1 /*
2 * jdhuff.c
3 *
4 * Copyright (C) 1991-1997, 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.
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 jdphuff.c */
21
22 #ifdef _FX_MANAGED_CODE_
23 #define savable_state savable_state_d
24 #endif
25
26 /*
27 * Expanded entropy decoder object for Huffman decoding.
28 *
29 * The savable_state subrecord contains fields that change within an MCU,
30 * but must not be updated permanently until we complete the MCU.
31 */
32
33 typedef struct {
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).last_dc_val[0] = (src).last_dc_val[0], \
48 (dest).last_dc_val[1] = (src).last_dc_val[1], \
49 (dest).last_dc_val[2] = (src).last_dc_val[2], \
50 (dest).last_dc_val[3] = (src).last_dc_val[3])
51 #endif
52 #endif
53
54
55 typedef struct {
56 struct jpeg_entropy_decoder pub; /* public fields */
57
58 /* These fields are loaded into local variables at start of each MCU.
59 * In case of suspension, we exit WITHOUT updating them.
60 */
61 bitread_perm_state bitstate; /* Bit buffer at start of MCU */
62 savable_state saved; /* Other state at start of MCU */
63
64 /* These fields are NOT loaded into local working state. */
65 unsigned int restarts_to_go; /* MCUs left in this restart interval */
66
67 /* Pointers to derived tables (these workspaces have image lifespan) */
68 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
69 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
70
71 /* Precalculated info set up by start_pass for use in decode_mcu: */
72
73 /* Pointers to derived tables to be used for each block within an MCU */
74 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
75 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
76 /* Whether we care about the DC and AC coefficient values for each block */
77 boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
78 boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
79 } huff_entropy_decoder;
80
81 typedef huff_entropy_decoder * huff_entropy_ptr;
82
83
84 /*
85 * Initialize for a Huffman-compressed scan.
86 */
87
88 METHODDEF(void)
start_pass_huff_decoder(j_decompress_ptr cinfo)89 start_pass_huff_decoder (j_decompress_ptr cinfo)
90 {
91 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
92 int ci, blkn, dctbl, actbl;
93 jpeg_component_info * compptr;
94
95 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
96 * This ought to be an error condition, but we make it a warning because
97 * there are some baseline files out there with all zeroes in these bytes.
98 */
99 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
100 cinfo->Ah != 0 || cinfo->Al != 0)
101 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
102
103 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
104 compptr = cinfo->cur_comp_info[ci];
105 dctbl = compptr->dc_tbl_no;
106 actbl = compptr->ac_tbl_no;
107 /* Compute derived values for Huffman tables */
108 /* We may do this more than once for a table, but it's not expensive */
109 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
110 & entropy->dc_derived_tbls[dctbl]);
111 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
112 & entropy->ac_derived_tbls[actbl]);
113 /* Initialize DC predictions to 0 */
114 entropy->saved.last_dc_val[ci] = 0;
115 }
116
117 /* Precalculate decoding info for each block in an MCU of this scan */
118 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
119 ci = cinfo->MCU_membership[blkn];
120 compptr = cinfo->cur_comp_info[ci];
121 /* Precalculate which table to use for each block */
122 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
123 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
124 /* Decide whether we really care about the coefficient values */
125 if (compptr->component_needed) {
126 entropy->dc_needed[blkn] = TRUE;
127 /* we don't need the ACs if producing a 1/8th-size image */
128 entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1);
129 } else {
130 entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
131 }
132 }
133
134 /* Initialize bitread state variables */
135 entropy->bitstate.bits_left = 0;
136 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
137 entropy->pub.insufficient_data = FALSE;
138
139 /* Initialize restart counter */
140 entropy->restarts_to_go = cinfo->restart_interval;
141 }
142
143
144 /*
145 * Compute the derived values for a Huffman table.
146 * This routine also performs some validation checks on the table.
147 *
148 * Note this is also used by jdphuff.c.
