source: rtems-graphics-toolkit/jpeg-8d/jchuff.c @ 86b99f7

Last change on this file since 86b99f7 was 86b99f7, checked in by Alexandru-Sever Horin <alex.sever.h@…>, on Aug 1, 2012 at 10:40:32 PM

Added jpeg-8d version. Made modifications to compile for RTEMS, without man or binaries

  • Property mode set to 100644
File size: 47.1 KB
Line 
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  /* Pointers to derived tables (these workspaces have image lifespan) */
91  c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
92  c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
93
94  /* Statistics tables for optimization */
95  long * dc_count_ptrs[NUM_HUFF_TBLS];
96  long * ac_count_ptrs[NUM_HUFF_TBLS];
97
98  /* Following fields used only in progressive mode */
99
100  /* Mode flag: TRUE for optimization, FALSE for actual data output */
101  boolean gather_statistics;
102
103  /* next_output_byte/free_in_buffer are local copies of cinfo->dest fields.
104   */
105  JOCTET * next_output_byte;    /* => next byte to write in buffer */
106  size_t free_in_buffer;        /* # of byte spaces remaining in buffer */
107  j_compress_ptr cinfo;         /* link to cinfo (needed for dump_buffer) */
108
109  /* Coding status for AC components */
110  int ac_tbl_no;                /* the table number of the single component */
111  unsigned int EOBRUN;          /* run length of EOBs */
112  unsigned int BE;              /* # of buffered correction bits before MCU */
113  char * bit_buffer;            /* buffer for correction bits (1 per char) */
114  /* packing correction bits tightly would save some space but cost time... */
115} huff_entropy_encoder;
116
117typedef huff_entropy_encoder * huff_entropy_ptr;
118
119/* Working state while writing an MCU (sequential mode).
120 * This struct contains all the fields that are needed by subroutines.
121 */
122
123typedef struct {
124  JOCTET * next_output_byte;    /* => next byte to write in buffer */
125  size_t free_in_buffer;        /* # of byte spaces remaining in buffer */
126  savable_state cur;            /* Current bit buffer & DC state */
127  j_compress_ptr cinfo;         /* dump_buffer needs access to this */
128} working_state;
129
130/* MAX_CORR_BITS is the number of bits the AC refinement correction-bit
131 * buffer can hold.  Larger sizes may slightly improve compression, but
132 * 1000 is already well into the realm of overkill.
133 * The minimum safe size is 64 bits.
134 */
135
136#define MAX_CORR_BITS  1000     /* Max # of correction bits I can buffer */
137
138/* IRIGHT_SHIFT is like RIGHT_SHIFT, but works on int rather than INT32.
139 * We assume that int right shift is unsigned if INT32 right shift is,
140 * which should be safe.
141 */
142
143#ifdef RIGHT_SHIFT_IS_UNSIGNED
144#define ISHIFT_TEMPS    int ishift_temp;
145#define IRIGHT_SHIFT(x,shft)  \
146        ((ishift_temp = (x)) < 0 ? \
147         (ishift_temp >> (shft)) | ((~0) << (16-(shft))) : \
148         (ishift_temp >> (shft)))
149#else
150#define ISHIFT_TEMPS
151#define IRIGHT_SHIFT(x,shft)    ((x) >> (shft))
152#endif
153
154
155/*
156 * Compute the derived values for a Huffman table.
157 * This routine also performs some validation checks on the table.
158 */
159
160LOCAL(void)
161jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,
162                         c_derived_tbl ** pdtbl)
163{
164  JHUFF_TBL *htbl;
165  c_derived_tbl *dtbl;
166  int p, i, l, lastp, si, maxsymbol;
167  char huffsize[257];
168  unsigned int huffcode[257];
169  unsigned int code;
170
171  /* Note that huffsize[] and huffcode[] are filled in code-length order,
172   * paralleling the order of the symbols themselves in htbl->huffval[].
173   */
174
175  /* Find the input Huffman table */
176  if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
177    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
178  htbl =
179    isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
180  if (htbl == NULL)
181    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
182
183  /* Allocate a workspace if we haven't already done so. */
184  if (*pdtbl == NULL)
185    *pdtbl = (c_derived_tbl *)
186      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
187                                  SIZEOF(c_derived_tbl));
188  dtbl = *pdtbl;
189 
190  /* Figure C.1: make table of Huffman code length for each symbol */
191
192  p = 0;
193  for (l = 1; l <= 16; l++) {
194    i = (int) htbl->bits[l];
195    if (i < 0 || p + i > 256)   /* protect against table overrun */
196      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
197    while (i--)
198      huffsize[p++] = (char) l;
199  }
200  huffsize[p] = 0;
201  lastp = p;
202 
203  /* Figure C.2: generate the codes themselves */
204  /* We also validate that the counts represent a legal Huffman code tree. */
205
206  code = 0;
207  si = huffsize[0];
208  p = 0;
209  while (huffsize[p]) {
210    while (((int) huffsize[p]) == si) {
211      huffcode[p++] = code;
212      code++;
213    }
214    /* code is now 1 more than the last code used for codelength si; but
215     * it must still fit in si bits, since no code is allowed to be all ones.
216     */
217    if (((INT32) code) >= (((INT32) 1) << si))
218      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
219    code <<= 1;
220    si++;
221  }
222 
223  /* Figure C.3: generate encoding tables */
224  /* These are code and size indexed by symbol value */
225
226  /* Set all codeless symbols to have code length 0;
227   * this lets us detect duplicate VAL entries here, and later
228   * allows emit_bits to detect any attempt to emit such symbols.
229   */
230  MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));
231
232  /* This is also a convenient place to check for out-of-range
233   * and duplicated VAL entries.  We allow 0..255 for AC symbols
234   * but only 0..15 for DC.  (We could constrain them further
235   * based on data depth and mode, but this seems enough.)
236   */
237  maxsymbol = isDC ? 15 : 255;
238
239  for (p = 0; p < lastp; p++) {
240    i = htbl->huffval[p];
241    if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
242      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
243    dtbl->ehufco[i] = huffcode[p];
244    dtbl->ehufsi[i] = huffsize[p];
245  }
246}
247
248
249/* Outputting bytes to the file.
250 * NB: these must be called only when actually outputting,
251 * that is, entropy->gather_statistics == FALSE.
