1 /*
2 * jdarith.c
3 *
4 * This file was part of the Independent JPEG Group's software:
5 * Developed 1997-2015 by Guido Vollbeding.
6 * libjpeg-turbo Modifications:
7 * Copyright (C) 2015-2016, D. R. Commander.
8 * For conditions of distribution and use, see the accompanying README.ijg
9 * file.
10 *
11 * This file contains portable arithmetic entropy decoding routines for JPEG
12 * (implementing the ISO/IEC IS 10918-1 and CCITT Recommendation ITU-T T.81).
13 *
14 * Both sequential and progressive modes are supported in this single module.
15 *
16 * Suspension is not currently supported in this module.
17 */
18
19 #define JPEG_INTERNALS
20 #include "jinclude.h"
21 #include "jpeglib.h"
22
23
24 #define NEG_1 ((unsigned int)-1)
25
26
27 /* Expanded entropy decoder object for arithmetic decoding. */
28
29 typedef struct {
30 struct jpeg_entropy_decoder pub; /* public fields */
31
32 JLONG c; /* C register, base of coding interval + input bit buffer */
33 JLONG a; /* A register, normalized size of coding interval */
34 int ct; /* bit shift counter, # of bits left in bit buffer part of C */
35 /* init: ct = -16 */
36 /* run: ct = 0..7 */
37 /* error: ct = -1 */
38 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
39 int dc_context[MAX_COMPS_IN_SCAN]; /* context index for DC conditioning */
40
41 unsigned int restarts_to_go; /* MCUs left in this restart interval */
42
43 /* Pointers to statistics areas (these workspaces have image lifespan) */
44 unsigned char *dc_stats[NUM_ARITH_TBLS];
45 unsigned char *ac_stats[NUM_ARITH_TBLS];
46
47 /* Statistics bin for coding with fixed probability 0.5 */
48 unsigned char fixed_bin[4];
49 } arith_entropy_decoder;
50
51 typedef arith_entropy_decoder *arith_entropy_ptr;
52
53 /* The following two definitions specify the allocation chunk size
54 * for the statistics area.
55 * According to sections F.1.4.4.1.3 and F.1.4.4.2, we need at least
56 * 49 statistics bins for DC, and 245 statistics bins for AC coding.
57 *
58 * We use a compact representation with 1 byte per statistics bin,
59 * thus the numbers directly represent byte sizes.
60 * This 1 byte per statistics bin contains the meaning of the MPS
61 * (more probable symbol) in the highest bit (mask 0x80), and the
62 * index into the probability estimation state machine table
63 * in the lower bits (mask 0x7F).
64 */
65
66 #define DC_STAT_BINS 64
67 #define AC_STAT_BINS 256
68
69
70 LOCAL(int)
get_byte(j_decompress_ptr cinfo)71 get_byte (j_decompress_ptr cinfo)
72 /* Read next input byte; we do not support suspension in this module. */
73 {
74 struct jpeg_source_mgr *src = cinfo->src;
75
76 if (src->bytes_in_buffer == 0)
77 if (! (*src->fill_input_buffer) (cinfo))
78 ERREXIT(cinfo, JERR_CANT_SUSPEND);
79 src->bytes_in_buffer--;
80 return GETJOCTET(*src->next_input_byte++);
81 }
82
83
84 /*
85 * The core arithmetic decoding routine (common in JPEG and JBIG).
86 * This needs to go as fast as possible.
87 * Machine-dependent optimization facilities
88 * are not utilized in this portable implementation.
89 * However, this code should be fairly efficient and
90 * may be a good base for further optimizations anyway.
91 *
92 * Return value is 0 or 1 (binary decision).
93 *
94 * Note: I've changed the handling of the code base & bit
95 * buffer register C compared to other implementations
96 * based on the standards layout & procedures.
97 * While it also contains both the actual base of the
98 * coding interval (16 bits) and the next-bits buffer,
99 * the cut-point between these two parts is floating
100 * (instead of fixed) with the bit shift counter CT.
