1 /*
2 * jdhuff.c
3 *
4 * This file was part of the Independent JPEG Group's software:
5 * Copyright (C) 1991-1997, Thomas G. Lane.
6 * libjpeg-turbo Modifications:
7 * Copyright (C) 2009-2011, 2016, 2018-2019, D. R. Commander.
8 * Copyright (C) 2018, Matthias Räncker.
9 * For conditions of distribution and use, see the accompanying README.ijg
10 * 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 * NOTE: All referenced figures are from
21 * Recommendation ITU-T T.81 (1992) | ISO/IEC 10918-1:1994.
22 */
23
24 #define JPEG_INTERNALS
25 #include "jinclude.h"
26 #include "jpeglib.h"
27 #include "jdhuff.h" /* Declarations shared with jdphuff.c */
28 #include "jpegcomp.h"
29 #include "jstdhuff.c"
30
31
32 /*
33 * Expanded entropy decoder object for Huffman decoding.
34 *
35 * The savable_state subrecord contains fields that change within an MCU,
36 * but must not be updated permanently until we complete the MCU.
37 */
38
39 typedef struct {
40 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
41 } savable_state;
42
43 typedef struct {
44 struct jpeg_entropy_decoder pub; /* public fields */
45
46 /* These fields are loaded into local variables at start of each MCU.
47 * In case of suspension, we exit WITHOUT updating them.
48 */
49 bitread_perm_state bitstate; /* Bit buffer at start of MCU */
50 savable_state saved; /* Other state at start of MCU */
51
52 /* These fields are NOT loaded into local working state. */
53 unsigned int restarts_to_go; /* MCUs left in this restart interval */
54
55 /* Pointers to derived tables (these workspaces have image lifespan) */
56 d_derived_tbl *dc_derived_tbls[NUM_HUFF_TBLS];
57 d_derived_tbl *ac_derived_tbls[NUM_HUFF_TBLS];
58
59 /* Precalculated info set up by start_pass for use in decode_mcu: */
60
61 /* Pointers to derived tables to be used for each block within an MCU */
62 d_derived_tbl *dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
63 d_derived_tbl *ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
64 /* Whether we care about the DC and AC coefficient values for each block */
65 boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
66 boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
67 } huff_entropy_decoder;
68
69 typedef huff_entropy_decoder *huff_entropy_ptr;
70
71
72 /*
73 * Initialize for a Huffman-compressed scan.
74 */
75
76 METHODDEF(void)
start_pass_huff_decoder(j_decompress_ptr cinfo)77 start_pass_huff_decoder(j_decompress_ptr cinfo)
78 {
79 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
80 int ci, blkn, dctbl, actbl;
81 d_derived_tbl **pdtbl;
82 jpeg_component_info *compptr;
83
84 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
85 * This ought to be an error condition, but we make it a warning because
86 * there are some baseline files out there with all zeroes in these bytes.
87 */
88 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2 - 1 ||
89 cinfo->Ah != 0 || cinfo->Al != 0)
90 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
91
92 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
93 compptr = cinfo->cur_comp_info[ci];
94 dctbl = compptr->dc_tbl_no;
95 actbl = compptr->ac_tbl_no;
96 /* Compute derived values for Huffman tables */
97 /* We may do this more than once for a table, but it's not expensive */
98 pdtbl = (d_derived_tbl **)(entropy->dc_derived_tbls) + dctbl;
99 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl, pdtbl);
100 pdtbl = (d_derived_tbl **)(entropy->ac_derived_tbls) + actbl;
101 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl, pdtbl);
102 /* Initialize DC predictions to 0 */
103 entropy->saved.last_dc_val[ci] = 0;
104 }
105
106 /* Precalculate decoding info for each block in an MCU of this scan */
107 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
108 ci = cinfo->MCU_membership[blkn];
109 compptr = cinfo->cur_comp_info[ci];
110 /* Precalculate which table to use for each block */
111 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
112 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
113 /* Decide whether we really care about the coefficient values */
114 if (compptr->component_needed) {
115 entropy->dc_needed[blkn] = TRUE;
116 /* we don't need the ACs if producing a 1/8th-size image */
117 entropy->ac_needed[blkn] = (compptr->_DCT_scaled_size > 1);
118 } else {
119 entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
120 }
121 }
122
123 /* Initialize bitread state variables */
124 entropy->bitstate.bits_left = 0;
125 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
126 entropy->pub.insufficient_data = FALSE;
127
128 /* Initialize restart counter */
129 entropy->restarts_to_go = cinfo->restart_interval;
130 }
131
132
133 /*
134 * Compute the derived values for a Huffman table.
