summaryrefslogtreecommitdiffstats
path: root/apps/codecs/libwavpack/words.c
blob: c7a8047d03cc972d282f7f9b6296746e239e99ac (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
////////////////////////////////////////////////////////////////////////////
//                           **** WAVPACK ****                            //
//                  Hybrid Lossless Wavefile Compressor                   //
//              Copyright (c) 1998 - 2004 Conifer Software.               //
//                          All Rights Reserved.                          //
////////////////////////////////////////////////////////////////////////////

// words.c

// This module provides entropy word encoding and decoding functions using
// a variation on the Rice method.  This was introduced in version 3.93
// because it allows splitting the data into a "lossy" stream and a
// "correction" stream in a very efficient manner and is therefore ideal
// for the "hybrid" mode.  For 4.0, the efficiency of this method was
// significantly improved by moving away from the normal Rice restriction of
// using powers of two for the modulus divisions and now the method can be
// used for both hybrid and pure lossless encoding.

// Samples are divided by median probabilities at 5/7 (71.43%), 10/49 (20.41%),
// and 20/343 (5.83%). Each zone has 3.5 times fewer samples than the
// previous. Using standard Rice coding on this data would result in 1.4
// bits per sample average (not counting sign bit). However, there is a
// very simple encoding that is over 99% efficient with this data and
// results in about 1.22 bits per sample.

#include "wavpack.h"

#include <string.h>

//////////////////////////////// local macros /////////////////////////////////

#define LIMIT_ONES 16   // maximum consecutive 1s sent for "div" data

// these control the time constant "slow_level" which is used for hybrid mode
// that controls bitrate as a function of residual level (HYBRID_BITRATE).
#define SLS 8
#define SLO ((1 << (SLS - 1)))

// these control the time constant of the 3 median level breakpoints
#define DIV0 128        // 5/7 of samples
#define DIV1 64         // 10/49 of samples
#define DIV2 32         // 20/343 of samples

// this macro retrieves the specified median breakpoint (without frac; min = 1)
#define GET_MED(med) (((c->median [med]) >> 4) + 1)

// These macros update the specified median breakpoints. Note that the median
// is incremented when the sample is higher than the median, else decremented.
// They are designed so that the median will never drop below 1 and the value
// is essentially stationary if there are 2 increments for every 5 decrements.

#define INC_MED0() (c->median [0] += ((c->median [0] + DIV0) / DIV0) * 5)
#define DEC_MED0() (c->median [0] -= ((c->median [0] + (DIV0-2)) / DIV0) * 2)
#define INC_MED1() (c->median [1] += ((c->median [1] + DIV1) / DIV1) * 5)
#define DEC_MED1() (c->median [1] -= ((c->median [1] + (DIV1-2)) / DIV1) * 2)
#define INC_MED2() (c->median [2] += ((c->median [2] + DIV2) / DIV2) * 5)
#define DEC_MED2() (c->median [2] -= ((c->median [2] + (DIV2-2)) / DIV2) * 2)

#define count_bits(av) ( \
 (av) < (1 << 8) ? nbits_table [av] : \
  ( \
   (av) < (1L << 16) ? nbits_table [(av) >> 8] + 8 : \
   ((av) < (1L << 24) ? nbits_table [(av) >> 16] + 16 : nbits_table [(av) >> 24] + 24) \
  ) \
)

///////////////////////////// local table storage ////////////////////////////

const char nbits_table [] = {
    0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,     // 0 - 15
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,     // 16 - 31
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,     // 32 - 47
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,     // 48 - 63
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,     // 64 - 79
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,     // 80 - 95
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,     // 96 - 111
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,     // 112 - 127
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,     // 128 - 143
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,     // 144 - 159
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,     // 160 - 175
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,     // 176 - 191
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,     // 192 - 207
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,     // 208 - 223
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,     // 224 - 239
    8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8      // 240 - 255
};

