source: trunk/libjpeg/jchuff.c @ 426

Last change on this file since 426 was 283, checked in by rbri, 12 years ago

JPEG plugin: libjpeg updated to version 7

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1/*
2 * jchuff.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 encoding 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 output suspension.
13 * If the data destination module demands suspension, we want to be able to
14 * back up to the start of the current MCU.  To do this, we copy state
15 * variables into local working storage, and update them back to the
16 * permanent JPEG objects only upon successful completion of an MCU.
17 *
18 * We do not support output suspension for the progressive JPEG mode, since
19 * the library currently does not allow multiple-scan files to be written
20 * with output suspension.
21 */
22
23#define JPEG_INTERNALS
24#include "jinclude.h"
25#include "jpeglib.h"
26
27
28/* The legal range of a DCT coefficient is
29 *  -1024 .. +1023  for 8-bit data;
30 * -16384 .. +16383 for 12-bit data.
31 * Hence the magnitude should always fit in 10 or 14 bits respectively.
32 */
33
34#if BITS_IN_JSAMPLE == 8
35#define MAX_COEF_BITS 10
36#else
37#define MAX_COEF_BITS 14
38#endif
39
40/* Derived data constructed for each Huffman table */
41
42typedef struct {
43  unsigned int ehufco[256];     /* code for each symbol */
44  char ehufsi[256];             /* length of code for each symbol */
45  /* If no code has been allocated for a symbol S, ehufsi[S] contains 0 */
46} c_derived_tbl;
47
48
49/* Expanded entropy encoder object for Huffman encoding.
50 *
51 * The savable_state subrecord contains fields that change within an MCU,
52 * but must not be updated permanently until we complete the MCU.
53 */
54
55typedef struct {
56  INT32 put_buffer;             /* current bit-accumulation buffer */
57  int put_bits;                 /* # of bits now in it */
58  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
59} savable_state;
60
61/* This macro is to work around compilers with missing or broken
62 * structure assignment.  You'll need to fix this code if you have
63 * such a compiler and you change MAX_COMPS_IN_SCAN.
64 */
65
66#ifndef NO_STRUCT_ASSIGN
67#define ASSIGN_STATE(dest,src)  ((dest) = (src))
68#else
69#if MAX_COMPS_IN_SCAN == 4
70#define ASSIGN_STATE(dest,src)  \
71        ((dest).put_buffer = (src).put_buffer, \
72         (dest).put_bits = (src).put_bits, \
73         (dest).last_dc_val[0] = (src).last_dc_val[0], \
74         (dest).last_dc_val[1] = (src).last_dc_val[1], \
75         (dest).last_dc_val[2] = (src).last_dc_val[2], \
76         (dest).last_dc_val[3] = (src).last_dc_val[3])
77#endif
78#endif
79
80
81typedef struct {
82  struct jpeg_entropy_encoder pub; /* public fields */
83
84  savable_state saved;          /* Bit buffer & DC state at start of MCU */
85
86  /* These fields are NOT loaded into local working state. */
87  unsigned int restarts_to_go;  /* MCUs left in this restart interval */
88  int next_restart_num;         /* next restart number to write (0-7) */
89
90  /* Following four fields used only in sequential mode */
91
92  /* Pointers to derived tables (these workspaces have image lifespan) */
93  c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
94  c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
95
96  /* Statistics tables for optimization */
97  long * dc_count_ptrs[NUM_HUFF_TBLS];
98  long * ac_count_ptrs[NUM_HUFF_TBLS];
99
100  /* Following fields used only in progressive mode */
101
102  /* Mode flag: TRUE for optimization, FALSE for actual data output */
103  boolean gather_statistics;
104
105  /* next_output_byte/free_in_buffer are local copies of cinfo->dest fields.
106   */
107  JOCTET * next_output_byte;    /* => next byte to write in buffer */
108  size_t free_in_buffer;        /* # of byte spaces remaining in buffer */
109  j_compress_ptr cinfo;         /* link to cinfo (needed for dump_buffer) */
110
111  /* Coding status for AC components */
112  int ac_tbl_no;                /* the table number of the single component */
113  unsigned int EOBRUN;          /* run length of EOBs */
114  unsigned int BE;              /* # of buffered correction bits before MCU */
115  char * bit_buffer;            /* buffer for correction bits (1 per char) */
116  /* packing correction bits tightly would save some space but cost time... */
117
118  /* Pointers to derived tables (these workspaces have image lifespan).
119   * Since any one scan in progressive mode codes only DC or only AC,
120   * we only need one set of tables, not one for DC and one for AC.
121   */
122  c_derived_tbl * derived_tbls[NUM_HUFF_TBLS];
123
124  /* Statistics tables for optimization; again, one set is enough */
125  long * count_ptrs[NUM_HUFF_TBLS];
126} huff_entropy_encoder;
127
128typedef huff_entropy_encoder * huff_entropy_ptr;
129
130/* Working state while writing an MCU (sequential mode).
131 * This struct contains all the fields that are needed by subroutines.
132 */
133
134typedef struct {
135  JOCTET * next_output_byte;    /* => next byte to write in buffer */
136  size_t free_in_buffer;        /* # of byte spaces remaining in buffer */
137  savable_state cur;            /* Current bit buffer & DC state */
138  j_compress_ptr cinfo;         /* dump_buffer needs access to this */
139} working_state;
140
141/* MAX_CORR_BITS is the number of bits the AC refinement correction-bit
142 * buffer can hold.  Larger sizes may slightly improve compression, but
143 * 1000 is already well into the realm of overkill.
144 * The minimum safe size is 64 bits.
145 */
146
147#define MAX_CORR_BITS  1000     /* Max # of correction bits I can buffer */
148
149/* IRIGHT_SHIFT is like RIGHT_SHIFT, but works on int rather than INT32.
150 * We assume that int right shift is unsigned if INT32 right shift is,
151 * which should be safe.
152 */
153
154#ifdef RIGHT_SHIFT_IS_UNSIGNED
155#define ISHIFT_TEMPS    int ishift_temp;
156#define IRIGHT_SHIFT(x,shft)  \
157        ((ishift_temp = (x)) < 0 ? \
158         (ishift_temp >> (shft)) | ((~0) << (16-(shft))) : \
159         (ishift_temp >> (shft)))
160#else
161#define ISHIFT_TEMPS
162#define IRIGHT_SHIFT(x,shft)    ((x) >> (shft))
163#endif
164
165
166/*
167 * Compute the derived values for a Huffman table.
168 * This routine also performs some validation checks on the table.
169 */
170
171LOCAL(void)
172jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,
173                         c_derived_tbl ** pdtbl)
174{
175  JHUFF_TBL *htbl;
176  c_derived_tbl *dtbl;
177  int p, i, l, lastp, si, maxsymbol;
178  char huffsize[257];
179  unsigned int huffcode[257];
180  unsigned int code;
181
182  /* Note that huffsize[] and huffcode[] are filled in code-length order,
183   * paralleling the order of the symbols themselves in htbl->huffval[].