135 * This routine also performs some validation checks on the table.
136 *
137 * Note this is also used by jdphuff.c.
138 */
139
140 GLOBAL(void)
jpeg_make_d_derived_tbl(j_decompress_ptr cinfo,boolean isDC,int tblno,d_derived_tbl ** pdtbl)141 jpeg_make_d_derived_tbl(j_decompress_ptr cinfo, boolean isDC, int tblno,
142 d_derived_tbl **pdtbl)
143 {
144 JHUFF_TBL *htbl;
145 d_derived_tbl *dtbl;
146 int p, i, l, si, numsymbols;
147 int lookbits, ctr;
148 char huffsize[257];
149 unsigned int huffcode[257];
150 unsigned int code;
151
152 /* Note that huffsize[] and huffcode[] are filled in code-length order,
153 * paralleling the order of the symbols themselves in htbl->huffval[].
154 */
155
156 /* Find the input Huffman table */
157 if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
158 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
159 htbl =
160 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
161 if (htbl == NULL)
162 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
163
164 /* Allocate a workspace if we haven't already done so. */
165 if (*pdtbl == NULL)
166 *pdtbl = (d_derived_tbl *)
167 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
168 sizeof(d_derived_tbl));
169 dtbl = *pdtbl;
170 dtbl->pub = htbl; /* fill in back link */
171
172 /* Figure C.1: make table of Huffman code length for each symbol */
173
174 p = 0;
175 for (l = 1; l <= 16; l++) {
176 i = (int)htbl->bits[l];
177 if (i < 0 || p + i > 256) /* protect against table overrun */
178 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
179 while (i--)
180 huffsize[p++] = (char)l;
181 }
182 huffsize[p] = 0;
183 numsymbols = p;
184
185 /* Figure C.2: generate the codes themselves */
186 /* We also validate that the counts represent a legal Huffman code tree. */
187
188 code = 0;
189 si = huffsize[0];
190 p = 0;
191 while (huffsize[p]) {
192 while (((int)huffsize[p]) == si) {
193 huffcode[p++] = code;
194 code++;
195 }
196 /* code is now 1 more than the last code used for codelength si; but
197 * it must still fit in si bits, since no code is allowed to be all ones.
198 */
199 if (((JLONG)code) >= (((JLONG)1) << si))
200 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
201 code <<= 1;
202 si++;
203 }
204
205 /* Figure F.15: generate decoding tables for bit-sequential decoding */
206
207 p = 0;
208 for (l = 1; l <= 16; l++) {
209 if (htbl->bits[l]) {
210 /* valoffset[l] = huffval[] index of 1st symbol of code length l,
211 * minus the minimum code of length l
212 */
213 dtbl->valoffset[l] = (JLONG)p - (JLONG)huffcode[p];
214 p += htbl->bits[l];
215 dtbl->maxcode[l] = huffcode[p - 1]; /* maximum code of length l */
216 } else {
217 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */
218 }
219 }
220 dtbl->valoffset[17] = 0;
221 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */
222
223 /* Compute lookahead tables to speed up decoding.
224 * First we set all the table entries to 0, indicating "too long";
225 * then we iterate through the Huffman codes that are short enough and
226 * fill in all the entries that correspond to bit sequences starting
227 * with that code.
228 */
229
230 for (i = 0; i < (1 << HUFF_LOOKAHEAD); i++)
231 dtbl->lookup[i] = (HUFF_LOOKAHEAD + 1) << HUFF_LOOKAHEAD;
232
233 p = 0;
234 for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
235 for (i = 1; i <= (int)htbl->bits[l]; i++, p++) {
236 /* l = current code's length, p = its index in huffcode[] & huffval[]. */
237 /* Generate left-justified code followed by all possible bit sequences */
238 lookbits = huffcode[p] << (HUFF_LOOKAHEAD - l);
239 for (ctr = 1 << (HUFF_LOOKAHEAD - l); ctr > 0; ctr--) {
240 dtbl->lookup[lookbits] = (l << HUFF_LOOKAHEAD) | htbl->huffval[p];
241 lookbits++;
242 }
243 }
244 }
245
246 /* Validate symbols as being reasonable.
