1 /*
2 * reserved comment block
3 * DO NOT REMOVE OR ALTER!
4 */
5 /*
6 * jdhuff.c
7 *
8 * Copyright (C) 1991-1997, Thomas G. Lane.
9 * This file is part of the Independent JPEG Group's software.
10 * For conditions of distribution and use, see the accompanying README file.
11 *
12 * This file contains Huffman entropy decoding routines.
13 *
14 * Much of the complexity here has to do with supporting input suspension.
15 * If the data source module demands suspension, we want to be able to back
16 * up to the start of the current MCU. To do this, we copy state variables
17 * into local working storage, and update them back to the permanent
18 * storage only upon successful completion of an MCU.
19 */
20
21 #define JPEG_INTERNALS
22 #include "jinclude.h"
23 #include "jpeglib.h"
24 #include "jdhuff.h" /* Declarations shared with jdphuff.c */
25
26
27 /*
28 * Expanded entropy decoder object for Huffman decoding.
29 *
30 * The savable_state subrecord contains fields that change within an MCU,
31 * but must not be updated permanently until we complete the MCU.
32 */
33
34 typedef struct {
35 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
36 } savable_state;
37
38 /* This macro is to work around compilers with missing or broken
39 * structure assignment. You'll need to fix this code if you have
40 * such a compiler and you change MAX_COMPS_IN_SCAN.
41 */
42
43 #ifndef NO_STRUCT_ASSIGN
44 #define ASSIGN_STATE(dest,src) ((dest) = (src))
45 #else
46 #if MAX_COMPS_IN_SCAN == 4
47 #define ASSIGN_STATE(dest,src) \
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 * dc_derived_tbls[NUM_HUFF_TBLS];
70 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
71
72 /* Precalculated info set up by start_pass for use in decode_mcu: */
73
74 /* Pointers to derived tables to be used for each block within an MCU */
75 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
76 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
77 /* Whether we care about the DC and AC coefficient values for each block */
78 boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
79 boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
80 } huff_entropy_decoder;
81
82 typedef huff_entropy_decoder * huff_entropy_ptr;
83
84
85 /*
86 * Initialize for a Huffman-compressed scan.
87 */
88
89 METHODDEF(void)
90 start_pass_huff_decoder (j_decompress_ptr cinfo)
91 {
92 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
93 int ci, blkn, dctbl, actbl;
94 jpeg_component_info * compptr;
95
96 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
97 * This ought to be an error condition, but we make it a warning because
98 * there are some baseline files out there with all zeroes in these bytes.
99 */
100 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
101 cinfo->Ah != 0 || cinfo->Al != 0)
102 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
103
104 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
105 compptr = cinfo->cur_comp_info[ci];
106 dctbl = compptr->dc_tbl_no;
107 actbl = compptr->ac_tbl_no;
108 /* Compute derived values for Huffman tables */
109 /* We may do this more than once for a table, but it's not expensive */
110 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
111 & entropy->dc_derived_tbls[dctbl]);
112 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
113 & entropy->ac_derived_tbls[actbl]);
114 /* Initialize DC predictions to 0 */
115 entropy->saved.last_dc_val[ci] = 0;
116 }
117
118 /* Precalculate decoding info for each block in an MCU of this scan */
119 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
120 ci = cinfo->MCU_membership[blkn];
121 compptr = cinfo->cur_comp_info[ci];
122 /* Precalculate which table to use for each block */
123 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
124 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
125 /* Decide whether we really care about the coefficient values */
126 if (compptr->component_needed) {
127 entropy->dc_needed[blkn] = TRUE;
128 /* we don't need the ACs if producing a 1/8th-size image */
129 entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1);
130 } else {
131 entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
132 }
133 }
134
135 /* Initialize bitread state variables */
136 entropy->bitstate.bits_left = 0;
137 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
138 entropy->pub.insufficient_data = FALSE;
139
140 /* Initialize restart counter */
141 entropy->restarts_to_go = cinfo->restart_interval;
142 }
143
144
145 /*
146 * Compute the derived values for a Huffman table.
