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1
/*
2
 * jchuff.c
3
 *
4
 * Copyright (C) 1991-1997, Thomas G. Lane.
5
 * This file is part of the Independent JPEG Group's software.
6
 * For conditions of distribution and use, see the accompanying README file.
7
 *
8
 * This file contains Huffman entropy encoding routines.
9
 *
10
 * Much of the complexity here has to do with supporting output suspension.
11
 * If the data destination module demands suspension, we want to be able to
12
 * back up to the start of the current MCU.  To do this, we copy state
13
 * variables into local working storage, and update them back to the
14
 * permanent JPEG objects only upon successful completion of an MCU.
15
 */
16

17
#define JPEG_INTERNALS
18
#include "jinclude.h"
19
#include "jpeglib.h"
20
#include "jchuff.h"		/* Declarations shared with jcphuff.c */
21

22

23
/* Expanded entropy encoder object for Huffman encoding.
24
 *
25
 * The savable_state subrecord contains fields that change within an MCU,
26
 * but must not be updated permanently until we complete the MCU.
27
 */
28

29
typedef struct {
30
  INT32 put_buffer;		/* current bit-accumulation buffer */
31
  int put_bits;			/* # of bits now in it */
32
  int last_dc_val[MAX_COMPS_IN_SCAN]; /* last DC coef for each component */
33
} savable_state;
34

35
/* This macro is to work around compilers with missing or broken
36
 * structure assignment.  You'll need to fix this code if you have
37
 * such a compiler and you change MAX_COMPS_IN_SCAN.
38
 */
39

40
#ifndef NO_STRUCT_ASSIGN
41
#define ASSIGN_STATE(dest,src)  ((dest) = (src))
42
#else
43
#if MAX_COMPS_IN_SCAN == 4
44
#define ASSIGN_STATE(dest,src)  \
45
	((dest).put_buffer = (src).put_buffer, \
46
	 (dest).put_bits = (src).put_bits, \
47
	 (dest).last_dc_val[0] = (src).last_dc_val[0], \
48
	 (dest).last_dc_val[1] = (src).last_dc_val[1], \
49
	 (dest).last_dc_val[2] = (src).last_dc_val[2], \
50
	 (dest).last_dc_val[3] = (src).last_dc_val[3])
51
#endif
52
#endif
53

54

55
typedef struct {
56
  struct jpeg_entropy_encoder pub; /* public fields */
57

58
  savable_state saved;		/* Bit buffer & DC state at start of MCU */
59

60
  /* These fields are NOT loaded into local working state. */
61
  unsigned int restarts_to_go;	/* MCUs left in this restart interval */
62
  int next_restart_num;		/* next restart number to write (0-7) */
63

64
  /* Pointers to derived tables (these workspaces have image lifespan) */
65
  c_derived_tbl * dc_derived_tbls[NUM_HUFF_TBLS];
66
  c_derived_tbl * ac_derived_tbls[NUM_HUFF_TBLS];
67

68
#ifdef ENTROPY_OPT_SUPPORTED	/* Statistics tables for optimization */
69
  long * dc_count_ptrs[NUM_HUFF_TBLS];
70
  long * ac_count_ptrs[NUM_HUFF_TBLS];
71
#endif
72
} huff_entropy_encoder;
73

74
typedef huff_entropy_encoder * huff_entropy_ptr;
75

76
/* Working state while writing an MCU.
77
 * This struct contains all the fields that are needed by subroutines.
78
 */
79

80
typedef struct {
81
  JOCTET * next_output_byte;	/* => next byte to write in buffer */
82
  size_t free_in_buffer;	/* # of byte spaces remaining in buffer */
83
  savable_state cur;		/* Current bit buffer & DC state */
84
  j_compress_ptr cinfo;		/* dump_buffer needs access to this */
85
} working_state;
86

87

88
/* Forward declarations */
89
METHODDEF(boolean) encode_mcu_huff JPP((j_compress_ptr cinfo,
90
					JBLOCKROW *MCU_data));
91
METHODDEF(void) finish_pass_huff JPP((j_compress_ptr cinfo));
92
#ifdef ENTROPY_OPT_SUPPORTED
93
METHODDEF(boolean) encode_mcu_gather JPP((j_compress_ptr cinfo,
94
					  JBLOCKROW *MCU_data));
95
METHODDEF(void) finish_pass_gather JPP((j_compress_ptr cinfo));
96
#endif
97

98

99
/*
100
 * Initialize for a Huffman-compressed scan.
101
 * If gather_statistics is TRUE, we do not output anything during the scan,
102
 * just count the Huffman symbols used and generate Huffman code tables.
103
 */
104

