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
169 sv ^= 0x80; /* Exchange LPS/MPS */
170 }
171 } else if (e->a < 0x8000L) {
172 /* Conditional MPS (more probable symbol) exchange */
173 if (e->a < qe) {
174 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
175 sv ^= 0x80; /* Exchange LPS/MPS */
176 } else {
177 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
178 }
179 }
180
181 return sv >> 7;
182 }
183
184
185 /*
186 * Check for a restart marker & resynchronize decoder.
187 */
188
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 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
201 compptr = cinfo->cur_comp_info[ci];
202 /* Re-initialize statistics areas */
203 if (cinfo->progressive_mode == 0 || (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 == 0 || cinfo->Ss) {
210 MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS);
211 }
212 }
213
214 /* Reset arithmetic decoding variables */
215 entropy->c = 0;
216 entropy->a = 0;
217 entropy->ct = -16; /* force reading 2 initial bytes to fill C */
218
219 /* Reset restart counter */
220 entropy->restarts_to_go = cinfo->restart_interval;
221 }
222
223
224 /*
225 * Arithmetic MCU decoding.
226 * Each of these routines decodes and returns one MCU's worth of
227 * arithmetic-compressed coefficients.
228 * The coefficients are reordered from zigzag order into natural array order,
229 * but are not dequantized.
230 *
231 * The i'th block of the MCU is stored into the block pointed to by
232 * MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
233 */
234
235 /*
236 * MCU decoding for DC initial scan (either spectral selection,
237 * or first pass of successive approximation).
238 */
239
240 METHODDEF(boolean)
241 decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
242 {
243 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
244 JBLOCKROW block;
245 unsigned char *st;
246 int blkn, ci, tbl, sign;
247 int v, m;
248
249 /* Process restart marker if needed */
250 if (cinfo->restart_interval) {
251 if (entropy->restarts_to_go == 0)
252 process_restart(cinfo);
253 entropy->restarts_to_go--;
254 }
255
256 if (entropy->ct == -1) return TRUE; /* if error do nothing */
257
258 /* Outer loop handles each block in the MCU */
259
260 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
261 block = MCU_data[blkn];
262 ci = cinfo->MCU_membership[blkn];
263 tbl = cinfo->cur_comp_info[ci]->dc_tbl_no;
264
265 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
266
267 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
268 st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
269
270 /* Figure F.19: Decode_DC_DIFF */
271 if (arith_decode(cinfo, st) == 0)
272 entropy->dc_context[ci] = 0;
273 else {
274 /* Figure F.21: Decoding nonzero value v */
275 /* Figure F.22: Decoding the sign of v */
276 sign = arith_decode(cinfo, st + 1);
277 st += 2; st += sign;
278 /* Figure F.23: Decoding the magnitude category of v */
279 if ((m = arith_decode(cinfo, st)) != 0) {
280 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
281 while (arith_decode(cinfo, st)) {
282 if ((m <<= 1) == 0x8000) {
283 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
284 entropy->ct = -1; /* magnitude overflow */
285 return TRUE;
286 }
287 st += 1;
288 }
289 }
290 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
291 if (m < (int) (((INT32) 1 << cinfo->arith_dc_L[tbl]) >> 1))
292 entropy->dc_context[ci] = 0; /* zero diff category */
293 else if (m > (int) (((INT32) 1 << cinfo->arith_dc_U[tbl]) >> 1))
294 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
295 else
296 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
297 v = m;
298 /* Figure F.24: Decoding the magnitude bit pattern of v */
299 st += 14;
300 while (m >>= 1)
301 if (arith_decode(cinfo, st)) v |= m;
302 v += 1; if (sign) v = -v;
303 entropy->last_dc_val[ci] += v;
304 }
305
306 /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */
307 (*block)[0] = (JCOEF) (entropy->last_dc_val[ci] << cinfo->Al);
308 }
309
310 return TRUE;
311 }
312
313
314 /*
315 * MCU decoding for AC initial scan (either spectral selection,
316 * or first pass of successive approximation).
