source: trunk/libjpeg/jdhuff.c @ 15

Last change on this file since 15 was 15, checked in by Eugene Romanenko, 15 years ago

needed libs update

File size: 21.0 KB
Line 
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
23/*
24 * Expanded entropy decoder object for Huffman decoding.
25 *
26 * The savable_state subrecord contains fields that change within an MCU,
27 * but must not be updated permanently until we complete the MCU.
28 */
29
30typedef struct {
31  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
32} savable_state;
33
34/* This macro is to work around compilers with missing or broken
35 * structure assignment.  You'll need to fix this code if you have
36 * such a compiler and you change MAX_COMPS_IN_SCAN.
37 */
38
39#ifndef NO_STRUCT_ASSIGN
40#define ASSIGN_STATE(dest,src)  ((dest) = (src))
41#else
42#if MAX_COMPS_IN_SCAN == 4
43#define ASSIGN_STATE(dest,src)  \
44        ((dest).last_dc_val[0] = (src).last_dc_val[0], \
45         (dest).last_dc_val[1] = (src).last_dc_val[1], \
46         (dest).last_dc_val[2] = (src).last_dc_val[2], \
47         (dest).last_dc_val[3] = (src).last_dc_val[3])
48#endif
49#endif
50
51
52typedef struct {
53  struct jpeg_entropy_decoder pub; /* public fields */
54
55  /* These fields are loaded into local variables at start of each MCU.
56   * In case of suspension, we exit WITHOUT updating them.
57   */
58  bitread_perm_state bitstate;  /* Bit buffer at start of MCU */
59  savable_state saved;          /* Other state at start of MCU */
60
61  /* These fields are NOT loaded into local working state. */
62  unsigned int restarts_to_go;  /* MCUs left in this restart interval */
63
64  /* Pointers to derived tables (these workspaces have image lifespan) */
65  d_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
66  d_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
67
68  /* Precalculated info set up by start_pass for use in decode_mcu: */
69
70  /* Pointers to derived tables to be used for each block within an MCU */
71  d_derived_tbl * dc_cur_tbls[D_MAX_BLOCKS_IN_MCU];
72  d_derived_tbl * ac_cur_tbls[D_MAX_BLOCKS_IN_MCU];
73  /* Whether we care about the DC and AC coefficient values for each block */
74  boolean dc_needed[D_MAX_BLOCKS_IN_MCU];
75  boolean ac_needed[D_MAX_BLOCKS_IN_MCU];
76} huff_entropy_decoder;
77
78typedef huff_entropy_decoder * huff_entropy_ptr;
79
80
81/*
82 * Initialize for a Huffman-compressed scan.
83 */
84
85METHODDEF(void)
86start_pass_huff_decoder (j_decompress_ptr cinfo)
87{
88  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
89  int ci, blkn, dctbl, actbl;
90  jpeg_component_info * compptr;
91
92  /* Check that the scan parameters Ss, Se, Ah/Al are OK for sequential JPEG.
93   * This ought to be an error condition, but we make it a warning because
94   * there are some baseline files out there with all zeroes in these bytes.