101 * Thus, we also need only one (variable instead of
102 * fixed size) shift for the LPS/MPS decision, and
103 * we can do away with any renormalization update
104 * of C (except for new data insertion, of course).
105 *
106 * I've also introduced a new scheme for accessing
107 * the probability estimation state machine table,
108 * derived from Markus Kuhn's JBIG implementation.
109 */
110
111 LOCAL(int)
arith_decode(j_decompress_ptr cinfo,unsigned char * st)112 arith_decode (j_decompress_ptr cinfo, unsigned char *st)
113 {
114 register arith_entropy_ptr e = (arith_entropy_ptr) cinfo->entropy;
115 register unsigned char nl, nm;
116 register JLONG qe, temp;
117 register int sv, data;
118
119 /* Renormalization & data input per section D.2.6 */
120 while (e->a < 0x8000L) {
121 if (--e->ct < 0) {
122 /* Need to fetch next data byte */
123 if (cinfo->unread_marker)
124 data = 0; /* stuff zero data */
125 else {
126 data = get_byte(cinfo); /* read next input byte */
127 if (data == 0xFF) { /* zero stuff or marker code */
128 do data = get_byte(cinfo);
129 while (data == 0xFF); /* swallow extra 0xFF bytes */
130 if (data == 0)
131 data = 0xFF; /* discard stuffed zero byte */
132 else {
133 /* Note: Different from the Huffman decoder, hitting
134 * a marker while processing the compressed data
135 * segment is legal in arithmetic coding.
136 * The convention is to supply zero data
137 * then until decoding is complete.
138 */
139 cinfo->unread_marker = data;
140 data = 0;
141 }
142 }
143 }
144 e->c = (e->c << 8) | data; /* insert data into C register */
145 if ((e->ct += 8) < 0) /* update bit shift counter */
146 /* Need more initial bytes */
147 if (++e->ct == 0)
148 /* Got 2 initial bytes -> re-init A and exit loop */
149 e->a = 0x8000L; /* => e->a = 0x10000L after loop exit */
150 }
151 e->a <<= 1;
152 }
153
154 /* Fetch values from our compact representation of Table D.2:
155 * Qe values and probability estimation state machine
156 */
157 sv = *st;
158 qe = jpeg_aritab[sv & 0x7F]; /* => Qe_Value */
159 nl = qe & 0xFF; qe >>= 8; /* Next_Index_LPS + Switch_MPS */
160 nm = qe & 0xFF; qe >>= 8; /* Next_Index_MPS */
161
162 /* Decode & estimation procedures per sections D.2.4 & D.2.5 */
163 temp = e->a - qe;
164 e->a = temp;
165 temp <<= e->ct;
166 if (e->c >= temp) {
167 e->c -= temp;
168 /* Conditional LPS (less probable symbol) exchange */
169 if (e->a < qe) {
170 e->a = qe;
171 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
172 } else {
173 e->a = qe;
174 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
175 sv ^= 0x80; /* Exchange LPS/MPS */
176 }
177 } else if (e->a < 0x8000L) {
178 /* Conditional MPS (more probable symbol) exchange */
179 if (e->a < qe) {
180 *st = (sv & 0x80) ^ nl; /* Estimate_after_LPS */
181 sv ^= 0x80; /* Exchange LPS/MPS */
182 } else {
183 *st = (sv & 0x80) ^ nm; /* Estimate_after_MPS */
184 }
185 }
186
187 return sv >> 7;
188 }
189
190
191 /*
192 * Check for a restart marker & resynchronize decoder.