247 * For AC tables, we make no check, but accept all byte values 0..255.
248 * For DC tables, we require the symbols to be in range 0..15.
249 * (Tighter bounds could be applied depending on the data depth and mode,
250 * but this is sufficient to ensure safe decoding.)
251 */
252 if (isDC) {
253 for (i = 0; i < numsymbols; i++) {
254 int sym = htbl->huffval[i];
255 if (sym < 0 || sym > 15)
256 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
257 }
258 }
259 }
260
261
262 /*
263 * Out-of-line code for bit fetching (shared with jdphuff.c).
264 * See jdhuff.h for info about usage.
265 * Note: current values of get_buffer and bits_left are passed as parameters,
266 * but are returned in the corresponding fields of the state struct.
267 *
268 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
269 * of get_buffer to be used. (On machines with wider words, an even larger
270 * buffer could be used.) However, on some machines 32-bit shifts are
271 * quite slow and take time proportional to the number of places shifted.
272 * (This is true with most PC compilers, for instance.) In this case it may
273 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
274 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
275 */
276
277 #ifdef SLOW_SHIFT_32
278 #define MIN_GET_BITS 15 /* minimum allowable value */
279 #else
280 #define MIN_GET_BITS (BIT_BUF_SIZE - 7)
281 #endif
282
283
284 GLOBAL(boolean)
jpeg_fill_bit_buffer(bitread_working_state * state,register bit_buf_type get_buffer,register int bits_left,int nbits)285 jpeg_fill_bit_buffer(bitread_working_state *state,
286 register bit_buf_type get_buffer, register int bits_left,
287 int nbits)
288 /* Load up the bit buffer to a depth of at least nbits */
289 {
290 /* Copy heavily used state fields into locals (hopefully registers) */
291 register const JOCTET *next_input_byte = state->next_input_byte;
292 register size_t bytes_in_buffer = state->bytes_in_buffer;
293 j_decompress_ptr cinfo = state->cinfo;
294
295 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
296 /* (It is assumed that no request will be for more than that many bits.) */
297 /* We fail to do so only if we hit a marker or are forced to suspend. */
298
299 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */
300 while (bits_left < MIN_GET_BITS) {
301 register int c;
302
303 /* Attempt to read a byte */
304 if (bytes_in_buffer == 0) {
305 if (!(*cinfo->src->fill_input_buffer) (cinfo))
306 return FALSE;
307 next_input_byte = cinfo->src->next_input_byte;
308 bytes_in_buffer = cinfo->src->bytes_in_buffer;
309 }
310 bytes_in_buffer--;
311 c = *next_input_byte++;
312
313 /* If it's 0xFF, check and discard stuffed zero byte */
314 if (c == 0xFF) {
315 /* Loop here to discard any padding FF's on terminating marker,
316 * so that we can save a valid unread_marker value. NOTE: we will
317 * accept multiple FF's followed by a 0 as meaning a single FF data
318 * byte. This data pattern is not valid according to the standard.
319 */
320 do {
321 if (bytes_in_buffer == 0) {
322 if (!(*cinfo->src->fill_input_buffer) (cinfo))
323 return FALSE;
324 next_input_byte = cinfo->src->next_input_byte;
325 bytes_in_buffer = cinfo->src->bytes_in_buffer;
326 }
327 bytes_in_buffer--;
328 c = *next_input_byte++;
329 } while (c == 0xFF);
330
331 if (c == 0) {
332 /* Found FF/00, which represents an FF data byte */
333 c = 0xFF;
334 } else {
335 /* Oops, it's actually a marker indicating end of compressed data.
336 * Save the marker code for later use.
337 * Fine point: it might appear that we should save the marker into
338 * bitread working state, not straight into permanent state. But
339 * once we have hit a marker, we cannot need to suspend within the
340 * current MCU, because we will read no more bytes from the data
341 * source. So it is OK to update permanent state right away.