184   */
185
186  /* Find the input Huffman table */
187  if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
188    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
189  htbl =
190    isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
191  if (htbl == NULL)
192    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
193
194  /* Allocate a workspace if we haven't already done so. */
195  if (*pdtbl == NULL)
196    *pdtbl = (c_derived_tbl *)
197      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
198                                  SIZEOF(c_derived_tbl));
199  dtbl = *pdtbl;
200 
201  /* Figure C.1: make table of Huffman code length for each symbol */
202
203  p = 0;
204  for (l = 1; l <= 16; l++) {
205    i = (int) htbl->bits[l];
206    if (i < 0 || p + i > 256)   /* protect against table overrun */
207      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
208    while (i--)
209      huffsize[p++] = (char) l;
210  }
211  huffsize[p] = 0;
212  lastp = p;
213 
214  /* Figure C.2: generate the codes themselves */
215  /* We also validate that the counts represent a legal Huffman code tree. */
216
217  code = 0;
218  si = huffsize[0];
219  p = 0;
220  while (huffsize[p]) {
221    while (((int) huffsize[p]) == si) {
222      huffcode[p++] = code;
223      code++;
224    }
225    /* code is now 1 more than the last code used for codelength si; but
226     * it must still fit in si bits, since no code is allowed to be all ones.
227     */
228    if (((INT32) code) >= (((INT32) 1) << si))
229      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
230    code <<= 1;
231    si++;
232  }
233 
234  /* Figure C.3: generate encoding tables */
235  /* These are code and size indexed by symbol value */
236
237  /* Set all codeless symbols to have code length 0;
238   * this lets us detect duplicate VAL entries here, and later
239   * allows emit_bits to detect any attempt to emit such symbols.
240   */
241  MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));
242
243  /* This is also a convenient place to check for out-of-range
244   * and duplicated VAL entries.  We allow 0..255 for AC symbols
245   * but only 0..15 for DC.  (We could constrain them further
246   * based on data depth and mode, but this seems enough.)
247   */
248  maxsymbol = isDC ? 15 : 255;
249
250  for (p = 0; p < lastp; p++) {
251    i = htbl->huffval[p];
252    if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
253      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
254    dtbl->ehufco[i] = huffcode[p];
255    dtbl->ehufsi[i] = huffsize[p];
256  }
257}
258
259
260/* Outputting bytes to the file.
261 * NB: these must be called only when actually outputting,
262 * that is, entropy->gather_statistics == FALSE.
263 */
264
265/* Emit a byte, taking 'action' if must suspend. */
266#define emit_byte_s(state,val,action)  \
267        { *(state)->next_output_byte++ = (JOCTET) (val);  \
268          if (--(state)->free_in_buffer == 0)  \
269            if (! dump_buffer_s(state))  \
270              { action; } }
271
272/* Emit a byte */
273#define emit_byte_e(entropy,val)  \
274        { *(entropy)->next_output_byte++ = (JOCTET) (val);  \
275          if (--(entropy)->free_in_buffer == 0)  \
276            dump_buffer_e(entropy); }
277
278
279LOCAL(boolean)
280dump_buffer_s (working_state * state)
281/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
282{
283  struct jpeg_destination_mgr * dest = state->cinfo->dest;
284
285  if (! (*dest->empty_output_buffer) (state->cinfo))
286    return FALSE;
287  /* After a successful buffer dump, must reset buffer pointers */
288  state->next_output_byte = dest->next_output_byte;
289  state->free_in_buffer = dest->free_in_buffer;
290  return TRUE;
291}
292
293
294LOCAL(void)
295dump_buffer_e (huff_entropy_ptr entropy)
296/* Empty the output buffer; we do not support suspension in this case. */
297{
298  struct jpeg_destination_mgr * dest = entropy->cinfo->dest;
299
300  if (! (*dest->empty_output_buffer) (entropy->cinfo))
301    ERREXIT(entropy->cinfo, JERR_CANT_SUSPEND);
302  /* After a successful buffer dump, must reset buffer pointers */
303  entropy->next_output_byte = dest->next_output_byte;
304  entropy->free_in_buffer = dest->free_in_buffer;
305}
306
307
308/* Outputting bits to the file */
309
310/* Only the right 24 bits of put_buffer are used; the valid bits are
311 * left-justified in this part.  At most 16 bits can be passed to emit_bits
312 * in one call, and we never retain more than 7 bits in put_buffer
313 * between calls, so 24 bits are sufficient.
314 */
315
316INLINE
317LOCAL(boolean)
318emit_bits_s (working_state * state, unsigned int code, int size)
319/* Emit some bits; return TRUE if successful, FALSE if must suspend */
320{
321  /* This routine is heavily used, so it's worth coding tightly. */
322  register INT32 put_buffer = (INT32) code;
323  register int put_bits = state->cur.put_bits;
324
325  /* if size is 0, caller used an invalid Huffman table entry */
326  if (size == 0)
327    ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);
328
329  put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
330 
331  put_bits += size;             /* new number of bits in buffer */
332 
333  put_buffer <<= 24 - put_bits; /* align incoming bits */
334
335  put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */
336 
337  while (put_bits >= 8) {
338    int c = (int) ((put_buffer >> 16) & 0xFF);
339   
340    emit_byte_s(state, c, return FALSE);
341    if (c == 0xFF) {            /* need to stuff a zero byte? */
342      emit_byte_s(state, 0, return FALSE);
343    }
344    put_buffer <<= 8;
345    put_bits -= 8;
346  }
347
348  state->cur.put_buffer = put_buffer; /* update state variables */
349  state->cur.put_bits = put_bits;
350
351  return TRUE;
352}
353
354
355INLINE
356LOCAL(void)
357emit_bits_e (huff_entropy_ptr entropy, unsigned int code, int size)
358/* Emit some bits, unless we are in gather mode */
359{
360  /* This routine is heavily used, so it's worth coding tightly. */
361  register INT32 put_buffer = (INT32) code;
362  register int put_bits = entropy->saved.put_bits;
363
364  /* if size is 0, caller used an invalid Huffman table entry */
365  if (size == 0)
366    ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);
367
368  if (entropy->gather_statistics)
369    return;                     /* do nothing if we're only getting stats */
370
371  put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
372 
373  put_bits += size;             /* new number of bits in buffer */
374
375  put_buffer <<= 24 - put_bits; /* align incoming bits */
376
377  /* and merge with old buffer contents */
378  put_buffer |= entropy->saved.put_buffer;
379
380  while (put_bits >= 8) {
381    int c = (int) ((put_buffer >> 16) & 0xFF);
382
383    emit_byte_e(entropy, c);
384    if (c == 0xFF) {            /* need to stuff a zero byte? */
385      emit_byte_e(entropy, 0);
386    }
387    put_buffer <<= 8;
388    put_bits -= 8;
389  }
390
391  entropy->saved.put_buffer = put_buffer; /* update variables */
392  entropy->saved.put_bits = put_bits;
393}
394
395
396LOCAL(boolean)
397flush_bits_s (working_state * state)
398{
399  if (! emit_bits_s(state, 0x7F, 7)) /* fill any partial byte with ones */
400    return FALSE;
401  state->cur.put_buffer = 0;         /* and reset bit-buffer to empty */
402  state->cur.put_bits = 0;
403  return TRUE;
404}
405
406
407LOCAL(void)
408flush_bits_e (huff_entropy_ptr entropy)
409{
410  emit_bits_e(entropy, 0x7F, 7); /* fill any partial byte with ones */
411  entropy->saved.put_buffer = 0; /* and reset bit-buffer to empty */
412  entropy->saved.put_bits = 0;
413}
414
415
416/*
417 * Emit (or just count) a Huffman symbol.