193 */
194
195 LOCAL(void)
process_restart(j_decompress_ptr cinfo)196 process_restart (j_decompress_ptr cinfo)
197 {
198 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
199 int ci;
200 jpeg_component_info *compptr;
201
202 /* Advance past the RSTn marker */
203 if (! (*cinfo->marker->read_restart_marker) (cinfo))
204 ERREXIT(cinfo, JERR_CANT_SUSPEND);
205
206 /* Re-initialize statistics areas */
207 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
208 compptr = cinfo->cur_comp_info[ci];
209 if (!cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
210 MEMZERO(entropy->dc_stats[compptr->dc_tbl_no], DC_STAT_BINS);
211 /* Reset DC predictions to 0 */
212 entropy->last_dc_val[ci] = 0;
213 entropy->dc_context[ci] = 0;
214 }
215 if (!cinfo->progressive_mode || cinfo->Ss) {
216 MEMZERO(entropy->ac_stats[compptr->ac_tbl_no], AC_STAT_BINS);
217 }
218 }
219
220 /* Reset arithmetic decoding variables */
221 entropy->c = 0;
222 entropy->a = 0;
223 entropy->ct = -16; /* force reading 2 initial bytes to fill C */
224
225 /* Reset restart counter */
226 entropy->restarts_to_go = cinfo->restart_interval;
227 }
228
229
230 /*
231 * Arithmetic MCU decoding.
232 * Each of these routines decodes and returns one MCU's worth of
233 * arithmetic-compressed coefficients.
234 * The coefficients are reordered from zigzag order into natural array order,
235 * but are not dequantized.
236 *
237 * The i'th block of the MCU is stored into the block pointed to by
238 * MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
239 */
240
241 /*
242 * MCU decoding for DC initial scan (either spectral selection,
243 * or first pass of successive approximation).
244 */
245
246 METHODDEF(boolean)
decode_mcu_DC_first(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)247 decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
248 {
249 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
250 JBLOCKROW block;
251 unsigned char *st;
252 int blkn, ci, tbl, sign;
253 int v, m;
254
255 /* Process restart marker if needed */
256 if (cinfo->restart_interval) {
257 if (entropy->restarts_to_go == 0)
258 process_restart(cinfo);
259 entropy->restarts_to_go--;
260 }
261
262 if (entropy->ct == -1) return TRUE; /* if error do nothing */
263
264 /* Outer loop handles each block in the MCU */
265
266 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
267 block = MCU_data[blkn];
268 ci = cinfo->MCU_membership[blkn];
269 tbl = cinfo->cur_comp_info[ci]->dc_tbl_no;
270
271 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
272
273 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
274 st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
275
276 /* Figure F.19: Decode_DC_DIFF */
277 if (arith_decode(cinfo, st) == 0)
278 entropy->dc_context[ci] = 0;
279 else {
280 /* Figure F.21: Decoding nonzero value v */
281 /* Figure F.22: Decoding the sign of v */
282 sign = arith_decode(cinfo, st + 1);
283 st += 2; st += sign;
284 /* Figure F.23: Decoding the magnitude category of v */
285 if ((m = arith_decode(cinfo, st)) != 0) {
286 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
287 while (arith_decode(cinfo, st)) {
288 if ((m <<= 1) == 0x8000) {
289 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
290 entropy->ct = -1; /* magnitude overflow */
291 return TRUE;
292 }
293 st += 1;
294 }
295 }
296 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
297 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
298 entropy->dc_context[ci] = 0; /* zero diff category */
299 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
300 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
301 else
302 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
303 v = m;
304 /* Figure F.24: Decoding the magnitude bit pattern of v */
305 st += 14;
306 while (m >>= 1)
307 if (arith_decode(cinfo, st)) v |= m;
308 v += 1; if (sign) v = -v;
309 entropy->last_dc_val[ci] += v;
310 }
311
312 /* Scale and output the DC coefficient (assumes jpeg_natural_order[0]=0) */
313 (*block)[0] = (JCOEF) LEFT_SHIFT(entropy->last_dc_val[ci], cinfo->Al);
314 }
315
316 return TRUE;
317 }
318
319
320 /*
321 * MCU decoding for AC initial scan (either spectral selection,
322 * or first pass of successive approximation).