317 */
318
319 METHODDEF(boolean)
320 decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
321 {
322 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
323 JBLOCKROW block;
324 unsigned char *st;
325 int tbl, sign, k;
326 int v, m;
327
328 /* Process restart marker if needed */
329 if (cinfo->restart_interval) {
330 if (entropy->restarts_to_go == 0)
331 process_restart(cinfo);
332 entropy->restarts_to_go--;
333 }
334
335 if (entropy->ct == -1) return TRUE; /* if error do nothing */
336
337 /* There is always only one block per MCU */
338 block = MCU_data[0];
339 tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
340
341 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
342
343 /* Figure F.20: Decode_AC_coefficients */
344 for (k = cinfo->Ss; k <= cinfo->Se; k++) {
345 st = entropy->ac_stats[tbl] + 3 * (k - 1);
346 if (arith_decode(cinfo, st)) break; /* EOB flag */
347 while (arith_decode(cinfo, st + 1) == 0) {
348 st += 3; k++;
349 if (k > cinfo->Se) {
350 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
351 entropy->ct = -1; /* spectral overflow */
352 return TRUE;
353 }
354 }
355 /* Figure F.21: Decoding nonzero value v */
356 /* Figure F.22: Decoding the sign of v */
357 entropy->ac_stats[tbl][245] = 0;
358 sign = arith_decode(cinfo, entropy->ac_stats[tbl] + 245);
359 st += 2;
360 /* Figure F.23: Decoding the magnitude category of v */
361 if ((m = arith_decode(cinfo, st)) != 0) {
362 if (arith_decode(cinfo, st)) {
363 m <<= 1;
364 st = entropy->ac_stats[tbl] +
365 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
366 while (arith_decode(cinfo, st)) {
367 if ((m <<= 1) == 0x8000) {
368 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
369 entropy->ct = -1; /* magnitude overflow */
370 return TRUE;
371 }
372 st += 1;
373 }
374 }
375 }
376 v = m;
377 /* Figure F.24: Decoding the magnitude bit pattern of v */
378 st += 14;
379 while (m >>= 1)
380 if (arith_decode(cinfo, st)) v |= m;
381 v += 1; if (sign) v = -v;
382 /* Scale and output coefficient in natural (dezigzagged) order */
383 (*block)[jpeg_natural_order[k]] = (JCOEF) (v << cinfo->Al);
384 }
385
386 return TRUE;
387 }
388
389
390 /*
391 * MCU decoding for DC successive approximation refinement scan.
392 */
393
394 METHODDEF(boolean)
395 decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
396 {
397 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
398 unsigned char st[4];
399 int p1, blkn;
400
401 /* Process restart marker if needed */
402 if (cinfo->restart_interval) {
403 if (entropy->restarts_to_go == 0)
404 process_restart(cinfo);
405 entropy->restarts_to_go--;
406 }
407
408 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
409
410 /* Outer loop handles each block in the MCU */
411
412 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
413 st[0] = 0; /* use fixed probability estimation */
414 /* Encoded data is simply the next bit of the two's-complement DC value */
415 if (arith_decode(cinfo, st))
416 MCU_data[blkn][0][0] |= p1;
417 }
418
419 return TRUE;
420 }
421
422
423 /*
424 * MCU decoding for AC successive approximation refinement scan.
425 */
426
427 METHODDEF(boolean)
428 decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
429 {
430 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
431 JBLOCKROW block;
432 JCOEFPTR thiscoef;
433 unsigned char *st;
434 int tbl, k, kex;
435 int p1, m1;
436
437 /* Process restart marker if needed */
438 if (cinfo->restart_interval) {
439 if (entropy->restarts_to_go == 0)
440 process_restart(cinfo);
441 entropy->restarts_to_go--;
442 }
443
444 if (entropy->ct == -1) return TRUE; /* if error do nothing */
445
446 /* There is always only one block per MCU */
447 block = MCU_data[0];
448 tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
449
450 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
451 m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */
452
453 /* Establish EOBx (previous stage end-of-block) index */
454 for (kex = cinfo->Se + 1; kex > 1; kex--)
455 if ((*block)[jpeg_natural_order[kex - 1]]) break;
456
457 for (k = cinfo->Ss; k <= cinfo->Se; k++) {
458 st = entropy->ac_stats[tbl] + 3 * (k - 1);
459 if (k >= kex)
460 if (arith_decode(cinfo, st)) break; /* EOB flag */
461 for (;;) {
462 thiscoef = *block + jpeg_natural_order[k];
463 if (*thiscoef) { /* previously nonzero coef */
464 if (arith_decode(cinfo, st + 2)) {
465 if (*thiscoef < 0)
466 *thiscoef += m1;
467 else
468 *thiscoef += p1;
469 }
470 break;
471 }
472 if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */
473 entropy->ac_stats[tbl][245] = 0;
474 if (arith_decode(cinfo, entropy->ac_stats[tbl] + 245))
475 *thiscoef = m1;
476 else
477 *thiscoef = p1;
478 break;
479 }
480 st += 3; k++;
481 if (k > cinfo->Se) {
482 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
483 entropy->ct = -1; /* spectral overflow */
484 return TRUE;
485 }
486 }
487 }
488
489 return TRUE;
490 }
491
492
493 /*
494 * Decode one MCU's worth of arithmetic-compressed coefficients.