418 */
419
420INLINE
421LOCAL(void)
422emit_symbol (huff_entropy_ptr entropy, int tbl_no, int symbol)
423{
424  if (entropy->gather_statistics)
425    entropy->count_ptrs[tbl_no][symbol]++;
426  else {
427    c_derived_tbl * tbl = entropy->derived_tbls[tbl_no];
428    emit_bits_e(entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol]);
429  }
430}
431
432
433/*
434 * Emit bits from a correction bit buffer.
435 */
436
437LOCAL(void)
438emit_buffered_bits (huff_entropy_ptr entropy, char * bufstart,
439                    unsigned int nbits)
440{
441  if (entropy->gather_statistics)
442    return;                     /* no real work */
443
444  while (nbits > 0) {
445    emit_bits_e(entropy, (unsigned int) (*bufstart), 1);
446    bufstart++;
447    nbits--;
448  }
449}
450
451
452/*
453 * Emit any pending EOBRUN symbol.
454 */
455
456LOCAL(void)
457emit_eobrun (huff_entropy_ptr entropy)
458{
459  register int temp, nbits;
460
461  if (entropy->EOBRUN > 0) {    /* if there is any pending EOBRUN */
462    temp = entropy->EOBRUN;
463    nbits = 0;
464    while ((temp >>= 1))
465      nbits++;
466    /* safety check: shouldn't happen given limited correction-bit buffer */
467    if (nbits > 14)
468      ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);
469
470    emit_symbol(entropy, entropy->ac_tbl_no, nbits << 4);
471    if (nbits)
472      emit_bits_e(entropy, entropy->EOBRUN, nbits);
473
474    entropy->EOBRUN = 0;
475
476    /* Emit any buffered correction bits */
477    emit_buffered_bits(entropy, entropy->bit_buffer, entropy->BE);
478    entropy->BE = 0;
479  }
480}
481
482
483/*
484 * Emit a restart marker & resynchronize predictions.
485 */
486
487LOCAL(boolean)
488emit_restart_s (working_state * state, int restart_num)
489{
490  int ci;
491
492  if (! flush_bits_s(state))
493    return FALSE;
494
495  emit_byte_s(state, 0xFF, return FALSE);
496  emit_byte_s(state, JPEG_RST0 + restart_num, return FALSE);
497
498  /* Re-initialize DC predictions to 0 */
499  for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
500    state->cur.last_dc_val[ci] = 0;
501
502  /* The restart counter is not updated until we successfully write the MCU. */
503
504  return TRUE;
505}
506
507
508LOCAL(void)
509emit_restart_e (huff_entropy_ptr entropy, int restart_num)
510{
511  int ci;
512
513  emit_eobrun(entropy);
514
515  if (! entropy->gather_statistics) {
516    flush_bits_e(entropy);
517    emit_byte_e(entropy, 0xFF);
518    emit_byte_e(entropy, JPEG_RST0 + restart_num);
519  }
520
521  if (entropy->cinfo->Ss == 0) {
522    /* Re-initialize DC predictions to 0 */
523    for (ci = 0; ci < entropy->cinfo->comps_in_scan; ci++)
524      entropy->saved.last_dc_val[ci] = 0;
525  } else {
526    /* Re-initialize all AC-related fields to 0 */
527    entropy->EOBRUN = 0;
528    entropy->BE = 0;
529  }
530}
531
532
533/*
534 * MCU encoding for DC initial scan (either spectral selection,
535 * or first pass of successive approximation).
536 */
537
538METHODDEF(boolean)
539encode_mcu_DC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
540{
541  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
542  register int temp, temp2;
543  register int nbits;
544  int blkn, ci;
545  int Al = cinfo->Al;
546  JBLOCKROW block;
547  jpeg_component_info * compptr;
548  ISHIFT_TEMPS
549
550  entropy->next_output_byte = cinfo->dest->next_output_byte;
551  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
552
553  /* Emit restart marker if needed */
554  if (cinfo->restart_interval)
555    if (entropy->restarts_to_go == 0)
556      emit_restart_e(entropy, entropy->next_restart_num);
557
558  /* Encode the MCU data blocks */
559  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
560    block = MCU_data[blkn];
561    ci = cinfo->MCU_membership[blkn];
562    compptr = cinfo->cur_comp_info[ci];
563
564    /* Compute the DC value after the required point transform by Al.
565     * This is simply an arithmetic right shift.
566     */
567    temp2 = IRIGHT_SHIFT((int) ((*block)[0]), Al);
568
569    /* DC differences are figured on the point-transformed values. */
570    temp = temp2 - entropy->saved.last_dc_val[ci];
571    entropy->saved.last_dc_val[ci] = temp2;
572
573    /* Encode the DC coefficient difference per section G.1.2.1 */
574    temp2 = temp;
575    if (temp < 0) {
576      temp = -temp;             /* temp is abs value of input */
577      /* For a negative input, want temp2 = bitwise complement of abs(input) */
578      /* This code assumes we are on a two's complement machine */
579      temp2--;
580    }
581   
582    /* Find the number of bits needed for the magnitude of the coefficient */
583    nbits = 0;
584    while (temp) {
585      nbits++;
586      temp >>= 1;
587    }
588    /* Check for out-of-range coefficient values.
589     * Since we're encoding a difference, the range limit is twice as much.
590     */
591    if (nbits > MAX_COEF_BITS+1)
592      ERREXIT(cinfo, JERR_BAD_DCT_COEF);
593   
594    /* Count/emit the Huffman-coded symbol for the number of bits */
595    emit_symbol(entropy, compptr->dc_tbl_no, nbits);
596   
597    /* Emit that number of bits of the value, if positive, */
598    /* or the complement of its magnitude, if negative. */
599    if (nbits)                  /* emit_bits rejects calls with size 0 */
600      emit_bits_e(entropy, (unsigned int) temp2, nbits);
601  }
602
603  cinfo->dest->next_output_byte = entropy->next_output_byte;
604  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
605
606  /* Update restart-interval state too */
607  if (cinfo->restart_interval) {
608    if (entropy->restarts_to_go == 0) {
609      entropy->restarts_to_go = cinfo->restart_interval;
610      entropy->next_restart_num++;
611      entropy->next_restart_num &= 7;
612    }
613    entropy->restarts_to_go--;
614  }
615
616  return TRUE;
617}
618
619
620/*
621 * MCU encoding for AC initial scan (either spectral selection,
622 * or first pass of successive approximation).