323 */
324
325 METHODDEF(boolean)
decode_mcu_AC_first(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)326 decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
327 {
328 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
329 JBLOCKROW block;
330 unsigned char *st;
331 int tbl, sign, k;
332 int v, m;
333
334 /* Process restart marker if needed */
335 if (cinfo->restart_interval) {
336 if (entropy->restarts_to_go == 0)
337 process_restart(cinfo);
338 entropy->restarts_to_go--;
339 }
340
341 if (entropy->ct == -1) return TRUE; /* if error do nothing */
342
343 /* There is always only one block per MCU */
344 block = MCU_data[0];
345 tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
346
347 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
348
349 /* Figure F.20: Decode_AC_coefficients */
350 for (k = cinfo->Ss; k <= cinfo->Se; k++) {
351 st = entropy->ac_stats[tbl] + 3 * (k - 1);
352 if (arith_decode(cinfo, st)) break; /* EOB flag */
353 while (arith_decode(cinfo, st + 1) == 0) {
354 st += 3; k++;
355 if (k > cinfo->Se) {
356 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
357 entropy->ct = -1; /* spectral overflow */
358 return TRUE;
359 }
360 }
361 /* Figure F.21: Decoding nonzero value v */
362 /* Figure F.22: Decoding the sign of v */
363 sign = arith_decode(cinfo, entropy->fixed_bin);
364 st += 2;
365 /* Figure F.23: Decoding the magnitude category of v */
366 if ((m = arith_decode(cinfo, st)) != 0) {
367 if (arith_decode(cinfo, st)) {
368 m <<= 1;
369 st = entropy->ac_stats[tbl] +
370 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
371 while (arith_decode(cinfo, st)) {
372 if ((m <<= 1) == 0x8000) {
373 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
374 entropy->ct = -1; /* magnitude overflow */
375 return TRUE;
376 }
377 st += 1;
378 }
379 }
380 }
381 v = m;
382 /* Figure F.24: Decoding the magnitude bit pattern of v */
383 st += 14;
384 while (m >>= 1)
385 if (arith_decode(cinfo, st)) v |= m;
386 v += 1; if (sign) v = -v;
387 /* Scale and output coefficient in natural (dezigzagged) order */
388 (*block)[jpeg_natural_order[k]] = (JCOEF) ((unsigned)v << cinfo->Al);
389 }
390
391 return TRUE;
392 }
393
394
395 /*
396 * MCU decoding for DC successive approximation refinement scan.
397 */
398
399 METHODDEF(boolean)
decode_mcu_DC_refine(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)400 decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
401 {
402 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
403 unsigned char *st;
404 int p1, blkn;
405
406 /* Process restart marker if needed */
407 if (cinfo->restart_interval) {
408 if (entropy->restarts_to_go == 0)
409 process_restart(cinfo);
410 entropy->restarts_to_go--;
411 }
412
413 st = entropy->fixed_bin; /* use fixed probability estimation */
414 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
415
416 /* Outer loop handles each block in the MCU */
417
418 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
419 /* Encoded data is simply the next bit of the two's-complement DC value */
420 if (arith_decode(cinfo, st))
421 MCU_data[blkn][0][0] |= p1;
422 }
423
424 return TRUE;
425 }
426
427
428 /*
429 * MCU decoding for AC successive approximation refinement scan.