147 * This routine also performs some validation checks on the table.
148 *
149 * Note this is also used by jdphuff.c.
150 */
151
152 GLOBAL(void)
153 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
154 d_derived_tbl ** pdtbl)
155 {
156 JHUFF_TBL *htbl;
157 d_derived_tbl *dtbl;
158 int p, i, l, si, numsymbols;
159 int lookbits, ctr;
160 char huffsize[257];
161 unsigned int huffcode[257];
162 unsigned int code;
163
164 /* Note that huffsize[] and huffcode[] are filled in code-length order,
165 * paralleling the order of the symbols themselves in htbl->huffval[].
166 */
167
168 /* Find the input Huffman table */
169 if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
170 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
171 htbl =
172 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
173 if (htbl == NULL)
174 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
175
176 /* Allocate a workspace if we haven't already done so. */
177 if (*pdtbl == NULL)
178 *pdtbl = (d_derived_tbl *)
179 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
180 SIZEOF(d_derived_tbl));
181 dtbl = *pdtbl;
182 dtbl->pub = htbl; /* fill in back link */
183
184 /* Figure C.1: make table of Huffman code length for each symbol */
185
186 p = 0;
187 for (l = 1; l <= 16; l++) {
188 i = (int) htbl->bits[l];
189 if (i < 0 || p + i > 256) /* protect against table overrun */
190 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
191 while (i--)
192 huffsize[p++] = (char) l;
193 }
194 huffsize[p] = 0;
195 numsymbols = p;
196
197 /* Figure C.2: generate the codes themselves */
198 /* We also validate that the counts represent a legal Huffman code tree. */
199
200 code = 0;
201 si = huffsize[0];
202 p = 0;
203 while (huffsize[p]) {
204 while (((int) huffsize[p]) == si) {
205 huffcode[p++] = code;
206 code++;
207 }
208 /* code is now 1 more than the last code used for codelength si; but
209 * it must still fit in si bits, since no code is allowed to be all ones.
210 */
211 if (((INT32) code) >= (((INT32) 1) << si))
212 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
213 code <<= 1;
214 si++;
215 }
216
217 /* Figure F.15: generate decoding tables for bit-sequential decoding */
218
219 p = 0;
220 for (l = 1; l <= 16; l++) {
221 if (htbl->bits[l]) {
222 /* valoffset[l] = huffval[] index of 1st symbol of code length l,
223 * minus the minimum code of length l
224 */
225 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
226 p += htbl->bits[l];
227 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
228 } else {
229 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */
230 }
231 }
232 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */
233
234 /* Compute lookahead tables to speed up decoding.
235 * First we set all the table entries to 0, indicating "too long";
236 * then we iterate through the Huffman codes that are short enough and
237 * fill in all the entries that correspond to bit sequences starting
238 * with that code.
239 */
240
241 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));
242
243 p = 0;
244 for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
245 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
246 /* l = current code's length, p = its index in huffcode[] & huffval[]. */
247 /* Generate left-justified code followed by all possible bit sequences */
248 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
249 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
250 dtbl->look_nbits[lookbits] = l;
251 dtbl->look_sym[lookbits] = htbl->huffval[p];
252 lookbits++;
253 }
254 }
255 }
256
257 /* Validate symbols as being reasonable.
258 * For AC tables, we make no check, but accept all byte values 0..255.
259 * For DC tables, we require the symbols to be in range 0..15.
260 * (Tighter bounds could be applied depending on the data depth and mode,
261 * but this is sufficient to ensure safe decoding.)
262 */
263 if (isDC) {
264 for (i = 0; i < numsymbols; i++) {
265 int sym = htbl->huffval[i];
266 if (sym < 0 || sym > 15)
267 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
268 }
269 }
270 }
271
272
273 /*
274 * Out-of-line code for bit fetching (shared with jdphuff.c).
275 * See jdhuff.h for info about usage.
276 * Note: current values of get_buffer and bits_left are passed as parameters,
277 * but are returned in the corresponding fields of the state struct.