105
METHODDEF(void)
106
start_pass_huff (j_compress_ptr cinfo, boolean gather_statistics)
107
{
108
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
109
  int ci, dctbl, actbl;
110
  jpeg_component_info * compptr;
111

112
  if (gather_statistics) {
113
#ifdef ENTROPY_OPT_SUPPORTED
114
    entropy->pub.encode_mcu = encode_mcu_gather;
115
    entropy->pub.finish_pass = finish_pass_gather;
116
#else
117
    ERREXIT(cinfo, JERR_NOT_COMPILED);
118
#endif
119
  } else {
120
    entropy->pub.encode_mcu = encode_mcu_huff;
121
    entropy->pub.finish_pass = finish_pass_huff;
122
  }
123

124
  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
125
    compptr = cinfo->cur_comp_info[ci];
126
    dctbl = compptr->dc_tbl_no;
127
    actbl = compptr->ac_tbl_no;
128
    if (gather_statistics) {
129
#ifdef ENTROPY_OPT_SUPPORTED
130
      /* Check for invalid table indexes */
131
      /* (make_c_derived_tbl does this in the other path) */
132
      if (dctbl < 0 || dctbl >= NUM_HUFF_TBLS)
133
	ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, dctbl);
134
      if (actbl < 0 || actbl >= NUM_HUFF_TBLS)
135
	ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, actbl);
136
      /* Allocate and zero the statistics tables */
137
      /* Note that jpeg_gen_optimal_table expects 257 entries in each table! */
138
      if (entropy->dc_count_ptrs[dctbl] == NULL)
139
	entropy->dc_count_ptrs[dctbl] = (long *)
140
	  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
141
				      257 * SIZEOF(long));
142
      MEMZERO(entropy->dc_count_ptrs[dctbl], 257 * SIZEOF(long));
143
      if (entropy->ac_count_ptrs[actbl] == NULL)
144
	entropy->ac_count_ptrs[actbl] = (long *)
145
	  (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
146
				      257 * SIZEOF(long));
147
      MEMZERO(entropy->ac_count_ptrs[actbl], 257 * SIZEOF(long));
148
#endif
149
    } else {
150
      /* Compute derived values for Huffman tables */
151
      /* We may do this more than once for a table, but it's not expensive */
152
      jpeg_make_c_derived_tbl(cinfo, TRUE, dctbl,
153
			      & entropy->dc_derived_tbls[dctbl]);
154
      jpeg_make_c_derived_tbl(cinfo, FALSE, actbl,
155
			      & entropy->ac_derived_tbls[actbl]);
156
    }
157
    /* Initialize DC predictions to 0 */
158
    entropy->saved.last_dc_val[ci] = 0;
159
  }
160

161
  /* Initialize bit buffer to empty */
162
  entropy->saved.put_buffer = 0;
163
  entropy->saved.put_bits = 0;
164

165
  /* Initialize restart stuff */
166
  entropy->restarts_to_go = cinfo->restart_interval;
167
  entropy->next_restart_num = 0;
168
}
169

170

171
/*
172
 * Compute the derived values for a Huffman table.
173
 * This routine also performs some validation checks on the table.
174
 *
175
 * Note this is also used by jcphuff.c.
176
 */
177

178
GLOBAL(void)
179
jpeg_make_c_derived_tbl (j_compress_ptr cinfo, boolean isDC, int tblno,
180
			 c_derived_tbl ** pdtbl)
181
{
182
  JHUFF_TBL *htbl;
183
  c_derived_tbl *dtbl;
184
  int p, i, l, lastp, si, maxsymbol;
185
  char huffsize[257];
186
  unsigned int huffcode[257];
187
  unsigned int code;
188

189
  /* Note that huffsize[] and huffcode[] are filled in code-length order,
190
   * paralleling the order of the symbols themselves in htbl->huffval[].
191
   */
192

193
  /* Find the input Huffman table */
194
  if (tblno < 0 || tblno >= NUM_HUFF_TBLS)
195
    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
196
  htbl =
197
    isDC ? cinfo->dc_huff_tbl_ptrs[tblno] : cinfo->ac_huff_tbl_ptrs[tblno];
198
  if (htbl == NULL)
199
    ERREXIT1(cinfo, JERR_NO_HUFF_TABLE, tblno);
200

201
  /* Allocate a workspace if we haven't already done so. */
202
  if (*pdtbl == NULL)
203
    *pdtbl = (c_derived_tbl *)
204
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
205
				  SIZEOF(c_derived_tbl));
206
  dtbl = *pdtbl;
207
  