430 */
431
432 METHODDEF(boolean)
decode_mcu_AC_refine(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)433 decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
434 {
435 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
436 JBLOCKROW block;
437 JCOEFPTR thiscoef;
438 unsigned char *st;
439 int tbl, k, kex;
440 int p1, m1;
441
442 /* Process restart marker if needed */
443 if (cinfo->restart_interval) {
444 if (entropy->restarts_to_go == 0)
445 process_restart(cinfo);
446 entropy->restarts_to_go--;
447 }
448
449 if (entropy->ct == -1) return TRUE; /* if error do nothing */
450
451 /* There is always only one block per MCU */
452 block = MCU_data[0];
453 tbl = cinfo->cur_comp_info[0]->ac_tbl_no;
454
455 p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
456 m1 = (NEG_1) << cinfo->Al; /* -1 in the bit position being coded */
457
458 /* Establish EOBx (previous stage end-of-block) index */
459 for (kex = cinfo->Se; kex > 0; kex--)
460 if ((*block)[jpeg_natural_order[kex]]) break;
461
462 for (k = cinfo->Ss; k <= cinfo->Se; k++) {
463 st = entropy->ac_stats[tbl] + 3 * (k - 1);
464 if (k > kex)
465 if (arith_decode(cinfo, st)) break; /* EOB flag */
466 for (;;) {
467 thiscoef = *block + jpeg_natural_order[k];
468 if (*thiscoef) { /* previously nonzero coef */
469 if (arith_decode(cinfo, st + 2)) {
470 if (*thiscoef < 0)
471 *thiscoef += m1;
472 else
473 *thiscoef += p1;
474 }
475 break;
476 }
477 if (arith_decode(cinfo, st + 1)) { /* newly nonzero coef */
478 if (arith_decode(cinfo, entropy->fixed_bin))
479 *thiscoef = m1;
480 else
481 *thiscoef = p1;
482 break;
483 }
484 st += 3; k++;
485 if (k > cinfo->Se) {
486 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
487 entropy->ct = -1; /* spectral overflow */
488 return TRUE;
489 }
490 }
491 }
492
493 return TRUE;
494 }
495
496
497 /*
498 * Decode one MCU's worth of arithmetic-compressed coefficients.
499 */
500
501 METHODDEF(boolean)
decode_mcu(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)502 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
503 {
504 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
505 jpeg_component_info *compptr;
506 JBLOCKROW block;
507 unsigned char *st;
508 int blkn, ci, tbl, sign, k;
509 int v, m;
510
511 /* Process restart marker if needed */
512 if (cinfo->restart_interval) {
513 if (entropy->restarts_to_go == 0)
514 process_restart(cinfo);
515 entropy->restarts_to_go--;
516 }
517
518 if (entropy->ct == -1) return TRUE; /* if error do nothing */
519
520 /* Outer loop handles each block in the MCU */
521
522 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
523 block = MCU_data ? MCU_data[blkn] : NULL;
524 ci = cinfo->MCU_membership[blkn];
525 compptr = cinfo->cur_comp_info[ci];
526
527 /* Sections F.2.4.1 & F.1.4.4.1: Decoding of DC coefficients */
528
529 tbl = compptr->dc_tbl_no;
530
531 /* Table F.4: Point to statistics bin S0 for DC coefficient coding */
532 st = entropy->dc_stats[tbl] + entropy->dc_context[ci];
533
534 /* Figure F.19: Decode_DC_DIFF */
535 if (arith_decode(cinfo, st) == 0)
536 entropy->dc_context[ci] = 0;
537 else {
538 /* Figure F.21: Decoding nonzero value v */
539 /* Figure F.22: Decoding the sign of v */
540 sign = arith_decode(cinfo, st + 1);
541 st += 2; st += sign;
542 /* Figure F.23: Decoding the magnitude category of v */
543 if ((m = arith_decode(cinfo, st)) != 0) {
544 st = entropy->dc_stats[tbl] + 20; /* Table F.4: X1 = 20 */
545 while (arith_decode(cinfo, st)) {
546 if ((m <<= 1) == 0x8000) {