623 */
624
625METHODDEF(boolean)
626encode_mcu_AC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
627{
628  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
629  register int temp, temp2;
630  register int nbits;
631  register int r, k;
632  int Se = cinfo->Se;
633  int Al = cinfo->Al;
634  JBLOCKROW block;
635
636  entropy->next_output_byte = cinfo->dest->next_output_byte;
637  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
638
639  /* Emit restart marker if needed */
640  if (cinfo->restart_interval)
641    if (entropy->restarts_to_go == 0)
642      emit_restart_e(entropy, entropy->next_restart_num);
643
644  /* Encode the MCU data block */
645  block = MCU_data[0];
646
647  /* Encode the AC coefficients per section G.1.2.2, fig. G.3 */
648 
649  r = 0;                        /* r = run length of zeros */
650   
651  for (k = cinfo->Ss; k <= Se; k++) {
652    if ((temp = (*block)[jpeg_natural_order[k]]) == 0) {
653      r++;
654      continue;
655    }
656    /* We must apply the point transform by Al.  For AC coefficients this
657     * is an integer division with rounding towards 0.  To do this portably
658     * in C, we shift after obtaining the absolute value; so the code is
659     * interwoven with finding the abs value (temp) and output bits (temp2).
660     */
661    if (temp < 0) {
662      temp = -temp;             /* temp is abs value of input */
663      temp >>= Al;              /* apply the point transform */
664      /* For a negative coef, want temp2 = bitwise complement of abs(coef) */
665      temp2 = ~temp;
666    } else {
667      temp >>= Al;              /* apply the point transform */
668      temp2 = temp;
669    }
670    /* Watch out for case that nonzero coef is zero after point transform */
671    if (temp == 0) {
672      r++;
673      continue;
674    }
675
676    /* Emit any pending EOBRUN */
677    if (entropy->EOBRUN > 0)
678      emit_eobrun(entropy);
679    /* if run length > 15, must emit special run-length-16 codes (0xF0) */
680    while (r > 15) {
681      emit_symbol(entropy, entropy->ac_tbl_no, 0xF0);
682      r -= 16;
683    }
684
685    /* Find the number of bits needed for the magnitude of the coefficient */
686    nbits = 1;                  /* there must be at least one 1 bit */
687    while ((temp >>= 1))
688      nbits++;
689    /* Check for out-of-range coefficient values */
690    if (nbits > MAX_COEF_BITS)
691      ERREXIT(cinfo, JERR_BAD_DCT_COEF);
692
693    /* Count/emit Huffman symbol for run length / number of bits */
694    emit_symbol(entropy, entropy->ac_tbl_no, (r << 4) + nbits);
695
696    /* Emit that number of bits of the value, if positive, */
697    /* or the complement of its magnitude, if negative. */
698    emit_bits_e(entropy, (unsigned int) temp2, nbits);
699
700    r = 0;                      /* reset zero run length */
701  }
702
703  if (r > 0) {                  /* If there are trailing zeroes, */
704    entropy->EOBRUN++;          /* count an EOB */
705    if (entropy->EOBRUN == 0x7FFF)
706      emit_eobrun(entropy);     /* force it out to avoid overflow */
707  }
708
709  cinfo->dest->next_output_byte = entropy->next_output_byte;
710  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
711
712  /* Update restart-interval state too */
713  if (cinfo->restart_interval) {
714    if (entropy->restarts_to_go == 0) {
715      entropy->restarts_to_go = cinfo->restart_interval;
716      entropy->next_restart_num++;
717      entropy->next_restart_num &= 7;
718    }
719    entropy->restarts_to_go--;
720  }
721
722  return TRUE;
723}
724
725
726/*
727 * MCU encoding for DC successive approximation refinement scan.
728 * Note: we assume such scans can be multi-component, although the spec
729 * is not very clear on the point.
730 */
731
732METHODDEF(boolean)
733encode_mcu_DC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
734{
735  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
736  register int temp;
737  int blkn;
738  int Al = cinfo->Al;
739  JBLOCKROW block;
740
741  entropy->next_output_byte = cinfo->dest->next_output_byte;
742  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
743
744  /* Emit restart marker if needed */
745  if (cinfo->restart_interval)
746    if (entropy->restarts_to_go == 0)
747      emit_restart_e(entropy, entropy->next_restart_num);
748
749  /* Encode the MCU data blocks */
750  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
751    block = MCU_data[blkn];
752
753    /* We simply emit the Al'th bit of the DC coefficient value. */
754    temp = (*block)[0];
755    emit_bits_e(entropy, (unsigned int) (temp >> Al), 1);
756  }
757
758  cinfo->dest->next_output_byte = entropy->next_output_byte;
759  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
760
761  /* Update restart-interval state too */
762  if (cinfo->restart_interval) {
763    if (entropy->restarts_to_go == 0) {
764      entropy->restarts_to_go = cinfo->restart_interval;
765      entropy->next_restart_num++;
766      entropy->next_restart_num &= 7;
767    }
768    entropy->restarts_to_go--;
769  }
770
771  return TRUE;
772}
773
774
775/*
776 * MCU encoding for AC successive approximation refinement scan.
777 */
778
779METHODDEF(boolean)
780encode_mcu_AC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
781{
782  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
783  register int temp;
784  register int r, k;
785  int EOB;
786  char *BR_buffer;
787  unsigned int BR;
788  int Se = cinfo->Se;
789  int Al = cinfo->Al;
790  JBLOCKROW block;
791  int absvalues[DCTSIZE2];
792
793  entropy->next_output_byte = cinfo->dest->next_output_byte;
794  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
795
796  /* Emit restart marker if needed */
797  if (cinfo->restart_interval)
798    if (entropy->restarts_to_go == 0)
799      emit_restart_e(entropy, entropy->next_restart_num);
800
801  /* Encode the MCU data block */
802  block = MCU_data[0];
803
804  /* It is convenient to make a pre-pass to determine the transformed
805   * coefficients' absolute values and the EOB position.
806   */
807  EOB = 0;
808  for (k = cinfo->Ss; k <= Se; k++) {
809    temp = (*block)[jpeg_natural_order[k]];
810    /* We must apply the point transform by Al.  For AC coefficients this
811     * is an integer division with rounding towards 0.  To do this portably
812     * in C, we shift after obtaining the absolute value.
813     */
814    if (temp < 0)
815      temp = -temp;             /* temp is abs value of input */
816    temp >>= Al;                /* apply the point transform */
817    absvalues[k] = temp;        /* save abs value for main pass */
818    if (temp == 1)
819      EOB = k;                  /* EOB = index of last newly-nonzero coef */
820  }
821
822  /* Encode the AC coefficients per section G.1.2.3, fig. G.7 */
823 
824  r = 0;                        /* r = run length of zeros */
825  BR = 0;                       /* BR = count of buffered bits added now */
826  BR_buffer = entropy->bit_buffer + entropy->BE; /* Append bits to buffer */
827
828  for (k = cinfo->Ss; k <= Se; k++) {
829    if ((temp = absvalues[k]) == 0) {
830      r++;
831      continue;
832    }
833
834    /* Emit any required ZRLs, but not if they can be folded into EOB */
835    while (r > 15 && k <= EOB) {
836      /* emit any pending EOBRUN and the BE correction bits */
837      emit_eobrun(entropy);
838      /* Emit ZRL */
839      emit_symbol(entropy, entropy->ac_tbl_no, 0xF0);
840      r -= 16;
841      /* Emit buffered correction bits that must be associated with ZRL */
842      emit_buffered_bits(entropy, BR_buffer, BR);
843      BR_buffer = entropy->bit_buffer; /* BE bits are gone now */
844      BR = 0;
845    }
846
847    /* If the coef was previously nonzero, it only needs a correction bit.
