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jdphuff.c (20559B)
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1 /*
2 * jdphuff.c
3 *
4 * Copyright (C) 1995-1997, Thomas G. Lane.
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 Huffman entropy decoding routines for progressive JPEG.
9 *
10 * Much of the complexity here has to do with supporting input suspension.
11 * If the data source module demands suspension, we want to be able to back
12 * up to the start of the current MCU. To do this, we copy state variables
13 * into local working storage, and update them back to the permanent
14 * storage only upon successful completion of an MCU.
15 */
16
17 #define JPEG_INTERNALS
18 #include "jinclude.h"
19 #include "jpeglib.h"
20 #include "jdhuff.h" /* Declarations shared with jdhuff.c */
21
22
23 #ifdef D_PROGRESSIVE_SUPPORTED
24
25 /*
26 * Expanded entropy decoder object for progressive Huffman decoding.
27 *
28 * The savable_state subrecord contains fields that change within an MCU,
29 * but must not be updated permanently until we complete the MCU.
30 */
31
32 typedef struct {
33 unsigned int EOBRUN; /* remaining EOBs in EOBRUN */
34 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
35 } savable_state;
36
37 /* This macro is to work around compilers with missing or broken
38 * structure assignment. You'll need to fix this code if you have
39 * such a compiler and you change MAX_COMPS_IN_SCAN.
40 */
41
42 #ifndef NO_STRUCT_ASSIGN
43 #define ASSIGN_STATE(dest,src) ((dest) = (src))
44 #else
45 #if MAX_COMPS_IN_SCAN == 4
46 #define ASSIGN_STATE(dest,src) \
47 ((dest).EOBRUN = (src).EOBRUN, \
48 (dest).last_dc_val[0] = (src).last_dc_val[0], \
49 (dest).last_dc_val[1] = (src).last_dc_val[1], \
50 (dest).last_dc_val[2] = (src).last_dc_val[2], \
51 (dest).last_dc_val[3] = (src).last_dc_val[3])
52 #endif
53 #endif
54
55
56 typedef struct {
57 struct jpeg_entropy_decoder pub; /* public fields */
58
59 /* These fields are loaded into local variables at start of each MCU.
60 * In case of suspension, we exit WITHOUT updating them.
61 */
62 bitread_perm_state bitstate; /* Bit buffer at start of MCU */
63 savable_state saved; /* Other state at start of MCU */
64
65 /* These fields are NOT loaded into local working state. */
66 unsigned int restarts_to_go; /* MCUs left in this restart interval */
67
68 /* Pointers to derived tables (these workspaces have image lifespan) */
69 d_derived_tbl * derived_tbls[NUM_HUFF_TBLS];
70
71 d_derived_tbl * ac_derived_tbl; /* active table during an AC scan */
72 } phuff_entropy_decoder;
73
74 typedef phuff_entropy_decoder * phuff_entropy_ptr;
75
76 /* Forward declarations */
77 METHODDEF(boolean) decode_mcu_DC_first JPP((j_decompress_ptr cinfo,
78 JBLOCKROW *MCU_data));
79 METHODDEF(boolean) decode_mcu_AC_first JPP((j_decompress_ptr cinfo,
80 JBLOCKROW *MCU_data));
81 METHODDEF(boolean) decode_mcu_DC_refine JPP((j_decompress_ptr cinfo,
82 JBLOCKROW *MCU_data));
83 METHODDEF(boolean) decode_mcu_AC_refine JPP((j_decompress_ptr cinfo,
84 JBLOCKROW *MCU_data));
85
86
87 /*
88 * Initialize for a Huffman-compressed scan.
89 */
90
91 METHODDEF(void)
92 start_pass_phuff_decoder (j_decompress_ptr cinfo)
93 {
94 phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
95 boolean is_DC_band, bad;
96 int ci, coefi, tbl;
97 int *coef_bit_ptr;
98 jpeg_component_info * compptr;
99
100 is_DC_band = (cinfo->Ss == 0);
101
102 /* Validate scan parameters */
103 bad = FALSE;
104 if (is_DC_band) {
105 if (cinfo->Se != 0)
106 bad = TRUE;
107 } else {
108 /* need not check Ss/Se < 0 since they came from unsigned bytes */
109 if (cinfo->Ss > cinfo->Se || cinfo->Se >= DCTSIZE2)
110 bad = TRUE;
111 /* AC scans may have only one component */
112 if (cinfo->comps_in_scan != 1)
113 bad = TRUE;
114 }
115 if (cinfo->Ah != 0) {
116 /* Successive approximation refinement scan: must have Al = Ah-1. */
117 if (cinfo->Al != cinfo->Ah-1)
118 bad = TRUE;
119 }
120 if (cinfo->Al > 13) /* need not check for < 0 */
121 bad = TRUE;
122 /* Arguably the maximum Al value should be less than 13 for 8-bit precision,
123 * but the spec doesn't say so, and we try to be liberal about what we
124 * accept. Note: large Al values could result in out-of-range DC
125 * coefficients during early scans, leading to bizarre displays due to
126 * overflows in the IDCT math. But we won't crash.