95   */
96  if (cinfo->Ss != 0 || cinfo->Se != DCTSIZE2-1 ||
97      cinfo->Ah != 0 || cinfo->Al != 0)
98    WARNMS(cinfo, JWRN_NOT_SEQUENTIAL);
99
100  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
101    compptr = cinfo->cur_comp_info[ci];
102    dctbl = compptr->dc_tbl_no;
103    actbl = compptr->ac_tbl_no;
104    /* Compute derived values for Huffman tables */
105    /* We may do this more than once for a table, but it's not expensive */
106    jpeg_make_d_derived_tbl(cinfo, TRUE, dctbl,
107                            & entropy->dc_derived_tbls[dctbl]);
108    jpeg_make_d_derived_tbl(cinfo, FALSE, actbl,
109                            & entropy->ac_derived_tbls[actbl]);
110    /* Initialize DC predictions to 0 */
111    entropy->saved.last_dc_val[ci] = 0;
112  }
113
114  /* Precalculate decoding info for each block in an MCU of this scan */
115  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
116    ci = cinfo->MCU_membership[blkn];
117    compptr = cinfo->cur_comp_info[ci];
118    /* Precalculate which table to use for each block */
119    entropy->dc_cur_tbls[blkn] = entropy->dc_derived_tbls[compptr->dc_tbl_no];
120    entropy->ac_cur_tbls[blkn] = entropy->ac_derived_tbls[compptr->ac_tbl_no];
121    /* Decide whether we really care about the coefficient values */
122    if (compptr->component_needed) {
123      entropy->dc_needed[blkn] = TRUE;
124      /* we don't need the ACs if producing a 1/8th-size image */
125      entropy->ac_needed[blkn] = (compptr->DCT_scaled_size > 1);
126    } else {
127      entropy->dc_needed[blkn] = entropy->ac_needed[blkn] = FALSE;
128    }
129  }
130
131  /* Initialize bitread state variables */
132  entropy->bitstate.bits_left = 0;
133  entropy->bitstate.get_buffer = 0; /* unnecessary, but keeps Purify quiet */
134  entropy->pub.insufficient_data = FALSE;
135
136  /* Initialize restart counter */
137  entropy->restarts_to_go = cinfo->restart_interval;
138}
139
140
141/*
142 * Compute the derived values for a Huffman table.
143 * This routine also performs some validation checks on the table.
144 *
145 * Note this is also used by jdphuff.c.
146 */
147
148GLOBAL(void)
149jpeg_make_d_derived_tbl (j_decompress_ptr cinfo, boolean isDC, int tblno,
150                         d_derived_tbl ** pdtbl)
151{
152  JHUFF_TBL *htbl;
153  d_derived_tbl *dtbl;
154  int p, i, l, si, numsymbols;
155  int lookbits, ctr;
156  char huffsize[257];
157  unsigned int huffcode[257];
158  unsigned int code;
159
160  /* Note that huffsize[] and huffcode[] are filled in code-length order,
161   * paralleling the order of the symbols themselves in htbl->huffval[].
162   */
163
164  /* Find the input Huffman table */
165  if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
166    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
167  htbl =
168    isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
169  if (htbl == NULL)
170    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
171
172  /* Allocate a workspace if we haven't already done so. */
173  if (*pdtbl == NULL)
174    *pdtbl = (d_derived_tbl *)
175      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
176                                  SIZEOF(d_derived_tbl));
177  dtbl = *pdtbl;
178  dtbl->pub = htbl;             /* fill in back link */
179 
180  /* Figure C.1: make table of Huffman code length for each symbol */
181
182  p = 0;
183  for (l = 1; l <= 16; l++) {
184    i = (int) htbl->bits[l];
185    if (i < 0 || p + i > 256)   /* protect against table overrun */
186      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
187    while (i--)
188      huffsize[p++] = (char) l;
189  }
190  huffsize[p] = 0;
191  numsymbols = p;
192 
193  /* Figure C.2: generate the codes themselves */
194  /* We also validate that the counts represent a legal Huffman code tree. */
195 
196  code = 0;
197  si = huffsize[0];
198  p = 0;
199  while (huffsize[p]) {
200    while (((int) huffsize[p]) == si) {
201      huffcode[p++] = code;
202      code++;
203    }
204    /* code is now 1 more than the last code used for codelength si; but
205     * it must still fit in si bits, since no code is allowed to be all ones.
206     */
207    if (((INT32) code) >= (((INT32) 1) << si))
208      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
209    code <<= 1;
210    si++;
211  }
212
213  /* Figure F.15: generate decoding tables for bit-sequential decoding */
214
215  p = 0;
216  for (l = 1; l <= 16; l++) {
217    if (htbl->bits[l]) {
218      /* valoffset[l] = huffval[] index of 1st symbol of code length l,
219       * minus the minimum code of length l
220       */
221      dtbl->valoffset[l] = (INT32) p - (INT32) huffcode[p];
222      p += htbl->bits[l];
223      dtbl->maxcode[l] = huffcode[p-1]; /* maximum code of length l */
224    } else {
225      dtbl->maxcode[l] = -1;    /* -1 if no codes of this length */
226    }
227  }
228  dtbl->maxcode[17] = 0xFFFFFL; /* ensures jpeg_huff_decode terminates */
229
230  /* Compute lookahead tables to speed up decoding.