848     * NOTE: a straight translation of the spec's figure G.7 would suggest
849     * that we also need to test r > 15.  But if r > 15, we can only get here
850     * if k > EOB, which implies that this coefficient is not 1.
851     */
852    if (temp > 1) {
853      /* The correction bit is the next bit of the absolute value. */
854      BR_buffer[BR++] = (char) (temp & 1);
855      continue;
856    }
857
858    /* Emit any pending EOBRUN and the BE correction bits */
859    emit_eobrun(entropy);
860
861    /* Count/emit Huffman symbol for run length / number of bits */
862    emit_symbol(entropy, entropy->ac_tbl_no, (r << 4) + 1);
863
864    /* Emit output bit for newly-nonzero coef */
865    temp = ((*block)[jpeg_natural_order[k]] < 0) ? 0 : 1;
866    emit_bits_e(entropy, (unsigned int) temp, 1);
867
868    /* Emit buffered correction bits that must be associated with this code */
869    emit_buffered_bits(entropy, BR_buffer, BR);
870    BR_buffer = entropy->bit_buffer; /* BE bits are gone now */
871    BR = 0;
872    r = 0;                      /* reset zero run length */
873  }
874
875  if (r > 0 || BR > 0) {        /* If there are trailing zeroes, */
876    entropy->EOBRUN++;          /* count an EOB */
877    entropy->BE += BR;          /* concat my correction bits to older ones */
878    /* We force out the EOB if we risk either:
879     * 1. overflow of the EOB counter;
880     * 2. overflow of the correction bit buffer during the next MCU.
881     */
882    if (entropy->EOBRUN == 0x7FFF || entropy->BE > (MAX_CORR_BITS-DCTSIZE2+1))
883      emit_eobrun(entropy);
884  }
885
886  cinfo->dest->next_output_byte = entropy->next_output_byte;
887  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
888
889  /* Update restart-interval state too */
890  if (cinfo->restart_interval) {
891    if (entropy->restarts_to_go == 0) {
892      entropy->restarts_to_go = cinfo->restart_interval;
893      entropy->next_restart_num++;
894      entropy->next_restart_num &= 7;
895    }
896    entropy->restarts_to_go--;
897  }
898
899  return TRUE;
900}
901
902
903/* Encode a single block's worth of coefficients */
904
905LOCAL(boolean)
906encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,
907                  c_derived_tbl *dctbl, c_derived_tbl *actbl)
908{
909  register int temp, temp2;
910  register int nbits;
911  register int k, r, i;
912
913  /* Encode the DC coefficient difference per section F.1.2.1 */
914
915  temp = temp2 = block[0] - last_dc_val;
916
917  if (temp < 0) {
918    temp = -temp;               /* temp is abs value of input */
919    /* For a negative input, want temp2 = bitwise complement of abs(input) */
920    /* This code assumes we are on a two's complement machine */
921    temp2--;
922  }
923
924  /* Find the number of bits needed for the magnitude of the coefficient */
925  nbits = 0;
926  while (temp) {
927    nbits++;
928    temp >>= 1;
929  }
930  /* Check for out-of-range coefficient values.
931   * Since we're encoding a difference, the range limit is twice as much.
932   */
933  if (nbits > MAX_COEF_BITS+1)
934    ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
935
936  /* Emit the Huffman-coded symbol for the number of bits */
937  if (! emit_bits_s(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
938    return FALSE;
939
940  /* Emit that number of bits of the value, if positive, */
941  /* or the complement of its magnitude, if negative. */
942  if (nbits)                    /* emit_bits rejects calls with size 0 */
943    if (! emit_bits_s(state, (unsigned int) temp2, nbits))
944      return FALSE;
945
946  /* Encode the AC coefficients per section F.1.2.2 */
947
948  r = 0;                        /* r = run length of zeros */
949
950  for (k = 1; k < DCTSIZE2; k++) {
951    if ((temp = block[jpeg_natural_order[k]]) == 0) {
952      r++;
953    } else {
954      /* if run length > 15, must emit special run-length-16 codes (0xF0) */
955      while (r > 15) {
956        if (! emit_bits_s(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
957          return FALSE;
958        r -= 16;
959      }
960
961      temp2 = temp;
962      if (temp < 0) {
963        temp = -temp;           /* temp is abs value of input */
964        /* This code assumes we are on a two's complement machine */
965        temp2--;
966      }
967
968      /* Find the number of bits needed for the magnitude of the coefficient */
969      nbits = 1;                /* there must be at least one 1 bit */
970      while ((temp >>= 1))
971        nbits++;
972      /* Check for out-of-range coefficient values */
973      if (nbits > MAX_COEF_BITS)
974        ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
975
976      /* Emit Huffman symbol for run length / number of bits */
977      i = (r << 4) + nbits;
978      if (! emit_bits_s(state, actbl->ehufco[i], actbl->ehufsi[i]))
979        return FALSE;
980
981      /* Emit that number of bits of the value, if positive, */
982      /* or the complement of its magnitude, if negative. */
983      if (! emit_bits_s(state, (unsigned int) temp2, nbits))
984        return FALSE;
985
986      r = 0;
987    }
988  }
989
990  /* If the last coef(s) were zero, emit an end-of-block code */
991  if (r > 0)
992    if (! emit_bits_s(state, actbl->ehufco[0], actbl->ehufsi[0]))
993      return FALSE;
994
995  return TRUE;
996}
997
998
999/*
1000 * Encode and output one MCU's worth of Huffman-compressed coefficients.
1001 */
1002
1003METHODDEF(boolean)
1004encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
1005{
1006  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1007  working_state state;
1008  int blkn, ci;
1009  jpeg_component_info * compptr;
1010
1011  /* Load up working state */
1012  state.next_output_byte = cinfo->dest->next_output_byte;
1013  state.free_in_buffer = cinfo->dest->free_in_buffer;
1014  ASSIGN_STATE(state.cur, entropy->saved);
1015  state.cinfo = cinfo;
1016
1017  /* Emit restart marker if needed */
1018  if (cinfo->restart_interval) {
1019    if (entropy->restarts_to_go == 0)
1020      if (! emit_restart_s(&state, entropy->next_restart_num))
1021        return FALSE;
1022  }
1023
1024  /* Encode the MCU data blocks */
1025  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
1026    ci = cinfo->MCU_membership[blkn];
1027    compptr = cinfo->cur_comp_info[ci];
1028    if (! encode_one_block(&state,
1029                           MCU_data[blkn][0], state.cur.last_dc_val[ci],
1030                           entropy->dc_derived_tbls[compptr->dc_tbl_no],
1031                           entropy->ac_derived_tbls[compptr->ac_tbl_no]))
1032      return FALSE;
1033    /* Update last_dc_val */
1034    state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
1035  }
1036
1037  /* Completed MCU, so update state */
1038  cinfo->dest->next_output_byte = state.next_output_byte;
1039  cinfo->dest->free_in_buffer = state.free_in_buffer;
1040  ASSIGN_STATE(entropy->saved, state.cur);
1041
1042  /* Update restart-interval state too */
1043  if (cinfo->restart_interval) {
1044    if (entropy->restarts_to_go == 0) {
1045      entropy->restarts_to_go = cinfo->restart_interval;
1046      entropy->next_restart_num++;
1047      entropy->next_restart_num &= 7;
1048    }
1049    entropy->restarts_to_go--;
1050  }
1051
1052  return TRUE;
1053}
1054
1055
1056/*
1057 * Finish up at the end of a Huffman-compressed scan.