127 */
128 if (bad)
129 ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
130 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
131 /* Update progression status, and verify that scan order is legal.
132 * Note that inter-scan inconsistencies are treated as warnings
133 * not fatal errors ... not clear if this is right way to behave.
134 */
135 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
136 int cindex = cinfo->cur_comp_info[ci]->component_index;
137 coef_bit_ptr = & cinfo->coef_bits[cindex][0];
138 if (!is_DC_band && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
139 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
140 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
141 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
142 if (cinfo->Ah != expected)
143 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
144 coef_bit_ptr[coefi] = cinfo->Al;
145 }
146 }
147
148 /* Select MCU decoding routine */
149 if (cinfo->Ah == 0) {
150 if (is_DC_band)
151 entropy->pub.decode_mcu = decode_mcu_DC_first;
152 else
153 entropy->pub.decode_mcu = decode_mcu_AC_first;
154 } else {
155 if (is_DC_band)
156 entropy->pub.decode_mcu = decode_mcu_DC_refine;
157 else
158 entropy->pub.decode_mcu = decode_mcu_AC_refine;
159 }
160
161 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
162 compptr = cinfo->cur_comp_info[ci];
163 /* Make sure requested tables are present, and compute derived tables.
164 * We may build same derived table more than once, but it's not expensive.
165 */
166 if (is_DC_band) {
167 if (cinfo->Ah == 0) { /* DC refinement needs no table */
168 tbl = compptr->dc_tbl_no;
169 jpeg_make_d_derived_tbl(cinfo, TRUE, tbl,
170 & entropy->derived_tbls[tbl]);
171 }
172 } else {
173 tbl = compptr->ac_tbl_no;
174 jpeg_make_d_derived_tbl(cinfo, FALSE, tbl,
175 & entropy->derived_tbls[tbl]);
176 /* remember the single active table */
177 entropy->ac_derived_tbl = entropy->derived_tbls[tbl];
178 }
179 /* Initialize DC predictions to 0 */
180 entropy->saved.last_dc_val[ci] = 0;
181 }
182
183 /* Initialize bitread state variables */
184 entropy->bitstate.bits_left = 0;
185 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
186 entropy->pub.insufficient_data = FALSE;
187
188 /* Initialize private state variables */
189 entropy->saved.EOBRUN = 0;
190
191 /* Initialize restart counter */
192 entropy->restarts_to_go = cinfo->restart_interval;
193 }
194
195
196 /*
197 * Figure F.12: extend sign bit.
198 * On some machines, a shift and add will be faster than a table lookup.
199 */
200
201 #ifdef AVOID_TABLES
202
203 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))
204
205 #else
206
207 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
208
209 static const int extend_test[16] = /* entry n is 2**(n-1) */
210 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
211 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
212
213 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
214 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
215 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
216 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
217 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
218
219 #endif /* AVOID_TABLES */
220
221
222 /*
223 * Check for a restart marker & resynchronize decoder.
224 * Returns FALSE if must suspend.
225 */
226
227 LOCAL(boolean)
228 process_restart (j_decompress_ptr cinfo)
229 {
230 phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
231 int ci;
232
233 /* Throw away any unused bits remaining in bit buffer; */
234 /* include any full bytes in next_marker's count of discarded bytes */
235 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
236 entropy->bitstate.bits_left = 0;
237
238 /* Advance past the RSTn marker */
239 if (! (*cinfo->marker->read_restart_marker) (cinfo))
240 return FALSE;
241
242 /* Re-initialize DC predictions to 0 */
243 for (ci = 0; ci < cinfo->comps_in_scan; ci++)
244 entropy->saved.last_dc_val[ci] = 0;
245 /* Re-init EOB run count, too */
246 entropy->saved.EOBRUN = 0;
247
248 /* Reset restart counter */
249 entropy->restarts_to_go = cinfo->restart_interval;
250
251 /* Reset out-of-data flag, unless read_restart_marker left us smack up
252 * against a marker. In that case we will end up treating the next data
253 * segment as empty, and we can avoid producing bogus output pixels by
254 * leaving the flag set.
