1 /*
2 * jdhuff.c
3 *
4 * Copyright (C) 1991-1997, Thomas G. Lane.
5 * Modified 2006-2009 by Guido Vollbeding.
6 * This file is part of the Independent JPEG Group's software.
7 * For conditions of distribution and use, see the accompanying README file.
8 *
9 * This file contains Huffman entropy decoding routines.
10 * Both sequential and progressive modes are supported in this single module.
11 *
12 * Much of the complexity here has to do with supporting input suspension.
13 * If the data source module demands suspension, we want to be able to back
14 * up to the start of the current MCU. To do this, we copy state variables
15 * into local working storage, and update them back to the permanent
16 * storage only upon successful completion of an MCU.
17 */
18
19 #define JPEG_INTERNALS
20 #include "jinclude.h"
21 #include "jpeglib.h"
22
23
24 /* Derived data constructed for each Huffman table */
25
26 #define HUFF_LOOKAHEAD 8 /* # of bits of lookahead */
27
28 typedef struct {
29 /* Basic tables: (element [0] of each array is unused) */
30 INT32 maxcode[18]; /* largest code of length k (-1 if none) */
31 /* (maxcode[17] is a sentinel to ensure jpeg_huff_decode terminates) */
32 INT32 valoffset[17]; /* huffval[] offset for codes of length k */
33 /* valoffset[k] = huffval[] index of 1st symbol of code length k, less
34 * the smallest code of length k; so given a code of length k, the
35 * corresponding symbol is huffval[code + valoffset[k]]
36 */
37
38 /* Link to public Huffman table (needed only in jpeg_huff_decode) */
39 JHUFF_TBL *pub;
40
41 /* Lookahead tables: indexed by the next HUFF_LOOKAHEAD bits of
42 * the input data stream. If the next Huffman code is no more
43 * than HUFF_LOOKAHEAD bits long, we can obtain its length and
44 * the corresponding symbol directly from these tables.
45 */
46 int look_nbits[1<<HUFF_LOOKAHEAD]; /* # bits, or 0 if too long */
47 UINT8 look_sym[1<<HUFF_LOOKAHEAD]; /* symbol, or unused */
48 } d_derived_tbl;
49
50
51 /*
52 * Fetching the next N bits from the input stream is a time-critical operation
53 * for the Huffman decoders. We implement it with a combination of inline
54 * macros and out-of-line subroutines. Note that N (the number of bits
55 * demanded at one time) never exceeds 15 for JPEG use.
56 *
57 * We read source bytes into get_buffer and dole out bits as needed.
58 * If get_buffer already contains enough bits, they are fetched in-line
59 * by the macros CHECK_BIT_BUFFER and GET_BITS. When there aren't enough
60 * bits, jpeg_fill_bit_buffer is called; it will attempt to fill get_buffer
61 * as full as possible (not just to the number of bits needed; this
62 * prefetching reduces the overhead cost of calling jpeg_fill_bit_buffer).
63 * Note that jpeg_fill_bit_buffer may return FALSE to indicate suspension.
64 * On TRUE return, jpeg_fill_bit_buffer guarantees that get_buffer contains
65 * at least the requested number of bits --- dummy zeroes are inserted if
66 * necessary.
67 */
68
69 typedef INT32 bit_buf_type; /* type of bit-extraction buffer */
70 #define BIT_BUF_SIZE 32 /* size of buffer in bits */
71
72 /* If long is > 32 bits on your machine, and shifting/masking longs is
73 * reasonably fast, making bit_buf_type be long and setting BIT_BUF_SIZE
74 * appropriately should be a win. Unfortunately we can't define the size
75 * with something like #define BIT_BUF_SIZE (sizeof(bit_buf_type)*8)
76 * because not all machines measure sizeof in 8-bit bytes.
77 */
78
79 typedef struct { /* Bitreading state saved across MCUs */
80 bit_buf_type get_buffer; /* current bit-extraction buffer */
81 int bits_left; /* # of unused bits in it */
82 } bitread_perm_state;
83
84 typedef struct { /* Bitreading working state within an MCU */
85 /* Current data source location */
86 /* We need a copy, rather than munging the original, in case of suspension */
87 const JOCTET * next_input_byte; /* => next byte to read from source */
88 size_t bytes_in_buffer; /* # of bytes remaining in source buffer */
89 /* Bit input buffer --- note these values are kept in register variables,
90 * not in this struct, inside the inner loops.
91 */
92 bit_buf_type get_buffer; /* current bit-extraction buffer */
93 int bits_left; /* # of unused bits in it */
94 /* Pointer needed by jpeg_fill_bit_buffer. */
95 j_decompress_ptr cinfo; /* back link to decompress master record */
96 } bitread_working_state;
97
98 /* Macros to declare and load/save bitread local variables. */
99 #define BITREAD_STATE_VARS \
100 register bit_buf_type get_buffer; \
101 register int bits_left; \
102 bitread_working_state br_state
103
104 #define BITREAD_LOAD_STATE(cinfop,permstate) \
105 br_state.cinfo = cinfop; \
106 br_state.next_input_byte = cinfop->src->next_input_byte; \
107 br_state.bytes_in_buffer = cinfop->src->bytes_in_buffer; \
108 get_buffer = permstate.get_buffer; \
109 bits_left = permstate.bits_left;
110
111 #define BITREAD_SAVE_STATE(cinfop,permstate) \
112 cinfop->src->next_input_byte = br_state.next_input_byte; \
113 cinfop->src->bytes_in_buffer = br_state.bytes_in_buffer; \
114 permstate.get_buffer = get_buffer; \
115 permstate.bits_left = bits_left
116
117 /*
118 * These macros provide the in-line portion of bit fetching.
119 * Use CHECK_BIT_BUFFER to ensure there are N bits in get_buffer
120 * before using GET_BITS, PEEK_BITS, or DROP_BITS.
121 * The variables get_buffer and bits_left are assumed to be locals,
122 * but the state struct might not be (jpeg_huff_decode needs this).
123 * CHECK_BIT_BUFFER(state,n,action);
124 * Ensure there are N bits in get_buffer; if suspend, take action.