208
  /* Figure C.1: make table of Huffman code length for each symbol */
209

210
  p = 0;
211
  for (l = 1; l <= 16; l++) {
212
    i = (int) htbl->bits[l];
213
    if (i < 0 || p + i > 256)	/* protect against table overrun */
214
      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
215
    while (i--)
216
      huffsize[p++] = (char) l;
217
  }
218
  huffsize[p] = 0;
219
  lastp = p;
220
  
221
  /* Figure C.2: generate the codes themselves */
222
  /* We also validate that the counts represent a legal Huffman code tree. */
223

224
  code = 0;
225
  si = huffsize[0];
226
  p = 0;
227
  while (huffsize[p]) {
228
    while (((int) huffsize[p]) == si) {
229
      huffcode[p++] = code;
230
      code++;
231
    }
232
    /* code is now 1 more than the last code used for codelength si; but
233
     * it must still fit in si bits, since no code is allowed to be all ones.
234
     */
235
    if (((INT32) code) >= (((INT32) 1) << si))
236
      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
237
    code <<= 1;
238
    si++;
239
  }
240
  
241
  /* Figure C.3: generate encoding tables */
242
  /* These are code and size indexed by symbol value */
243

244
  /* Set all codeless symbols to have code length 0;
245
   * this lets us detect duplicate VAL entries here, and later
246
   * allows emit_bits to detect any attempt to emit such symbols.
247
   */
248
  MEMZERO(dtbl->ehufsi, SIZEOF(dtbl->ehufsi));
249

250
  /* This is also a convenient place to check for out-of-range
251
   * and duplicated VAL entries.  We allow 0..255 for AC symbols
252
   * but only 0..15 for DC.  (We could constrain them further
253
   * based on data depth and mode, but this seems enough.)
254
   */
255
  maxsymbol = isDC ? 15 : 255;
256

257
  for (p = 0; p < lastp; p++) {
258
    i = htbl->huffval[p];
259
    if (i < 0 || i > maxsymbol || dtbl->ehufsi[i])
260
      ERREXIT(cinfo, JERR_BAD_HUFF_TABLE);
261
    dtbl->ehufco[i] = huffcode[p];
262
    dtbl->ehufsi[i] = huffsize[p];
263
  }
264
}
265

266

267
/* Outputting bytes to the file */
268

269
/* Emit a byte, taking 'action' if must suspend. */
270
#define emit_byte(state,val,action)  \
271
	{ *(state)->next_output_byte++ = (JOCTET) (val);  \
272
	  if (--(state)->free_in_buffer == 0)  \
273
	    if (! dump_buffer(state))  \
274
	      { action; } }
275

276

277
LOCAL(boolean)
278
dump_buffer (working_state * state)
279
/* Empty the output buffer; return TRUE if successful, FALSE if must suspend */
280
{
281
  struct jpeg_destination_mgr * dest = state->cinfo->dest;
282

283
  if (! (*dest->empty_output_buffer) (state->cinfo))
284
    return FALSE;
285
  /* After a successful buffer dump, must reset buffer pointers */
286
  state->next_output_byte = dest->next_output_byte;
287
  state->free_in_buffer = dest->free_in_buffer;
288
  return TRUE;
289
}
290

291

292
/* Outputting bits to the file */
293

294
/* Only the right 24 bits of put_buffer are used; the valid bits are
295
 * left-justified in this part.  At most 16 bits can be passed to emit_bits
296
 * in one call, and we never retain more than 7 bits in put_buffer
297
 * between calls, so 24 bits are sufficient.
298
 */
299

300
INLINE
301
LOCAL(boolean)
302
emit_bits (working_state * state, unsigned int code, int size)
303
/* Emit some bits; return TRUE if successful, FALSE if must suspend */
304
{
305
  /* This routine is heavily used, so it's worth coding tightly. */
306
  register INT32 put_buffer = (INT32) code;
307
  register int put_bits = state->cur.put_bits;
308

309
  /* if size is 0, caller used an invalid Huffman table entry */
310
  if (size == 0)
311
    ERREXIT(state->cinfo, JERR_HUFF_MISSING_CODE);
312

313
  put_buffer &= (((INT32) 1)<<size) - 1; /* mask off any extra bits in code */
314
  
315
  put_bits += size;		/* new number of bits in buffer */
316
  
317
  put_buffer <<= 24 - put_bits; /* align incoming bits */
318

319
  put_buffer |= state->cur.put_buffer; /* and merge with old buffer contents */
320
  
321
  while (put_bits >= 8) {
322
    int c = (int) ((put_buffer >> 16) & 0xFF);
323
    