1058 */
1059
1060METHODDEF(void)
1061finish_pass_huff (j_compress_ptr cinfo)
1062{
1063  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1064  working_state state;
1065
1066  if (cinfo->progressive_mode) {
1067    entropy->next_output_byte = cinfo->dest->next_output_byte;
1068    entropy->free_in_buffer = cinfo->dest->free_in_buffer;
1069
1070    /* Flush out any buffered data */
1071    emit_eobrun(entropy);
1072    flush_bits_e(entropy);
1073
1074    cinfo->dest->next_output_byte = entropy->next_output_byte;
1075    cinfo->dest->free_in_buffer = entropy->free_in_buffer;
1076  } else {
1077    /* Load up working state ... flush_bits needs it */
1078    state.next_output_byte = cinfo->dest->next_output_byte;
1079    state.free_in_buffer = cinfo->dest->free_in_buffer;
1080    ASSIGN_STATE(state.cur, entropy->saved);
1081    state.cinfo = cinfo;
1082
1083    /* Flush out the last data */
1084    if (! flush_bits_s(&state))
1085      ERREXIT(cinfo, JERR_CANT_SUSPEND);
1086
1087    /* Update state */
1088    cinfo->dest->next_output_byte = state.next_output_byte;
1089    cinfo->dest->free_in_buffer = state.free_in_buffer;
1090    ASSIGN_STATE(entropy->saved, state.cur);
1091  }
1092}
1093
1094
1095/*
1096 * Huffman coding optimization.
1097 *
1098 * We first scan the supplied data and count the number of uses of each symbol
1099 * that is to be Huffman-coded. (This process MUST agree with the code above.)
1100 * Then we build a Huffman coding tree for the observed counts.
1101 * Symbols which are not needed at all for the particular image are not
1102 * assigned any code, which saves space in the DHT marker as well as in
1103 * the compressed data.
1104 */
1105
1106
1107/* Process a single block's worth of coefficients */
1108
1109LOCAL(void)
1110htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,
1111                 long dc_counts[], long ac_counts[])
1112{
1113  register int temp;
1114  register int nbits;
1115  register int k, r;
1116 
1117  /* Encode the DC coefficient difference per section F.1.2.1 */
1118 
1119  temp = block[0] - last_dc_val;
1120  if (temp < 0)
1121    temp = -temp;
1122 
1123  /* Find the number of bits needed for the magnitude of the coefficient */
1124  nbits = 0;
1125  while (temp) {
1126    nbits++;
1127    temp >>= 1;
1128  }
1129  /* Check for out-of-range coefficient values.
1130   * Since we're encoding a difference, the range limit is twice as much.
1131   */
1132  if (nbits > MAX_COEF_BITS+1)
1133    ERREXIT(cinfo, JERR_BAD_DCT_COEF);
1134
1135  /* Count the Huffman symbol for the number of bits */
1136  dc_counts[nbits]++;
1137 
1138  /* Encode the AC coefficients per section F.1.2.2 */
1139 
1140  r = 0;                        /* r = run length of zeros */
1141 
1142  for (k = 1; k < DCTSIZE2; k++) {
1143    if ((temp = block[jpeg_natural_order[k]]) == 0) {
1144      r++;
1145    } else {
1146      /* if run length > 15, must emit special run-length-16 codes (0xF0) */
1147      while (r > 15) {
1148        ac_counts[0xF0]++;
1149        r -= 16;
1150      }
1151     
1152      /* Find the number of bits needed for the magnitude of the coefficient */
1153      if (temp < 0)
1154        temp = -temp;
1155     
1156      /* Find the number of bits needed for the magnitude of the coefficient */
1157      nbits = 1;                /* there must be at least one 1 bit */
1158      while ((temp >>= 1))
1159        nbits++;
1160      /* Check for out-of-range coefficient values */
1161      if (nbits > MAX_COEF_BITS)
1162        ERREXIT(cinfo, JERR_BAD_DCT_COEF);
1163     
1164      /* Count Huffman symbol for run length / number of bits */
1165      ac_counts[(r << 4) + nbits]++;
1166     
1167      r = 0;
1168    }
1169  }
1170
1171  /* If the last coef(s) were zero, emit an end-of-block code */
1172  if (r > 0)
1173    ac_counts[0]++;
1174}
1175
1176
1177/*
1178 * Trial-encode one MCU's worth of Huffman-compressed coefficients.
1179 * No data is actually output, so no suspension return is possible.
1180 */
1181
1182METHODDEF(boolean)
1183encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
1184{
1185  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1186  int blkn, ci;
1187  jpeg_component_info * compptr;
1188
1189  /* Take care of restart intervals if needed */
1190  if (cinfo->restart_interval) {
1191    if (entropy->restarts_to_go == 0) {
1192      /* Re-initialize DC predictions to 0 */
1193      for (ci = 0; ci < cinfo->comps_in_scan; ci++)
1194        entropy->saved.last_dc_val[ci] = 0;
1195      /* Update restart state */
1196      entropy->restarts_to_go = cinfo->restart_interval;
1197    }
1198    entropy->restarts_to_go--;
1199  }
1200
1201  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
1202    ci = cinfo->MCU_membership[blkn];
1203    compptr = cinfo->cur_comp_info[ci];
1204    htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
1205                    entropy->dc_count_ptrs[compptr->dc_tbl_no],
1206                    entropy->ac_count_ptrs[compptr->ac_tbl_no]);
1207    entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
1208  }
1209
1210  return TRUE;
1211}
1212
1213
1214/*
1215 * Generate the best Huffman code table for the given counts, fill htbl.
1216 *
1217 * The JPEG standard requires that no symbol be assigned a codeword of all
1218 * one bits (so that padding bits added at the end of a compressed segment
1219 * can't look like a valid code).  Because of the canonical ordering of
1220 * codewords, this just means that there must be an unused slot in the
1221 * longest codeword length category.  Section K.2 of the JPEG spec suggests
1222 * reserving such a slot by pretending that symbol 256 is a valid symbol
1223 * with count 1.  In theory that's not optimal; giving it count zero but
1224 * including it in the symbol set anyway should give a better Huffman code.
1225 * But the theoretically better code actually seems to come out worse in
1226 * practice, because it produces more all-ones bytes (which incur stuffed
1227 * zero bytes in the final file).  In any case the difference is tiny.
1228 *
1229 * The JPEG standard requires Huffman codes to be no more than 16 bits long.
1230 * If some symbols have a very small but nonzero probability, the Huffman tree
1231 * must be adjusted to meet the code length restriction.  We currently use
1232 * the adjustment method suggested in JPEG section K.2.  This method is *not*
1233 * optimal; it may not choose the best possible limited-length code.  But
1234 * typically only very-low-frequency symbols will be given less-than-optimal
1235 * lengths, so the code is almost optimal.  Experimental comparisons against
1236 * an optimal limited-length-code algorithm indicate that the difference is
1237 * microscopic --- usually less than a hundredth of a percent of total size.