231   * First we set all the table entries to 0, indicating "too long";
232   * then we iterate through the Huffman codes that are short enough and
233   * fill in all the entries that correspond to bit sequences starting
234   * with that code.
235   */
236
237  MEMZERO(dtbl->look_nbits, SIZEOF(dtbl->look_nbits));
238
239  p = 0;
240  for (l = 1; l <= HUFF_LOOKAHEAD; l++) {
241    for (i = 1; i <= (int) htbl->bits[l]; i++, p++) {
242      /* l = current code's length, p = its index in huffcode[] & huffval[]. */
243      /* Generate left-justified code followed by all possible bit sequences */
244      lookbits = huffcode[p] << (HUFF_LOOKAHEAD-l);
245      for (ctr = 1 << (HUFF_LOOKAHEAD-l); ctr > 0; ctr--) {
246        dtbl->look_nbits[lookbits] = l;
247        dtbl->look_sym[lookbits] = htbl->huffval[p];
248        lookbits++;
249      }
250    }
251  }
252
253  /* Validate symbols as being reasonable.
254   * For AC tables, we make no check, but accept all byte values 0..255.
255   * For DC tables, we require the symbols to be in range 0..15.
256   * (Tighter bounds could be applied depending on the data depth and mode,
257   * but this is sufficient to ensure safe decoding.)
258   */
259  if (isDC) {
260    for (i = 0; i < numsymbols; i++) {
261      int sym = htbl->huffval[i];
262      if (sym < 0 || sym > 15)
263        ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
264    }
265  }
266}
267
268
269/*
270 * Out-of-line code for bit fetching (shared with jdphuff.c).
271 * See jdhuff.h for info about usage.
272 * Note: current values of get_buffer and bits_left are passed as parameters,
273 * but are returned in the corresponding fields of the state struct.
274 *
275 * On most machines MIN_GET_BITS should be 25 to allow the full 32-bit width
276 * of get_buffer to be used.  (On machines with wider words, an even larger
277 * buffer could be used.)  However, on some machines 32-bit shifts are
278 * quite slow and take time proportional to the number of places shifted.
279 * (This is true with most PC compilers, for instance.)  In this case it may
280 * be a win to set MIN_GET_BITS to the minimum value of 15.  This reduces the
281 * average shift distance at the cost of more calls to jpeg_fill_bit_buffer.
282 */
283
284#ifdef SLOW_SHIFT_32
285#define MIN_GET_BITS  15        /* minimum allowable value */
286#else
287#define MIN_GET_BITS  (BIT_BUF_SIZE-7)
288#endif
289
290
291GLOBAL(boolean)
292jpeg_fill_bit_buffer (bitread_working_state * state,
293                      register bit_buf_type get_buffer, register int bits_left,
294                      int nbits)
295/* Load up the bit buffer to a depth of at least nbits */
296{
297  /* Copy heavily used state fields into locals (hopefully registers) */
298  register const JOCTET * next_input_byte = state->next_input_byte;
299  register size_t bytes_in_buffer = state->bytes_in_buffer;
300  j_decompress_ptr cinfo = state->cinfo;
301
302  /* Attempt to load at least MIN_GET_BITS bits into get_buffer. */
303  /* (It is assumed that no request will be for more than that many bits.) */
304  /* We fail to do so only if we hit a marker or are forced to suspend. */
305
306  if (cinfo->unread_marker == 0) {      /* cannot advance past a marker */
307    while (bits_left < MIN_GET_BITS) {
308      register int c;
309
310      /* Attempt to read a byte */
311      if (bytes_in_buffer == 0) {
312        if (! (*cinfo->src->fill_input_buffer) (cinfo))
313          return FALSE;
314        next_input_byte = cinfo->src->next_input_byte;
315        bytes_in_buffer = cinfo->src->bytes_in_buffer;
316      }
317      bytes_in_buffer--;
318      c = GETJOCTET(*next_input_byte++);
319
320      /* If it's 0xFF, check and discard stuffed zero byte */
321      if (c == 0xFF) {
322        /* Loop here to discard any padding FF's on terminating marker,
323         * so that we can save a valid unread_marker value.  NOTE: we will
324         * accept multiple FF's followed by a 0 as meaning a single FF data
325         * byte.  This data pattern is not valid according to the standard.