125 * val = GET_BITS(n);
126 * Fetch next N bits.
127 * val = PEEK_BITS(n);
128 * Fetch next N bits without removing them from the buffer.
129 * DROP_BITS(n);
130 * Discard next N bits.
131 * The value N should be a simple variable, not an expression, because it
132 * is evaluated multiple times.
133 */
134
135 #define CHECK_BIT_BUFFER(state,nbits,action) \
136 { if (bits_left < (nbits)) { \
137 if (! jpeg_fill_bit_buffer(&(state),get_buffer,bits_left,nbits)) \
138 { action; } \
139 get_buffer = (state).get_buffer; bits_left = (state).bits_left; } }
140
141 #define GET_BITS(nbits) \
142 (((int) (get_buffer >> (bits_left -= (nbits)))) & BIT_MASK(nbits))
143
144 #define PEEK_BITS(nbits) \
145 (((int) (get_buffer >> (bits_left - (nbits)))) & BIT_MASK(nbits))
146
147 #define DROP_BITS(nbits) \
148 (bits_left -= (nbits))
149
150
151 /*
152 * Code for extracting next Huffman-coded symbol from input bit stream.
153 * Again, this is time-critical and we make the main paths be macros.
154 *
155 * We use a lookahead table to process codes of up to HUFF_LOOKAHEAD bits
156 * without looping. Usually, more than 95% of the Huffman codes will be 8
157 * or fewer bits long. The few overlength codes are handled with a loop,
158 * which need not be inline code.
159 *
160 * Notes about the HUFF_DECODE macro:
161 * 1. Near the end of the data segment, we may fail to get enough bits
162 * for a lookahead. In that case, we do it the hard way.
163 * 2. If the lookahead table contains no entry, the next code must be
164 * more than HUFF_LOOKAHEAD bits long.
165 * 3. jpeg_huff_decode returns -1 if forced to suspend.
166 */
167
168 #define HUFF_DECODE(result,state,htbl,failaction,slowlabel) \
169 { register int nb, look; \
170 if (bits_left < HUFF_LOOKAHEAD) { \
171 if (! jpeg_fill_bit_buffer(&state,get_buffer,bits_left, 0)) {failaction;} \
172 get_buffer = state.get_buffer; bits_left = state.bits_left; \
173 if (bits_left < HUFF_LOOKAHEAD) { \
174 nb = 1; goto slowlabel; \
175 } \
176 } \
177 look = PEEK_BITS(HUFF_LOOKAHEAD); \
178 if ((nb = htbl->look_nbits[look]) != 0) { \
179 DROP_BITS(nb); \
180 result = htbl->look_sym[look]; \
181 } else { \
182 nb = HUFF_LOOKAHEAD+1; \
183 slowlabel: \
184 if ((result=jpeg_huff_decode(&state,get_buffer,bits_left,htbl,nb)) < 0) \
185 { failaction; } \
186 get_buffer = state.get_buffer; bits_left = state.bits_left; \
187 } \
188 }
189
190
191 /*
192 * Expanded entropy decoder object for Huffman decoding.
193 *
194 * The savable_state subrecord contains fields that change within an MCU,
195 * but must not be updated permanently until we complete the MCU.
196 */
197
198 typedef struct {
199 unsigned int EOBRUN; /* remaining EOBs in EOBRUN */
200 int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
201 } savable_state;
202
203 /* This macro is to work around compilers with missing or broken
204 * structure assignment. You'll need to fix this code if you have
205 * such a compiler and you change MAX_COMPS_IN_SCAN.
206 */
207
208 #ifndef NO_STRUCT_ASSIGN
209 #define ASSIGN_STATE(dest,src) ((dest) = (src))
210 #else
211 #if MAX_COMPS_IN_SCAN == 4
212 #define ASSIGN_STATE(dest,src) \
213 ((dest).EOBRUN = (src).EOBRUN, \
214 (dest).last_dc_val[0] = (src).last_dc_val[0], \
215 (dest).last_dc_val[1] = (src).last_dc_val[1], \
216 (dest).last_dc_val[2] = (src).last_dc_val[2], \
217 (dest).last_dc_val[3] = (src).last_dc_val[3])
218 #endif
219 #endif
220
221
222 typedef struct {
223 struct jpeg_entropy_decoder pub; /* public fields */
224
225 /* These fields are loaded into local variables at start of each MCU.
226 * In case of suspension, we exit WITHOUT updating them.
227 */
228 bitread_perm_state bitstate; /* Bit buffer at start of MCU */
229 savable_state saved; /* Other state at start of MCU */
230
231 /* These fields are NOT loaded into local working state. */
232 unsigned int restarts_to_go; /* MCUs left in this restart interval */
233
234 /* Following two fields used only in progressive mode */
235
236 /* Pointers to derived tables (these workspaces have image lifespan) */
237 d_derived_tbl * derived_tbls[NUM_HUFF_TBLS];
238
239 d_derived_tbl * ac_derived_tbl; /* active table during an AC scan */
240
241 /* Following fields used only in sequential mode */
242
243 /* Pointers to derived tables (these workspaces have image lifespan) */
244 d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
245 d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
246
247 /* Precalculated info set up by start_pass for use in decode_mcu: */
248
249 /* Pointers to derived tables to be used for each block within an MCU */
250 d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
251 d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
252 /* Whether we care about the DC and AC coefficient values for each block */
253 int coef_limit[D_MAX_BLOCKS_IN_MCU];
254 } huff_entropy_decoder;
255
256 typedef huff_entropy_decoder * huff_entropy_ptr;
257
258
259 static const int jpeg_zigzag_order[8][8] = {
260 { 0, 1, 5, 6, 14, 15, 27, 28 },
261 { 2, 4, 7, 13, 16, 26, 29, 42 },
262 { 3, 8, 12, 17, 25, 30, 41, 43 },
263 { 9, 11, 18, 24, 31, 40, 44, 53 },
264 { 10, 19, 23, 32, 39, 45, 52, 54 },
265 { 20, 22, 33, 38, 46, 51, 55, 60 },
266 { 21, 34, 37, 47, 50, 56, 59, 61 },
267 { 35, 36, 48, 49, 57, 58, 62, 63 }
268 };
269
270
271 /*
272 * Compute the derived values for a Huffman table.