static const uchar log2_table [] = {
    0x00, 0x01, 0x03, 0x04, 0x06, 0x07, 0x09, 0x0a, 0x0b, 0x0d, 0x0e, 0x10, 0x11, 0x12, 0x14, 0x15,
    0x16, 0x18, 0x19, 0x1a, 0x1c, 0x1d, 0x1e, 0x20, 0x21, 0x22, 0x24, 0x25, 0x26, 0x28, 0x29, 0x2a,
    0x2c, 0x2d, 0x2e, 0x2f, 0x31, 0x32, 0x33, 0x34, 0x36, 0x37, 0x38, 0x39, 0x3b, 0x3c, 0x3d, 0x3e,
    0x3f, 0x41, 0x42, 0x43, 0x44, 0x45, 0x47, 0x48, 0x49, 0x4a, 0x4b, 0x4d, 0x4e, 0x4f, 0x50, 0x51,
    0x52, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x5c, 0x5d, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63,
    0x64, 0x66, 0x67, 0x68, 0x69, 0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x74, 0x75,
    0x76, 0x77, 0x78, 0x79, 0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82, 0x83, 0x84, 0x85,
    0x86, 0x87, 0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e, 0x8f, 0x90, 0x91, 0x92, 0x93, 0x94, 0x95,
    0x96, 0x97, 0x98, 0x99, 0x9a, 0x9b, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f, 0xa0, 0xa1, 0xa2, 0xa3, 0xa4,
    0xa5, 0xa6, 0xa7, 0xa8, 0xa9, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb0, 0xb1, 0xb2, 0xb2,
    0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xb9, 0xba, 0xbb, 0xbc, 0xbd, 0xbe, 0xbf, 0xc0, 0xc0,
    0xc1, 0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xcb, 0xcb, 0xcc, 0xcd, 0xce,
    0xcf, 0xd0, 0xd0, 0xd1, 0xd2, 0xd3, 0xd4, 0xd4, 0xd5, 0xd6, 0xd7, 0xd8, 0xd8, 0xd9, 0xda, 0xdb,
    0xdc, 0xdc, 0xdd, 0xde, 0xdf, 0xe0, 0xe0, 0xe1, 0xe2, 0xe3, 0xe4, 0xe4, 0xe5, 0xe6, 0xe7, 0xe7,
    0xe8, 0xe9, 0xea, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xee, 0xef, 0xf0, 0xf1, 0xf1, 0xf2, 0xf3, 0xf4,
    0xf4, 0xf5, 0xf6, 0xf7, 0xf7, 0xf8, 0xf9, 0xf9, 0xfa, 0xfb, 0xfc, 0xfc, 0xfd, 0xfe, 0xff, 0xff
};

static const uchar exp2_table [] = {
    0x00, 0x01, 0x01, 0x02, 0x03, 0x03, 0x04, 0x05, 0x06, 0x06, 0x07, 0x08, 0x08, 0x09, 0x0a, 0x0b,
    0x0b, 0x0c, 0x0d, 0x0e, 0x0e, 0x0f, 0x10, 0x10, 0x11, 0x12, 0x13, 0x13, 0x14, 0x15, 0x16, 0x16,
    0x17, 0x18, 0x19, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1d, 0x1e, 0x1f, 0x20, 0x20, 0x21, 0x22, 0x23,
    0x24, 0x24, 0x25, 0x26, 0x27, 0x28, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2c, 0x2d, 0x2e, 0x2f, 0x30,
    0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3a, 0x3b, 0x3c, 0x3d,
    0x3e, 0x3f, 0x40, 0x41, 0x41, 0x42, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x48, 0x49, 0x4a, 0x4b,
    0x4c, 0x4d, 0x4e, 0x4f, 0x50, 0x51, 0x51, 0x52, 0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a,
    0x5b, 0x5c, 0x5d, 0x5e, 0x5e, 0x5f, 0x60, 0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69,
    0x6a, 0x6b, 0x6c, 0x6d, 0x6e, 0x6f, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79,
    0x7a, 0x7b, 0x7c, 0x7d, 0x7e, 0x7f, 0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x87, 0x88, 0x89, 0x8a,
    0x8b, 0x8c, 0x8d, 0x8e, 0x8f, 0x90, 0x91, 0x92, 0x93, 0x95, 0x96, 0x97, 0x98, 0x99, 0x9a, 0x9b,
    0x9c, 0x9d, 0x9f, 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad,
    0xaf, 0xb0, 0xb1, 0xb2, 0xb3, 0xb4, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xbc, 0xbd, 0xbe, 0xbf, 0xc0,
    0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc8, 0xc9, 0xca, 0xcb, 0xcd, 0xce, 0xcf, 0xd0, 0xd2, 0xd3, 0xd4,
    0xd6, 0xd7, 0xd8, 0xd9, 0xdb, 0xdc, 0xdd, 0xde, 0xe0, 0xe1, 0xe2, 0xe4, 0xe5, 0xe6, 0xe8, 0xe9,
    0xea, 0xec, 0xed, 0xee, 0xf0, 0xf1, 0xf2, 0xf4, 0xf5, 0xf6, 0xf8, 0xf9, 0xfa, 0xfc, 0xfd, 0xff
};

static const char ones_count_table [] = {
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,6,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,7,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,6,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,5,
    0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,4,0,1,0,2,0,1,0,3,0,1,0,2,0,1,0,8
};