495 */
496
497 METHODDEF(boolean)
498 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
499 {
500 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
501 jpeg_component_info * compptr;
502 JBLOCKROW block;
503 unsigned char *st;
504 int blkn, ci, tbl, sign, k;
505 int v, m;
506
507 /* Process restart marker if needed */
508 if (cinfo->restart_interval) {
509 if (entropy->restarts_to_go == 0)
510 process_restart(cinfo);
511 entropy->restarts_to_go--;
512 }
513
514 if (entropy->ct == -1) return TRUE; /* if error do nothing */
515
516 /* Outer loop handles each block in the MCU */
517
518 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
519 block = MCU_data[blkn];
520 ci = cinfo->MCU_membership[blkn];
521 compptr = cinfo->cur_comp_info[ci];
522
523 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
524
525 tbl = compptr->dc_tbl_no;
526
527 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
528 st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
529
530 /* Figure F.19: Decode_DC_DIFF */
531 if (arith_decode(cinfo, st) == 0)
532 entropy->dc_context[ci] = 0;
533 else {
534 /* Figure F.21: Decoding nonzero value v */
535 /* Figure F.22: Decoding the sign of v */
536 sign = arith_decode(cinfo, st + 1);
537 st += 2; st += sign;
538 /* Figure F.23: Decoding the magnitude category of v */
539 if ((m = arith_decode(cinfo, st)) != 0) {
540 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
541 while (arith_decode(cinfo, st)) {
542 if ((m <<= 1) == 0x8000) {
543 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
544 entropy->ct = -1; /* magnitude overflow */
545 return TRUE;
546 }
547 st += 1;
548 }
549 }
550 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
551 if (m < (int) (((INT32) 1 << cinfo->arith_dc_L[tbl]) >> 1))
552 entropy->dc_context[ci] = 0; /* zero diff category */
553 else if (m > (int) (((INT32) 1 << cinfo->arith_dc_U[tbl]) >> 1))
554 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
555 else
556 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
557 v = m;
558 /* Figure F.24: Decoding the magnitude bit pattern of v */
559 st += 14;
560 while (m >>= 1)
561 if (arith_decode(cinfo, st)) v |= m;
562 v += 1; if (sign) v = -v;
563 entropy->last_dc_val[ci] += v;
564 }
565
566 (*block)[0] = (JCOEF) entropy->last_dc_val[ci];
567
568 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
569
570 tbl = compptr->ac_tbl_no;
571
572 /* Figure F.20: Decode_AC_coefficients */
573 for (k = 1; k < DCTSIZE2; k++) {
574 st = entropy->ac_stats[tbl] + 3 * (k - 1);
575 if (arith_decode(cinfo, st)) break; /* EOB flag */
576 while (arith_decode(cinfo, st + 1) == 0) {
577 st += 3; k++;
578 if (k >= DCTSIZE2) {
579 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
580 entropy->ct = -1; /* spectral overflow */
581 return TRUE;
582 }
583 }
584 /* Figure F.21: Decoding nonzero value v */
585 /* Figure F.22: Decoding the sign of v */
586 entropy->ac_stats[tbl][245] = 0;
587 sign = arith_decode(cinfo, entropy->ac_stats[tbl] + 245);
588 st += 2;
589 /* Figure F.23: Decoding the magnitude category of v */
590 if ((m = arith_decode(cinfo, st)) != 0) {
591 if (arith_decode(cinfo, st)) {
592 m <<= 1;
593 st = entropy->ac_stats[tbl] +
594 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
595 while (arith_decode(cinfo, st)) {
596 if ((m <<= 1) == 0x8000) {
597 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
598 entropy->ct = -1; /* magnitude overflow */
599 return TRUE;
600 }
601 st += 1;
602 }
603 }
604 }
605 v = m;
606 /* Figure F.24: Decoding the magnitude bit pattern of v */
607 st += 14;
608 while (m >>= 1)
609 if (arith_decode(cinfo, st)) v |= m;
610 v += 1; if (sign) v = -v;
611 (*block)[jpeg_natural_order[k]] = (JCOEF) v;
612 }
613 }
614
615 return TRUE;
616 }
617
618
619 /*
620 * Initialize for an arithmetic-compressed scan.