278 *
279 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
280 * of get_buffer to be used. (On machines with wider words, an even larger
281 * buffer could be used.) However, on some machines 32-bit shifts are
282 * quite slow and take time proportional to the number of places shifted.
283 * (This is true with most PC compilers, for instance.) In this case it may
284 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
285 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
286 */
287
288 #ifdef SLOW_SHIFT_32
289 #define MIN_GET_BITS 15 /* minimum allowable value */
290 #else
291 #define MIN_GET_BITS (BIT_BUF_SIZE-7)
292 #endif
293
294
295 GLOBAL(boolean)
296 jpeg_fill_bit_buffer (bitread_working_state * state,
297 register bit_buf_type get_buffer, register int bits_left,
298 int nbits)
299 /* Load up the bit buffer to a depth of at least nbits */
300 {
301 /* Copy heavily used state fields into locals (hopefully registers) */
302 register const JOCTET * next_input_byte = state->next_input_byte;
303 register size_t bytes_in_buffer = state->bytes_in_buffer;
304 j_decompress_ptr cinfo = state->cinfo;
305
306 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
307 /* (It is assumed that no request will be for more than that many bits.) */
308 /* We fail to do so only if we hit a marker or are forced to suspend. */
309
310 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */
311 while (bits_left < MIN_GET_BITS) {
312 register int c;
313
314 /* Attempt to read a byte */
315 if (bytes_in_buffer == 0) {
316 if (! (*cinfo->src->fill_input_buffer) (cinfo))
317 return FALSE;
318 next_input_byte = cinfo->src->next_input_byte;
319 bytes_in_buffer = cinfo->src->bytes_in_buffer;
320 }
321 bytes_in_buffer--;
322 c = GETJOCTET(*next_input_byte++);
323
324 /* If it's 0xFF, check and discard stuffed zero byte */
325 if (c == 0xFF) {
326 /* Loop here to discard any padding FF's on terminating marker,
327 * so that we can save a valid unread_marker value. NOTE: we will
328 * accept multiple FF's followed by a 0 as meaning a single FF data
329 * byte. This data pattern is not valid according to the standard.
330 */
331 do {
332 if (bytes_in_buffer == 0) {
333 if (! (*cinfo->src->fill_input_buffer) (cinfo))
334 return FALSE;
335 next_input_byte = cinfo->src->next_input_byte;
336 bytes_in_buffer = cinfo->src->bytes_in_buffer;
337 }
338 bytes_in_buffer--;
339 c = GETJOCTET(*next_input_byte++);
340 } while (c == 0xFF);
341
342 if (c == 0) {
343 /* Found FF/00, which represents an FF data byte */
344 c = 0xFF;
345 } else {
346 /* Oops, it's actually a marker indicating end of compressed data.
347 * Save the marker code for later use.
348 * Fine point: it might appear that we should save the marker into
349 * bitread working state, not straight into permanent state. But
350 * once we have hit a marker, we cannot need to suspend within the
351 * current MCU, because we will read no more bytes from the data
352 * source. So it is OK to update permanent state right away.
353 */
354 cinfo->unread_marker = c;
355 /* See if we need to insert some fake zero bits. */
356 goto no_more_bytes;
357 }
358 }
359
360 /* OK, load c into get_buffer */
361 get_buffer = (get_buffer << 8) | c;
362 bits_left += 8;
363 } /* end while */
364 } else {
365 no_more_bytes:
366 /* We get here if we've read the marker that terminates the compressed
367 * data segment. There should be enough bits in the buffer register
368 * to satisfy the request; if so, no problem.
369 */
370 if (nbits > bits_left) {
371 /* Uh-oh. Report corrupted data to user and stuff zeroes into
372 * the data stream, so that we can produce some kind of image.
373 * We use a nonvolatile flag to ensure that only one warning message
374 * appears per data segment.