///////////////////////////// executable code ////////////////////////////////

void init_words (WavpackStream *wps)
{
    CLEAR (wps->w);
}

static int mylog2 (unsigned int32_t avalue);

// Read the median log2 values from the specifed metadata structure, convert
// them back to 32-bit unsigned values and store them. If length is not
// exactly correct then we flag and return an error.

int read_entropy_vars (WavpackStream *wps, WavpackMetadata *wpmd)
{
    uchar *byteptr = wpmd->data;

    if (wpmd->byte_length != ((wps->wphdr.flags & MONO_DATA) ? 6 : 12))
        return FALSE;

    wps->w.c [0].median [0] = exp2s (byteptr [0] + (byteptr [1] << 8));
    wps->w.c [0].median [1] = exp2s (byteptr [2] + (byteptr [3] << 8));
    wps->w.c [0].median [2] = exp2s (byteptr [4] + (byteptr [5] << 8));

    if (!(wps->wphdr.flags & MONO_DATA)) {
        wps->w.c [1].median [0] = exp2s (byteptr [6] + (byteptr [7] << 8));
        wps->w.c [1].median [1] = exp2s (byteptr [8] + (byteptr [9] << 8));
        wps->w.c [1].median [2] = exp2s (byteptr [10] + (byteptr [11] << 8));
    }

    return TRUE;
}

// Allocates the correct space in the metadata structure and writes the
// current median values to it. Values are converted from 32-bit unsigned
// to our internal 16-bit mylog2 values, and read_entropy_vars () is called
// to read the values back because we must compensate for the loss through
// the log function.

void write_entropy_vars (WavpackStream *wps, WavpackMetadata *wpmd)
{
    uchar *byteptr;
    int temp;

    byteptr = wpmd->data = wpmd->temp_data;
    wpmd->id = ID_ENTROPY_VARS;

    *byteptr++ = temp = mylog2 (wps->w.c [0].median [0]);
    *byteptr++ = temp >> 8;
    *byteptr++ = temp = mylog2 (wps->w.c [0].median [1]);
    *byteptr++ = temp >> 8;
    *byteptr++ = temp = mylog2 (wps->w.c [0].median [2]);
    *byteptr++ = temp >> 8;

    if (!(wps->wphdr.flags & MONO_FLAG)) {
        *byteptr++ = temp = mylog2 (wps->w.c [1].median [0]);
        *byteptr++ = temp >> 8;
        *byteptr++ = temp = mylog2 (wps->w.c [1].median [1]);
        *byteptr++ = temp >> 8;
        *byteptr++ = temp = mylog2 (wps->w.c [1].median [2]);
        *byteptr++ = temp >> 8;
    }

    wpmd->byte_length = byteptr - (uchar *) wpmd->data;
    read_entropy_vars (wps, wpmd);
}

// Read the hybrid related values from the specifed metadata structure, convert
// them back to their internal formats and store them. The extended profile
// stuff is not implemented yet, so return an error if we get more data than
// we know what to do with.

int read_hybrid_profile (WavpackStream *wps, WavpackMetadata *wpmd)
{
    uchar *byteptr = wpmd->data;
    uchar *endptr = byteptr + wpmd->byte_length;

    if (wps->wphdr.flags & HYBRID_BITRATE) {
        wps->w.c [0].slow_level = exp2s (byteptr [0] + (byteptr [1] << 8));
        byteptr += 2;

        if (!(wps->wphdr.flags & MONO_DATA)) {
            wps->w.c [1].slow_level = exp2s (byteptr [0] + (byteptr [1] << 8));
            byteptr += 2;
        }
    }

    wps->w.bitrate_acc [0] = (int32_t)(byteptr [0] + (byteptr [1] << 8)) << 16;
    byteptr += 2;