324
    emit_byte(state, c, return FALSE);
325
    if (c == 0xFF) {		/* need to stuff a zero byte? */
326
      emit_byte(state, 0, return FALSE);
327
    }
328
    put_buffer <<= 8;
329
    put_bits -= 8;
330
  }
331

332
  state->cur.put_buffer = put_buffer; /* update state variables */
333
  state->cur.put_bits = put_bits;
334

335
  return TRUE;
336
}
337

338

339
LOCAL(boolean)
340
flush_bits (working_state * state)
341
{
342
  if (! emit_bits(state, 0x7F, 7)) /* fill any partial byte with ones */
343
    return FALSE;
344
  state->cur.put_buffer = 0;	/* and reset bit-buffer to empty */
345
  state->cur.put_bits = 0;
346
  return TRUE;
347
}
348

349

350
/* Encode a single block's worth of coefficients */
351

352
LOCAL(boolean)
353
encode_one_block (working_state * state, JCOEFPTR block, int last_dc_val,
354
		  c_derived_tbl *dctbl, c_derived_tbl *actbl)
355
{
356
  register int temp, temp2;
357
  register int nbits;
358
  register int k, r, i;
359
  
360
  /* Encode the DC coefficient difference per section F.1.2.1 */
361
  
362
  temp = temp2 = block[0] - last_dc_val;
363

364
  if (temp < 0) {
365
    temp = -temp;		/* temp is abs value of input */
366
    /* For a negative input, want temp2 = bitwise complement of abs(input) */
367
    /* This code assumes we are on a two's complement machine */
368
    temp2--;
369
  }
370
  
371
  /* Find the number of bits needed for the magnitude of the coefficient */
372
  nbits = 0;
373
  while (temp) {
374
    nbits++;
375
    temp >>= 1;
376
  }
377
  /* Check for out-of-range coefficient values.
378
   * Since we're encoding a difference, the range limit is twice as much.
379
   */
380
  if (nbits > MAX_COEF_BITS+1)
381
    ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
382
  
383
  /* Emit the Huffman-coded symbol for the number of bits */
384
  if (! emit_bits(state, dctbl->ehufco[nbits], dctbl->ehufsi[nbits]))
385
    return FALSE;
386

387
  /* Emit that number of bits of the value, if positive, */
388
  /* or the complement of its magnitude, if negative. */
389
  if (nbits)			/* emit_bits rejects calls with size 0 */
390
    if (! emit_bits(state, (unsigned int) temp2, nbits))
391
      return FALSE;
392

393
  /* Encode the AC coefficients per section F.1.2.2 */
394
  
395
  r = 0;			/* r = run length of zeros */
396
  
397
  for (k = 1; k < DCTSIZE2; k++) {
398
    if ((temp = block[jpeg_natural_order[k]]) == 0) {
399
      r++;
400
    } else {
401
      /* if run length > 15, must emit special run-length-16 codes (0xF0) */
402
      while (r > 15) {
403
	if (! emit_bits(state, actbl->ehufco[0xF0], actbl->ehufsi[0xF0]))
404
	  return FALSE;
405
	r -= 16;
406
      }
407

408
      temp2 = temp;
409
      if (temp < 0) {
410
	temp = -temp;		/* temp is abs value of input */
411
	/* This code assumes we are on a two's complement machine */
412
	temp2--;
413
      }
414
      
415
      /* Find the number of bits needed for the magnitude of the coefficient */
416
      nbits = 1;		/* there must be at least one 1 bit */
417
      while ((temp >>= 1))
418
	nbits++;
419
      /* Check for out-of-range coefficient values */
420
      if (nbits > MAX_COEF_BITS)
421
	ERREXIT(state->cinfo, JERR_BAD_DCT_COEF);
422
      
423
      /* Emit Huffman symbol for run length / number of bits */
424
      i = (r << 4) + nbits;
425
      if (! emit_bits(state, actbl->ehufco[i], actbl->ehufsi[i]))
426
	return FALSE;
427

428
      /* Emit that number of bits of the value, if positive, */
429
      /* or the complement of its magnitude, if negative. */
430
      if (! emit_bits(state, (unsigned int) temp2, nbits))
431
	return FALSE;
432
      
433
      r = 0;
434
    }
435
  }
436

437
  /* If the last coef(s) were zero, emit an end-of-block code */
438
  if (r > 0)
439
    if (! emit_bits(state, actbl->ehufco[0], actbl->ehufsi[0]))
440
      return FALSE;
441