252 */
253
254/* Emit a byte, taking 'action' if must suspend. */
255#define emit_byte_s(state,val,action)  \
256        { *(state)->next_output_byte++ = (JOCTET) (val);  \
257          if (--(state)->free_in_buffer == 0)  \
258            if (! dump_buffer_s(state))  \
259              { action; } }
260
261/* Emit a byte */
262#define emit_byte_e(entropy,val)  \
263        { *(entropy)->next_output_byte++ = (JOCTET) (val);  \
264          if (--(entropy)->free_in_buffer == 0)  \
265            dump_buffer_e(entropy); }
266
267
268LOCAL(boolean)
269dump_buffer_s (working_state * state)
270/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
271{
272  struct jpeg_destination_mgr * dest = state->cinfo->dest;
273
274  if (! (*dest->empty_output_buffer) (state->cinfo))
275    return FALSE;
276  /* After a successful buffer dump, must reset buffer pointers */
277  state->next_output_byte = dest->next_output_byte;
278  state->free_in_buffer = dest->free_in_buffer;
279  return TRUE;
280}
281
282
283LOCAL(void)
284dump_buffer_e (huff_entropy_ptr entropy)
285/* Empty the output buffer; we do not support suspension in this case. */
286{
287  struct jpeg_destination_mgr * dest = entropy->cinfo->dest;
288
289  if (! (*dest->empty_output_buffer) (entropy->cinfo))
290    ERREXIT(entropy->cinfo, JERR_CANT_SUSPEND);
291  /* After a successful buffer dump, must reset buffer pointers */
292  entropy->next_output_byte = dest->next_output_byte;
293  entropy->free_in_buffer = dest->free_in_buffer;
294}
295
296
297/* Outputting bits to the file */
298
299/* Only the right 24 bits of put_buffer are used; the valid bits are
300 * left-justified in this part.  At most 16 bits can be passed to emit_bits
301 * in one call, and we never retain more than 7 bits in put_buffer
302 * between calls, so 24 bits are sufficient.
303 */
304
305INLINE
306LOCAL(boolean)
307emit_bits_s (working_state * state, unsigned int code, int size)
308/* Emit some bits; return TRUE if successful, FALSE if must suspend */
309{
310  /* This routine is heavily used, so it's worth coding tightly. */
311  register INT32 put_buffer = (INT32) code;
312  register int put_bits = state->cur.put_bits;
313
314  /* if size is 0, caller used an invalid Huffman table entry */
315  if (size == 0)
316    ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);
317
318  put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
319 
320  put_bits += size;             /* new number of bits in buffer */
321 
322  put_buffer <<= 24 - put_bits; /* align incoming bits */
323
324  put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */
325 
326  while (put_bits >= 8) {
327    int c = (int) ((put_buffer >> 16) & 0xFF);
328   
329    emit_byte_s(state, c, return FALSE);
330    if (c == 0xFF) {            /* need to stuff a zero byte? */
331      emit_byte_s(state, 0, return FALSE);
332    }
333    put_buffer <<= 8;
334    put_bits -= 8;
335  }
336
337  state->cur.put_buffer = put_buffer; /* update state variables */
338  state->cur.put_bits = put_bits;
339
340  return TRUE;
341}
342
343
344INLINE
345LOCAL(void)
346emit_bits_e (huff_entropy_ptr entropy, unsigned int code, int size)
347/* Emit some bits, unless we are in gather mode */
348{
349  /* This routine is heavily used, so it's worth coding tightly. */
350  register INT32 put_buffer = (INT32) code;
351  register int put_bits = entropy->saved.put_bits;
352
353  /* if size is 0, caller used an invalid Huffman table entry */
354  if (size == 0)
355    ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);
356
357  if (entropy->gather_statistics)
358    return;                     /* do nothing if we're only getting stats */
359
360  put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
361 
362  put_bits += size;             /* new number of bits in buffer */
363
364  put_buffer <<= 24 - put_bits; /* align incoming bits */
365
366  /* and merge with old buffer contents */
367  put_buffer |= entropy->saved.put_buffer;
368
369  while (put_bits >= 8) {
370    int c = (int) ((put_buffer >> 16) & 0xFF);
371
372    emit_byte_e(entropy, c);
373    if (c == 0xFF) {            /* need to stuff a zero byte? */
374      emit_byte_e(entropy, 0);
375    }
376    put_buffer <<= 8;
377    put_bits -= 8;
378  }
379
380  entropy->saved.put_buffer = put_buffer; /* update variables */
381  entropy->saved.put_bits = put_bits;
382}
383
384
385LOCAL(boolean)
386flush_bits_s (working_state * state)
387{
388  if (! emit_bits_s(state, 0x7F, 7)) /* fill any partial byte with ones */
389    return FALSE;
390  state->cur.put_buffer = 0;         /* and reset bit-buffer to empty */
391  state->cur.put_bits = 0;
392  return TRUE;
393}
394
395
396LOCAL(void)
397flush_bits_e (huff_entropy_ptr entropy)
398{
399  emit_bits_e(entropy, 0x7F, 7); /* fill any partial byte with ones */
400  entropy->saved.put_buffer = 0; /* and reset bit-buffer to empty */
401  entropy->saved.put_bits = 0;
402}
403
404
405/*
406 * Emit (or just count) a Huffman symbol.
407 */
408
409INLINE
410LOCAL(void)
411emit_dc_symbol (huff_entropy_ptr entropy, int tbl_no, int symbol)
412{
413  if (entropy->gather_statistics)
414    entropy->dc_count_ptrs[tbl_no][symbol]++;
415  else {
416    c_derived_tbl * tbl = entropy->dc_derived_tbls[tbl_no];
417    emit_bits_e(entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol]);
418  }
419}
420
421
422INLINE
423LOCAL(void)
424emit_ac_symbol (huff_entropy_ptr entropy, int tbl_no, int symbol)
425{
426  if (entropy->gather_statistics)
427    entropy->ac_count_ptrs[tbl_no][symbol]++;
428  else {
429    c_derived_tbl * tbl = entropy->ac_derived_tbls[tbl_no];
430    emit_bits_e(entropy, tbl->ehufco[symbol], tbl->ehufsi[symbol]);
431  }
432}
433
434
435/*
436 * Emit bits from a correction bit buffer.
437 */
438
439LOCAL(void)
440emit_buffered_bits (huff_entropy_ptr entropy, char * bufstart,
441                    unsigned int nbits)
442{
443  if (entropy->gather_statistics)
444    return;                     /* no real work */
445
446  while (nbits > 0) {
447    emit_bits_e(entropy, (unsigned int) (*bufstart), 1);
448    bufstart++;
449    nbits--;
450  }
451}
452
453
454/*
455 * Emit any pending EOBRUN symbol.