547 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
548 entropy->ct = -1; /* magnitude overflow */
549 return TRUE;
550 }
551 st += 1;
552 }
553 }
554 /* Section F.1.4.4.1.2: Establish dc_context conditioning category */
555 if (m < (int) ((1L << cinfo->arith_dc_L[tbl]) >> 1))
556 entropy->dc_context[ci] = 0; /* zero diff category */
557 else if (m > (int) ((1L << cinfo->arith_dc_U[tbl]) >> 1))
558 entropy->dc_context[ci] = 12 + (sign * 4); /* large diff category */
559 else
560 entropy->dc_context[ci] = 4 + (sign * 4); /* small diff category */
561 v = m;
562 /* Figure F.24: Decoding the magnitude bit pattern of v */
563 st += 14;
564 while (m >>= 1)
565 if (arith_decode(cinfo, st)) v |= m;
566 v += 1; if (sign) v = -v;
567 entropy->last_dc_val[ci] += v;
568 }
569
570 if (block)
571 (*block)[0] = (JCOEF) entropy->last_dc_val[ci];
572
573 /* Sections F.2.4.2 & F.1.4.4.2: Decoding of AC coefficients */
574
575 tbl = compptr->ac_tbl_no;
576
577 /* Figure F.20: Decode_AC_coefficients */
578 for (k = 1; k <= DCTSIZE2 - 1; k++) {
579 st = entropy->ac_stats[tbl] + 3 * (k - 1);
580 if (arith_decode(cinfo, st)) break; /* EOB flag */
581 while (arith_decode(cinfo, st + 1) == 0) {
582 st += 3; k++;
583 if (k > DCTSIZE2 - 1) {
584 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
585 entropy->ct = -1; /* spectral overflow */
586 return TRUE;
587 }
588 }
589 /* Figure F.21: Decoding nonzero value v */
590 /* Figure F.22: Decoding the sign of v */
591 sign = arith_decode(cinfo, entropy->fixed_bin);
592 st += 2;
593 /* Figure F.23: Decoding the magnitude category of v */
594 if ((m = arith_decode(cinfo, st)) != 0) {
595 if (arith_decode(cinfo, st)) {
596 m <<= 1;
597 st = entropy->ac_stats[tbl] +
598 (k <= cinfo->arith_ac_K[tbl] ? 189 : 217);
599 while (arith_decode(cinfo, st)) {
600 if ((m <<= 1) == 0x8000) {
601 WARNMS(cinfo, JWRN_ARITH_BAD_CODE);
602 entropy->ct = -1; /* magnitude overflow */
603 return TRUE;
604 }
605 st += 1;
606 }
607 }
608 }
609 v = m;
610 /* Figure F.24: Decoding the magnitude bit pattern of v */
611 st += 14;
612 while (m >>= 1)
613 if (arith_decode(cinfo, st)) v |= m;
614 v += 1; if (sign) v = -v;
615 if (block)
616 (*block)[jpeg_natural_order[k]] = (JCOEF) v;
617 }
618 }
619
620 return TRUE;
621 }
622
623
624 /*
625 * Initialize for an arithmetic-compressed scan.
626 */
627
628 METHODDEF(void)
start_pass(j_decompress_ptr cinfo)629 start_pass (j_decompress_ptr cinfo)
630 {
631 arith_entropy_ptr entropy = (arith_entropy_ptr) cinfo->entropy;
632 int ci, tbl;
633 jpeg_component_info *compptr;
634
635 if (cinfo->progressive_mode) {
636 /* Validate progressive scan parameters */
637 if (cinfo->Ss == 0) {
638 if (cinfo->Se != 0)
639 goto bad;
640 } else {
641 /* need not check Ss/Se < 0 since they came from unsigned bytes */
642 if (cinfo->Se < cinfo->Ss || cinfo->Se > DCTSIZE2 - 1)
643 goto bad;
644 /* AC scans may have only one component */
645 if (cinfo->comps_in_scan != 1)
646 goto bad;
647 }
648 if (cinfo->Ah != 0) {
649 /* Successive approximation refinement scan: must have Al = Ah-1. */
650 if (cinfo->Ah-1 != cinfo->Al)
651 goto bad;
652 }
653 if (cinfo->Al > 13) { /* need not check for < 0 */
654 bad:
655 ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
656 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
657 }
658 /* Update progression status, and verify that scan order is legal.
659 * Note that inter-scan inconsistencies are treated as warnings
660 * not fatal errors ... not clear if this is right way to behave.