273 * This routine also performs some validation checks on the table.
274 */
275
276 LOCAL(void)
277 jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
278 d_derived_tbl ** pdtbl)
279 {
280 JHUFF_TBL *htbl;
281 d_derived_tbl *dtbl;
282 int p, i, l, si, numsymbols;
283 int lookbits, ctr;
284 char huffsize[257];
285 unsigned int huffcode[257];
286 unsigned int code;
287
288 MEMZERO(huffsize, SIZEOF(huffsize));
289 MEMZERO(huffcode, SIZEOF(huffcode));
290
291 /* Note that huffsize[] and huffcode[] are filled in code-length order,
292 * paralleling the order of the symbols themselves in htbl->huffval[].
293 */
294
295 /* Find the input Huffman table */
296 if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
297 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
298 htbl =
299 isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
300 if (htbl == NULL)
301 ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
302
303 /* Allocate a workspace if we haven't already done so. */
304 if (*pdtbl == NULL)
305 *pdtbl = (d_derived_tbl *)
306 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
307 SIZEOF(d_derived_tbl));
308 dtbl = *pdtbl;
309 dtbl->pub = htbl; /* fill in back link */
310
311 /* Figure C.1: make table of Huffman code length for each symbol */
312
313 p = 0;
314 for (l = 1; l <= 16; l++) {
315 i = (int) htbl->bits[l];
316 if (i < 0 || p + i > 256) /* protect against table overrun */
317 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
318 while (i--)
319 huffsize[p++] = (char) l;
320 }
321 huffsize[p] = 0;
322 numsymbols = p;
323
324 /* Figure C.2: generate the codes themselves */
325 /* We also validate that the counts represent a legal Huffman code tree. */
326
327 code = 0;
328 si = huffsize[0];
329 p = 0;
330 while (huffsize[p]) {
331 while (((int) huffsize[p]) == si) {
332 huffcode[p++] = code;
333 code++;
334 }
335 /* code is now 1 more than the last code used for codelength si; but
336 * it must still fit in si bits, since no code is allowed to be all ones.
337 */
338 if (((INT32) code) >= (((INT32) 1) << si))
339 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
340 code <<= 1;
341 si++;
342 }
343
344 /* Figure F.15: generate decoding tables for bit-sequential decoding */
345
346 p = 0;
347 for (l = 1; l <= 16; l++) {
348 if (htbl->bits[l]) {
349 /* valoffset[l] = huffval[] index of 1st symbol of code length l,
350 * minus the minimum code of length l
351 */
352 dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
353 p += htbl->bits[l];
354 dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
355 } else {
356 dtbl->maxcode[l] = -1; /* -1 if no codes of this length */
357 }
358 }
359 dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */
360
361 /* Compute lookahead tables to speed up decoding.
362 * First we set all the table entries to 0, indicating "too long";
363 * then we iterate through the Huffman codes that are short enough and
364 * fill in all the entries that correspond to bit sequences starting
365 * with that code.
366 */
367
368 MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));
369
370 p = 0;
371 for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
372 for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
373 /* l = current code's length, p = its index in huffcode[] & huffval[]. */
374 /* Generate left-justified code followed by all possible bit sequences */
375 lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
376 for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
377 dtbl->look_nbits[lookbits] = l;
378 dtbl->look_sym[lookbits] = htbl->huffval[p];
379 lookbits++;
380 }
381 }
382 }
383
384 /* Validate symbols as being reasonable.
385 * For AC tables, we make no check, but accept all byte values 0..255.
386 * For DC tables, we require the symbols to be in range 0..15.
387 * (Tighter bounds could be applied depending on the data depth and mode,
388 * but this is sufficient to ensure safe decoding.)
389 */
390 if (isDC) {
391 for (i = 0; i < numsymbols; i++) {
392 int sym = htbl->huffval[i];
393 if (sym < 0 || sym > 15)
394 ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
395 }
396 }
397 }
398
399
400 /*
401 * Out-of-line code for bit fetching.
402 * Note: current values of get_buffer and bits_left are passed as parameters,
403 * but are returned in the corresponding fields of the state struct.
404 *
405 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
406 * of get_buffer to be used. (On machines with wider words, an even larger
407 * buffer could be used.) However, on some machines 32-bit shifts are
408 * quite slow and take time proportional to the number of places shifted.
409 * (This is true with most PC compilers, for instance.) In this case it may
410 * be a win to set MIN_GET_BITS to the minimum value of 15. This reduces the
411 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
412 */
413
414 #ifdef SLOW_SHIFT_32
415 #define MIN_GET_BITS 15 /* minimum allowable value */
416 #else
417 #define MIN_GET_BITS (BIT_BUF_SIZE-7)
418 #endif
419
420
421 LOCAL(boolean)
422 jpeg_fill_bit_buffer (bitread_working_state * state,
423 register bit_buf_type get_buffer, register int bits_left,
424 int nbits)
425 /* Load up the bit buffer to a depth of at least nbits */
426 {
427 /* Copy heavily used state fields into locals (hopefully registers) */
428 register const JOCTET * next_input_byte = state->next_input_byte;
429 register size_t bytes_in_buffer = state->bytes_in_buffer;
430 j_decompress_ptr cinfo = state->cinfo;
431
432 /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
433 /* (It is assumed that no request will be for more than that many bits.) */
434 /* We fail to do so only if we hit a marker or are forced to suspend. */
435
436 if (cinfo->unread_marker == 0) { /* cannot advance past a marker */
437 while (bits_left < MIN_GET_BITS) {
438 register int c;
439
440 /* Attempt to read a byte */
441 if (bytes_in_buffer == 0) {
442 if (! (*cinfo->src->fill_input_buffer) (cinfo))
443 return FALSE;
444 next_input_byte = cinfo->src->next_input_byte;
445 bytes_in_buffer = cinfo->src->bytes_in_buffer;
446 }
447 bytes_in_buffer--;
448 c = GETJOCTET(*next_input_byte++);
449
450 /* If it's 0xFF, check and discard stuffed zero byte */
451 if (c == 0xFF) {
452 /* Loop here to discard any padding FF's on terminating marker,
453 * so that we can save a valid unread_marker value. NOTE: we will
454 * accept multiple FF's followed by a 0 as meaning a single FF data
455 * byte. This data pattern is not valid according to the standard.