456 */
457
458LOCAL(void)
459emit_eobrun (huff_entropy_ptr entropy)
460{
461  register int temp, nbits;
462
463  if (entropy->EOBRUN > 0) {    /* if there is any pending EOBRUN */
464    temp = entropy->EOBRUN;
465    nbits = 0;
466    while ((temp >>= 1))
467      nbits++;
468    /* safety check: shouldn't happen given limited correction-bit buffer */
469    if (nbits > 14)
470      ERREXIT(entropy->cinfo, JERR_HUFF_MISSING_CODE);
471
472    emit_ac_symbol(entropy, entropy->ac_tbl_no, nbits << 4);
473    if (nbits)
474      emit_bits_e(entropy, entropy->EOBRUN, nbits);
475
476    entropy->EOBRUN = 0;
477
478    /* Emit any buffered correction bits */
479    emit_buffered_bits(entropy, entropy->bit_buffer, entropy->BE);
480    entropy->BE = 0;
481  }
482}
483
484
485/*
486 * Emit a restart marker & resynchronize predictions.
487 */
488
489LOCAL(boolean)
490emit_restart_s (working_state * state, int restart_num)
491{
492  int ci;
493
494  if (! flush_bits_s(state))
495    return FALSE;
496
497  emit_byte_s(state, 0xFF, return FALSE);
498  emit_byte_s(state, JPEG_RST0 + restart_num, return FALSE);
499
500  /* Re-initialize DC predictions to 0 */
501  for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
502    state->cur.last_dc_val[ci] = 0;
503
504  /* The restart counter is not updated until we successfully write the MCU. */
505
506  return TRUE;
507}
508
509
510LOCAL(void)
511emit_restart_e (huff_entropy_ptr entropy, int restart_num)
512{
513  int ci;
514
515  emit_eobrun(entropy);
516
517  if (! entropy->gather_statistics) {
518    flush_bits_e(entropy);
519    emit_byte_e(entropy, 0xFF);
520    emit_byte_e(entropy, JPEG_RST0 + restart_num);
521  }
522
523  if (entropy->cinfo->Ss == 0) {
524    /* Re-initialize DC predictions to 0 */
525    for (ci = 0; ci < entropy->cinfo->comps_in_scan; ci++)
526      entropy->saved.last_dc_val[ci] = 0;
527  } else {
528    /* Re-initialize all AC-related fields to 0 */
529    entropy->EOBRUN = 0;
530    entropy->BE = 0;
531  }
532}
533
534
535/*
536 * MCU encoding for DC initial scan (either spectral selection,
537 * or first pass of successive approximation).
538 */
539
540METHODDEF(boolean)
541encode_mcu_DC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
542{
543  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
544  register int temp, temp2;
545  register int nbits;
546  int blkn, ci;
547  int Al = cinfo->Al;
548  JBLOCKROW block;
549  jpeg_component_info * compptr;
550  ISHIFT_TEMPS
551
552  entropy->next_output_byte = cinfo->dest->next_output_byte;
553  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
554
555  /* Emit restart marker if needed */
556  if (cinfo->restart_interval)
557    if (entropy->restarts_to_go == 0)
558      emit_restart_e(entropy, entropy->next_restart_num);
559
560  /* Encode the MCU data blocks */
561  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
562    block = MCU_data[blkn];
563    ci = cinfo->MCU_membership[blkn];
564    compptr = cinfo->cur_comp_info[ci];
565
566    /* Compute the DC value after the required point transform by Al.
567     * This is simply an arithmetic right shift.
568     */
569    temp2 = IRIGHT_SHIFT((int) ((*block)[0]), Al);
570
571    /* DC differences are figured on the point-transformed values. */
572    temp = temp2 - entropy->saved.last_dc_val[ci];
573    entropy->saved.last_dc_val[ci] = temp2;
574
575    /* Encode the DC coefficient difference per section G.1.2.1 */
576    temp2 = temp;
577    if (temp < 0) {
578      temp = -temp;             /* temp is abs value of input */
579      /* For a negative input, want temp2 = bitwise complement of abs(input) */
580      /* This code assumes we are on a two's complement machine */
581      temp2--;
582    }
583   
584    /* Find the number of bits needed for the magnitude of the coefficient */
585    nbits = 0;
586    while (temp) {
587      nbits++;
588      temp >>= 1;
589    }
590    /* Check for out-of-range coefficient values.
591     * Since we're encoding a difference, the range limit is twice as much.
592     */
593    if (nbits > MAX_COEF_BITS+1)
594      ERREXIT(cinfo, JERR_BAD_DCT_COEF);
595   
596    /* Count/emit the Huffman-coded symbol for the number of bits */
597    emit_dc_symbol(entropy, compptr->dc_tbl_no, nbits);
598   
599    /* Emit that number of bits of the value, if positive, */
600    /* or the complement of its magnitude, if negative. */
601    if (nbits)                  /* emit_bits rejects calls with size 0 */
602      emit_bits_e(entropy, (unsigned int) temp2, nbits);
603  }
604
605  cinfo->dest->next_output_byte = entropy->next_output_byte;
606  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
607
608  /* Update restart-interval state too */
609  if (cinfo->restart_interval) {
610    if (entropy->restarts_to_go == 0) {
611      entropy->restarts_to_go = cinfo->restart_interval;
612      entropy->next_restart_num++;
613      entropy->next_restart_num &= 7;
614    }
615    entropy->restarts_to_go--;
616  }
617
618  return TRUE;
619}
620
621
622/*
623 * MCU encoding for AC initial scan (either spectral selection,
624 * or first pass of successive approximation).
625 */
626
627METHODDEF(boolean)
628encode_mcu_AC_first (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
629{
630  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
631  register int temp, temp2;
632  register int nbits;
633  register int r, k;
634  int Se, Al;
635  const int * natural_order;
636  JBLOCKROW block;
637
638  entropy->next_output_byte = cinfo->dest->next_output_byte;
639  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
640
641  /* Emit restart marker if needed */
642  if (cinfo->restart_interval)
643    if (entropy->restarts_to_go == 0)
644      emit_restart_e(entropy, entropy->next_restart_num);
645
646  Se = cinfo->Se;
647  Al = cinfo->Al;
648  natural_order = cinfo->natural_order;
649
650  /* Encode the MCU data block */
651  block = MCU_data[0];
652
653  /* Encode the AC coefficients per section G.1.2.2, fig. G.3 */
654 
655  r = 0;                        /* r = run length of zeros */
656   
657  for (k = cinfo->Ss; k <= Se; k++) {
658    if ((temp = (*block)[natural_order[k]]) == 0) {
659      r++;
660      continue;
661    }
662    /* We must apply the point transform by Al.  For AC coefficients this
663     * is an integer division with rounding towards 0.  To do this portably
664     * in C, we shift after obtaining the absolute value; so the code is
665     * interwoven with finding the abs value (temp) and output bits (temp2).