661 */
662 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
663 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
664 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
665 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
666 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
667 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
668 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
669 if (cinfo->Ah != expected)
670 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
671 coef_bit_ptr[coefi] = cinfo->Al;
672 }
673 }
674 /* Select MCU decoding routine */
675 if (cinfo->Ah == 0) {
676 if (cinfo->Ss == 0)
677 entropy->pub.decode_mcu = decode_mcu_DC_first;
678 else
679 entropy->pub.decode_mcu = decode_mcu_AC_first;
680 } else {
681 if (cinfo->Ss == 0)
682 entropy->pub.decode_mcu = decode_mcu_DC_refine;
683 else
684 entropy->pub.decode_mcu = decode_mcu_AC_refine;
685 }
686 } else {
687 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
688 * This ought to be an error condition, but we make it a warning.
689 */
690 if (cinfo->Ss != 0 || cinfo->Ah != 0 || cinfo->Al != 0 ||
691 (cinfo->Se < DCTSIZE2 && cinfo->Se != DCTSIZE2 - 1))
692 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
693 /* Select MCU decoding routine */
694 entropy->pub.decode_mcu = decode_mcu;
695 }
696
697 /* Allocate & initialize requested statistics areas */
698 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
699 compptr = cinfo->cur_comp_info[ci];
700 if (!cinfo->progressive_mode || (cinfo->Ss == 0 && cinfo->Ah == 0)) {
701 tbl = compptr->dc_tbl_no;
702 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
703 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
704 if (entropy->dc_stats[tbl] == NULL)
705 entropy->dc_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
706 ((j_common_ptr) cinfo, JPOOL_IMAGE, DC_STAT_BINS);
707 MEMZERO(entropy->dc_stats[tbl], DC_STAT_BINS);
708 /* Initialize DC predictions to 0 */
709 entropy->last_dc_val[ci] = 0;
710 entropy->dc_context[ci] = 0;
711 }
712 if (!cinfo->progressive_mode || cinfo->Ss) {
713 tbl = compptr->ac_tbl_no;
714 if (tbl < 0 || tbl >= NUM_ARITH_TBLS)
715 ERREXIT1(cinfo, JERR_NO_ARITH_TABLE, tbl);
716 if (entropy->ac_stats[tbl] == NULL)
717 entropy->ac_stats[tbl] = (unsigned char *) (*cinfo->mem->alloc_small)
718 ((j_common_ptr) cinfo, JPOOL_IMAGE, AC_STAT_BINS);
719 MEMZERO(entropy->ac_stats[tbl], AC_STAT_BINS);
720 }
721 }
722
723 /* Initialize arithmetic decoding variables */
724 entropy->c = 0;
725 entropy->a = 0;
726 entropy->ct = -16; /* force reading 2 initial bytes to fill C */
727
728 /* Initialize restart counter */
729 entropy->restarts_to_go = cinfo->restart_interval;
730 }
731
732
733 /*
734 * Module initialization routine for arithmetic entropy decoding.
735 */
736
737 GLOBAL(void)
jinit_arith_decoder(j_decompress_ptr cinfo)738 jinit_arith_decoder (j_decompress_ptr cinfo)
739 {
740 arith_entropy_ptr entropy;
741 int i;
742
743 entropy = (arith_entropy_ptr)
744 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
745 sizeof(arith_entropy_decoder));
746 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
747 entropy->pub.start_pass = start_pass;
748
749 /* Mark tables unallocated */
750 for (i = 0; i < NUM_ARITH_TBLS; i++) {
751 entropy->dc_stats[i] = NULL;
752 entropy->ac_stats[i] = NULL;
753 }
754
755 /* Initialize index for fixed probability estimation */
756 entropy->fixed_bin[0] = 113;
757
758 if (cinfo->progressive_mode) {
759 /* Create progression status table */
760 int *coef_bit_ptr, ci;
761 cinfo->coef_bits = (int (*)[DCTSIZE2])
762 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
763 cinfo->num_components*DCTSIZE2*sizeof(int));
764 coef_bit_ptr = & cinfo->coef_bits[0][0];
765 for (ci = 0; ci < cinfo->num_components; ci++)
766 for (i = 0; i < DCTSIZE2; i++)
767 *coef_bit_ptr++ = -1;
768 }
769 }
770