1 /*
2 * jdarith.c
3 *
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.
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)
get_byte(j_decompress_ptr cinfo)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 get 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)
arith_decode(j_decompress_ptr cinfo,unsigned char * st)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.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)
process_restart(j_decompress_ptr cinfo)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->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)
decode_mcu_DC_first(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)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) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
292 entropy->dc_context[ci] = 0; /* zero diff category */
293 else if (m > (int) ((1L << 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)
decode_mcu_AC_first(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)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 sign = arith_decode(cinfo, entropy->fixed_bin);
358 st += 2;
359 /* Figure F.23: Decoding the magnitude category of v */
360 if ((m = arith_decode(cinfo, st)) != 0) {
361 if (arith_decode(cinfo, st)) {
362 m <<= 1;
363 st = entropy->ac_stats[tbl] +
364 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
365 while (arith_decode(cinfo, st)) {
366 if ((m <<= 1) == 0x8000) {
367 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
368 entropy->ct = -1; /* magnitude overflow */
369 return TRUE;
370 }
371 st += 1;
372 }
373 }
374 }
375 v = m;
376 /* Figure F.24: Decoding the magnitude bit pattern of v */
377 st += 14;
378 while (m >>= 1)
379 if (arith_decode(cinfo, st)) v |= m;
380 v += 1; if (sign) v = -v;
381 /* Scale and output coefficient in natural (dezigzagged) order */
382 (*block)[jpeg_natural_order[k]] = (JCOEF) (v << cinfo->Al);
383 }
384
385 return TRUE;
386 }
387
388
389 /*
390 * MCU decoding for DC successive approximation refinement scan.
391 */
392
393 METHODDEF(boolean)
decode_mcu_DC_refine(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)394 decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
395 {
396 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
397 unsigned char *st;
398 int p1, blkn;
399
400 /* Process restart marker if needed */
401 if (cinfo->restart_interval) {
402 if (entropy->restarts_to_go == 0)
403 process_restart(cinfo);
404 entropy->restarts_to_go--;
405 }
406
407 st = entropy->fixed_bin; /* use fixed probability estimation */
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 /* Encoded data is simply the next bit of the two's-complement DC value */
414 if (arith_decode(cinfo, st))
415 MCU_data[blkn][0][0] |= p1;
416 }
417
418 return TRUE;
419 }
420
421
422 /*
423 * MCU decoding for AC successive approximation refinement scan.
424 */
425
426 METHODDEF(boolean)
decode_mcu_AC_refine(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)427 decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
428 {
429 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
430 JBLOCKROW block;
431 JCOEFPTR thiscoef;
432 unsigned char *st;
433 int tbl, k, kex;
434 int p1, m1;
435
436 /* Process restart marker if needed */
437 if (cinfo->restart_interval) {
438 if (entropy->restarts_to_go == 0)
439 process_restart(cinfo);
440 entropy->restarts_to_go--;
441 }
442
443 if (entropy->ct == -1) return TRUE; /* if error do nothing */
444
445 /* There is always only one block per MCU */
446 block = MCU_data[0];
447 tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
448
449 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
450 m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */
451
452 /* Establish EOBx (previous stage end-of-block) index */
453 for (kex = cinfo->Se; kex > 0; kex--)
454 if ((*block)[jpeg_natural_order[kex]]) break;
455
456 for (k = cinfo->Ss; k <= cinfo->Se; k++) {
457 st = entropy->ac_stats[tbl] + 3 * (k - 1);
458 if (k > kex)
459 if (arith_decode(cinfo, st)) break; /* EOB flag */
460 for (;;) {
461 thiscoef = *block + jpeg_natural_order[k];
462 if (*thiscoef) { /* previously nonzero coef */
463 if (arith_decode(cinfo, st + 2)) {
464 if (*thiscoef < 0)
465 *thiscoef += m1;
466 else
467 *thiscoef += p1;
468 }
469 break;
470 }
471 if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */
472 if (arith_decode(cinfo, entropy->fixed_bin))
473 *thiscoef = m1;
474 else
475 *thiscoef = p1;
476 break;
477 }
478 st += 3; k++;
479 if (k > cinfo->Se) {
480 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
481 entropy->ct = -1; /* spectral overflow */
482 return TRUE;
483 }
484 }
485 }
486
487 return TRUE;
488 }
489
490
491 /*
492 * Decode one MCU's worth of arithmetic-compressed coefficients.