442
  return TRUE;
443
}
444

445

446
/*
447
 * Emit a restart marker & resynchronize predictions.
448
 */
449

450
LOCAL(boolean)
451
emit_restart (working_state * state, int restart_num)
452
{
453
  int ci;
454

455
  if (! flush_bits(state))
456
    return FALSE;
457

458
  emit_byte(state, 0xFF, return FALSE);
459
  emit_byte(state, JPEG_RST0 + restart_num, return FALSE);
460

461
  /* Re-initialize DC predictions to 0 */
462
  for (ci = 0; ci < state->cinfo->comps_in_scan; ci++)
463
    state->cur.last_dc_val[ci] = 0;
464

465
  /* The restart counter is not updated until we successfully write the MCU. */
466

467
  return TRUE;
468
}
469

470

471
/*
472
 * Encode and output one MCU's worth of Huffman-compressed coefficients.
473
 */
474

475
METHODDEF(boolean)
476
encode_mcu_huff (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
477
{
478
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
479
  working_state state;
480
  int blkn, ci;
481
  jpeg_component_info * compptr;
482

483
  /* Load up working state */
484
  state.next_output_byte = cinfo->dest->next_output_byte;
485
  state.free_in_buffer = cinfo->dest->free_in_buffer;
486
  ASSIGN_STATE(state.cur, entropy->saved);
487
  state.cinfo = cinfo;
488

489
  /* Emit restart marker if needed */
490
  if (cinfo->restart_interval) {
491
    if (entropy->restarts_to_go == 0)
492
      if (! emit_restart(&state, entropy->next_restart_num))
493
	return FALSE;
494
  }
495

496
  /* Encode the MCU data blocks */
497
  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
498
    ci = cinfo->MCU_membership[blkn];
499
    compptr = cinfo->cur_comp_info[ci];
500
    if (! encode_one_block(&state,
501
			   MCU_data[blkn][0], state.cur.last_dc_val[ci],
502
			   entropy->dc_derived_tbls[compptr->dc_tbl_no],
503
			   entropy->ac_derived_tbls[compptr->ac_tbl_no]))
504
      return FALSE;
505
    /* Update last_dc_val */
506
    state.cur.last_dc_val[ci] = MCU_data[blkn][0][0];
507
  }
508

509
  /* Completed MCU, so update state */
510
  cinfo->dest->next_output_byte = state.next_output_byte;
511
  cinfo->dest->free_in_buffer = state.free_in_buffer;
512
  ASSIGN_STATE(entropy->saved, state.cur);
513

514
  /* Update restart-interval state too */
515
  if (cinfo->restart_interval) {
516
    if (entropy->restarts_to_go == 0) {
517
      entropy->restarts_to_go = cinfo->restart_interval;
518
      entropy->next_restart_num++;
519
      entropy->next_restart_num &= 7;
520
    }
521
    entropy->restarts_to_go--;
522
  }
523

524
  return TRUE;
525
}
526

527

528
/*
529
 * Finish up at the end of a Huffman-compressed scan.
530
 */
531

532
METHODDEF(void)
533
finish_pass_huff (j_compress_ptr cinfo)
534
{
535
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
536
  working_state state;
537

538
  /* Load up working state ... flush_bits needs it */
539
  state.next_output_byte = cinfo->dest->next_output_byte;
540
  state.free_in_buffer = cinfo->dest->free_in_buffer;
541
  ASSIGN_STATE(state.cur, entropy->saved);
542
  state.cinfo = cinfo;
543

544
  /* Flush out the last data */
545
  if (! flush_bits(&state))
546
    ERREXIT(cinfo, JERR_CANT_SUSPEND);
547

548
  /* Update state */
549
  cinfo->dest->next_output_byte = state.next_output_byte;
550
  cinfo->dest->free_in_buffer = state.free_in_buffer;
551
  ASSIGN_STATE(entropy->saved, state.cur);
552
}
553

554

555
/*
556
 * Huffman coding optimization.
557
 *
558
 * We first scan the supplied data and count the number of uses of each symbol
559
 * that is to be Huffman-coded. (This process MUST agree with the code above.)
560
 * Then we build a Huffman coding tree for the observed counts.
561
 * Symbols which are not needed at all for the particular image are not
562
 * assigned any code, which saves space in the DHT marker as well as in
563
 * the compressed data.
564
 */
565

566
#ifdef ENTROPY_OPT_SUPPORTED
567

568

569
/* Process a single block's worth of coefficients */
570

571
LOCAL(void)
572
htest_one_block (j_compress_ptr cinfo, JCOEFPTR block, int last_dc_val,
573
		 long dc_counts[], long ac_counts[])
574
{
575
  register int temp;
576
  register int nbits;
577
  register int k, r;
578
  