1238 * So the extra complexity of an optimal algorithm doesn't seem worthwhile.
1239 */
1240
1241LOCAL(void)
1242jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[])
1243{
1244#define MAX_CLEN 32             /* assumed maximum initial code length */
1245  UINT8 bits[MAX_CLEN+1];       /* bits[k] = # of symbols with code length k */
1246  int codesize[257];            /* codesize[k] = code length of symbol k */
1247  int others[257];              /* next symbol in current branch of tree */
1248  int c1, c2;
1249  int p, i, j;
1250  long v;
1251
1252  /* This algorithm is explained in section K.2 of the JPEG standard */
1253
1254  MEMZERO(bits, SIZEOF(bits));
1255  MEMZERO(codesize, SIZEOF(codesize));
1256  for (i = 0; i < 257; i++)
1257    others[i] = -1;             /* init links to empty */
1258 
1259  freq[256] = 1;                /* make sure 256 has a nonzero count */
1260  /* Including the pseudo-symbol 256 in the Huffman procedure guarantees
1261   * that no real symbol is given code-value of all ones, because 256
1262   * will be placed last in the largest codeword category.
1263   */
1264
1265  /* Huffman's basic algorithm to assign optimal code lengths to symbols */
1266
1267  for (;;) {
1268    /* Find the smallest nonzero frequency, set c1 = its symbol */
1269    /* In case of ties, take the larger symbol number */
1270    c1 = -1;
1271    v = 1000000000L;
1272    for (i = 0; i <= 256; i++) {
1273      if (freq[i] && freq[i] <= v) {
1274        v = freq[i];
1275        c1 = i;
1276      }
1277    }
1278
1279    /* Find the next smallest nonzero frequency, set c2 = its symbol */
1280    /* In case of ties, take the larger symbol number */
1281    c2 = -1;
1282    v = 1000000000L;
1283    for (i = 0; i <= 256; i++) {
1284      if (freq[i] && freq[i] <= v && i != c1) {
1285        v = freq[i];
1286        c2 = i;
1287      }
1288    }
1289
1290    /* Done if we've merged everything into one frequency */
1291    if (c2 < 0)
1292      break;
1293   
1294    /* Else merge the two counts/trees */
1295    freq[c1] += freq[c2];
1296    freq[c2] = 0;
1297
1298    /* Increment the codesize of everything in c1's tree branch */
1299    codesize[c1]++;
1300    while (others[c1] >= 0) {
1301      c1 = others[c1];
1302      codesize[c1]++;
1303    }
1304   
1305    others[c1] = c2;            /* chain c2 onto c1's tree branch */
1306   
1307    /* Increment the codesize of everything in c2's tree branch */
1308    codesize[c2]++;
1309    while (others[c2] >= 0) {
1310      c2 = others[c2];
1311      codesize[c2]++;
1312    }
1313  }
1314
1315  /* Now count the number of symbols of each code length */
1316  for (i = 0; i <= 256; i++) {
1317    if (codesize[i]) {
1318      /* The JPEG standard seems to think that this can't happen, */
1319      /* but I'm paranoid... */
1320      if (codesize[i] > MAX_CLEN)
1321        ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);
1322
1323      bits[codesize[i]]++;
1324    }
1325  }
1326
1327  /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure
1328   * Huffman procedure assigned any such lengths, we must adjust the coding.
1329   * Here is what the JPEG spec says about how this next bit works:
1330   * Since symbols are paired for the longest Huffman code, the symbols are
1331   * removed from this length category two at a time.  The prefix for the pair
1332   * (which is one bit shorter) is allocated to one of the pair; then,
1333   * skipping the BITS entry for that prefix length, a code word from the next
1334   * shortest nonzero BITS entry is converted into a prefix for two code words
1335   * one bit longer.
1336   */
1337 
1338  for (i = MAX_CLEN; i > 16; i--) {
1339    while (bits[i] > 0) {
1340      j = i - 2;                /* find length of new prefix to be used */
1341      while (bits[j] == 0)
1342        j--;
1343     
1344      bits[i] -= 2;             /* remove two symbols */
1345      bits[i-1]++;              /* one goes in this length */
1346      bits[j+1] += 2;           /* two new symbols in this length */
1347      bits[j]--;                /* symbol of this length is now a prefix */
1348    }
1349  }
1350
1351  /* Remove the count for the pseudo-symbol 256 from the largest codelength */
1352  while (bits[i] == 0)          /* find largest codelength still in use */
1353    i--;
1354  bits[i]--;
1355 
1356  /* Return final symbol counts (only for lengths 0..16) */
1357  MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits));
1358 
1359  /* Return a list of the symbols sorted by code length */
1360  /* It's not real clear to me why we don't need to consider the codelength
1361   * changes made above, but the JPEG spec seems to think this works.
1362   */
1363  p = 0;
1364  for (i = 1; i <= MAX_CLEN; i++) {
1365    for (j = 0; j <= 255; j++) {
1366      if (codesize[j] == i) {
1367        htbl->huffval[p] = (UINT8) j;
1368        p++;
1369      }
1370    }
1371  }
1372
1373  /* Set sent_table FALSE so updated table will be written to JPEG file. */
1374  htbl->sent_table = FALSE;
1375}
1376
1377
1378/*
1379 * Finish up a statistics-gathering pass and create the new Huffman tables.
1380 */
1381
1382METHODDEF(void)
1383finish_pass_gather (j_compress_ptr cinfo)
1384{
1385  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1386  int ci, dctbl, actbl, tbl;
1387  jpeg_component_info * compptr;
1388  JHUFF_TBL **htblptr;
1389  boolean did_dc[NUM_HUFF_TBLS];
1390  boolean did_ac[NUM_HUFF_TBLS];
1391  boolean did[NUM_HUFF_TBLS];
1392
1393  /* It's important not to apply jpeg_gen_optimal_table more than once
1394   * per table, because it clobbers the input frequency counts!
1395   */
1396  if (cinfo->progressive_mode) {
1397    /* Flush out buffered data (all we care about is counting the EOB symbol) */
1398    emit_eobrun(entropy);
1399
1400    MEMZERO(did, SIZEOF(did));
1401
1402    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1403      compptr = cinfo->cur_comp_info[ci];
1404      if (cinfo->Ss == 0) {
1405        if (cinfo->Ah != 0)     /* DC refinement needs no table */
1406          continue;
1407        tbl = compptr->dc_tbl_no;
1408      } else {
1409        tbl = compptr->ac_tbl_no;
1410      }
1411      if (! did[tbl]) {
1412        if (cinfo->Ss == 0)
1413          htblptr = & cinfo->dc_huff_tbl_ptrs[tbl];
1414        else
1415          htblptr = & cinfo->ac_huff_tbl_ptrs[tbl];
1416        if (*htblptr == NULL)
1417          *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
1418        jpeg_gen_optimal_table(cinfo, *htblptr, entropy->count_ptrs[tbl]);
1419        did[tbl] = TRUE;
1420      }
1421    }
1422  } else {
1423    MEMZERO(did_dc, SIZEOF(did_dc));
1424    MEMZERO(did_ac, SIZEOF(did_ac));
1425
1426    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1427      compptr = cinfo->cur_comp_info[ci];
1428      dctbl = compptr->dc_tbl_no;
1429      actbl = compptr->ac_tbl_no;
1430      if (! did_dc[dctbl]) {
1431        htblptr = & cinfo->dc_huff_tbl_ptrs[dctbl];
1432        if (*htblptr == NULL)
1433          *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
1434        jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]);
1435        did_dc[dctbl] = TRUE;
1436      }
1437      if (! did_ac[actbl]) {
1438        htblptr = & cinfo->ac_huff_tbl_ptrs[actbl];
1439        if (*htblptr == NULL)
1440          *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
1441        jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]);
1442        did_ac[actbl] = TRUE;
1443      }
1444    }
1445  }
1446}
1447
1448
1449/*
1450 * Initialize for a Huffman-compressed scan.