149 */
150
151 GLOBAL(void)
jpeg_make_d_derived_tbl(j_decompress_ptr cinfo,boolean isDC,int tblno,d_derived_tbl ** pdtbl)152 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
153 d_derived_tbl ** pdtbl)
154 {
155 JHUFF_TBL *htbl;
156 d_derived_tbl *dtbl;
157 int p, i, l, _si, numsymbols;
158 int lookbits, ctr;
159 char huffsize[257];
160 unsigned int huffcode[257];
161 unsigned int code;
162
163 /* Note that huffsize[] and huffcode[] are filled in code-length order,
164 * paralleling the order of the symbols themselves in htbl->huffval[].
165 */
166
167 /* Find the input Huffman table */
168 if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
169 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
170 htbl =
171 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
172 if (htbl == NULL)
173 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
174
175 /* Allocate a workspace if we haven't already done so. */
176 if (*pdtbl == NULL)
177 *pdtbl = (d_derived_tbl *)
178 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
179 SIZEOF(d_derived_tbl));
180 dtbl = *pdtbl;
181 dtbl->pub = htbl; /* fill in back link */
182
183 /* Figure C.1: make table of Huffman code length for each symbol */
184
185 p = 0;
186 for (l = 1; l <= 16; l++) {
187 i = (int) htbl->bits[l];
188 if (i < 0 || p + i > 256) /* protect against table overrun */
189 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
190 while (i--)
191 huffsize[p++] = (char) l;
192 }
193 huffsize[p] = 0;
194 numsymbols = p;
195
196 /* Figure C.2: generate the codes themselves */
197 /* We also validate that the counts represent a legal Huffman code tree. */
198
199 code = 0;
200 _si = huffsize[0];
201 p = 0;
202 while (huffsize[p]) {
203 while (((int) huffsize[p]) == _si) {
204 huffcode[p++] = code;
205 code++;
206 }
207 /* code is now 1 more than the last code used for codelength si; but
208 * it must still fit in si bits, since no code is allowed to be all ones.
209 */
210 if (((INT32) code) >= (((INT32) 1) << _si))
211 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
212 code <<= 1;
213 _si++;
214 }
215
216 /* Figure F.15: generate decoding tables for bit-sequential decoding */
217
218 p = 0;
219 for (l = 1; l <= 16; l++) {
220 if (htbl->bits[l]) {
221 /* valoffset[l] = huffval[] index of 1st symbol of code length l,
222 * minus the minimum code of length l
223 */
224 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
225 p += htbl->bits[l];
226 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
227 } else {
228 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */
229 }
230 }
231 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */
232
233 /* Compute lookahead tables to speed up decoding.
234 * First we set all the table entries to 0, indicating "too long";
235 * then we iterate through the Huffman codes that are short enough and
236 * fill in all the entries that correspond to bit sequences starting
237 * with that code.
238 */
239
240 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));
241
242 p = 0;
243 for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
244 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
245 /* l = current code's length, p = its index in huffcode[] & huffval[]. */
246 /* Generate left-justified code followed by all possible bit sequences */
247 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
248 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
249 dtbl->look_nbits[lookbits] = l;
250 dtbl->look_sym[lookbits] = htbl->huffval[p];
251 lookbits++;
252 }
253 }
254 }
255
256 /* Validate symbols as being reasonable.
257 * For AC tables, we make no check, but accept all byte values 0..255.
258 * For DC tables, we require the symbols to be in range 0..15.
259 * (Tighter bounds could be applied depending on the data depth and mode,
260 * but this is sufficient to ensure safe decoding.)
261 */
262 if (isDC) {
263 for (i = 0; i < numsymbols; i++) {
264 int sym = htbl->huffval[i];
265 if (sym < 0 || sym > 15)
266 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
267 }
268 }
269 }
270
271
272 /*
273 * Out-of-line code for bit fetching (shared with jdphuff.c).
274 * See jdhuff.h for info about usage.
275 * Note: current values of get_buffer and bits_left are passed as parameters,
276 * but are returned in the corresponding fields of the state struct.
277 *
278 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
279 * of get_buffer to be used. (On machines with wider words, an even larger
280 * buffer could be used.) However, on some machines 32-bit shifts are
281 * quite slow and take time proportional to the number of places shifted.