326         */
327        do {
328          if (bytes_in_buffer == 0) {
329            if (! (*cinfo->src->fill_input_buffer) (cinfo))
330              return FALSE;
331            next_input_byte = cinfo->src->next_input_byte;
332            bytes_in_buffer = cinfo->src->bytes_in_buffer;
333          }
334          bytes_in_buffer--;
335          c = GETJOCTET(*next_input_byte++);
336        } while (c == 0xFF);
337
338        if (c == 0) {
339          /* Found FF/00, which represents an FF data byte */
340          c = 0xFF;
341        } else {
342          /* Oops, it's actually a marker indicating end of compressed data.
343           * Save the marker code for later use.
344           * Fine point: it might appear that we should save the marker into
345           * bitread working state, not straight into permanent state.  But
346           * once we have hit a marker, we cannot need to suspend within the
347           * current MCU, because we will read no more bytes from the data
348           * source.  So it is OK to update permanent state right away.
349           */
350          cinfo->unread_marker = c;
351          /* See if we need to insert some fake zero bits. */
352          goto no_more_bytes;
353        }
354      }
355
356      /* OK, load c into get_buffer */
357      get_buffer = (get_buffer << 8) | c;
358      bits_left += 8;
359    } /* end while */
360  } else {
361  no_more_bytes:
362    /* We get here if we've read the marker that terminates the compressed
363     * data segment.  There should be enough bits in the buffer register
364     * to satisfy the request; if so, no problem.
365     */
366    if (nbits > bits_left) {
367      /* Uh-oh.  Report corrupted data to user and stuff zeroes into
368       * the data stream, so that we can produce some kind of image.
369       * We use a nonvolatile flag to ensure that only one warning message
370       * appears per data segment.
371       */
372      if (! cinfo->entropy->insufficient_data) {
373        WARNMS(cinfo, JWRN_HIT_MARKER);
374        cinfo->entropy->insufficient_data = TRUE;
375      }
376      /* Fill the buffer with zero bits */
377      get_buffer <<= MIN_GET_BITS - bits_left;
378      bits_left = MIN_GET_BITS;
379    }
380  }
381
382  /* Unload the local registers */
383  state->next_input_byte = next_input_byte;
384  state->bytes_in_buffer = bytes_in_buffer;
385  state->get_buffer = get_buffer;
386  state->bits_left = bits_left;
387
388  return TRUE;
389}
390
391
392/*
393 * Out-of-line code for Huffman code decoding.
394 * See jdhuff.h for info about usage.
395 */
396
397GLOBAL(int)
398jpeg_huff_decode (bitread_working_state * state,
399                  register bit_buf_type get_buffer, register int bits_left,
400                  d_derived_tbl * htbl, int min_bits)
401{
402  register int l = min_bits;
403  register INT32 code;
404
405  /* HUFF_DECODE has determined that the code is at least min_bits */
406  /* bits long, so fetch that many bits in one swoop. */
407
408  CHECK_BIT_BUFFER(*state, l, return -1);
409  code = GET_BITS(l);
410
411  /* Collect the rest of the Huffman code one bit at a time. */
412  /* This is per Figure F.16 in the JPEG spec. */
413
414  while (code > htbl->maxcode[l]) {
415    code <<= 1;
416    CHECK_BIT_BUFFER(*state, 1, return -1);
417    code |= GET_BITS(1);
418    l++;
419  }
420
421  /* Unload the local registers */
422  state->get_buffer = get_buffer;
423  state->bits_left = bits_left;
424
425  /* With garbage input we may reach the sentinel value l = 17. */
426
427  if (l > 16) {
428    WARNMS(state->cinfo, JWRN_HUFF_BAD_CODE);
429    return 0;                   /* fake a zero as the safest result */
430  }
431
432  return htbl->pub->huffval[ (int) (code + htbl->valoffset[l]) ];
433}
434
435
436/*
437 * Figure F.12: extend sign bit.