1451 * If gather_statistics is TRUE, we do not output anything during the scan,
1452 * just count the Huffman symbols used and generate Huffman code tables.
1453 */
1454
1455METHODDEF(void)
1456start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics)
1457{
1458  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1459  int ci, dctbl, actbl, tbl;
1460  jpeg_component_info * compptr;
1461
1462  if (gather_statistics)
1463    entropy->pub.finish_pass = finish_pass_gather;
1464  else
1465    entropy->pub.finish_pass = finish_pass_huff;
1466
1467  if (cinfo->progressive_mode) {
1468    entropy->cinfo = cinfo;
1469    entropy->gather_statistics = gather_statistics;
1470
1471    /* We assume jcmaster.c already validated the scan parameters. */
1472
1473    /* Select execution routine */
1474    if (cinfo->Ah == 0) {
1475      if (cinfo->Ss == 0)
1476        entropy->pub.encode_mcu = encode_mcu_DC_first;
1477      else
1478        entropy->pub.encode_mcu = encode_mcu_AC_first;
1479    } else {
1480      if (cinfo->Ss == 0)
1481        entropy->pub.encode_mcu = encode_mcu_DC_refine;
1482      else {
1483        entropy->pub.encode_mcu = encode_mcu_AC_refine;
1484        /* AC refinement needs a correction bit buffer */
1485        if (entropy->bit_buffer == NULL)
1486          entropy->bit_buffer = (char *)
1487            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1488                                        MAX_CORR_BITS * SIZEOF(char));
1489      }
1490    }
1491
1492    /* Only DC coefficients may be interleaved, so cinfo->comps_in_scan = 1
1493     * for AC coefficients.
1494     */
1495    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1496      compptr = cinfo->cur_comp_info[ci];
1497      /* Initialize DC predictions to 0 */
1498      entropy->saved.last_dc_val[ci] = 0;
1499      /* Get table index */
1500      if (cinfo->Ss == 0) {
1501        if (cinfo->Ah != 0)     /* DC refinement needs no table */
1502          continue;
1503        tbl = compptr->dc_tbl_no;
1504      } else {
1505        entropy->ac_tbl_no = tbl = compptr->ac_tbl_no;
1506      }
1507      if (gather_statistics) {
1508        /* Check for invalid table index */
1509        /* (make_c_derived_tbl does this in the other path) */
1510        if (tbl < 0 || tbl >= NUM_HUFF_TBLS)
1511          ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tbl);
1512        /* Allocate and zero the statistics tables */
1513        /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
1514        if (entropy->count_ptrs[tbl] == NULL)
1515          entropy->count_ptrs[tbl] = (long *)
1516            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1517                                        257 * SIZEOF(long));
1518        MEMZERO(entropy->count_ptrs[tbl], 257 * SIZEOF(long));
1519      } else {
1520        /* Compute derived values for Huffman table */
1521        /* We may do this more than once for a table, but it's not expensive */
1522        jpeg_make_c_derived_tbl(cinfo, cinfo->Ss == 0, tbl,
1523                                & entropy->derived_tbls[tbl]);
1524      }
1525    }
1526
1527    /* Initialize AC stuff */
1528    entropy->EOBRUN = 0;
1529    entropy->BE = 0;
1530  } else {
1531    if (gather_statistics)
1532      entropy->pub.encode_mcu = encode_mcu_gather;
1533    else
1534      entropy->pub.encode_mcu = encode_mcu_huff;
1535
1536    for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1537      compptr = cinfo->cur_comp_info[ci];
1538      dctbl = compptr->dc_tbl_no;
1539      actbl = compptr->ac_tbl_no;
1540      if (gather_statistics) {
1541        /* Check for invalid table indexes */
1542        /* (make_c_derived_tbl does this in the other path) */
1543        if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS)
1544          ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
1545        if (actbl < 0 || actbl >= NUM_HUFF_TBLS)
1546          ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
1547        /* Allocate and zero the statistics tables */
1548        /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
1549        if (entropy->dc_count_ptrs[dctbl] == NULL)
1550          entropy->dc_count_ptrs[dctbl] = (long *)
1551            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1552                                        257 * SIZEOF(long));
1553        MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * SIZEOF(long));
1554        if (entropy->ac_count_ptrs[actbl] == NULL)
1555          entropy->ac_count_ptrs[actbl] = (long *)
1556            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1557                                        257 * SIZEOF(long));
1558        MEMZERO(entropy->ac_count_ptrs[actbl], 257 * SIZEOF(long));
1559      } else {
1560        /* Compute derived values for Huffman tables */
1561        /* We may do this more than once for a table, but it's not expensive */
1562        jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl,
1563                                & entropy->dc_derived_tbls[dctbl]);
1564        jpeg_make_c_derived_tbl(cinfo, FALSE, actbl,
1565                                & entropy->ac_derived_tbls[actbl]);
1566      }
1567      /* Initialize DC predictions to 0 */
1568      entropy->saved.last_dc_val[ci] = 0;
1569    }
1570  }
1571
1572  /* Initialize bit buffer to empty */
1573  entropy->saved.put_buffer = 0;
1574  entropy->saved.put_bits = 0;
1575
1576  /* Initialize restart stuff */
1577  entropy->restarts_to_go = cinfo->restart_interval;
1578  entropy->next_restart_num = 0;
1579}
1580
1581
1582/*
1583 * Module initialization routine for Huffman entropy encoding.
1584 */
1585
1586GLOBAL(void)
1587jinit_huff_encoder (j_compress_ptr cinfo)
1588{
1589  huff_entropy_ptr entropy;
1590  int i;
1591
1592  entropy = (huff_entropy_ptr)
1593    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1594                                SIZEOF(huff_entropy_encoder));
1595  cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;
1596  entropy->pub.start_pass = start_pass_huff;
1597
1598  if (cinfo->progressive_mode) {
1599    /* Mark tables unallocated */
1600    for (i = 0; i < NUM_HUFF_TBLS; i++) {
1601      entropy->derived_tbls[i] = NULL;
1602      entropy->count_ptrs[i] = NULL;
1603    }
1604    entropy->bit_buffer = NULL; /* needed only in AC refinement scan */
1605  } else {
1606    /* Mark tables unallocated */
1607    for (i = 0; i < NUM_HUFF_TBLS; i++) {
1608      entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
1609      entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
1610    }
1611  }
1612}
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