282 * (This is true with most PC compilers, for instance.) In this case it may
283 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
284 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
285 */
286
287 #ifdef SLOW_SHIFT_32
288 #define MIN_GET_BITS 15 /* minimum allowable value */
289 #else
290 #define MIN_GET_BITS (BIT_BUF_SIZE-7)
291 #endif
292
293
294 GLOBAL(boolean)
jpeg_fill_bit_buffer(bitread_working_state * state,register bit_buf_type get_buffer,register int bits_left,int nbits)295 jpeg_fill_bit_buffer (bitread_working_state * state,
296 register bit_buf_type get_buffer, register int bits_left,
297 int nbits)
298 /* Load up the bit buffer to a depth of at least nbits */
299 {
300 /* Copy heavily used state fields into locals (hopefully registers) */
301 register const JOCTET * next_input_byte = state->next_input_byte;
302 register size_t bytes_in_buffer = state->bytes_in_buffer;
303 j_decompress_ptr cinfo = state->cinfo;
304
305 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
306 /* (It is assumed that no request will be for more than that many bits.) */
307 /* We fail to do so only if we hit a marker or are forced to suspend. */
308
309 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */
310 while (bits_left < MIN_GET_BITS) {
311 register int c;
312
313 /* Attempt to read a byte */
314 if (bytes_in_buffer == 0) {
315 if (! (*cinfo->src->fill_input_buffer) (cinfo))
316 return FALSE;
317 next_input_byte = cinfo->src->next_input_byte;
318 bytes_in_buffer = cinfo->src->bytes_in_buffer;
319 }
320 bytes_in_buffer--;
321 c = GETJOCTET(*next_input_byte++);
322
323 /* If it's 0xFF, check and discard stuffed zero byte */
324 if (c == 0xFF) {
325 /* Loop here to discard any padding FF's on terminating marker,
326 * so that we can save a valid unread_marker value. NOTE: we will
327 * accept multiple FF's followed by a 0 as meaning a single FF data
328 * byte. This data pattern is not valid according to the standard.
329 */
330 do {
331 if (bytes_in_buffer == 0) {
332 if (! (*cinfo->src->fill_input_buffer) (cinfo))
333 return FALSE;
334 next_input_byte = cinfo->src->next_input_byte;
335 bytes_in_buffer = cinfo->src->bytes_in_buffer;
336 }
337 bytes_in_buffer--;
338 c = GETJOCTET(*next_input_byte++);
339 } while (c == 0xFF);
340
341 if (c == 0) {
342 /* Found FF/00, which represents an FF data byte */
343 c = 0xFF;
344 } else {
345 /* Oops, it's actually a marker indicating end of compressed data.
346 * Save the marker code for later use.
347 * Fine point: it might appear that we should save the marker into
348 * bitread working state, not straight into permanent state. But
349 * once we have hit a marker, we cannot need to suspend within the
350 * current MCU, because we will read no more bytes from the data
351 * source. So it is OK to update permanent state right away.
352 */
353 cinfo->unread_marker = c;
354 /* See if we need to insert some fake zero bits. */
355 goto no_more_bytes;
356 }
357 }
358
359 /* OK, load c into get_buffer */
360 get_buffer = (get_buffer << 8) | c;
361 bits_left += 8;
362 } /* end while */
363 } else {
364 no_more_bytes:
365 /* We get here if we've read the marker that terminates the compressed
366 * data segment. There should be enough bits in the buffer register
367 * to satisfy the request; if so, no problem.
368 */
369 if (nbits > bits_left) {
370 /* Uh-oh. Report corrupted data to user and stuff zeroes into
371 * the data stream, so that we can produce some kind of image.
372 * We use a nonvolatile flag to ensure that only one warning message
373 * appears per data segment.