438 * On some machines, a shift and add will be faster than a table lookup.
439 */
440
441#ifdef AVOID_TABLES
442
443#define HUFF_EXTEND(x,s)  ((x) < (1<<((s)-1)) ? (x) + (((-1)<<(s)) + 1) : (x))
444
445#else
446
447#define HUFF_EXTEND(x,s)  ((x) < extend_test[s] ? (x) + extend_offset[s] : (x))
448
449static const int extend_test[16] =   /* entry n is 2**(n-1) */
450  { 0, 0x0001, 0x0002, 0x0004, 0x0008, 0x0010, 0x0020, 0x0040, 0x0080,
451    0x0100, 0x0200, 0x0400, 0x0800, 0x1000, 0x2000, 0x4000 };
452
453static const int extend_offset[16] = /* entry n is (-1 << n) + 1 */
454  { 0, ((-1)<<1) + 1, ((-1)<<2) + 1, ((-1)<<3) + 1, ((-1)<<4) + 1,
455    ((-1)<<5) + 1, ((-1)<<6) + 1, ((-1)<<7) + 1, ((-1)<<8) + 1,
456    ((-1)<<9) + 1, ((-1)<<10) + 1, ((-1)<<11) + 1, ((-1)<<12) + 1,
457    ((-1)<<13) + 1, ((-1)<<14) + 1, ((-1)<<15) + 1 };
458
459#endif /* AVOID_TABLES */
460
461
462/*
463 * Check for a restart marker & resynchronize decoder.
464 * Returns FALSE if must suspend.
465 */
466
467LOCAL(boolean)
468process_restart (j_decompress_ptr cinfo)
469{
470  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
471  int ci;
472
473  /* Throw away any unused bits remaining in bit buffer; */
474  /* include any full bytes in next_marker's count of discarded bytes */
475  cinfo->marker->discarded_bytes += entropy->bitstate.bits_left / 8;
476  entropy->bitstate.bits_left = 0;
477
478  /* Advance past the RSTn marker */
479  if (! (*cinfo->marker->read_restart_marker) (cinfo))
480    return FALSE;
481
482  /* Re-initialize DC predictions to 0 */
483  for (ci = 0; ci < cinfo->comps_in_scan; ci++)
484    entropy->saved.last_dc_val[ci] = 0;
485
486  /* Reset restart counter */
487  entropy->restarts_to_go = cinfo->restart_interval;
488
489  /* Reset out-of-data flag, unless read_restart_marker left us smack up
490   * against a marker.  In that case we will end up treating the next data
491   * segment as empty, and we can avoid producing bogus output pixels by
492   * leaving the flag set.
493   */
494  if (cinfo->unread_marker == 0)
495    entropy->pub.insufficient_data = FALSE;
496
497  return TRUE;
498}
499
500
501/*
502 * Decode and return one MCU's worth of Huffman-compressed coefficients.
503 * The coefficients are reordered from zigzag order into natural array order,
504 * but are not dequantized.
505 *
506 * The i'th block of the MCU is stored into the block pointed to by
507 * MCU_data[i].  WE ASSUME THIS AREA HAS BEEN ZEROED BY THE CALLER.
508 * (Wholesale zeroing is usually a little faster than retail...)
509 *
510 * Returns FALSE if data source requested suspension.  In that case no
511 * changes have been made to permanent state.  (Exception: some output
512 * coefficients may already have been assigned.  This is harmless for
513 * this module, since we'll just re-assign them on the next call.)
514 */
515
516METHODDEF(boolean)
517decode_mcu (j_decompress_ptr cinfo, JBLOCKROW *MCU_data)
518{
519  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
520  int blkn;
521  BITREAD_STATE_VARS;
522  savable_state state;
523
524  /* Process restart marker if needed; may have to suspend */
525  if (cinfo->restart_interval) {
526    if (entropy->restarts_to_go == 0)
527      if (! process_restart(cinfo))
528        return FALSE;
529  }
530
531  /* If we've run out of data, just leave the MCU set to zeroes.