255 */
256 if (cinfo->unread_marker == 0)
257 entropy->pub.insufficient_data = FALSE;
258
259 return TRUE;
260 }
261
262
263 /*
264 * Huffman MCU decoding.
265 * Each of these routines decodes and returns one MCU's worth of
266 * Huffman-compressed coefficients.
267 * The coefficients are reordered from zigzag order into natural array order,
268 * but are not dequantized.
269 *
270 * The i'th block of the MCU is stored into the block pointed to by
271 * MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
272 *
273 * We return FALSE if data source requested suspension. In that case no
274 * changes have been made to permanent state. (Exception: some output
275 * coefficients may already have been assigned. This is harmless for
276 * spectral selection, since we'll just re-assign them on the next call.
277 * Successive approximation AC refinement has to be more careful, however.)
278 */
279
280 /*
281 * MCU decoding for DC initial scan (either spectral selection,
282 * or first pass of successive approximation).
283 */
284
285 METHODDEF(boolean)
286 decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
287 {
288 phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
289 int Al = cinfo->Al;
290 register int s, r;
291 int blkn, ci;
292 JBLOCKROW block;
293 BITREAD_STATE_VARS;
294 savable_state state;
295 d_derived_tbl * tbl;
296 jpeg_component_info * compptr;
297
298 /* Process restart marker if needed; may have to suspend */
299 if (cinfo->restart_interval) {
300 if (entropy->restarts_to_go == 0)
301 if (! process_restart(cinfo))
302 return FALSE;
303 }
304
305 /* If we've run out of data, just leave the MCU set to zeroes.
306 * This way, we return uniform gray for the remainder of the segment.
307 */
308 if (! entropy->pub.insufficient_data) {
309
310 /* Load up working state */
311 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
312 ASSIGN_STATE(state, entropy->saved);
313
314 /* Outer loop handles each block in the MCU */
315
316 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
317 block = MCU_data[blkn];
318 ci = cinfo->MCU_membership[blkn];
319 compptr = cinfo->cur_comp_info[ci];
320 tbl = entropy->derived_tbls[compptr->dc_tbl_no];
321
322 /* Decode a single block's worth of coefficients */
323
324 /* Section F.2.2.1: decode the DC coefficient difference */
325 HUFF_DECODE(s, br_state, tbl, return FALSE, label1);
326 if (s) {
327 CHECK_BIT_BUFFER(br_state, s, return FALSE);
328 r = GET_BITS(s);
329 s = HUFF_EXTEND(r, s);
330 }
331
332 /* Convert DC difference to actual value, update last_dc_val */
333 s += state.last_dc_val[ci];
334 state.last_dc_val[ci] = s;
335 /* Scale and output the coefficient (assumes jpeg_natural_order[0]=0) */
336 (*block)[0] = (JCOEF) (s << Al);
337 }
338
339 /* Completed MCU, so update state */
340 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
341 ASSIGN_STATE(entropy->saved, state);
342 }
343
344 /* Account for restart interval (no-op if not using restarts) */
345 entropy->restarts_to_go--;
346
347 return TRUE;
348 }
349
350
351 /*
352 * MCU decoding for AC initial scan (either spectral selection,
353 * or first pass of successive approximation).
354 */
355
356 METHODDEF(boolean)
357 decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
358 {
359 phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
360 int Se = cinfo->Se;
361 int Al = cinfo->Al;
362 register int s, k, r;
363 unsigned int EOBRUN;
364 JBLOCKROW block;
365 BITREAD_STATE_VARS;
366 d_derived_tbl * tbl;
367
368 /* Process restart marker if needed; may have to suspend */
369 if (cinfo->restart_interval) {
370 if (entropy->restarts_to_go == 0)
371 if (! process_restart(cinfo))
372 return FALSE;
373 }
374
375 /* If we've run out of data, just leave the MCU set to zeroes.
376 * This way, we return uniform gray for the remainder of the segment.
377 */
378 if (! entropy->pub.insufficient_data) {
379
380 /* Load up working state.
381 * We can avoid loading/saving bitread state if in an EOB run.