456 */
457 do {
458 if (bytes_in_buffer == 0) {
459 if (! (*cinfo->src->fill_input_buffer) (cinfo))
460 return FALSE;
461 next_input_byte = cinfo->src->next_input_byte;
462 bytes_in_buffer = cinfo->src->bytes_in_buffer;
463 }
464 bytes_in_buffer--;
465 c = GETJOCTET(*next_input_byte++);
466 } while (c == 0xFF);
467
468 if (c == 0) {
469 /* Found FF/00, which represents an FF data byte */
470 c = 0xFF;
471 } else {
472 /* Oops, it's actually a marker indicating end of compressed data.
473 * Save the marker code for later use.
474 * Fine point: it might appear that we should save the marker into
475 * bitread working state, not straight into permanent state. But
476 * once we have hit a marker, we cannot need to suspend within the
477 * current MCU, because we will read no more bytes from the data
478 * source. So it is OK to update permanent state right away.
479 */
480 cinfo->unread_marker = c;
481 /* See if we need to insert some fake zero bits. */
482 goto no_more_bytes;
483 }
484 }
485
486 /* OK, load c into get_buffer */
487 get_buffer = (get_buffer << 8) | c;
488 bits_left += 8;
489 } /* end while */
490 } else {
491 no_more_bytes:
492 /* We get here if we've read the marker that terminates the compressed
493 * data segment. There should be enough bits in the buffer register
494 * to satisfy the request; if so, no problem.
495 */
496 if (nbits > bits_left) {
497 /* Uh-oh. Report corrupted data to user and stuff zeroes into
498 * the data stream, so that we can produce some kind of image.
499 * We use a nonvolatile flag to ensure that only one warning message
500 * appears per data segment.
501 */
502 if (! cinfo->entropy->insufficient_data) {
503 WARNMS(cinfo, JWRN_HIT_MARKER);
504 cinfo->entropy->insufficient_data = TRUE;
505 }
506 /* Fill the buffer with zero bits */
507 get_buffer <<= MIN_GET_BITS - bits_left;
508 bits_left = MIN_GET_BITS;
509 }
510 }
511
512 /* Unload the local registers */
513 state->next_input_byte = next_input_byte;
514 state->bytes_in_buffer = bytes_in_buffer;
515 state->get_buffer = get_buffer;
516 state->bits_left = bits_left;
517
518 return TRUE;
519 }
520
521
522 /*
523 * Figure F.12: extend sign bit.
524 * On some machines, a shift and sub will be faster than a table lookup.
525 */
526
527 #ifdef AVOID_TABLES
528
529 #define BIT_MASK(nbits) ((1<<(nbits))-1)
530 #define HUFF_EXTEND(x,s) ((x) < (1<<((s)-1)) ? (x) - ((1<<(s))-1) : (x))
531
532 #else
533
534 #define BIT_MASK(nbits) bmask[nbits]
535 #define HUFF_EXTEND(x,s) ((x) <= bmask[(s) - 1] ? (x) - bmask[s] : (x))
536
537 static const int bmask[16] = /* bmask[n] is mask for n rightmost bits */
538 { 0, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF,
539 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF };
540
541 #endif /* AVOID_TABLES */
542
543
544 /*
545 * Out-of-line code for Huffman code decoding.
546 */
547
548 LOCAL(int)
549 jpeg_huff_decode (bitread_working_state * state,
550 register bit_buf_type get_buffer, register int bits_left,
551 d_derived_tbl * htbl, int min_bits)
552 {
553 register int l = min_bits;
554 register INT32 code;
555
556 /* HUFF_DECODE has determined that the code is at least min_bits */
557 /* bits long, so fetch that many bits in one swoop. */
558
559 CHECK_BIT_BUFFER(*state, l, return -1);
560 code = GET_BITS(l);
561
562 /* Collect the rest of the Huffman code one bit at a time. */
563 /* This is per Figure F.16 in the JPEG spec. */
564
565 while (code > htbl->maxcode[l]) {
566 code <<= 1;
567 CHECK_BIT_BUFFER(*state, 1, return -1);
568 code |= GET_BITS(1);
569 l++;
570 }
571
572 /* Unload the local registers */
573 state->get_buffer = get_buffer;
574 state->bits_left = bits_left;
575
576 /* With garbage input we may reach the sentinel value l = 17. */
577
578 if (l > 16) {
579 int br_offset = state->next_input_byte - state->cinfo->src->next_input_byte;
580 WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
581 state->next_input_byte = state->cinfo->src->next_input_byte + br_offset;
582 return 0; /* fake a zero as the safest result */
583 }
584
585 return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ];
586 }
587
588
589 /*
590 * Check for a restart marker & resynchronize decoder.
591 * Returns FALSE if must suspend.
592 */
593
594 LOCAL(boolean)
595 process_restart (j_decompress_ptr cinfo)
596 {
597 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
598 int ci;
599
600 /* Throw away any unused bits remaining in bit buffer; */
601 /* include any full bytes in next_marker's count of discarded bytes */
602 cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
603 entropy->bitstate.bits_left = 0;
604
605 /* Advance past the RSTn marker */
606 if (! (*cinfo->marker->read_restart_marker) (cinfo))
607 return FALSE;
608
609 /* Re-initialize DC predictions to 0 */
610 for (ci = 0; ci < cinfo->comps_in_scan; ci++)
611 entropy->saved.last_dc_val[ci] = 0;
612 /* Re-init EOB run count, too */
613 entropy->saved.EOBRUN = 0;
614
615 /* Reset restart counter */
616 entropy->restarts_to_go = cinfo->restart_interval;
617
618 /* Reset out-of-data flag, unless read_restart_marker left us smack up
619 * against a marker. In that case we will end up treating the next data
620 * segment as empty, and we can avoid producing bogus output pixels by
621 * leaving the flag set.