579
  /* Encode the DC coefficient difference per section F.1.2.1 */
580
  
581
  temp = block[0] - last_dc_val;
582
  if (temp < 0)
583
    temp = -temp;
584
  
585
  /* Find the number of bits needed for the magnitude of the coefficient */
586
  nbits = 0;
587
  while (temp) {
588
    nbits++;
589
    temp >>= 1;
590
  }
591
  /* Check for out-of-range coefficient values.
592
   * Since we're encoding a difference, the range limit is twice as much.
593
   */
594
  if (nbits > MAX_COEF_BITS+1)
595
    ERREXIT(cinfo, JERR_BAD_DCT_COEF);
596

597
  /* Count the Huffman symbol for the number of bits */
598
  dc_counts[nbits]++;
599
  
600
  /* Encode the AC coefficients per section F.1.2.2 */
601
  
602
  r = 0;			/* r = run length of zeros */
603
  
604
  for (k = 1; k < DCTSIZE2; k++) {
605
    if ((temp = block[jpeg_natural_order[k]]) == 0) {
606
      r++;
607
    } else {
608
      /* if run length > 15, must emit special run-length-16 codes (0xF0) */
609
      while (r > 15) {
610
	ac_counts[0xF0]++;
611
	r -= 16;
612
      }
613
      
614
      /* Find the number of bits needed for the magnitude of the coefficient */
615
      if (temp < 0)
616
	temp = -temp;
617
      
618
      /* Find the number of bits needed for the magnitude of the coefficient */
619
      nbits = 1;		/* there must be at least one 1 bit */
620
      while ((temp >>= 1))
621
	nbits++;
622
      /* Check for out-of-range coefficient values */
623
      if (nbits > MAX_COEF_BITS)
624
	ERREXIT(cinfo, JERR_BAD_DCT_COEF);
625
      
626
      /* Count Huffman symbol for run length / number of bits */
627
      ac_counts[(r << 4) + nbits]++;
628
      
629
      r = 0;
630
    }
631
  }
632

633
  /* If the last coef(s) were zero, emit an end-of-block code */
634
  if (r > 0)
635
    ac_counts[0]++;
636
}
637

638

639
/*
640
 * Trial-encode one MCU's worth of Huffman-compressed coefficients.
641
 * No data is actually output, so no suspension return is possible.
642
 */
643

644
METHODDEF(boolean)
645
encode_mcu_gather (j_compress_ptr cinfo, JBLOCKROW *MCU_data)
646
{
647
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
648
  int blkn, ci;
649
  jpeg_component_info * compptr;
650

651
  /* Take care of restart intervals if needed */
652
  if (cinfo->restart_interval) {
653
    if (entropy->restarts_to_go == 0) {
654
      /* Re-initialize DC predictions to 0 */
655
      for (ci = 0; ci < cinfo->comps_in_scan; ci++)
656
	entropy->saved.last_dc_val[ci] = 0;
657
      /* Update restart state */
658
      entropy->restarts_to_go = cinfo->restart_interval;
659
    }
660
    entropy->restarts_to_go--;
661
  }
662

663
  for (blkn = 0; blkn < cinfo->blocks_in_MCU; blkn++) {
664
    ci = cinfo->MCU_membership[blkn];
665
    compptr = cinfo->cur_comp_info[ci];
666
    htest_one_block(cinfo, MCU_data[blkn][0], entropy->saved.last_dc_val[ci],
667
		    entropy->dc_count_ptrs[compptr->dc_tbl_no],
668
		    entropy->ac_count_ptrs[compptr->ac_tbl_no]);
669
    entropy->saved.last_dc_val[ci] = MCU_data[blkn][0][0];
670
  }
671

672
  return TRUE;
673
}
674

675

676
/*
677
 * Generate the best Huffman code table for the given counts, fill htbl.
678
 * Note this is also used by jcphuff.c.
679
 *
680
 * The JPEG standard requires that no symbol be assigned a codeword of all
681
 * one bits (so that padding bits added at the end of a compressed segment
682
 * can't look like a valid code).  Because of the canonical ordering of
683
 * codewords, this just means that there must be an unused slot in the
684
 * longest codeword length category.  Section K.2 of the JPEG spec suggests
685
 * reserving such a slot by pretending that symbol 256 is a valid symbol
686
 * with count 1.  In theory that's not optimal; giving it count zero but
687
 * including it in the symbol set anyway should give a better Huffman code.
688
 * But the theoretically better code actually seems to come out worse in
689
 * practice, because it produces more all-ones bytes (which incur stuffed
690
 * zero bytes in the final file).  In any case the difference is tiny.
691
 *
692
 * The JPEG standard requires Huffman codes to be no more than 16 bits long.
693
 * If some symbols have a very small but nonzero probability, the Huffman tree
694
 * must be adjusted to meet the code length restriction.  We currently use
695
 * the adjustment method suggested in JPEG section K.2.  This method is *not*
696
 * optimal; it may not choose the best possible limited-length code.  But
697
 * typically only very-low-frequency symbols will be given less-than-optimal
698
 * lengths, so the code is almost optimal.  Experimental comparisons against
699
 * an optimal limited-length-code algorithm indicate that the difference is
700
 * microscopic --- usually less than a hundredth of a percent of total size.
701
 * So the extra complexity of an optimal algorithm doesn't seem worthwhile.
702
 */
703