342 */
343 cinfo->unread_marker = c;
344 /* See if we need to insert some fake zero bits. */
345 goto no_more_bytes;
346 }
347 }
348
349 /* OK, load c into get_buffer */
350 get_buffer = (get_buffer << 8) | c;
351 bits_left += 8;
352 } /* end while */
353 } else {
354 no_more_bytes:
355 /* We get here if we've read the marker that terminates the compressed
356 * data segment. There should be enough bits in the buffer register
357 * to satisfy the request; if so, no problem.
358 */
359 if (nbits > bits_left) {
360 /* Uh-oh. Report corrupted data to user and stuff zeroes into
361 * the data stream, so that we can produce some kind of image.
362 * We use a nonvolatile flag to ensure that only one warning message
363 * appears per data segment.
364 */
365 if (!cinfo->entropy->insufficient_data) {
366 WARNMS(cinfo, JWRN_HIT_MARKER);
367 cinfo->entropy->insufficient_data = TRUE;
368 }
369 /* Fill the buffer with zero bits */
370 get_buffer <<= MIN_GET_BITS - bits_left;
371 bits_left = MIN_GET_BITS;
372 }
373 }
374
375 /* Unload the local registers */
376 state->next_input_byte = next_input_byte;
377 state->bytes_in_buffer = bytes_in_buffer;
378 state->get_buffer = get_buffer;
379 state->bits_left = bits_left;
380
381 return TRUE;
382 }
383
384
385 /* Macro version of the above, which performs much better but does not
386 handle markers. We have to hand off any blocks with markers to the
387 slower routines. */
388
389 #define GET_BYTE { \
390 register int c0, c1; \
391 c0 = *buffer++; \
392 c1 = *buffer; \
393 /* Pre-execute most common case */ \
394 get_buffer = (get_buffer << 8) | c0; \
395 bits_left += 8; \
396 if (c0 == 0xFF) { \
397 /* Pre-execute case of FF/00, which represents an FF data byte */ \
398 buffer++; \
399 if (c1 != 0) { \
400 /* Oops, it's actually a marker indicating end of compressed data. */ \
401 cinfo->unread_marker = c1; \
402 /* Back out pre-execution and fill the buffer with zero bits */ \
403 buffer -= 2; \
404 get_buffer &= ~0xFF; \
405 } \
406 } \
407 }
408
409 #if SIZEOF_SIZE_T == 8 || defined(_WIN64) || (defined(__x86_64__) && defined(__ILP32__))
410
411 /* Pre-fetch 48 bytes, because the holding register is 64-bit */
412 #define FILL_BIT_BUFFER_FAST \
413 if (bits_left <= 16) { \
414 GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE GET_BYTE \
415 }
416
417 #else
418
419 /* Pre-fetch 16 bytes, because the holding register is 32-bit */
420 #define FILL_BIT_BUFFER_FAST \
421 if (bits_left <= 16) { \
422 GET_BYTE GET_BYTE \
423 }
424
425 #endif
426
427
428 /*
429 * Out-of-line code for Huffman code decoding.
430 * See jdhuff.h for info about usage.
431 */
432
433 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)434 jpeg_huff_decode(bitread_working_state *state,
435 register bit_buf_type get_buffer, register int bits_left,
436 d_derived_tbl *htbl, int min_bits)
437 {
438 register int l = min_bits;
439 register JLONG code;
440
441 /* HUFF_DECODE has determined that the code is at least min_bits */
442 /* bits long, so fetch that many bits in one swoop. */
443
444 CHECK_BIT_BUFFER(*state, l, return -1);
445 code = GET_BITS(l);
446
447 /* Collect the rest of the Huffman code one bit at a time. */
448 /* This is per Figure F.16. */
449
450 while (code > htbl->maxcode[l]) {
451 code <<= 1;
452 CHECK_BIT_BUFFER(*state, 1, return -1);
453 code |= GET_BITS(1);
454 l++;
455 }
456
457 /* Unload the local registers */
458 state->get_buffer = get_buffer;
459 state->bits_left = bits_left;
460
461 /* With garbage input we may reach the sentinel value l = 17. */
462
463 if (l > 16) {
464 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
465 return 0; /* fake a zero as the safest result */
466 }
467
468 return htbl->pub->huffval[(int)(code + htbl->valoffset[l])];
469 }
470
471
472 /*
473 * Figure F.12: extend sign bit.