666     */
667    if (temp < 0) {
668      temp = -temp;             /* temp is abs value of input */
669      temp >>= Al;              /* apply the point transform */
670      /* For a negative coef, want temp2 = bitwise complement of abs(coef) */
671      temp2 = ~temp;
672    } else {
673      temp >>= Al;              /* apply the point transform */
674      temp2 = temp;
675    }
676    /* Watch out for case that nonzero coef is zero after point transform */
677    if (temp == 0) {
678      r++;
679      continue;
680    }
681
682    /* Emit any pending EOBRUN */
683    if (entropy->EOBRUN > 0)
684      emit_eobrun(entropy);
685    /* if run length > 15, must emit special run-length-16 codes (0xF0) */
686    while (r > 15) {
687      emit_ac_symbol(entropy, entropy->ac_tbl_no, 0xF0);
688      r -= 16;
689    }
690
691    /* Find the number of bits needed for the magnitude of the coefficient */
692    nbits = 1;                  /* there must be at least one 1 bit */
693    while ((temp >>= 1))
694      nbits++;
695    /* Check for out-of-range coefficient values */
696    if (nbits > MAX_COEF_BITS)
697      ERREXIT(cinfo, JERR_BAD_DCT_COEF);
698
699    /* Count/emit Huffman symbol for run length / number of bits */
700    emit_ac_symbol(entropy, entropy->ac_tbl_no, (r << 4) + nbits);
701
702    /* Emit that number of bits of the value, if positive, */
703    /* or the complement of its magnitude, if negative. */
704    emit_bits_e(entropy, (unsigned int) temp2, nbits);
705
706    r = 0;                      /* reset zero run length */
707  }
708
709  if (r > 0) {                  /* If there are trailing zeroes, */
710    entropy->EOBRUN++;          /* count an EOB */
711    if (entropy->EOBRUN == 0x7FFF)
712      emit_eobrun(entropy);     /* force it out to avoid overflow */
713  }
714
715  cinfo->dest->next_output_byte = entropy->next_output_byte;
716  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
717
718  /* Update restart-interval state too */
719  if (cinfo->restart_interval) {
720    if (entropy->restarts_to_go == 0) {
721      entropy->restarts_to_go = cinfo->restart_interval;
722      entropy->next_restart_num++;
723      entropy->next_restart_num &= 7;
724    }
725    entropy->restarts_to_go--;
726  }
727
728  return TRUE;
729}
730
731
732/*
733 * MCU encoding for DC successive approximation refinement scan.
734 * Note: we assume such scans can be multi-component, although the spec
735 * is not very clear on the point.
736 */
737
738METHODDEF(boolean)
739encode_mcu_DC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
740{
741  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
742  register int temp;
743  int blkn;
744  int Al = cinfo->Al;
745  JBLOCKROW block;
746
747  entropy->next_output_byte = cinfo->dest->next_output_byte;
748  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
749
750  /* Emit restart marker if needed */
751  if (cinfo->restart_interval)
752    if (entropy->restarts_to_go == 0)
753      emit_restart_e(entropy, entropy->next_restart_num);
754
755  /* Encode the MCU data blocks */
756  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
757    block = MCU_data[blkn];
758
759    /* We simply emit the Al'th bit of the DC coefficient value. */
760    temp = (*block)[0];
761    emit_bits_e(entropy, (unsigned int) (temp >> Al), 1);
762  }
763
764  cinfo->dest->next_output_byte = entropy->next_output_byte;
765  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
766
767  /* Update restart-interval state too */
768  if (cinfo->restart_interval) {
769    if (entropy->restarts_to_go == 0) {
770      entropy->restarts_to_go = cinfo->restart_interval;
771      entropy->next_restart_num++;
772      entropy->next_restart_num &= 7;
773    }
774    entropy->restarts_to_go--;
775  }
776
777  return TRUE;
778}
779
780
781/*
782 * MCU encoding for AC successive approximation refinement scan.
783 */
784
785METHODDEF(boolean)
786encode_mcu_AC_refine (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
787{
788  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
789  register int temp;
790  register int r, k;
791  int EOB;
792  char *BR_buffer;
793  unsigned int BR;
794  int Se, Al;
795  const int * natural_order;
796  JBLOCKROW block;
797  int absvalues[DCTSIZE2];
798
799  entropy->next_output_byte = cinfo->dest->next_output_byte;
800  entropy->free_in_buffer = cinfo->dest->free_in_buffer;
801
802  /* Emit restart marker if needed */
803  if (cinfo->restart_interval)
804    if (entropy->restarts_to_go == 0)
805      emit_restart_e(entropy, entropy->next_restart_num);
806
807  Se = cinfo->Se;
808  Al = cinfo->Al;
809  natural_order = cinfo->natural_order;
810
811  /* Encode the MCU data block */
812  block = MCU_data[0];
813
814  /* It is convenient to make a pre-pass to determine the transformed
815   * coefficients' absolute values and the EOB position.
816   */
817  EOB = 0;
818  for (k = cinfo->Ss; k <= Se; k++) {
819    temp = (*block)[natural_order[k]];
820    /* We must apply the point transform by Al.  For AC coefficients this
821     * is an integer division with rounding towards 0.  To do this portably
822     * in C, we shift after obtaining the absolute value.
823     */
824    if (temp < 0)
825      temp = -temp;             /* temp is abs value of input */
826    temp >>= Al;                /* apply the point transform */
827    absvalues[k] = temp;        /* save abs value for main pass */
828    if (temp == 1)
829      EOB = k;                  /* EOB = index of last newly-nonzero coef */
830  }
831
832  /* Encode the AC coefficients per section G.1.2.3, fig. G.7 */
833 
834  r = 0;                        /* r = run length of zeros */
835  BR = 0;                       /* BR = count of buffered bits added now */
836  BR_buffer = entropy->bit_buffer + entropy->BE; /* Append bits to buffer */
837
838  for (k = cinfo->Ss; k <= Se; k++) {
839    if ((temp = absvalues[k]) == 0) {
840      r++;
841      continue;
842    }
843
844    /* Emit any required ZRLs, but not if they can be folded into EOB */
845    while (r > 15 && k <= EOB) {
846      /* emit any pending EOBRUN and the BE correction bits */
847      emit_eobrun(entropy);
848      /* Emit ZRL */
849      emit_ac_symbol(entropy, entropy->ac_tbl_no, 0xF0);
850      r -= 16;
851      /* Emit buffered correction bits that must be associated with ZRL */
852      emit_buffered_bits(entropy, BR_buffer, BR);
853      BR_buffer = entropy->bit_buffer; /* BE bits are gone now */
854      BR = 0;
855    }
856
857    /* If the coef was previously nonzero, it only needs a correction bit.
858     * NOTE: a straight translation of the spec's figure G.7 would suggest
859     * that we also need to test r > 15.  But if r > 15, we can only get here
860     * if k > EOB, which implies that this coefficient is not 1.