704
GLOBAL(void)
705
jpeg_gen_optimal_table (j_compress_ptr cinfo, JHUFF_TBL * htbl, long freq[])
706
{
707
#define MAX_CLEN 32		/* assumed maximum initial code length */
708
  UINT8 bits[MAX_CLEN+1];	/* bits[k] = # of symbols with code length k */
709
  int codesize[257];		/* codesize[k] = code length of symbol k */
710
  int others[257];		/* next symbol in current branch of tree */
711
  int c1, c2;
712
  int p, i, j;
713
  long v;
714

715
  /* This algorithm is explained in section K.2 of the JPEG standard */
716

717
  MEMZERO(bits, SIZEOF(bits));
718
  MEMZERO(codesize, SIZEOF(codesize));
719
  for (i = 0; i < 257; i++)
720
    others[i] = -1;		/* init links to empty */
721
  
722
  freq[256] = 1;		/* make sure 256 has a nonzero count */
723
  /* Including the pseudo-symbol 256 in the Huffman procedure guarantees
724
   * that no real symbol is given code-value of all ones, because 256
725
   * will be placed last in the largest codeword category.
726
   */
727

728
  /* Huffman's basic algorithm to assign optimal code lengths to symbols */
729

730
  for (;;) {
731
    /* Find the smallest nonzero frequency, set c1 = its symbol */
732
    /* In case of ties, take the larger symbol number */
733
    c1 = -1;
734
    v = 1000000000L;
735
    for (i = 0; i <= 256; i++) {
736
      if (freq[i] && freq[i] <= v) {
737
	v = freq[i];
738
	c1 = i;
739
      }
740
    }
741

742
    /* Find the next smallest nonzero frequency, set c2 = its symbol */
743
    /* In case of ties, take the larger symbol number */
744
    c2 = -1;
745
    v = 1000000000L;
746
    for (i = 0; i <= 256; i++) {
747
      if (freq[i] && freq[i] <= v && i != c1) {
748
	v = freq[i];
749
	c2 = i;
750
      }
751
    }
752

753
    /* Done if we've merged everything into one frequency */
754
    if (c2 < 0)
755
      break;
756
    
757
    /* Else merge the two counts/trees */
758
    freq[c1] += freq[c2];
759
    freq[c2] = 0;
760

761
    /* Increment the codesize of everything in c1's tree branch */
762
    codesize[c1]++;
763
    while (others[c1] >= 0) {
764
      c1 = others[c1];
765
      codesize[c1]++;
766
    }
767
    
768
    others[c1] = c2;		/* chain c2 onto c1's tree branch */
769
    
770
    /* Increment the codesize of everything in c2's tree branch */
771
    codesize[c2]++;
772
    while (others[c2] >= 0) {
773
      c2 = others[c2];
774
      codesize[c2]++;
775
    }
776
  }
777

778
  /* Now count the number of symbols of each code length */
779
  for (i = 0; i <= 256; i++) {
780
    if (codesize[i]) {
781
      /* The JPEG standard seems to think that this can't happen, */
782
      /* but I'm paranoid... */
783
      if (codesize[i] > MAX_CLEN)
784
	ERREXIT(cinfo, JERR_HUFF_CLEN_OVERFLOW);
785

786
      bits[codesize[i]]++;
787
    }
788
  }
789

790
  /* JPEG doesn't allow symbols with code lengths over 16 bits, so if the pure
791
   * Huffman procedure assigned any such lengths, we must adjust the coding.
792
   * Here is what the JPEG spec says about how this next bit works:
793
   * Since symbols are paired for the longest Huffman code, the symbols are
794
   * removed from this length category two at a time.  The prefix for the pair
795
   * (which is one bit shorter) is allocated to one of the pair; then,
796
   * skipping the BITS entry for that prefix length, a code word from the next
797
   * shortest nonzero BITS entry is converted into a prefix for two code words
798
   * one bit longer.
799
   */
800
  