622 */
623 if (cinfo->unread_marker == 0)
624 entropy->pub.insufficient_data = FALSE;
625
626 return TRUE;
627 }
628
629
630 /*
631 * Huffman MCU decoding.
632 * Each of these routines decodes and returns one MCU's worth of
633 * Huffman-compressed coefficients.
634 * The coefficients are reordered from zigzag order into natural array order,
635 * but are not dequantized.
636 *
637 * The i'th block of the MCU is stored into the block pointed to by
638 * MCU_data[i]. WE ASSUME THIS AREA IS INITIALLY ZEROED BY THE CALLER.
639 * (Wholesale zeroing is usually a little faster than retail...)
640 *
641 * We return FALSE if data source requested suspension. In that case no
642 * changes have been made to permanent state. (Exception: some output
643 * coefficients may already have been assigned. This is harmless for
644 * spectral selection, since we'll just re-assign them on the next call.
645 * Successive approximation AC refinement has to be more careful, however.)
646 */
647
648 /*
649 * MCU decoding for DC initial scan (either spectral selection,
650 * or first pass of successive approximation).
651 */
652
653 METHODDEF(boolean)
654 decode_mcu_DC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
655 {
656 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
657 int Al = cinfo->Al;
658 register int s, r;
659 int blkn, ci;
660 JBLOCKROW block;
661 BITREAD_STATE_VARS;
662 savable_state state;
663 d_derived_tbl * tbl;
664 jpeg_component_info * compptr;
665
666 /* Process restart marker if needed; may have to suspend */
667 if (cinfo->restart_interval) {
668 if (entropy->restarts_to_go == 0)
669 if (! process_restart(cinfo))
670 return FALSE;
671 }
672
673 /* If we've run out of data, just leave the MCU set to zeroes.
674 * This way, we return uniform gray for the remainder of the segment.
675 */
676 if (! entropy->pub.insufficient_data) {
677
678 /* Load up working state */
679 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
680 ASSIGN_STATE(state, entropy->saved);
681
682 /* Outer loop handles each block in the MCU */
683
684 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
685 block = MCU_data[blkn];
686 ci = cinfo->MCU_membership[blkn];
687 compptr = cinfo->cur_comp_info[ci];
688 tbl = entropy->derived_tbls[compptr->dc_tbl_no];
689
690 /* Decode a single block's worth of coefficients */
691
692 /* Section F.2.2.1: decode the DC coefficient difference */
693 HUFF_DECODE(s, br_state, tbl, return FALSE, label1);
694 if (s) {
695 CHECK_BIT_BUFFER(br_state, s, return FALSE);
696 r = GET_BITS(s);
697 s = HUFF_EXTEND(r, s);
698 }
699
700 /* Convert DC difference to actual value, update last_dc_val */
701 s += state.last_dc_val[ci];
702 state.last_dc_val[ci] = s;
703 /* Scale and output the coefficient (assumes jpeg_natural_order[0]=0) */
704 (*block)[0] = (JCOEF) (s << Al);
705 }
706
707 /* Completed MCU, so update state */
708 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
709 ASSIGN_STATE(entropy->saved, state);
710 }
711
712 /* Account for restart interval (no-op if not using restarts) */
713 entropy->restarts_to_go--;
714
715 return TRUE;
716 }
717
718
719 /*
720 * MCU decoding for AC initial scan (either spectral selection,
721 * or first pass of successive approximation).
722 */
723
724 METHODDEF(boolean)
725 decode_mcu_AC_first (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
726 {
727 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
728 int Se = cinfo->Se;
729 int Al = cinfo->Al;
730 register int s, k, r;
731 unsigned int EOBRUN;
732 JBLOCKROW block;
733 BITREAD_STATE_VARS;
734 d_derived_tbl * tbl;
735
736 /* Process restart marker if needed; may have to suspend */
737 if (cinfo->restart_interval) {
738 if (entropy->restarts_to_go == 0)
739 if (! process_restart(cinfo))
740 return FALSE;
741 }
742
743 /* If we've run out of data, just leave the MCU set to zeroes.
744 * This way, we return uniform gray for the remainder of the segment.
745 */
746 if (! entropy->pub.insufficient_data) {
747
748 /* Load up working state.
749 * We can avoid loading/saving bitread state if in an EOB run.
750 */
751 EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */
752
753 /* There is always only one block per MCU */
754
755 if (EOBRUN > 0) /* if it's a band of zeroes... */
756 EOBRUN--; /* ...process it now (we do nothing) */
757 else {
758 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
759 block = MCU_data[0];
760 tbl = entropy->ac_derived_tbl;
761
762 for (k = cinfo->Ss; k <= Se; k++) {
763 HUFF_DECODE(s, br_state, tbl, return FALSE, label2);
764 r = s >> 4;
765 s &= 15;
766 if (s) {
767 k += r;
768 CHECK_BIT_BUFFER(br_state, s, return FALSE);
769 r = GET_BITS(s);
770 s = HUFF_EXTEND(r, s);
771 /* Scale and output coefficient in natural (dezigzagged) order */
772 (*block)[jpeg_natural_order[k]] = (JCOEF) (s << Al);
773 } else {
774 if (r == 15) { /* ZRL */
775 k += 15; /* skip 15 zeroes in band */
776 } else { /* EOBr, run length is 2^r + appended bits */
777 EOBRUN = 1 << r;
778 if (r) { /* EOBr, r > 0 */
779 CHECK_BIT_BUFFER(br_state, r, return FALSE);
780 r = GET_BITS(r);
781 EOBRUN += r;
782 }
783 EOBRUN--; /* this band is processed at this moment */
784 break; /* force end-of-band */
785 }
786 }
787 }
788
789 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
790 }
791
792 /* Completed MCU, so update state */
793 entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */
794 }
795
796 /* Account for restart interval (no-op if not using restarts) */
797 entropy->restarts_to_go--;
798
799 return TRUE;
800 }
801
802
803 /*
804 * MCU decoding for DC successive approximation refinement scan.
805 * Note: we assume such scans can be multi-component, although the spec
806 * is not very clear on the point.