493 */
494
495 METHODDEF(boolean)
decode_mcu(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)496 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
497 {
498 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
499 jpeg_component_info * compptr;
500 JBLOCKROW block;
501 unsigned char *st;
502 int blkn, ci, tbl, sign, k;
503 int v, m;
504
505 /* Process restart marker if needed */
506 if (cinfo->restart_interval) {
507 if (entropy->restarts_to_go == 0)
508 process_restart(cinfo);
509 entropy->restarts_to_go--;
510 }
511
512 if (entropy->ct == -1) return TRUE; /* if error do nothing */
513
514 /* Outer loop handles each block in the MCU */
515
516 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
517 block = MCU_data[blkn];
518 ci = cinfo->MCU_membership[blkn];
519 compptr = cinfo->cur_comp_info[ci];
520
521 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
522
523 tbl = compptr->dc_tbl_no;
524
525 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
526 st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
527
528 /* Figure F.19: Decode_DC_DIFF */
529 if (arith_decode(cinfo, st) == 0)
530 entropy->dc_context[ci] = 0;
531 else {
532 /* Figure F.21: Decoding nonzero value v */
533 /* Figure F.22: Decoding the sign of v */
534 sign = arith_decode(cinfo, st + 1);
535 st += 2; st += sign;
536 /* Figure F.23: Decoding the magnitude category of v */
537 if ((m = arith_decode(cinfo, st)) != 0) {
538 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
539 while (arith_decode(cinfo, st)) {
540 if ((m <<= 1) == 0x8000) {
541 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
542 entropy->ct = -1; /* magnitude overflow */
543 return TRUE;
544 }
545 st += 1;
546 }
547 }
548 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
549 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
550 entropy->dc_context[ci] = 0; /* zero diff category */
551 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
552 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
553 else
554 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
555 v = m;
556 /* Figure F.24: Decoding the magnitude bit pattern of v */
557 st += 14;
558 while (m >>= 1)
559 if (arith_decode(cinfo, st)) v |= m;
560 v += 1; if (sign) v = -v;
561 entropy->last_dc_val[ci] += v;
562 }
563
564 (*block)[0] = (JCOEF) entropy->last_dc_val[ci];
565
566 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
567
568 tbl = compptr->ac_tbl_no;
569
570 /* Figure F.20: Decode_AC_coefficients */
571 for (k = 1; k <= DCTSIZE2 - 1; k++) {
572 st = entropy->ac_stats[tbl] + 3 * (k - 1);
573 if (arith_decode(cinfo, st)) break; /* EOB flag */
574 while (arith_decode(cinfo, st + 1) == 0) {
575 st += 3; k++;
576 if (k > DCTSIZE2 - 1) {
577 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
578 entropy->ct = -1; /* spectral overflow */
579 return TRUE;
580 }
581 }
582 /* Figure F.21: Decoding nonzero value v */
583 /* Figure F.22: Decoding the sign of v */
584 sign = arith_decode(cinfo, entropy->fixed_bin);
585 st += 2;
586 /* Figure F.23: Decoding the magnitude category of v */
587 if ((m = arith_decode(cinfo, st)) != 0) {
588 if (arith_decode(cinfo, st)) {
589 m <<= 1;
590 st = entropy->ac_stats[tbl] +
591 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
592 while (arith_decode(cinfo, st)) {
593 if ((m <<= 1) == 0x8000) {
594 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
595 entropy->ct = -1; /* magnitude overflow */
596 return TRUE;
597 }
598 st += 1;
599 }
600 }
601 }
602 v = m;
603 /* Figure F.24: Decoding the magnitude bit pattern of v */
604 st += 14;
605 while (m >>= 1)
606 if (arith_decode(cinfo, st)) v |= m;
607 v += 1; if (sign) v = -v;
608 (*block)[jpeg_natural_order[k]] = (JCOEF) v;
609 }
610 }
611
612 return TRUE;
613 }
614
615
616 /*
617 * Initialize for an arithmetic-compressed scan.