801
  for (i = MAX_CLEN; i > 16; i--) {
802
    while (bits[i] > 0) {
803
      j = i - 2;		/* find length of new prefix to be used */
804
      while (bits[j] == 0)
805
	j--;
806
      
807
      bits[i] -= 2;		/* remove two symbols */
808
      bits[i-1]++;		/* one goes in this length */
809
      bits[j+1] += 2;		/* two new symbols in this length */
810
      bits[j]--;		/* symbol of this length is now a prefix */
811
    }
812
  }
813

814
  /* Remove the count for the pseudo-symbol 256 from the largest codelength */
815
  while (bits[i] == 0)		/* find largest codelength still in use */
816
    i--;
817
  bits[i]--;
818
  
819
  /* Return final symbol counts (only for lengths 0..16) */
820
  MEMCOPY(htbl->bits, bits, SIZEOF(htbl->bits));
821
  
822
  /* Return a list of the symbols sorted by code length */
823
  /* It's not real clear to me why we don't need to consider the codelength
824
   * changes made above, but the JPEG spec seems to think this works.
825
   */
826
  p = 0;
827
  for (i = 1; i <= MAX_CLEN; i++) {
828
    for (j = 0; j <= 255; j++) {
829
      if (codesize[j] == i) {
830
	htbl->huffval[p] = (UINT8) j;
831
	p++;
832
      }
833
    }
834
  }
835

836
  /* Set sent_table FALSE so updated table will be written to JPEG file. */
837
  htbl->sent_table = FALSE;
838
}
839

840

841
/*
842
 * Finish up a statistics-gathering pass and create the new Huffman tables.
843
 */
844

845
METHODDEF(void)
846
finish_pass_gather (j_compress_ptr cinfo)
847
{
848
  huff_entropy_ptr entropy = (huff_entropy_ptr) cinfo->entropy;
849
  int ci, dctbl, actbl;
850
  jpeg_component_info * compptr;
851
  JHUFF_TBL **htblptr;
852
  boolean did_dc[NUM_HUFF_TBLS];
853
  boolean did_ac[NUM_HUFF_TBLS];
854

855
  /* It's important not to apply jpeg_gen_optimal_table more than once
856
   * per table, because it clobbers the input frequency counts!
857
   */
858
  MEMZERO(did_dc, SIZEOF(did_dc));
859
  MEMZERO(did_ac, SIZEOF(did_ac));
860

861
  for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
862
    compptr = cinfo->cur_comp_info[ci];
863
    dctbl = compptr->dc_tbl_no;
864
    actbl = compptr->ac_tbl_no;
865
    if (! did_dc[dctbl]) {
866
      htblptr = & cinfo->dc_huff_tbl_ptrs[dctbl];
867
      if (*htblptr == NULL)
868
	*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
869
      jpeg_gen_optimal_table(cinfo, *htblptr, entropy->dc_count_ptrs[dctbl]);
870
      did_dc[dctbl] = TRUE;
871
    }
872
    if (! did_ac[actbl]) {
873
      htblptr = & cinfo->ac_huff_tbl_ptrs[actbl];
874
      if (*htblptr == NULL)
875
	*htblptr = jpeg_alloc_huff_table((j_common_ptr) cinfo);
876
      jpeg_gen_optimal_table(cinfo, *htblptr, entropy->ac_count_ptrs[actbl]);
877
      did_ac[actbl] = TRUE;
878
    }
879
  }
880
}
881

882

883
#endif /* ENTROPY_OPT_SUPPORTED */
884

885

886
/*
887
 * Module initialization routine for Huffman entropy encoding.
888
 */
889

890
GLOBAL(void)
891
jinit_huff_encoder (j_compress_ptr cinfo)
892
{
893
  huff_entropy_ptr entropy;
894
  int i;
895

896
  entropy = (huff_entropy_ptr)
897
    (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
898
				SIZEOF(huff_entropy_encoder));
899
  cinfo->entropy = (struct jpeg_entropy_encoder *) entropy;
900
  entropy->pub.start_pass = start_pass_huff;
901

902
  /* Mark tables unallocated */
903
  for (i = 0; i < NUM_HUFF_TBLS; i++) {
904
    entropy->dc_derived_tbls[i] = entropy->ac_derived_tbls[i] = NULL;
905
#ifdef ENTROPY_OPT_SUPPORTED
906
    entropy->dc_count_ptrs[i] = entropy->ac_count_ptrs[i] = NULL;
907
#endif
908
  }
909
}
910

911