474 * On some machines, a shift and add will be faster than a table lookup.
475 */
476
477 #define AVOID_TABLES
478 #ifdef AVOID_TABLES
479
480 #define NEG_1 ((unsigned int)-1)
481 #define HUFF_EXTEND(x, s) \
482 ((x) + ((((x) - (1 << ((s) - 1))) >> 31) & (((NEG_1) << (s)) + 1)))
483
484 #else
485
486 #define HUFF_EXTEND(x, s) \
487 ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
488
489 static const int extend_test[16] = { /* entry n is 2**(n-1) */
490 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
491 0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000
492 };
493
494 static const int extend_offset[16] = { /* entry n is (-1 << n) + 1 */
495 0, ((-1) << 1) + 1, ((-1) << 2) + 1, ((-1) << 3) + 1, ((-1) << 4) + 1,
496 ((-1) << 5) + 1, ((-1) << 6) + 1, ((-1) << 7) + 1, ((-1) << 8) + 1,
497 ((-1) << 9) + 1, ((-1) << 10) + 1, ((-1) << 11) + 1, ((-1) << 12) + 1,
498 ((-1) << 13) + 1, ((-1) << 14) + 1, ((-1) << 15) + 1
499 };
500
501 #endif /* AVOID_TABLES */
502
503
504 /*
505 * Check for a restart marker & resynchronize decoder.
506 * Returns FALSE if must suspend.
507 */
508
509 LOCAL(boolean)
process_restart(j_decompress_ptr cinfo)510 process_restart(j_decompress_ptr cinfo)
511 {
512 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
513 int ci;
514
515 /* Throw away any unused bits remaining in bit buffer; */
516 /* include any full bytes in next_marker's count of discarded bytes */
517 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
518 entropy->bitstate.bits_left = 0;
519
520 /* Advance past the RSTn marker */
521 if (!(*cinfo->marker->read_restart_marker) (cinfo))
522 return FALSE;
523
524 /* Re-initialize DC predictions to 0 */
525 for (ci = 0; ci < cinfo->comps_in_scan; ci++)
526 entropy->saved.last_dc_val[ci] = 0;
527
528 /* Reset restart counter */
529 entropy->restarts_to_go = cinfo->restart_interval;
530
531 /* Reset out-of-data flag, unless read_restart_marker left us smack up
532 * against a marker. In that case we will end up treating the next data
533 * segment as empty, and we can avoid producing bogus output pixels by
534 * leaving the flag set.
535 */
536 if (cinfo->unread_marker == 0)
537 entropy->pub.insufficient_data = FALSE;
538
539 return TRUE;
540 }
541
542
543 #if defined(__has_feature)
544 #if __has_feature(undefined_behavior_sanitizer)
545 __attribute__((no_sanitize("signed-integer-overflow"),
546 no_sanitize("unsigned-integer-overflow")))
547 #endif
548 #endif
549 LOCAL(boolean)
decode_mcu_slow(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)550 decode_mcu_slow(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
551 {
552 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
553 BITREAD_STATE_VARS;
554 int blkn;
555 savable_state state;
556 /* Outer loop handles each block in the MCU */
557
558 /* Load up working state */
559 BITREAD_LOAD_STATE(cinfo, entropy->bitstate);
560 state = entropy->saved;
561
562 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
563 JBLOCKROW block = MCU_data ? MCU_data[blkn] : NULL;
564 d_derived_tbl *dctbl = entropy->dc_cur_tbls[blkn];
565 d_derived_tbl *actbl = entropy->ac_cur_tbls[blkn];
566 register int s, k, r;
567
568 /* Decode a single block's worth of coefficients */
569
570 /* Section F.2.2.1: decode the DC coefficient difference */
571 HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
572 if (s) {
573 CHECK_BIT_BUFFER(br_state, s, return FALSE);
574 r = GET_BITS(s);
575 s = HUFF_EXTEND(r, s);
576 }
577
578 if (entropy->dc_needed[blkn]) {
579 /* Convert DC difference to actual value, update last_dc_val */
580 int ci = cinfo->MCU_membership[blkn];
581 /* Certain malformed JPEG images produce repeated DC coefficient
582 * differences of 2047 or -2047, which causes state.last_dc_val[ci] to
583 * grow until it overflows or underflows a 32-bit signed integer. This
584 * behavior is, to the best of our understanding, innocuous, and it is
585 * unclear how to work around it without potentially affecting
586 * performance. Thus, we (hopefully temporarily) suppress UBSan integer
587 * overflow errors for this function.