382 */
383 EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */
384
385 /* There is always only one block per MCU */
386
387 if (EOBRUN > 0) /* if it's a band of zeroes... */
388 EOBRUN--; /* ...process it now (we do nothing) */
389 else {
390 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
391 block = MCU_data[0];
392 tbl = entropy->ac_derived_tbl;
393
394 for (k = cinfo->Ss; k <= Se; k++) {
395 HUFF_DECODE(s, br_state, tbl, return FALSE, label2);
396 r = s >> 4;
397 s &= 15;
398 if (s) {
399 k += r;
400 CHECK_BIT_BUFFER(br_state, s, return FALSE);
401 r = GET_BITS(s);
402 s = HUFF_EXTEND(r, s);
403 /* Scale and output coefficient in natural (dezigzagged) order */
404 (*block)[jpeg_natural_order[k]] = (JCOEF) (s << Al);
405 } else {
406 if (r == 15) { /* ZRL */
407 k += 15; /* skip 15 zeroes in band */
408 } else { /* EOBr, run length is 2^r + appended bits */
409 EOBRUN = 1 << r;
410 if (r) { /* EOBr, r > 0 */
411 CHECK_BIT_BUFFER(br_state, r, return FALSE);
412 r = GET_BITS(r);
413 EOBRUN += r;
414 }
415 EOBRUN--; /* this band is processed at this moment */
416 break; /* force end-of-band */
417 }
418 }
419 }
420
421 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
422 }
423
424 /* Completed MCU, so update state */
425 entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */
426 }
427
428 /* Account for restart interval (no-op if not using restarts) */
429 entropy->restarts_to_go--;
430
431 return TRUE;
432 }
433
434
435 /*
436 * MCU decoding for DC successive approximation refinement scan.
437 * Note: we assume such scans can be multi-component, although the spec
438 * is not very clear on the point.
439 */
440
441 METHODDEF(boolean)
442 decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
443 {
444 phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
445 int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
446 int blkn;
447 JBLOCKROW block;
448 BITREAD_STATE_VARS;
449
450 /* Process restart marker if needed; may have to suspend */
451 if (cinfo->restart_interval) {
452 if (entropy->restarts_to_go == 0)
453 if (! process_restart(cinfo))
454 return FALSE;
455 }
456
457 /* Not worth the cycles to check insufficient_data here,
458 * since we will not change the data anyway if we read zeroes.
459 */
460
461 /* Load up working state */
462 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
463
464 /* Outer loop handles each block in the MCU */
465
466 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
467 block = MCU_data[blkn];
468
469 /* Encoded data is simply the next bit of the two's-complement DC value */
470 CHECK_BIT_BUFFER(br_state, 1, return FALSE);
471 if (GET_BITS(1))
472 (*block)[0] |= p1;
473 /* Note: since we use |=, repeating the assignment later is safe */
474 }
475
476 /* Completed MCU, so update state */
477 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
478
479 /* Account for restart interval (no-op if not using restarts) */
480 entropy->restarts_to_go--;
481
482 return TRUE;
483 }
484
485
486 /*
487 * MCU decoding for AC successive approximation refinement scan.
488 */
489
490 METHODDEF(boolean)
491 decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
492 {
493 phuff_entropy_ptr entropy = (phuff_entropy_ptr) cinfo->entropy;
494 int Se = cinfo->Se;
495 int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
496 int m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */
497 register int s, k, r;
498 unsigned int EOBRUN;
499 JBLOCKROW block;
500 JCOEFPTR thiscoef;
501 BITREAD_STATE_VARS;
502 d_derived_tbl * tbl;
503 int num_newnz;
504 int newnz_pos[DCTSIZE2];
505
506 /* Process restart marker if needed; may have to suspend */
507 if (cinfo->restart_interval) {
508 if (entropy->restarts_to_go == 0)
509 if (! process_restart(cinfo))
510 return FALSE;
511 }
512
513 /* If we've run out of data, don't modify the MCU.
514 */
515 if (! entropy->pub.insufficient_data) {
516
517 /* Load up working state */
518 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
519 EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */
520
521 /* There is always only one block per MCU */
522 block = MCU_data[0];
523 tbl = entropy->ac_derived_tbl;
524
525 /* If we are forced to suspend, we must undo the assignments to any newly
526 * nonzero coefficients in the block, because otherwise we'd get confused
527 * next time about which coefficients were already nonzero.
528 * But we need not undo addition of bits to already-nonzero coefficients;
529 * instead, we can test the current bit to see if we already did it.