374 */
375 if (! cinfo->entropy->insufficient_data) {
376 WARNMS(cinfo, JWRN_HIT_MARKER);
377 cinfo->entropy->insufficient_data = TRUE;
378 }
379 /* Fill the buffer with zero bits */
380 get_buffer <<= MIN_GET_BITS - bits_left;
381 bits_left = MIN_GET_BITS;
382 }
383 }
384
385 /* Unload the local registers */
386 state->next_input_byte = next_input_byte;
387 state->bytes_in_buffer = bytes_in_buffer;
388 state->get_buffer = get_buffer;
389 state->bits_left = bits_left;
390
391 return TRUE;
392 }
393
394
395 /*
396 * Out-of-line code for Huffman code decoding.
397 * See jdhuff.h for info about usage.
398 */
399
400 GLOBAL(int)
jpeg_huff_decode(bitread_working_state * state,register bit_buf_type get_buffer,register int bits_left,d_derived_tbl * htbl,int min_bits)401 jpeg_huff_decode (bitread_working_state * state,
402 register bit_buf_type get_buffer, register int bits_left,
403 d_derived_tbl * htbl, int min_bits)
404 {
405 register int l = min_bits;
406 register INT32 code;
407
408 /* HUFF_DECODE has determined that the code is at least min_bits */
409 /* bits long, so fetch that many bits in one swoop. */
410
411 CHECK_BIT_BUFFER(*state, l, return -1);
412 code = GET_BITS(l);
413
414 /* Collect the rest of the Huffman code one bit at a time. */
415 /* This is per Figure F.16 in the JPEG spec. */
416
417 while (code > htbl->maxcode[l]) {
418 code <<= 1;
419 CHECK_BIT_BUFFER(*state, 1, return -1);
420 code |= GET_BITS(1);
421 l++;
422 }
423
424 /* Unload the local registers */
425 state->get_buffer = get_buffer;
426 state->bits_left = bits_left;
427
428 /* With garbage input we may reach the sentinel value l = 17. */
429
430 if (l > 16) {
431 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
432 return 0; /* fake a zero as the safest result */
433 }
434
435 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ];
436 }
437
438
439 /*
440 * Figure F.12: extend sign bit.
441 * On some machines, a shift and add will be faster than a table lookup.
442 */
443
444 #ifdef AVOID_TABLES
445
446 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))
447
448 #else
449
450 #define HUFF_EXTEND(x,s) ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
451
452 static const int extend_test[16] = /* entry n is 2**(n-1) */
453 { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
454 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
455
456 static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
457 { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
458 ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
459 ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
460 ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
461
462 #endif /* AVOID_TABLES */
463
464
465 /*
466 * Check for a restart marker & resynchronize decoder.
467 * Returns FALSE if must suspend.
468 */
469
470 LOCAL(boolean)
process_restart(j_decompress_ptr cinfo)471 process_restart (j_decompress_ptr cinfo)
472 {
473 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
474 int ci;
475
476 /* Throw away any unused bits remaining in bit buffer; */
477 /* include any full bytes in next_marker's count of discarded bytes */
478 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
479 entropy->bitstate.bits_left = 0;
480
481 /* Advance past the RSTn marker */
482 if (! (*cinfo->marker->read_restart_marker) (cinfo))
483 return FALSE;
484
485 /* Re-initialize DC predictions to 0 */
486 for (ci = 0; ci < cinfo->comps_in_scan; ci++)
487 entropy->saved.last_dc_val[ci] = 0;
488
489 /* Reset restart counter */
490 entropy->restarts_to_go = cinfo->restart_interval;
491
492 /* Reset out-of-data flag, unless read_restart_marker left us smack up
493 * against a marker. In that case we will end up treating the next data
494 * segment as empty, and we can avoid producing bogus output pixels by
495 * leaving the flag set.
496 */
497 if (cinfo->unread_marker == 0)
498 entropy->pub.insufficient_data = FALSE;
499
500 return TRUE;
501 }
502
503
504 /*
505 * Decode and return one MCU's worth of Huffman-compressed coefficients.
506 * The coefficients are reordered from zigzag order into natural array order,
507 * but are not dequantized.
508 *
509 * The i'th block of the MCU is stored into the block pointed to by
510 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
511 * (Wholesale zeroing is usually a little faster than retail...)
512 *
513 * Returns FALSE if data source requested suspension. In that case no
514 * changes have been made to permanent state. (Exception: some output
515 * coefficients may already have been assigned. This is harmless for
516 * this module, since we'll just re-assign them on the next call.)