807 */
808
809 METHODDEF(boolean)
810 decode_mcu_DC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
811 {
812 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
813 int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
814 int blkn;
815 JBLOCKROW block;
816 BITREAD_STATE_VARS;
817
818 /* Process restart marker if needed; may have to suspend */
819 if (cinfo->restart_interval) {
820 if (entropy->restarts_to_go == 0)
821 if (! process_restart(cinfo))
822 return FALSE;
823 }
824
825 /* Not worth the cycles to check insufficient_data here,
826 * since we will not change the data anyway if we read zeroes.
827 */
828
829 /* Load up working state */
830 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
831
832 /* Outer loop handles each block in the MCU */
833
834 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
835 block = MCU_data[blkn];
836
837 /* Encoded data is simply the next bit of the two's-complement DC value */
838 CHECK_BIT_BUFFER(br_state, 1, return FALSE);
839 if (GET_BITS(1))
840 (*block)[0] |= p1;
841 /* Note: since we use |=, repeating the assignment later is safe */
842 }
843
844 /* Completed MCU, so update state */
845 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
846
847 /* Account for restart interval (no-op if not using restarts) */
848 entropy->restarts_to_go--;
849
850 return TRUE;
851 }
852
853
854 /*
855 * MCU decoding for AC successive approximation refinement scan.
856 */
857
858 METHODDEF(boolean)
859 decode_mcu_AC_refine (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
860 {
861 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
862 int Se = cinfo->Se;
863 int p1 = 1 << cinfo->Al; /* 1 in the bit position being coded */
864 int m1 = (-1) << cinfo->Al; /* -1 in the bit position being coded */
865 register int s, k, r;
866 unsigned int EOBRUN;
867 JBLOCKROW block;
868 JCOEFPTR thiscoef;
869 BITREAD_STATE_VARS;
870 d_derived_tbl * tbl;
871 int num_newnz;
872 int newnz_pos[DCTSIZE2];
873
874 /* Process restart marker if needed; may have to suspend */
875 if (cinfo->restart_interval) {
876 if (entropy->restarts_to_go == 0)
877 if (! process_restart(cinfo))
878 return FALSE;
879 }
880
881 /* If we've run out of data, don't modify the MCU.
882 */
883 if (! entropy->pub.insufficient_data) {
884
885 /* Load up working state */
886 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
887 EOBRUN = entropy->saved.EOBRUN; /* only part of saved state we need */
888
889 /* There is always only one block per MCU */
890 block = MCU_data[0];
891 tbl = entropy->ac_derived_tbl;
892
893 /* If we are forced to suspend, we must undo the assignments to any newly
894 * nonzero coefficients in the block, because otherwise we'd get confused
895 * next time about which coefficients were already nonzero.
896 * But we need not undo addition of bits to already-nonzero coefficients;
897 * instead, we can test the current bit to see if we already did it.
898 */
899 num_newnz = 0;
900
901 /* initialize coefficient loop counter to start of band */
902 k = cinfo->Ss;
903
904 if (EOBRUN == 0) {
905 for (; k <= Se; k++) {
906 HUFF_DECODE(s, br_state, tbl, goto undoit, label3);
907 r = s >> 4;
908 s &= 15;
909 if (s) {
910 if (s != 1) /* size of new coef should always be 1 */
911 WARNMS(cinfo, JWRN_HUFF_BAD_CODE);
912 CHECK_BIT_BUFFER(br_state, 1, goto undoit);
913 if (GET_BITS(1))
914 s = p1; /* newly nonzero coef is positive */
915 else
916 s = m1; /* newly nonzero coef is negative */
917 } else {
918 if (r != 15) {
919 EOBRUN = 1 << r; /* EOBr, run length is 2^r + appended bits */
920 if (r) {
921 CHECK_BIT_BUFFER(br_state, r, goto undoit);
922 r = GET_BITS(r);
923 EOBRUN += r;
924 }
925 break; /* rest of block is handled by EOB logic */
926 }
927 /* note s = 0 for processing ZRL */
928 }
929 /* Advance over already-nonzero coefs and r still-zero coefs,
930 * appending correction bits to the nonzeroes. A correction bit is 1
931 * if the absolute value of the coefficient must be increased.
932 */
933 do {
934 thiscoef = *block + jpeg_natural_order[k];
935 if (*thiscoef != 0) {
936 CHECK_BIT_BUFFER(br_state, 1, goto undoit);
937 if (GET_BITS(1)) {
938 if ((*thiscoef & p1) == 0) { /* do nothing if already set it */
939 if (*thiscoef >= 0)
940 *thiscoef += p1;
941 else
942 *thiscoef += m1;
943 }
944 }
945 } else {
946 if (--r < 0)
947 break; /* reached target zero coefficient */
948 }
949 k++;
950 } while (k <= Se);
951 if (s) {
952 int pos = jpeg_natural_order[k];
953 /* Output newly nonzero coefficient */
954 (*block)[pos] = (JCOEF) s;
955 /* Remember its position in case we have to suspend */
956 newnz_pos[num_newnz++] = pos;
957 }
958 }
959 }
960
961 if (EOBRUN > 0) {
962 /* Scan any remaining coefficient positions after the end-of-band
963 * (the last newly nonzero coefficient, if any). Append a correction
964 * bit to each already-nonzero coefficient. A correction bit is 1
965 * if the absolute value of the coefficient must be increased.
966 */
967 for (; k <= Se; k++) {
968 thiscoef = *block + jpeg_natural_order[k];
969 if (*thiscoef != 0) {
970 CHECK_BIT_BUFFER(br_state, 1, goto undoit);
971 if (GET_BITS(1)) {
972 if ((*thiscoef & p1) == 0) { /* do nothing if already changed it */
973 if (*thiscoef >= 0)
974 *thiscoef += p1;
975 else
976 *thiscoef += m1;
977 }
978 }
979 }
980 }
981 /* Count one block completed in EOB run */
982 EOBRUN--;
983 }
984
985 /* Completed MCU, so update state */
986 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
987 entropy->saved.EOBRUN = EOBRUN; /* only part of saved state we need */
988 }
989
990 /* Account for restart interval (no-op if not using restarts) */
991 entropy->restarts_to_go--;
992
993 return TRUE;
994
995 undoit:
996 /* Re-zero any output coefficients that we made newly nonzero */
997 while (num_newnz > 0)
998 (*block)[newnz_pos[--num_newnz]] = 0;
999
1000 return FALSE;
1001 }
1002
1003
1004 /*
1005 * Decode one MCU's worth of Huffman-compressed coefficients.