    if (!(wps->wphdr.flags & MONO_DATA)) {
        wps->w.bitrate_acc [1] = (int32_t)(byteptr [0] + (byteptr [1] << 8)) << 16;
        byteptr += 2;
    }

    if (byteptr < endptr) {
        wps->w.bitrate_delta [0] = exp2s ((short)(byteptr [0] + (byteptr [1] << 8)));
        byteptr += 2;

        if (!(wps->wphdr.flags & MONO_DATA)) {
            wps->w.bitrate_delta [1] = exp2s ((short)(byteptr [0] + (byteptr [1] << 8)));
            byteptr += 2;
        }

        if (byteptr < endptr)
            return FALSE;
    }
    else
        wps->w.bitrate_delta [0] = wps->w.bitrate_delta [1] = 0;

    return TRUE;
}

// This function is called during both encoding and decoding of hybrid data to
// update the "error_limit" variable which determines the maximum sample error
// allowed in the main bitstream. In the HYBRID_BITRATE mode (which is the only
// currently implemented) this is calculated from the slow_level values and the
// bitrate accumulators. Note that the bitrate accumulators can be changing.

void update_error_limit (struct words_data *w, uint32_t flags)
{
    int bitrate_0 = (w->bitrate_acc [0] += w->bitrate_delta [0]) >> 16;

    if (flags & MONO_DATA) {
        if (flags & HYBRID_BITRATE) {
            int slow_log_0 = (w->c [0].slow_level + SLO) >> SLS;

            if (slow_log_0 - bitrate_0 > -0x100)
                w->c [0].error_limit = exp2s (slow_log_0 - bitrate_0 + 0x100);
            else
                w->c [0].error_limit = 0;
        }
        else
            w->c [0].error_limit = exp2s (bitrate_0);
    }
    else {
        int bitrate_1 = (w->bitrate_acc [1] += w->bitrate_delta [1]) >> 16;

        if (flags & HYBRID_BITRATE) {
            int slow_log_0 = (w->c [0].slow_level + SLO) >> SLS;
            int slow_log_1 = (w->c [1].slow_level + SLO) >> SLS;

            if (flags & HYBRID_BALANCE) {
                int balance = (slow_log_1 - slow_log_0 + bitrate_1 + 1) >> 1;

                if (balance > bitrate_0) {
                    bitrate_1 = bitrate_0 * 2;
                    bitrate_0 = 0;
                }
                else if (-balance > bitrate_0) {
                    bitrate_0 = bitrate_0 * 2;
                    bitrate_1 = 0;
                }
                else {
                    bitrate_1 = bitrate_0 + balance;
                    bitrate_0 = bitrate_0 - balance;
                }
            }

            if (slow_log_0 - bitrate_0 > -0x100)
                w->c [0].error_limit = exp2s (slow_log_0 - bitrate_0 + 0x100);
            else
                w->c [0].error_limit = 0;

            if (slow_log_1 - bitrate_1 > -0x100)
                w->c [1].error_limit = exp2s (slow_log_1 - bitrate_1 + 0x100);
            else
                w->c [1].error_limit = 0;
        }
        else {
            w->c [0].error_limit = exp2s (bitrate_0);
            w->c [1].error_limit = exp2s (bitrate_1);
        }
    }
}

static uint32_t read_code (Bitstream *bs, uint32_t maxcode);

// Read the next word from the bitstream "wvbits" and return the value. This
// function can be used for hybrid or lossless streams, but since an
// optimized version is available for lossless this function would normally
// be used for hybrid only. If a hybrid lossless stream is being read then
// the "correction" offset is written at the specified pointer. A return value
// of WORD_EOF indicates that the end of the bitstream was reached (all 1s) or
// some other error occurred.