375 */
376 if (! cinfo->entropy->insufficient_data) {
377 WARNMS(cinfo, JWRN_HIT_MARKER);
378 cinfo->entropy->insufficient_data = TRUE;
379 }
380 /* Fill the buffer with zero bits */
381 get_buffer <<= MIN_GET_BITS - bits_left;
382 bits_left = MIN_GET_BITS;
383 }
384 }
385
386 /* Unload the local registers */
387 state->next_input_byte = next_input_byte;
388 state->bytes_in_buffer = bytes_in_buffer;
389 state->get_buffer = get_buffer;
390 state->bits_left = bits_left;
391
392 return TRUE;
393 }
394
395
396 /*
397 * Out-of-line code for Huffman code decoding.
398 * See jdhuff.h for info about usage.
399 */
400
401 GLOBAL(int)
402 jpeg_huff_decode (bitread_working_state * state,
403 register bit_buf_type get_buffer, register int bits_left,
404 d_derived_tbl * htbl, int min_bits)
405 {
406 register int l = min_bits;
407 register INT32 code;
408
409 /* HUFF_DECODE has determined that the code is at least min_bits */
410 /* bits long, so fetch that many bits in one swoop. */
411
412 CHECK_BIT_BUFFER(*state, l, return -1);
413 code = GET_BITS(l);
414
415 /* Collect the rest of the Huffman code one bit at a time. */
416 /* This is per Figure F.16 in the JPEG spec. */
417
418 while (code > htbl->maxcode[l]) {
419 code <<= 1;
420 CHECK_BIT_BUFFER(*state, 1, return -1);
421 code |= GET_BITS(1);
422 l++;
423 }
424
425 /* Unload the local registers */
426 state->get_buffer = get_buffer;
427 state->bits_left = bits_left;
428
429 /* With garbage input we may reach the sentinel value l = 17. */
430
431 if (l > 16) {
432 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
433 return 0; /* fake a zero as the safest result */
434 }
435
436 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ];
437 }
438
439
440 /*
441 * Figure F.12: extend sign bit.
442 * On some machines, a shift and add will be faster than a table lookup.
443 */
444
445 #ifdef AVOID_TABLES
446
447 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))
448
449 #else
450
451 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
452
453 static const int extend_test[16] = /* entry n is 2**(n-1) */
454 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
455 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
456
457 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
458 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
459 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
460 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
461 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
462
463 #endif /* AVOID_TABLES */
464
465
466 /*
467 * Check for a restart marker & resynchronize decoder.
468 * Returns FALSE if must suspend.
469 */
470
471 LOCAL(boolean)
472 process_restart (j_decompress_ptr cinfo)
473 {
474 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
475 int ci;
476
477 /* Throw away any unused bits remaining in bit buffer; */
478 /* include any full bytes in next_marker's count of discarded bytes */
479 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
480 entropy->bitstate.bits_left = 0;
481
482 /* Advance past the RSTn marker */
483 if (! (*cinfo->marker->read_restart_marker) (cinfo))
484 return FALSE;
485
486 /* Re-initialize DC predictions to 0 */
487 for (ci = 0; ci < cinfo->comps_in_scan; ci++)
488 entropy->saved.last_dc_val[ci] = 0;
489
490 /* Reset restart counter */
491 entropy->restarts_to_go = cinfo->restart_interval;
492
493 /* Reset out-of-data flag, unless read_restart_marker left us smack up
494 * against a marker. In that case we will end up treating the next data
495 * segment as empty, and we can avoid producing bogus output pixels by
496 * leaving the flag set.
497 */
498 if (cinfo->unread_marker == 0)
499 entropy->pub.insufficient_data = FALSE;
500
501 return TRUE;
502 }
503
504
505 /*
506 * Decode and return one MCU's worth of Huffman-compressed coefficients.
507 * The coefficients are reordered from zigzag order into natural array order,
508 * but are not dequantized.
509 *
510 * The i'th block of the MCU is stored into the block pointed to by
511 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
512 * (Wholesale zeroing is usually a little faster than retail...)
513 *
514 * Returns FALSE if data source requested suspension. In that case no
515 * changes have been made to permanent state. (Exception: some output
516 * coefficients may already have been assigned. This is harmless for
517 * this module, since we'll just re-assign them on the next call.)