530 */
531 num_newnz = 0;
532
533 /* initialize coefficient loop counter to start of band */
534 k = cinfo->Ss;
535
536 if (EOBRUN == 0) {
537 for (; k <= Se; k++) {
538 HUFF_DECODE(s, br_state, tbl, goto undoit, label3);
539 r = s >> 4;
540 s &= 15;
541 if (s) {
542 if (s != 1) /* size of new coef should always be 1 */
543 WARNMS(cinfo, JWRN_HUFF_BAD_CODE);
544 CHECK_BIT_BUFFER(br_state, 1, goto undoit);
545 if (GET_BITS(1))
546 s = p1; /* newly nonzero coef is positive */
547 else
548 s = m1; /* newly nonzero coef is negative */
549 } else {
550 if (r != 15) {
551 EOBRUN = 1 << r; /* EOBr, run length is 2^r + appended bits */
552 if (r) {
553 CHECK_BIT_BUFFER(br_state, r, goto undoit);
554 r = GET_BITS(r);
555 EOBRUN += r;
556 }
557 break; /* rest of block is handled by EOB logic */
558 }
559 /* note s = 0 for processing ZRL */
560 }
561 /* Advance over already-nonzero coefs and r still-zero coefs,
562 * appending correction bits to the nonzeroes. A correction bit is 1
563 * if the absolute value of the coefficient must be increased.
564 */
565 do {
566 thiscoef = *block + jpeg_natural_order[k];
567 if (*thiscoef != 0) {
568 CHECK_BIT_BUFFER(br_state, 1, goto undoit);
569 if (GET_BITS(1)) {
570 if ((*thiscoef & p1) == 0) { /* do nothing if already set it */
571 if (*thiscoef >= 0)
572 *thiscoef += p1;
573 else
574 *thiscoef += m1;
575 }
576 }
577 } else {
578 if (--r < 0)
579 break; /* reached target zero coefficient */
580 }
581 k++;
582 } while (k <= Se);
583 if (s) {
584 int pos = jpeg_natural_order[k];
585 /* Output newly nonzero coefficient */
586 (*block)[pos] = (JCOEF) s;
587 /* Remember its position in case we have to suspend */
588 newnz_pos[num_newnz++] = pos;
589 }
590 }
591 }
592
593 if (EOBRUN > 0) {
594 /* Scan any remaining coefficient positions after the end-of-band
595 * (the last newly nonzero coefficient, if any). Append a correction
596 * bit to each already-nonzero coefficient. A correction bit is 1
597 * if the absolute value of the coefficient must be increased.
598 */
599 for (; k <= Se; k++) {
600 thiscoef = *block + jpeg_natural_order[k];
601 if (*thiscoef != 0) {
602 CHECK_BIT_BUFFER(br_state, 1, goto undoit);
603 if (GET_BITS(1)) {
604 if ((*thiscoef & p1) == 0) { /* do nothing if already changed it */
605 if (*thiscoef >= 0)
606 *thiscoef += p1;
607 else
608 *thiscoef += m1;
609 }
610 }
611 }
612 }
613 /* Count one block completed in EOB run */
614 EOBRUN--;
615 }
616
617 /* Completed MCU, so update state */
618 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
619 entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */
620 }
621
622 /* Account for restart interval (no-op if not using restarts) */
623 entropy->restarts_to_go--;
624
625 return TRUE;
626
627 undoit:
628 /* Re-zero any output coefficients that we made newly nonzero */
629 while (num_newnz > 0)
630 (*block)[newnz_pos[--num_newnz]] = 0;
631
632 return FALSE;
633 }
634
635
636 /*
637 * Module initialization routine for progressive Huffman entropy decoding.
638 */
639
640 GLOBAL(void)
641 jinit_phuff_decoder (j_decompress_ptr cinfo)
642 {
643 phuff_entropy_ptr entropy;
644 int *coef_bit_ptr;
645 int ci, i;
646
647 entropy = (phuff_entropy_ptr)
648 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
649 SIZEOF(phuff_entropy_decoder));
650 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
651 entropy->pub.start_pass = start_pass_phuff_decoder;
652
653 /* Mark derived tables unallocated */
654 for (i = 0; i < NUM_HUFF_TBLS; i++) {
655 entropy->derived_tbls[i] = NULL;
656 }
657
658 /* Create progression status table */
659 cinfo->coef_bits = (int (*)[DCTSIZE2])
660 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
661 cinfo->num_components*DCTSIZE2*SIZEOF(int));
662 coef_bit_ptr = & cinfo->coef_bits[0][0];
663 for (ci = 0; ci < cinfo->num_components; ci++)
664 for (i = 0; i < DCTSIZE2; i++)
665 *coef_bit_ptr++ = -1;
666 }
667
668 #endif /* D_PROGRESSIVE_SUPPORTED */