861     */
862    if (temp > 1) {
863      /* The correction bit is the next bit of the absolute value. */
864      BR_buffer[BR++] = (char) (temp & 1);
865      continue;
866    }
867
868    /* Emit any pending EOBRUN and the BE correction bits */
869    emit_eobrun(entropy);
870
871    /* Count/emit Huffman symbol for run length / number of bits */
872    emit_ac_symbol(entropy, entropy->ac_tbl_no, (r << 4) + 1);
873
874    /* Emit output bit for newly-nonzero coef */
875    temp = ((*block)[natural_order[k]] < 0) ? 0 : 1;
876    emit_bits_e(entropy, (unsigned int) temp, 1);
877
878    /* Emit buffered correction bits that must be associated with this code */
879    emit_buffered_bits(entropy, BR_buffer, BR);
880    BR_buffer = entropy->bit_buffer; /* BE bits are gone now */
881    BR = 0;
882    r = 0;                      /* reset zero run length */
883  }
884
885  if (r > 0 || BR > 0) {        /* If there are trailing zeroes, */
886    entropy->EOBRUN++;          /* count an EOB */
887    entropy->BE += BR;          /* concat my correction bits to older ones */
888    /* We force out the EOB if we risk either:
889     * 1. overflow of the EOB counter;
890     * 2. overflow of the correction bit buffer during the next MCU.
891     */
892    if (entropy->EOBRUN == 0x7FFF || entropy->BE > (MAX_CORR_BITS-DCTSIZE2+1))
893      emit_eobrun(entropy);
894  }
895
896  cinfo->dest->next_output_byte = entropy->next_output_byte;
897  cinfo->dest->free_in_buffer = entropy->free_in_buffer;
898
899  /* Update restart-interval state too */
900  if (cinfo->restart_interval) {
901    if (entropy->restarts_to_go == 0) {
902      entropy->restarts_to_go = cinfo->restart_interval;
903      entropy->next_restart_num++;
904      entropy->next_restart_num &= 7;
905    }
906    entropy->restarts_to_go--;
907  }
908
909  return TRUE;
910}
911
912
913/* Encode a single block's worth of coefficients */
914
915LOCAL(boolean)
916encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,
917                  c_derived_tbl *dctbl, c_derived_tbl *actbl)
918{
919  register int temp, temp2;
920  register int nbits;
921  register int k, r, i;
922  int Se = state->cinfo->lim_Se;
923  const int * natural_order = state->cinfo->natural_order;
924
925  /* Encode the DC coefficient difference per section F.1.2.1 */
926
927  temp = temp2 = block[0] - last_dc_val;
928
929  if (temp < 0) {
930    temp = -temp;               /* temp is abs value of input */
931    /* For a negative input, want temp2 = bitwise complement of abs(input) */
932    /* This code assumes we are on a two's complement machine */
933    temp2--;
934  }
935
936  /* Find the number of bits needed for the magnitude of the coefficient */
937  nbits = 0;
938  while (temp) {
939    nbits++;
940    temp >>= 1;
941  }
942  /* Check for out-of-range coefficient values.
943   * Since we're encoding a difference, the range limit is twice as much.
944   */
945  if (nbits > MAX_COEF_BITS+1)
946    ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
947
948  /* Emit the Huffman-coded symbol for the number of bits */
949  if (! emit_bits_s(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
950    return FALSE;
951
952  /* Emit that number of bits of the value, if positive, */
953  /* or the complement of its magnitude, if negative. */
954  if (nbits)                    /* emit_bits rejects calls with size 0 */
955    if (! emit_bits_s(state, (unsigned int) temp2, nbits))
956      return FALSE;
957
958  /* Encode the AC coefficients per section F.1.2.2 */
959
960  r = 0;                        /* r = run length of zeros */
961
962  for (k = 1; k <= Se; k++) {
963    if ((temp = block[natural_order[k]]) == 0) {
964      r++;
965    } else {
966      /* if run length > 15, must emit special run-length-16 codes (0xF0) */
967      while (r > 15) {
968        if (! emit_bits_s(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
969          return FALSE;
970        r -= 16;
971      }
972
973      temp2 = temp;
974      if (temp < 0) {
975        temp = -temp;           /* temp is abs value of input */
976        /* This code assumes we are on a two's complement machine */
977        temp2--;
978      }
979
980      /* Find the number of bits needed for the magnitude of the coefficient */
981      nbits = 1;                /* there must be at least one 1 bit */
982      while ((temp >>= 1))
983        nbits++;
984      /* Check for out-of-range coefficient values */
985      if (nbits > MAX_COEF_BITS)
986        ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
987
988      /* Emit Huffman symbol for run length / number of bits */
989      i = (r << 4) + nbits;
990      if (! emit_bits_s(state, actbl->ehufco[i], actbl->ehufsi[i]))
991        return FALSE;
992
993      /* Emit that number of bits of the value, if positive, */
994      /* or the complement of its magnitude, if negative. */
995      if (! emit_bits_s(state, (unsigned int) temp2, nbits))
996        return FALSE;
997
998      r = 0;
999    }
1000  }
1001
1002  /* If the last coef(s) were zero, emit an end-of-block code */
1003  if (r > 0)
1004    if (! emit_bits_s(state, actbl->ehufco[0], actbl->ehufsi[0]))
1005      return FALSE;
1006
1007  return TRUE;
1008}
1009
1010
1011/*
1012 * Encode and output one MCU's worth of Huffman-compressed coefficients.
1013 */
1014
1015METHODDEF(boolean)
1016encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
1017{
1018  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1019  working_state state;
1020  int blkn, ci;
1021  jpeg_component_info * compptr;
1022
1023  /* Load up working state */
1024  state.next_output_byte = cinfo->dest->next_output_byte;
1025  state.free_in_buffer = cinfo->dest->free_in_buffer;
1026  ASSIGN_STATE(state.cur, entropy->saved);
1027  state.cinfo = cinfo;
1028
1029  /* Emit restart marker if needed */
1030  if (cinfo->restart_interval) {
1031    if (entropy->restarts_to_go == 0)
1032      if (! emit_restart_s(&state, entropy->next_restart_num))
1033        return FALSE;
1034  }
1035
1036  /* Encode the MCU data blocks */
1037  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
1038    ci = cinfo->MCU_membership[blkn];
1039    compptr = cinfo->cur_comp_info[ci];
1040    if (! encode_one_block(&state,
1041                           MCU_data[blkn][0], state.cur.last_dc_val[ci],
1042                           entropy->dc_derived_tbls[compptr->dc_tbl_no],
1043                           entropy->ac_derived_tbls[compptr->ac_tbl_no]))
1044      return FALSE;
1045    /* Update last_dc_val */
1046    state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
1047  }
1048
1049  /* Completed MCU, so update state */
1050  cinfo->dest->next_output_byte = state.next_output_byte;
1051  cinfo->dest->free_in_buffer = state.free_in_buffer;
1052  ASSIGN_STATE(entropy->saved, state.cur);
1053
1054  /* Update restart-interval state too */
1055  if (cinfo->restart_interval) {
1056    if (entropy->restarts_to_go == 0) {
1057      entropy->restarts_to_go = cinfo->restart_interval;
1058      entropy->next_restart_num++;
1059      entropy->next_restart_num &= 7;
1060    }
1061    entropy->restarts_to_go--;
1062  }
1063
1064  return TRUE;
1065}
1066
1067
1068/*
1069 * Finish up at the end of a Huffman-compressed scan.