588 */
589 s += state.last_dc_val[ci];
590 state.last_dc_val[ci] = s;
591 if (block) {
592 /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
593 (*block)[0] = (JCOEF)s;
594 }
595 }
596
597 if (entropy->ac_needed[blkn] && block) {
598
599 /* Section F.2.2.2: decode the AC coefficients */
600 /* Since zeroes are skipped, output area must be cleared beforehand */
601 for (k = 1; k < DCTSIZE2; k++) {
602 HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
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 r = GET_BITS(s);
611 s = HUFF_EXTEND(r, s);
612 /* Output coefficient in natural (dezigzagged) order.
613 * Note: the extra entries in jpeg_natural_order[] will save us
614 * if k >= DCTSIZE2, which could happen if the data is corrupted.
615 */
616 (*block)[jpeg_natural_order[k]] = (JCOEF)s;
617 } else {
618 if (r != 15)
619 break;
620 k += 15;
621 }
622 }
623
624 } else {
625
626 /* Section F.2.2.2: decode the AC coefficients */
627 /* In this path we just discard the values */
628 for (k = 1; k < DCTSIZE2; k++) {
629 HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
630
631 r = s >> 4;
632 s &= 15;
633
634 if (s) {
635 k += r;
636 CHECK_BIT_BUFFER(br_state, s, return FALSE);
637 DROP_BITS(s);
638 } else {
639 if (r != 15)
640 break;
641 k += 15;
642 }
643 }
644 }
645 }
646
647 /* Completed MCU, so update state */
648 BITREAD_SAVE_STATE(cinfo, entropy->bitstate);
649 entropy->saved = state;
650 return TRUE;
651 }
652
653
654 LOCAL(boolean)
decode_mcu_fast(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)655 decode_mcu_fast(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
656 {
657 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
658 BITREAD_STATE_VARS;
659 JOCTET *buffer;
660 int blkn;
661 savable_state state;
662 /* Outer loop handles each block in the MCU */
663
664 /* Load up working state */
665 BITREAD_LOAD_STATE(cinfo, entropy->bitstate);
666 buffer = (JOCTET *)br_state.next_input_byte;
667 state = entropy->saved;
668
669 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
670 JBLOCKROW block = MCU_data ? MCU_data[blkn] : NULL;
671 d_derived_tbl *dctbl = entropy->dc_cur_tbls[blkn];
672 d_derived_tbl *actbl = entropy->ac_cur_tbls[blkn];
673 register int s, k, r, l;
674
675 HUFF_DECODE_FAST(s, l, dctbl);
676 if (s) {
677 FILL_BIT_BUFFER_FAST
678 r = GET_BITS(s);
679 s = HUFF_EXTEND(r, s);
680 }
681
682 if (entropy->dc_needed[blkn]) {
683 int ci = cinfo->MCU_membership[blkn];
684 s += state.last_dc_val[ci];
685 state.last_dc_val[ci] = s;
686 if (block)
687 (*block)[0] = (JCOEF)s;
688 }
689
690 if (entropy->ac_needed[blkn] && block) {
691
692 for (k = 1; k < DCTSIZE2; k++) {
693 HUFF_DECODE_FAST(s, l, actbl);
694 r = s >> 4;
695 s &= 15;
696
697 if (s) {
698 k += r;
699 FILL_BIT_BUFFER_FAST
700 r = GET_BITS(s);
701 s = HUFF_EXTEND(r, s);
702 (*block)[jpeg_natural_order[k]] = (JCOEF)s;
703 } else {
704 if (r != 15) break;
705 k += 15;
706 }
707 }
708
709 } else {
710
711 for (k = 1; k < DCTSIZE2; k++) {
712 HUFF_DECODE_FAST(s, l, actbl);
713 r = s >> 4;
714 s &= 15;
715
716 if (s) {
717 k += r;
718 FILL_BIT_BUFFER_FAST
719 DROP_BITS(s);
720 } else {
721 if (r != 15) break;
722 k += 15;
723 }
724 }
725 }
726 }
727
728 if (cinfo->unread_marker != 0) {
729 cinfo->unread_marker = 0;
730 return FALSE;
731 }
732
733 br_state.bytes_in_buffer -= (buffer - br_state.next_input_byte);
734 br_state.next_input_byte = buffer;
735 BITREAD_SAVE_STATE(cinfo, entropy->bitstate);
736 entropy->saved = state;
737 return TRUE;
738 }
739
740
741 /*
742 * Decode and return one MCU's worth of Huffman-compressed coefficients.