1006 */
1007
1008 METHODDEF(boolean)
1009 decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
1010 {
1011 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1012 int blkn;
1013 BITREAD_STATE_VARS;
1014 savable_state state;
1015
1016 /* Process restart marker if needed; may have to suspend */
1017 if (cinfo->restart_interval) {
1018 if (entropy->restarts_to_go == 0)
1019 if (! process_restart(cinfo))
1020 return FALSE;
1021 }
1022
1023 /* If we've run out of data, just leave the MCU set to zeroes.
1024 * This way, we return uniform gray for the remainder of the segment.
1025 */
1026 if (! entropy->pub.insufficient_data) {
1027
1028 /* Load up working state */
1029 BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
1030 ASSIGN_STATE(state, entropy->saved);
1031
1032 /* Outer loop handles each block in the MCU */
1033
1034 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
1035 JBLOCKROW block = MCU_data[blkn];
1036 d_derived_tbl * htbl;
1037 register int s, k, r;
1038 int coef_limit, ci;
1039
1040 /* Decode a single block's worth of coefficients */
1041
1042 /* Section F.2.2.1: decode the DC coefficient difference */
1043 htbl = entropy->dc_cur_tbls[blkn];
1044 HUFF_DECODE(s, br_state, htbl, return FALSE, label1);
1045
1046 htbl = entropy->ac_cur_tbls[blkn];
1047 k = 1;
1048 coef_limit = entropy->coef_limit[blkn];
1049 if (coef_limit) {
1050 /* Convert DC difference to actual value, update last_dc_val */
1051 if (s) {
1052 CHECK_BIT_BUFFER(br_state, s, return FALSE);
1053 r = GET_BITS(s);
1054 s = HUFF_EXTEND(r, s);
1055 }
1056 ci = cinfo->MCU_membership[blkn];
1057 s += state.last_dc_val[ci];
1058 state.last_dc_val[ci] = s;
1059 /* Output the DC coefficient */
1060 (*block)[0] = (JCOEF) s;
1061
1062 /* Section F.2.2.2: decode the AC coefficients */
1063 /* Since zeroes are skipped, output area must be cleared beforehand */
1064 for (; k < coef_limit; k++) {
1065 HUFF_DECODE(s, br_state, htbl, return FALSE, label2);
1066
1067 r = s >> 4;
1068 s &= 15;
1069
1070 if (s) {
1071 k += r;
1072 CHECK_BIT_BUFFER(br_state, s, return FALSE);
1073 r = GET_BITS(s);
1074 s = HUFF_EXTEND(r, s);
1075 /* Output coefficient in natural (dezigzagged) order.
1076 * Note: the extra entries in jpeg_natural_order[] will save us
1077 * if k >= DCTSIZE2, which could happen if the data is corrupted.
1078 */
1079 (*block)[jpeg_natural_order[k]] = (JCOEF) s;
1080 } else {
1081 if (r != 15)
1082 goto EndOfBlock;
1083 k += 15;
1084 }
1085 }
1086 } else {
1087 if (s) {
1088 CHECK_BIT_BUFFER(br_state, s, return FALSE);
1089 DROP_BITS(s);
1090 }
1091 }
1092
1093 /* Section F.2.2.2: decode the AC coefficients */
1094 /* In this path we just discard the values */
1095 for (; k < DCTSIZE2; k++) {
1096 HUFF_DECODE(s, br_state, htbl, return FALSE, label3);
1097
1098 r = s >> 4;
1099 s &= 15;
1100
1101 if (s) {
1102 k += r;
1103 CHECK_BIT_BUFFER(br_state, s, return FALSE);
1104 DROP_BITS(s);
1105 } else {
1106 if (r != 15)
1107 break;
1108 k += 15;
1109 }
1110 }
1111
1112 EndOfBlock: ;
1113 }
1114
1115 /* Completed MCU, so update state */
1116 BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
1117 ASSIGN_STATE(entropy->saved, state);
1118 }
1119
1120 /* Account for restart interval (no-op if not using restarts) */
1121 entropy->restarts_to_go--;
1122
1123 return TRUE;
1124 }
1125
1126
1127 /*
1128 * Initialize for a Huffman-compressed scan.
1129 */
1130
1131 METHODDEF(void)
1132 start_pass_huff_decoder (j_decompress_ptr cinfo)
1133 {
1134 huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1135 int ci, blkn, dctbl, actbl, i;
1136 jpeg_component_info * compptr;
1137
1138 if (cinfo->progressive_mode) {
1139 /* Validate progressive scan parameters */
1140 if (cinfo->Ss == 0) {
1141 if (cinfo->Se != 0)
1142 goto bad;
1143 } else {
1144 /* need not check Ss/Se < 0 since they came from unsigned bytes */
1145 if (cinfo->Se < cinfo->Ss || cinfo->Se >= DCTSIZE2)
1146 goto bad;
1147 /* AC scans may have only one component */
1148 if (cinfo->comps_in_scan != 1)
1149 goto bad;
1150 }
1151 if (cinfo->Ah != 0) {
1152 /* Successive approximation refinement scan: must have Al = Ah-1. */
1153 if (cinfo->Ah-1 != cinfo->Al)
1154 goto bad;
1155 }
1156 if (cinfo->Al > 13) { /* need not check for < 0 */
1157 /* Arguably the maximum Al value should be less than 13 for 8-bit precision,
1158 * but the spec doesn't say so, and we try to be liberal about what we
1159 * accept. Note: large Al values could result in out-of-range DC
1160 * coefficients during early scans, leading to bizarre displays due to
1161 * overflows in the IDCT math. But we won't crash.
1162 */
1163 bad:
1164 ERREXIT4(cinfo, JERR_BAD_PROGRESSION,
1165 cinfo->Ss, cinfo->Se, cinfo->Ah, cinfo->Al);
1166 }
1167 /* Update progression status, and verify that scan order is legal.