1070 */
1071
1072METHODDEF(void)
1073finish_pass_huff (j_compress_ptr cinfo)
1074{
1075  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1076  working_state state;
1077
1078  if (cinfo->progressive_mode) {
1079    entropy->next_output_byte = cinfo->dest->next_output_byte;
1080    entropy->free_in_buffer = cinfo->dest->free_in_buffer;
1081
1082    /* Flush out any buffered data */
1083    emit_eobrun(entropy);
1084    flush_bits_e(entropy);
1085
1086    cinfo->dest->next_output_byte = entropy->next_output_byte;
1087    cinfo->dest->free_in_buffer = entropy->free_in_buffer;
1088  } else {
1089    /* Load up working state ... flush_bits needs it */
1090    state.next_output_byte = cinfo->dest->next_output_byte;
1091    state.free_in_buffer = cinfo->dest->free_in_buffer;
1092    ASSIGN_STATE(state.cur, entropy->saved);
1093    state.cinfo = cinfo;
1094
1095    /* Flush out the last data */
1096    if (! flush_bits_s(&state))
1097      ERREXIT(cinfo, JERR_CANT_SUSPEND);
1098
1099    /* Update state */
1100    cinfo->dest->next_output_byte = state.next_output_byte;
1101    cinfo->dest->free_in_buffer = state.free_in_buffer;
1102    ASSIGN_STATE(entropy->saved, state.cur);
1103  }
1104}
1105
1106
1107/*
1108 * Huffman coding optimization.
1109 *
1110 * We first scan the supplied data and count the number of uses of each symbol
1111 * that is to be Huffman-coded. (This process MUST agree with the code above.)
1112 * Then we build a Huffman coding tree for the observed counts.
1113 * Symbols which are not needed at all for the particular image are not
1114 * assigned any code, which saves space in the DHT marker as well as in
1115 * the compressed data.
1116 */
1117
1118
1119/* Process a single block's worth of coefficients */
1120
1121LOCAL(void)
1122htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,
1123                 long dc_counts[], long ac_counts[])
1124{
1125  register int temp;
1126  register int nbits;
1127  register int k, r;
1128  int Se = cinfo->lim_Se;
1129  const int * natural_order = cinfo->natural_order;
1130 
1131  /* Encode the DC coefficient difference per section F.1.2.1 */
1132 
1133  temp = block[0] - last_dc_val;
1134  if (temp < 0)
1135    temp = -temp;
1136 
1137  /* Find the number of bits needed for the magnitude of the coefficient */
1138  nbits = 0;
1139  while (temp) {
1140    nbits++;
1141    temp >>= 1;
1142  }
1143  /* Check for out-of-range coefficient values.
1144   * Since we're encoding a difference, the range limit is twice as much.
1145   */
1146  if (nbits > MAX_COEF_BITS+1)
1147    ERREXIT(cinfo, JERR_BAD_DCT_COEF);
1148
1149  /* Count the Huffman symbol for the number of bits */
1150  dc_counts[nbits]++;
1151 
1152  /* Encode the AC coefficients per section F.1.2.2 */
1153 
1154  r = 0;                        /* r = run length of zeros */
1155 
1156  for (k = 1; k <= Se; k++) {
1157    if ((temp = block[natural_order[k]]) == 0) {
1158      r++;
1159    } else {
1160      /* if run length > 15, must emit special run-length-16 codes (0xF0) */
1161      while (r > 15) {
1162        ac_counts[0xF0]++;
1163        r -= 16;
1164      }
1165     
1166      /* Find the number of bits needed for the magnitude of the coefficient */
1167      if (temp < 0)
1168        temp = -temp;
1169     
1170      /* Find the number of bits needed for the magnitude of the coefficient */
1171      nbits = 1;                /* there must be at least one 1 bit */
1172      while ((temp >>= 1))
1173        nbits++;
1174      /* Check for out-of-range coefficient values */
1175      if (nbits > MAX_COEF_BITS)
1176        ERREXIT(cinfo, JERR_BAD_DCT_COEF);
1177     
1178      /* Count Huffman symbol for run length / number of bits */
1179      ac_counts[(r << 4) + nbits]++;
1180     
1181      r = 0;
1182    }
1183  }
1184
1185  /* If the last coef(s) were zero, emit an end-of-block code */
1186  if (r > 0)
1187    ac_counts[0]++;
1188}
1189
1190
1191/*
1192 * Trial-encode one MCU's worth of Huffman-compressed coefficients.
1193 * No data is actually output, so no suspension return is possible.
1194 */
1195
1196METHODDEF(boolean)
1197encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
1198{
1199  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1200  int blkn, ci;
1201  jpeg_component_info * compptr;
1202
1203  /* Take care of restart intervals if needed */
1204  if (cinfo->restart_interval) {
1205    if (entropy->restarts_to_go == 0) {
1206      /* Re-initialize DC predictions to 0 */
1207      for (ci = 0; ci < cinfo->comps_in_scan; ci++)
1208        entropy->saved.last_dc_val[ci] = 0;
1209      /* Update restart state */
1210      entropy->restarts_to_go = cinfo->restart_interval;
1211    }
1212    entropy->restarts_to_go--;
1213  }
1214
1215  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
1216    ci = cinfo->MCU_membership[blkn];
1217    compptr = cinfo->cur_comp_info[ci];
1218    htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
1219                    entropy->dc_count_ptrs[compptr->dc_tbl_no],
1220                    entropy->ac_count_ptrs[compptr->ac_tbl_no]);
1221    entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
1222  }
1223
1224  return TRUE;
1225}
1226
1227
1228/*
1229 * Generate the best Huffman code table for the given counts, fill htbl.
1230 *
1231 * The JPEG standard requires that no symbol be assigned a codeword of all
1232 * one bits (so that padding bits added at the end of a compressed segment
1233 * can't look like a valid code).  Because of the canonical ordering of
1234 * codewords, this just means that there must be an unused slot in the
1235 * longest codeword length category.  Section K.2 of the JPEG spec suggests
1236 * reserving such a slot by pretending that symbol 256 is a valid symbol
1237 * with count 1.  In theory that's not optimal; giving it count zero but
1238 * including it in the symbol set anyway should give a better Huffman code.