618 */
619
620 METHODDEF(void)
start_pass(j_decompress_ptr cinfo)621 start_pass (j_decompress_ptr cinfo)
622 {
623 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
624 int ci, tbl;
625 jpeg_component_info * compptr;
626
627 if (cinfo->progressive_mode) {
628 /* Validate progressive scan parameters */
629 if (cinfo->Ss == 0) {
630 if (cinfo->Se != 0)
631 goto bad;
632 } else {
633 /* need not check Ss/Se < 0 since they came from unsigned bytes */
634 if (cinfo->Se < cinfo->Ss || cinfo->Se > DCTSIZE2 - 1)
635 goto bad;
636 /* AC scans may have only one component */
637 if (cinfo->comps_in_scan != 1)
638 goto bad;
639 }
640 if (cinfo->Ah != 0) {
641 /* Successive approximation refinement scan: must have Al = Ah-1. */
642 if (cinfo->Ah-1 != cinfo->Al)
643 goto bad;
644 }
645 if (cinfo->Al > 13) { /* need not check for < 0 */
646 bad:
647 ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
648 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
649 }
650 /* Update progression status, and verify that scan order is legal.
651 * Note that inter-scan inconsistencies are treated as warnings
652 * not fatal errors ... not clear if this is right way to behave.
653 */
654 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
655 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
656 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
657 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
658 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
659 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
660 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
661 if (cinfo->Ah != expected)
662 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
663 coef_bit_ptr[coefi] = cinfo->Al;
664 }
665 }
666 /* Select MCU decoding routine */
667 if (cinfo->Ah == 0) {
668 if (cinfo->Ss == 0)
669 entropy->pub.decode_mcu = decode_mcu_DC_first;
670 else
671 entropy->pub.decode_mcu = decode_mcu_AC_first;
672 } else {
673 if (cinfo->Ss == 0)
674 entropy->pub.decode_mcu = decode_mcu_DC_refine;
675 else
676 entropy->pub.decode_mcu = decode_mcu_AC_refine;
677 }
678 } else {
679 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
680 * This ought to be an error condition, but we make it a warning.
681 */
682 if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
683 (cinfo->Se < DCTSIZE2 && cinfo->Se != DCTSIZE2 - 1))
684 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
685 /* Select MCU decoding routine */
686 entropy->pub.decode_mcu = decode_mcu;
687 }
688
689 /* Allocate & initialize requested statistics areas */
690 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
691 compptr = cinfo->cur_comp_info[ci];
692 if (! cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
693 tbl = compptr->dc_tbl_no;
694 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
695 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
696 if (entropy->dc_stats[tbl] == NULL)
697 entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
698 ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
699 MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
700 /* Initialize DC predictions to 0 */
701 entropy->last_dc_val[ci] = 0;
702 entropy->dc_context[ci] = 0;
703 }
704 if (! cinfo->progressive_mode || cinfo->Ss) {
705 tbl = compptr->ac_tbl_no;
706 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
707 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
708 if (entropy->ac_stats[tbl] == NULL)
709 entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
710 ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
711 MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
712 }
713 }
714
715 /* Initialize arithmetic decoding variables */
716 entropy->c = 0;
717 entropy->a = 0;
718 entropy->ct = -16; /* force reading 2 initial bytes to fill C */
719
720 /* Initialize restart counter */
721 entropy->restarts_to_go = cinfo->restart_interval;
722 }
723
724
725 /*
726 * Module initialization routine for arithmetic entropy decoding.
727 */
728
729 GLOBAL(void)
jinit_arith_decoder(j_decompress_ptr cinfo)730 jinit_arith_decoder (j_decompress_ptr cinfo)
731 {
732 arith_entropy_ptr entropy;
733 int i;
734
735 entropy = (arith_entropy_ptr)
736 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
737 SIZEOF(arith_entropy_decoder));
738 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
739 entropy->pub.start_pass = start_pass;
740
741 /* Mark tables unallocated */
742 for (i = 0; i < NUM_ARITH_TBLS; i++) {
743 entropy->dc_stats[i] = NULL;
744 entropy->ac_stats[i] = NULL;
745 }
746
747 /* Initialize index for fixed probability estimation */
748 entropy->fixed_bin[0] = 113;
749
750 if (cinfo->progressive_mode) {
751 /* Create progression status table */
752 int *coef_bit_ptr, ci;
753 cinfo->coef_bits = (int (*)[DCTSIZE2])
754 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
755 cinfo->num_components*DCTSIZE2*SIZEOF(int));
756 coef_bit_ptr = & cinfo->coef_bits[0][0];
757 for (ci = 0; ci < cinfo->num_components; ci++)
758 for (i = 0; i < DCTSIZE2; i++)
759 *coef_bit_ptr++ = -1;
760 }
761 }
762