621 */
622
623 METHODDEF(void)
624 start_pass (j_decompress_ptr cinfo)
625 {
626 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
627 int ci, tbl;
628 jpeg_component_info * compptr;
629
630 if (cinfo->progressive_mode) {
631 /* Validate progressive scan parameters */
632 if (cinfo->Ss == 0) {
633 if (cinfo->Se != 0)
634 goto bad;
635 } else {
636 /* need not check Ss/Se < 0 since they came from unsigned bytes */
637 if (cinfo->Se < cinfo->Ss || cinfo->Se >= DCTSIZE2)
638 goto bad;
639 /* AC scans may have only one component */
640 if (cinfo->comps_in_scan != 1)
641 goto bad;
642 }
643 if (cinfo->Ah != 0) {
644 /* Successive approximation refinement scan: must have Al = Ah-1. */
645 if (cinfo->Ah-1 != cinfo->Al)
646 goto bad;
647 }
648 if (cinfo->Al > 13) { /* need not check for < 0 */
649 bad:
650 ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
651 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
652 }
653 /* Update progression status, and verify that scan order is legal.
654 * Note that inter-scan inconsistencies are treated as warnings
655 * not fatal errors ... not clear if this is right way to behave.
656 */
657 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
658 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
659 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
660 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
661 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
662 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
663 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
664 if (cinfo->Ah != expected)
665 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
666 coef_bit_ptr[coefi] = cinfo->Al;
667 }
668 }
669 /* Select MCU decoding routine */
670 if (cinfo->Ah == 0) {
671 if (cinfo->Ss == 0)
672 entropy->pub.decode_mcu = decode_mcu_DC_first;
673 else
674 entropy->pub.decode_mcu = decode_mcu_AC_first;
675 } else {
676 if (cinfo->Ss == 0)
677 entropy->pub.decode_mcu = decode_mcu_DC_refine;
678 else
679 entropy->pub.decode_mcu = decode_mcu_AC_refine;
680 }
681 } else {
682 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
683 * This ought to be an error condition, but we make it a warning because
684 * there are some baseline files out there with all zeroes in these bytes.
685 */
686 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
687 cinfo->Ah != 0 || cinfo->Al != 0)
688 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
689 /* Select MCU decoding routine */
690 entropy->pub.decode_mcu = decode_mcu;
691 }
692
693 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
694 compptr = cinfo->cur_comp_info[ci];
695 /* Allocate & initialize requested statistics areas */
696 if (cinfo->progressive_mode == 0 || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
697 tbl = compptr->dc_tbl_no;
698 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
699 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
700 if (entropy->dc_stats[tbl] == NULL)
701 entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
702 ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
703 MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
704 /* Initialize DC predictions to 0 */
705 entropy->last_dc_val[ci] = 0;
706 entropy->dc_context[ci] = 0;
707 }
708 if (cinfo->progressive_mode == 0 || cinfo->Ss) {
709 tbl = compptr->ac_tbl_no;
710 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
711 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
712 if (entropy->ac_stats[tbl] == NULL)
713 entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
714 ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
715 MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
716 }
717 }
718
719 /* Initialize arithmetic decoding variables */
720 entropy->c = 0;
721 entropy->a = 0;
722 entropy->ct = -16; /* force reading 2 initial bytes to fill C */
723
724 /* Initialize restart counter */
725 entropy->restarts_to_go = cinfo->restart_interval;
726 }
727
728
729 /*
730 * Module initialization routine for arithmetic entropy decoding.
731 */
732
733 GLOBAL(void)
734 jinit_arith_decoder (j_decompress_ptr cinfo)
735 {
736 arith_entropy_ptr entropy;
737 int i;
738
739 entropy = (arith_entropy_ptr)
740 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
741 SIZEOF(arith_entropy_decoder));
742 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
743 entropy->pub.start_pass = start_pass;
744
745 /* Mark tables unallocated */
746 for (i = 0; i < NUM_ARITH_TBLS; i++) {
747 entropy->dc_stats[i] = NULL;
748 entropy->ac_stats[i] = NULL;
749 }
750
751 if (cinfo->progressive_mode) {
752 /* Create progression status table */
753 int *coef_bit_ptr, ci;
754 cinfo->coef_bits = (int (*)[DCTSIZE2])
755 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
756 cinfo->num_components*DCTSIZE2*SIZEOF(int));
757 coef_bit_ptr = & cinfo->coef_bits[0][0];
758 for (ci = 0; ci < cinfo->num_components; ci++)
759 for (i = 0; i < DCTSIZE2; i++)
760 *coef_bit_ptr++ = -1;
761 }
762 }

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