1239 * But the theoretically better code actually seems to come out worse in
1240 * practice, because it produces more all-ones bytes (which incur stuffed
1241 * zero bytes in the final file).  In any case the difference is tiny.
1242 *
1243 * The JPEG standard requires Huffman codes to be no more than 16 bits long.
1244 * If some symbols have a very small but nonzero probability, the Huffman tree
1245 * must be adjusted to meet the code length restriction.  We currently use
1246 * the adjustment method suggested in JPEG section K.2.  This method is *not*
1247 * optimal; it may not choose the best possible limited-length code.  But
1248 * typically only very-low-frequency symbols will be given less-than-optimal
1249 * lengths, so the code is almost optimal.  Experimental comparisons against
1250 * an optimal limited-length-code algorithm indicate that the difference is
1251 * microscopic --- usually less than a hundredth of a percent of total size.
1252 * So the extra complexity of an optimal algorithm doesn't seem worthwhile.
1253 */
1254
1255LOCAL(void)
1256jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[])
1257{
1258#define MAX_CLEN 32             /* assumed maximum initial code length */
1259  UINT8 bits[MAX_CLEN+1];       /* bits[k] = # of symbols with code length k */
1260  int codesize[257];            /* codesize[k] = code length of symbol k */
1261  int others[257];              /* next symbol in current branch of tree */
1262  int c1, c2;
1263  int p, i, j;
1264  long v;
1265
1266  /* This algorithm is explained in section K.2 of the JPEG standard */
1267
1268  MEMZERO(bits, SIZEOF(bits));
1269  MEMZERO(codesize, SIZEOF(codesize));
1270  for (i = 0; i < 257; i++)
1271    others[i] = -1;             /* init links to empty */
1272 
1273  freq[256] = 1;                /* make sure 256 has a nonzero count */
1274  /* Including the pseudo-symbol 256 in the Huffman procedure guarantees
1275   * that no real symbol is given code-value of all ones, because 256
1276   * will be placed last in the largest codeword category.
1277   */
1278
1279  /* Huffman's basic algorithm to assign optimal code lengths to symbols */
1280
1281  for (;;) {
1282    /* Find the smallest nonzero frequency, set c1 = its symbol */
1283    /* In case of ties, take the larger symbol number */
1284    c1 = -1;
1285    v = 1000000000L;
1286    for (i = 0; i <= 256; i++) {
1287      if (freq[i] && freq[i] <= v) {
1288        v = freq[i];
1289        c1 = i;
1290      }
1291    }
1292
1293    /* Find the next smallest nonzero frequency, set c2 = its symbol */
1294    /* In case of ties, take the larger symbol number */
1295    c2 = -1;
1296    v = 1000000000L;
1297    for (i = 0; i <= 256; i++) {
1298      if (freq[i] && freq[i] <= v && i != c1) {
1299        v = freq[i];
1300        c2 = i;
1301      }
1302    }
1303
1304    /* Done if we've merged everything into one frequency */
1305    if (c2 < 0)
1306      break;
1307   
1308    /* Else merge the two counts/trees */
1309    freq[c1] += freq[c2];
1310    freq[c2] = 0;
1311
1312    /* Increment the codesize of everything in c1's tree branch */
1313    codesize[c1]++;
1314    while (others[c1] >= 0) {
1315      c1 = others[c1];
1316      codesize[c1]++;
1317    }
1318   
1319    others[c1] = c2;            /* chain c2 onto c1's tree branch */
1320   
1321    /* Increment the codesize of everything in c2's tree branch */
1322    codesize[c2]++;
1323    while (others[c2] >= 0) {
1324      c2 = others[c2];
1325      codesize[c2]++;
1326    }
1327  }
1328
1329  /* Now count the number of symbols of each code length */
1330  for (i = 0; i <= 256; i++) {
1331    if (codesize[i]) {
1332      /* The JPEG standard seems to think that this can't happen, */
1333      /* but I'm paranoid... */
1334      if (codesize[i] > MAX_CLEN)
1335        ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);
1336
1337      bits[codesize[i]]++;
1338    }
1339  }
1340
1341  /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure
1342   * Huffman procedure assigned any such lengths, we must adjust the coding.
1343   * Here is what the JPEG spec says about how this next bit works:
1344   * Since symbols are paired for the longest Huffman code, the symbols are
1345   * removed from this length category two at a time.  The prefix for the pair
1346   * (which is one bit shorter) is allocated to one of the pair; then,
1347   * skipping the BITS entry for that prefix length, a code word from the next
1348   * shortest nonzero BITS entry is converted into a prefix for two code words
1349   * one bit longer.
1350   */
1351 
1352  for (i = MAX_CLEN; i > 16; i--) {
1353    while (bits[i] > 0) {
1354      j = i - 2;                /* find length of new prefix to be used */
1355      while (bits[j] == 0)
1356        j--;
1357     
1358      bits[i] -= 2;             /* remove two symbols */
1359      bits[i-1]++;              /* one goes in this length */
1360      bits[j+1] += 2;           /* two new symbols in this length */
1361      bits[j]--;                /* symbol of this length is now a prefix */
1362    }
1363  }
1364
1365  /* Remove the count for the pseudo-symbol 256 from the largest codelength */
1366  while (bits[i] == 0)          /* find largest codelength still in use */
1367    i--;
1368  bits[i]--;
1369 
1370  /* Return final symbol counts (only for lengths 0..16) */
1371  MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits));
1372 
1373  /* Return a list of the symbols sorted by code length */
1374  /* It's not real clear to me why we don't need to consider the codelength
1375   * changes made above, but the JPEG spec seems to think this works.
1376   */
1377  p = 0;
1378  for (i = 1; i <= MAX_CLEN; i++) {
1379    for (j = 0; j <= 255; j++) {
1380      if (codesize[j] == i) {
1381        htbl->huffval[p] = (UINT8) j;
1382        p++;
1383      }
1384    }
1385  }
1386
1387  /* Set sent_table FALSE so updated table will be written to JPEG file. */
1388  htbl->sent_table = FALSE;
1389}
1390
1391
1392/*
1393 * Finish up a statistics-gathering pass and create the new Huffman tables.
1394 */
1395
1396METHODDEF(void)
1397finish_pass_gather (j_compress_ptr cinfo)
1398{
1399  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1400  int ci, tbl;
1401  jpeg_component_info * compptr;
1402  JHUFF_TBL **htblptr;
1403  boolean did_dc[NUM_HUFF_TBLS];
1404  boolean did_ac[NUM_HUFF_TBLS];
1405
1406  /* It's important not to apply jpeg_gen_optimal_table more than once
1407   * per table, because it clobbers the input frequency counts!