518 */
519
520 METHODDEF(boolean)
521 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
522 {
523 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
524 int blkn;
525 BITREAD_STATE_VARS;
526 savable_state state;
527
528 /* Process restart marker if needed; may have to suspend */
529 if (cinfo->restart_interval) {
530 if (entropy->restarts_to_go == 0)
531 if (! process_restart(cinfo))
532 return FALSE;
533 }
534
535 /* If we've run out of data, just leave the MCU set to zeroes.
536 * This way, we return uniform gray for the remainder of the segment.
537 */
538 if (! entropy->pub.insufficient_data) {
539
540 /* Load up working state */
541 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
542 ASSIGN_STATE(state, entropy->saved);
543
544 /* Outer loop handles each block in the MCU */
545
546 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
547 JBLOCKROW block = MCU_data[blkn];
548 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
549 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
550 register int s, k, r;
551
552 /* Decode a single block's worth of coefficients */
553
554 /* Section F.2.2.1: decode the DC coefficient difference */
555 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
556 if (s) {
557 CHECK_BIT_BUFFER(br_state, s, return FALSE);
558 r = GET_BITS(s);
559 s = HUFF_EXTEND(r, s);
560 }
561
562 if (entropy->dc_needed[blkn]) {
563 /* Convert DC difference to actual value, update last_dc_val */
564 int ci = cinfo->MCU_membership[blkn];
565 s += state.last_dc_val[ci];
566 state.last_dc_val[ci] = s;
567 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
568 (*block)[0] = (JCOEF) s;
569 }
570
571 if (entropy->ac_needed[blkn]) {
572
573 /* Section F.2.2.2: decode the AC coefficients */
574 /* Since zeroes are skipped, output area must be cleared beforehand */
575 for (k = 1; k < DCTSIZE2; k++) {
576 HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
577
578 r = s >> 4;
579 s &= 15;
580
581 if (s) {
582 k += r;
583 CHECK_BIT_BUFFER(br_state, s, return FALSE);
584 r = GET_BITS(s);
585 s = HUFF_EXTEND(r, s);
586 /* Output coefficient in natural (dezigzagged) order.
587 * Note: the extra entries in jpeg_natural_order[] will save us
588 * if k >= DCTSIZE2, which could happen if the data is corrupted.
589 */
590 (*block)[jpeg_natural_order[k]] = (JCOEF) s;
591 } else {
592 if (r != 15)
593 break;
594 k += 15;
595 }
596 }
597
598 } else {
599
600 /* Section F.2.2.2: decode the AC coefficients */
601 /* In this path we just discard the values */
602 for (k = 1; k < DCTSIZE2; k++) {
603 HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
604
605 r = s >> 4;
606 s &= 15;
607
608 if (s) {
609 k += r;
610 CHECK_BIT_BUFFER(br_state, s, return FALSE);
611 DROP_BITS(s);
612 } else {
613 if (r != 15)
614 break;
615 k += 15;
616 }
617 }
618
619 }
620 }
621
622 /* Completed MCU, so update state */
623 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
624 ASSIGN_STATE(entropy->saved, state);
625 }
626
627 /* Account for restart interval (no-op if not using restarts) */
628 entropy->restarts_to_go--;
629
630 return TRUE;
631 }
632
633
634 /*
635 * Module initialization routine for Huffman entropy decoding.
636 */
637
638 GLOBAL(void)
639 jinit_huff_decoder (j_decompress_ptr cinfo)
640 {
641 huff_entropy_ptr entropy;
642 int i;
643
644 entropy = (huff_entropy_ptr)
645 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
646 SIZEOF(huff_entropy_decoder));
647 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
648 entropy->pub.start_pass = start_pass_huff_decoder;
649 entropy->pub.decode_mcu = decode_mcu;
650
651 /* Mark tables unallocated */
652 for (i = 0; i < NUM_HUFF_TBLS; i++) {
653 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
654 }
655 }