743 * The coefficients are reordered from zigzag order into natural array order,
744 * but are not dequantized.
745 *
746 * The i'th block of the MCU is stored into the block pointed to by
747 * MCU_data[i]. WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
748 * (Wholesale zeroing is usually a little faster than retail...)
749 *
750 * Returns FALSE if data source requested suspension. In that case no
751 * changes have been made to permanent state. (Exception: some output
752 * coefficients may already have been assigned. This is harmless for
753 * this module, since we'll just re-assign them on the next call.)
754 */
755
756 #define BUFSIZE (DCTSIZE2 * 8)
757
758 METHODDEF(boolean)
decode_mcu(j_decompress_ptr cinfo,JBLOCKROW * MCU_data)759 decode_mcu(j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
760 {
761 huff_entropy_ptr entropy = (huff_entropy_ptr)cinfo->entropy;
762 int usefast = 1;
763
764 /* Process restart marker if needed; may have to suspend */
765 if (cinfo->restart_interval) {
766 if (entropy->restarts_to_go == 0)
767 if (!process_restart(cinfo))
768 return FALSE;
769 usefast = 0;
770 }
771
772 if (cinfo->src->bytes_in_buffer < BUFSIZE * (size_t)cinfo->blocks_in_MCU ||
773 cinfo->unread_marker != 0)
774 usefast = 0;
775
776 /* If we've run out of data, just leave the MCU set to zeroes.
777 * This way, we return uniform gray for the remainder of the segment.
778 */
779 if (!entropy->pub.insufficient_data) {
780
781 if (usefast) {
782 if (!decode_mcu_fast(cinfo, MCU_data)) goto use_slow;
783 } else {
784 use_slow:
785 if (!decode_mcu_slow(cinfo, MCU_data)) return FALSE;
786 }
787
788 }
789
790 /* Account for restart interval (no-op if not using restarts) */
791 if (cinfo->restart_interval)
792 entropy->restarts_to_go--;
793
794 return TRUE;
795 }
796
797
798 /*
799 * Module initialization routine for Huffman entropy decoding.
800 */
801
802 GLOBAL(void)
jinit_huff_decoder(j_decompress_ptr cinfo)803 jinit_huff_decoder(j_decompress_ptr cinfo)
804 {
805 huff_entropy_ptr entropy;
806 int i;
807
808 /* Motion JPEG frames typically do not include the Huffman tables if they
809 are the default tables. Thus, if the tables are not set by the time
810 the Huffman decoder is initialized (usually within the body of
811 jpeg_start_decompress()), we set them to default values. */
812 std_huff_tables((j_common_ptr)cinfo);
813
814 entropy = (huff_entropy_ptr)
815 (*cinfo->mem->alloc_small) ((j_common_ptr)cinfo, JPOOL_IMAGE,
816 sizeof(huff_entropy_decoder));
817 cinfo->entropy = (struct jpeg_entropy_decoder *)entropy;
818 entropy->pub.start_pass = start_pass_huff_decoder;
819 entropy->pub.decode_mcu = decode_mcu;
820
821 /* Mark tables unallocated */
822 for (i = 0; i < NUM_HUFF_TBLS; i++) {
823 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
824 }
825 }
826