532   * This way, we return uniform gray for the remainder of the segment.
533   */
534  if (! entropy->pub.insufficient_data) {
535
536    /* Load up working state */
537    BITREAD_LOAD_STATE(cinfo,entropy->bitstate);
538    ASSIGN_STATE(state, entropy->saved);
539
540    /* Outer loop handles each block in the MCU */
541
542    for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
543      JBLOCKROW block = MCU_data[blkn];
544      d_derived_tbl * dctbl = entropy->dc_cur_tbls[blkn];
545      d_derived_tbl * actbl = entropy->ac_cur_tbls[blkn];
546      register int s, k, r;
547
548      /* Decode a single block's worth of coefficients */
549
550      /* Section F.2.2.1: decode the DC coefficient difference */
551      HUFF_DECODE(s, br_state, dctbl, return FALSE, label1);
552      if (s) {
553        CHECK_BIT_BUFFER(br_state, s, return FALSE);
554        r = GET_BITS(s);
555        s = HUFF_EXTEND(r, s);
556      }
557
558      if (entropy->dc_needed[blkn]) {
559        /* Convert DC difference to actual value, update last_dc_val */
560        int ci = cinfo->MCU_membership[blkn];
561        s += state.last_dc_val[ci];
562        state.last_dc_val[ci] = s;
563        /* Output the DC coefficient (assumes jpeg_natural_order[0] = 0) */
564        (*block)[0] = (JCOEF) s;
565      }
566
567      if (entropy->ac_needed[blkn]) {
568
569        /* Section F.2.2.2: decode the AC coefficients */
570        /* Since zeroes are skipped, output area must be cleared beforehand */
571        for (k = 1; k < DCTSIZE2; k++) {
572          HUFF_DECODE(s, br_state, actbl, return FALSE, label2);
573     
574          r = s >> 4;
575          s &= 15;
576     
577          if (s) {
578            k += r;
579            CHECK_BIT_BUFFER(br_state, s, return FALSE);
580            r = GET_BITS(s);
581            s = HUFF_EXTEND(r, s);
582            /* Output coefficient in natural (dezigzagged) order.
583             * Note: the extra entries in jpeg_natural_order[] will save us
584             * if k >= DCTSIZE2, which could happen if the data is corrupted.
585             */
586            (*block)[jpeg_natural_order[k]] = (JCOEF) s;
587          } else {
588            if (r != 15)
589              break;
590            k += 15;
591          }
592        }
593
594      } else {
595
596        /* Section F.2.2.2: decode the AC coefficients */
597        /* In this path we just discard the values */
598        for (k = 1; k < DCTSIZE2; k++) {
599          HUFF_DECODE(s, br_state, actbl, return FALSE, label3);
600     
601          r = s >> 4;
602          s &= 15;
603     
604          if (s) {
605            k += r;
606            CHECK_BIT_BUFFER(br_state, s, return FALSE);
607            DROP_BITS(s);
608          } else {
609            if (r != 15)
610              break;
611            k += 15;
612          }
613        }
614
615      }
616    }
617
618    /* Completed MCU, so update state */
619    BITREAD_SAVE_STATE(cinfo,entropy->bitstate);
620    ASSIGN_STATE(entropy->saved, state);
621  }
622
623  /* Account for restart interval (no-op if not using restarts) */
624  entropy->restarts_to_go--;
625
626  return TRUE;
627}
628
629
630/*
631 * Module initialization routine for Huffman entropy decoding.
632 */
633
634GLOBAL(void)
635jinit_huff_decoder (j_decompress_ptr cinfo)
636{
637  huff_entropy_ptr entropy;
638  int i;
639
640  entropy = (huff_entropy_ptr)
641    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
642                                SIZEOF(huff_entropy_decoder));
643  cinfo->entropy = (struct jpeg_entropy_decoder *) entropy;
644  entropy->pub.start_pass = start_pass_huff_decoder;
645  entropy->pub.decode_mcu = decode_mcu;
646
647  /* Mark tables unallocated */
648  for (i = 0; i < NUM_HUFF_TBLS; i++) {
649    entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
650  }
651}
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