517 */
518
519 METHODDEF(boolean)
decode_mcu(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)520 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
521 {
522 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
523 int blkn;
524 BITREAD_STATE_VARS;
525 savable_state state;
526
527 /* Process restart marker if needed; may have to suspend */
528 if (cinfo->restart_interval) {
529 if (entropy->restarts_to_go == 0)
530 if (! process_restart(cinfo))
531 return FALSE;
532 }
533
534 /* If we've run out of data, just leave the MCU set to zeroes.
535 * This way, we return uniform gray for the remainder of the segment.
536 */
537 if (! entropy->pub.insufficient_data) {
538
539 /* Load up working state */
540 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
541 ASSIGN_STATE(state, entropy->saved);
542
543 /* Outer loop handles each block in the MCU */
544
545 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
546 JBLOCKROW block = MCU_data[blkn];
547 d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
548 d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
549 register int s, k, r;
550
551 /* Decode a single block's worth of coefficients */
552
553 /* Section F.2.2.1: decode the DC coefficient difference */
554 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
555 if (s) {
556 CHECK_BIT_BUFFER(br_state, s, return FALSE);
557 r = GET_BITS(s);
558 s = HUFF_EXTEND(r, s);
559 }
560
561 if (entropy->dc_needed[blkn]) {
562 /* Convert DC difference to actual value, update last_dc_val */
563 int ci = cinfo->MCU_membership[blkn];
564 s += state.last_dc_val[ci];
565 state.last_dc_val[ci] = s;
566 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
567 (*block)[0] = (JCOEF) s;
568 }
569
570 if (entropy->ac_needed[blkn]) {
571
572 /* Section F.2.2.2: decode the AC coefficients */
573 /* Since zeroes are skipped, output area must be cleared beforehand */
574 for (k = 1; k < DCTSIZE2; k++) {
575 HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
576
577 r = s >> 4;
578 s &= 15;
579
580 if (s) {
581 k += r;
582 CHECK_BIT_BUFFER(br_state, s, return FALSE);
583 r = GET_BITS(s);
584 s = HUFF_EXTEND(r, s);
585 /* Output coefficient in natural (dezigzagged) order.
586 * Note: the extra entries in jpeg_natural_order[] will save us
587 * if k >= DCTSIZE2, which could happen if the data is corrupted.
588 */
589 (*block)[jpeg_natural_order[k]] = (JCOEF) s;
590 } else {
591 if (r != 15)
592 break;
593 k += 15;
594 }
595 }
596
597 } else {
598
599 /* Section F.2.2.2: decode the AC coefficients */
600 /* In this path we just discard the values */
601 for (k = 1; k < DCTSIZE2; k++) {
602 HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
603
604 r = s >> 4;
605 s &= 15;
606
607 if (s) {
608 k += r;
609 CHECK_BIT_BUFFER(br_state, s, return FALSE);
610 DROP_BITS(s);
611 } else {
612 if (r != 15)
613 break;
614 k += 15;
615 }
616 }
617
618 }
619 }
620
621 /* Completed MCU, so update state */
622 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
623 ASSIGN_STATE(entropy->saved, state);
624 }
625
626 /* Account for restart interval (no-op if not using restarts) */
627 entropy->restarts_to_go--;
628
629 return TRUE;
630 }
631
632
633 /*
634 * Module initialization routine for Huffman entropy decoding.
635 */
636
637 GLOBAL(void)
jinit_huff_decoder(j_decompress_ptr cinfo)638 jinit_huff_decoder (j_decompress_ptr cinfo)
639 {
640 huff_entropy_ptr entropy;
641 int i;
642
643 entropy = (huff_entropy_ptr)
644 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
645 SIZEOF(huff_entropy_decoder));
646 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
647 entropy->pub.start_pass = start_pass_huff_decoder;
648 entropy->pub.decode_mcu = decode_mcu;
649
650 /* Mark tables unallocated */
651 for (i = 0; i < NUM_HUFF_TBLS; i++) {
652 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
653 }
654 }
655