1168 * Note that inter-scan inconsistencies are treated as warnings
1169 * not fatal errors ... not clear if this is right way to behave.
1170 */
1171 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1172 int coefi, cindex = cinfo->cur_comp_info[ci]->component_index;
1173 int *coef_bit_ptr = & cinfo->coef_bits[cindex][0];
1174 if (cinfo->Ss && coef_bit_ptr[0] < 0) /* AC without prior DC scan */
1175 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, 0);
1176 for (coefi = cinfo->Ss; coefi <= cinfo->Se; coefi++) {
1177 int expected = (coef_bit_ptr[coefi] < 0) ? 0 : coef_bit_ptr[coefi];
1178 if (cinfo->Ah != expected)
1179 WARNMS2(cinfo, JWRN_BOGUS_PROGRESSION, cindex, coefi);
1180 coef_bit_ptr[coefi] = cinfo->Al;
1181 }
1182 }
1183
1184 /* Select MCU decoding routine */
1185 if (cinfo->Ah == 0) {
1186 if (cinfo->Ss == 0)
1187 entropy->pub.decode_mcu = decode_mcu_DC_first;
1188 else
1189 entropy->pub.decode_mcu = decode_mcu_AC_first;
1190 } else {
1191 if (cinfo->Ss == 0)
1192 entropy->pub.decode_mcu = decode_mcu_DC_refine;
1193 else
1194 entropy->pub.decode_mcu = decode_mcu_AC_refine;
1195 }
1196
1197 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1198 compptr = cinfo->cur_comp_info[ci];
1199 /* Make sure requested tables are present, and compute derived tables.
1200 * We may build same derived table more than once, but it's not expensive.
1201 */
1202 if (cinfo->Ss == 0) {
1203 if (cinfo->Ah == 0) { /* DC refinement needs no table */
1204 i = compptr->dc_tbl_no;
1205 jpeg_make_d_derived_tbl(cinfo, TRUE, i,
1206 & entropy->derived_tbls[i]);
1207 }
1208 } else {
1209 i = compptr->ac_tbl_no;
1210 jpeg_make_d_derived_tbl(cinfo, FALSE, i,
1211 & entropy->derived_tbls[i]);
1212 /* remember the single active table */
1213 entropy->ac_derived_tbl = entropy->derived_tbls[i];
1214 }
1215 /* Initialize DC predictions to 0 */
1216 entropy->saved.last_dc_val[ci] = 0;
1217 }
1218
1219 /* Initialize private state variables */
1220 entropy->saved.EOBRUN = 0;
1221 } else {
1222 /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
1223 * This ought to be an error condition, but we make it a warning because
1224 * there are some baseline files out there with all zeroes in these bytes.
1225 */
1226 if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
1227 cinfo->Ah != 0 || cinfo->Al != 0)
1228 WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
1229
1230 /* Select MCU decoding routine */
1231 entropy->pub.decode_mcu = decode_mcu;
1232
1233 for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1234 compptr = cinfo->cur_comp_info[ci];
1235 dctbl = compptr->dc_tbl_no;
1236 actbl = compptr->ac_tbl_no;
1237 /* Compute derived values for Huffman tables */
1238 /* We may do this more than once for a table, but it's not expensive */
1239 jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
1240 & entropy->dc_derived_tbls[dctbl]);
1241 jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
1242 & entropy->ac_derived_tbls[actbl]);
1243 /* Initialize DC predictions to 0 */
1244 entropy->saved.last_dc_val[ci] = 0;
1245 }
1246
1247 /* Precalculate decoding info for each block in an MCU of this scan */
1248 for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
1249 ci = cinfo->MCU_membership[blkn];
1250 compptr = cinfo->cur_comp_info[ci];
1251 /* Precalculate which table to use for each block */
1252 entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
1253 entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
1254 /* Decide whether we really care about the coefficient values */
1255 if (compptr->component_needed) {
1256 ci = compptr->DCT_v_scaled_size;
1257 if (ci <= 0 || ci > 8) ci = 8;
1258 i = compptr->DCT_h_scaled_size;
1259 if (i <= 0 || i > 8) i = 8;
1260 entropy->coef_limit[blkn] = 1 + jpeg_zigzag_order[ci - 1][i - 1];
1261 } else {
1262 entropy->coef_limit[blkn] = 0;
1263 }
1264 }
1265 }
1266
1267 /* Initialize bitread state variables */
1268 entropy->bitstate.bits_left = 0;
1269 entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
1270 entropy->pub.insufficient_data = FALSE;
1271
1272 /* Initialize restart counter */
1273 entropy->restarts_to_go = cinfo->restart_interval;
1274 }
1275
1276
1277 /*
1278 * Module initialization routine for Huffman entropy decoding.
1279 */
1280
1281 GLOBAL(void)
1282 jinit_huff_decoder (j_decompress_ptr cinfo)
1283 {
1284 huff_entropy_ptr entropy;
1285 int i;
1286
1287 entropy = (huff_entropy_ptr)
1288 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1289 SIZEOF(huff_entropy_decoder));
1290 cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
1291 entropy->pub.start_pass = start_pass_huff_decoder;
1292
1293 if (cinfo->progressive_mode) {
1294 /* Create progression status table */
1295 int *coef_bit_ptr, ci;
1296 cinfo->coef_bits = (int (*)[DCTSIZE2])
1297 (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1298 cinfo->num_components*DCTSIZE2*SIZEOF(int));
1299 coef_bit_ptr = & cinfo->coef_bits[0][0];
1300 for (ci = 0; ci < cinfo->num_components; ci++)
1301 for (i = 0; i < DCTSIZE2; i++)
1302 *coef_bit_ptr++ = -1;
1303
1304 /* Mark derived tables unallocated */
1305 for (i = 0; i < NUM_HUFF_TBLS; i++) {
1306 entropy->derived_tbls[i] = NULL;
1307 }
1308 } else {
1309 /* Mark tables unallocated */
1310 for (i = 0; i < NUM_HUFF_TBLS; i++) {
1311 entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
1312 }
1313 }
1314 }