1408   */
1409  if (cinfo->progressive_mode)
1410    /* Flush out buffered data (all we care about is counting the EOB symbol) */
1411    emit_eobrun(entropy);
1412
1413  MEMZERO(did_dc, SIZEOF(did_dc));
1414  MEMZERO(did_ac, SIZEOF(did_ac));
1415
1416  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1417    compptr = cinfo->cur_comp_info[ci];
1418    /* DC needs no table for refinement scan */
1419    if (cinfo->Ss == 0 && cinfo->Ah == 0) {
1420      tbl = compptr->dc_tbl_no;
1421      if (! did_dc[tbl]) {
1422        htblptr = & cinfo->dc_huff_tbl_ptrs[tbl];
1423        if (*htblptr == NULL)
1424          *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
1425        jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[tbl]);
1426        did_dc[tbl] = TRUE;
1427      }
1428    }
1429    /* AC needs no table when not present */
1430    if (cinfo->Se) {
1431      tbl = compptr->ac_tbl_no;
1432      if (! did_ac[tbl]) {
1433        htblptr = & cinfo->ac_huff_tbl_ptrs[tbl];
1434        if (*htblptr == NULL)
1435          *htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
1436        jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[tbl]);
1437        did_ac[tbl] = TRUE;
1438      }
1439    }
1440  }
1441}
1442
1443
1444/*
1445 * Initialize for a Huffman-compressed scan.
1446 * If gather_statistics is TRUE, we do not output anything during the scan,
1447 * just count the Huffman symbols used and generate Huffman code tables.
1448 */
1449
1450METHODDEF(void)
1451start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics)
1452{
1453  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
1454  int ci, tbl;
1455  jpeg_component_info * compptr;
1456
1457  if (gather_statistics)
1458    entropy->pub.finish_pass = finish_pass_gather;
1459  else
1460    entropy->pub.finish_pass = finish_pass_huff;
1461
1462  if (cinfo->progressive_mode) {
1463    entropy->cinfo = cinfo;
1464    entropy->gather_statistics = gather_statistics;
1465
1466    /* We assume jcmaster.c already validated the scan parameters. */
1467
1468    /* Select execution routine */
1469    if (cinfo->Ah == 0) {
1470      if (cinfo->Ss == 0)
1471        entropy->pub.encode_mcu = encode_mcu_DC_first;
1472      else
1473        entropy->pub.encode_mcu = encode_mcu_AC_first;
1474    } else {
1475      if (cinfo->Ss == 0)
1476        entropy->pub.encode_mcu = encode_mcu_DC_refine;
1477      else {
1478        entropy->pub.encode_mcu = encode_mcu_AC_refine;
1479        /* AC refinement needs a correction bit buffer */
1480        if (entropy->bit_buffer == NULL)
1481          entropy->bit_buffer = (char *)
1482            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1483                                        MAX_CORR_BITS * SIZEOF(char));
1484      }
1485    }
1486
1487    /* Initialize AC stuff */
1488    entropy->ac_tbl_no = cinfo->cur_comp_info[0]->ac_tbl_no;
1489    entropy->EOBRUN = 0;
1490    entropy->BE = 0;
1491  } else {
1492    if (gather_statistics)
1493      entropy->pub.encode_mcu = encode_mcu_gather;
1494    else
1495      entropy->pub.encode_mcu = encode_mcu_huff;
1496  }
1497
1498  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
1499    compptr = cinfo->cur_comp_info[ci];
1500    /* DC needs no table for refinement scan */
1501    if (cinfo->Ss == 0 && cinfo->Ah == 0) {
1502      tbl = compptr->dc_tbl_no;
1503      if (gather_statistics) {
1504        /* Check for invalid table index */
1505        /* (make_c_derived_tbl does this in the other path) */
1506        if (tbl < 0 || tbl >= NUM_HUFF_TBLS)
1507          ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tbl);
1508        /* Allocate and zero the statistics tables */
1509        /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
1510        if (entropy->dc_count_ptrs[tbl] == NULL)
1511          entropy->dc_count_ptrs[tbl] = (long *)
1512            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1513                                        257 * SIZEOF(long));
1514        MEMZERO(entropy->dc_count_ptrs[tbl], 257 * SIZEOF(long));
1515      } else {
1516        /* Compute derived values for Huffman tables */
1517        /* We may do this more than once for a table, but it's not expensive */
1518        jpeg_make_c_derived_tbl(cinfo, TRUE, tbl,
1519                                & entropy->dc_derived_tbls[tbl]);
1520      }
1521      /* Initialize DC predictions to 0 */
1522      entropy->saved.last_dc_val[ci] = 0;
1523    }
1524    /* AC needs no table when not present */
1525    if (cinfo->Se) {
1526      tbl = compptr->ac_tbl_no;
1527      if (gather_statistics) {
1528        if (tbl < 0 || tbl >= NUM_HUFF_TBLS)
1529          ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tbl);
1530        if (entropy->ac_count_ptrs[tbl] == NULL)
1531          entropy->ac_count_ptrs[tbl] = (long *)
1532            (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1533                                        257 * SIZEOF(long));
1534        MEMZERO(entropy->ac_count_ptrs[tbl], 257 * SIZEOF(long));
1535      } else {
1536        jpeg_make_c_derived_tbl(cinfo, FALSE, tbl,
1537                                & entropy->ac_derived_tbls[tbl]);
1538      }
1539    }
1540  }
1541
1542  /* Initialize bit buffer to empty */
1543  entropy->saved.put_buffer = 0;
1544  entropy->saved.put_bits = 0;
1545
1546  /* Initialize restart stuff */
1547  entropy->restarts_to_go = cinfo->restart_interval;
1548  entropy->next_restart_num = 0;
1549}
1550
1551
1552/*
1553 * Module initialization routine for Huffman entropy encoding.
1554 */
1555
1556GLOBAL(void)
1557jinit_huff_encoder (j_compress_ptr cinfo)
1558{
1559  huff_entropy_ptr entropy;
1560  int i;
1561
1562  entropy = (huff_entropy_ptr)
1563    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
1564                                SIZEOF(huff_entropy_encoder));
1565  cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;
1566  entropy->pub.start_pass = start_pass_huff;
1567
1568  /* Mark tables unallocated */
1569  for (i = 0; i < NUM_HUFF_TBLS; i++) {
1570    entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
1571    entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
1572  }
1573
1574  if (cinfo->progressive_mode)
1575    entropy->bit_buffer = NULL; /* needed only in AC refinement scan */
1576}
Note: See TracBrowser for help on using the repository browser.