int32_t get_words (int32_t *buffer, int nsamples, uint32_t flags,
                struct words_data *w, Bitstream *bs)
{
    register struct entropy_data *c = w->c;
    int csamples;

    if (!(flags & MONO_DATA))
        nsamples *= 2;

    for (csamples = 0; csamples < nsamples; ++csamples) {
        uint32_t ones_count, low, mid, high;

        if (!(flags & MONO_DATA))
            c = w->c + (csamples & 1);

        if (!(w->c [0].median [0] & ~1) && !w->holding_zero && !w->holding_one && !(w->c [1].median [0] & ~1)) {
            uint32_t mask;
            int cbits;

            if (w->zeros_acc) {
                if (--w->zeros_acc) {
                    c->slow_level -= (c->slow_level + SLO) >> SLS;
                    *buffer++ = 0;
                    continue;
                }
            }
            else {
                for (cbits = 0; cbits < 33 && getbit (bs); ++cbits);

                if (cbits == 33)
                    break;

                if (cbits < 2)
                    w->zeros_acc = cbits;
                else {
                    for (mask = 1, w->zeros_acc = 0; --cbits; mask <<= 1)
                        if (getbit (bs))
                            w->zeros_acc |= mask;

                    w->zeros_acc |= mask;
                }

                if (w->zeros_acc) {
                    c->slow_level -= (c->slow_level + SLO) >> SLS;
                    CLEAR (w->c [0].median);
                    CLEAR (w->c [1].median);
                    *buffer++ = 0;
                    continue;
                }
            }
        }

        if (w->holding_zero)
            ones_count = w->holding_zero = 0;
        else {
            int next8;

            if (bs->bc < 8) {
                if (++(bs->ptr) == bs->end)
                    bs->wrap (bs);

                next8 = (bs->sr |= *(bs->ptr) << bs->bc) & 0xff;
                bs->bc += 8;
            }
            else
                next8 = bs->sr & 0xff;

            if (next8 == 0xff) {
                bs->bc -= 8;
                bs->sr >>= 8;

                for (ones_count = 8; ones_count < (LIMIT_ONES + 1) && getbit (bs); ++ones_count);

                if (ones_count == (LIMIT_ONES + 1))
                    break;

                if (ones_count == LIMIT_ONES) {
                    uint32_t mask;
                    int cbits;

                    for (cbits = 0; cbits < 33 && getbit (bs); ++cbits);

                    if (cbits == 33)
                        break;

                    if (cbits < 2)
                        ones_count = cbits;
                    else {
                        for (mask = 1, ones_count = 0; --cbits; mask <<= 1)
                            if (getbit (bs))
                                ones_count |= mask;

                        ones_count |= mask;
                    }

                    ones_count += LIMIT_ONES;
                }
            }
            else {
                bs->bc -= (ones_count = ones_count_table [next8]) + 1;
                bs->sr >>= ones_count + 1;
            }

            if (w->holding_one) {
                w->holding_one = ones_count & 1;
                ones_count = (ones_count >> 1) + 1;
            }
            else {
                w->holding_one = ones_count & 1;
                ones_count >>= 1;
            }

            w->holding_zero = ~w->holding_one & 1;
        }

        if ((flags & HYBRID_FLAG) && ((flags & MONO_DATA) || !(csamples & 1)))
            update_error_limit (w, flags);

        if (ones_count == 0) {
            low = 0;
            high = GET_MED (0) - 1;
            DEC_MED0 ();
        }
        else {
            low = GET_MED (0);
            INC_MED0 ();

            if (ones_count == 1) {
                high = low + GET_MED (1) - 1;
                DEC_MED1 ();
            }
            else {
                low += GET_MED (1);
                INC_MED1 ();

                if (ones_count == 2) {
                    high = low + GET_MED (2) - 1;
                    DEC_MED2 ();
                }
                else {
                    low += (ones_count - 2) * GET_MED (2);
                    high = low + GET_MED (2) - 1;
                    INC_MED2 ();
                }
            }
        }

        mid = (high + low + 1) >> 1;

        if (!c->error_limit)
            mid = read_code (bs, high - low) + low;
        else while (high - low > c->error_limit) {
            if (getbit (bs))
                mid = (high + (low = mid) + 1) >> 1;
            else
                mid = ((high = mid - 1) + low + 1) >> 1;
        }

        *buffer++ = getbit (bs) ? ~mid : mid;

        if (flags & HYBRID_BITRATE)
            c->slow_level = c->slow_level - ((c->slow_level + SLO) >> SLS) + mylog2 (mid);
    }

    return (flags & MONO_DATA) ? csamples : (csamples / 2);
}

// Read a single unsigned value from the specified bitstream with a value
// from 0 to maxcode. If there are exactly a power of two number of possible
// codes then this will read a fixed number of bits; otherwise it reads the
// minimum number of bits and then determines whether another bit is needed
// to define the code.

static uint32_t read_code (Bitstream *bs, uint32_t maxcode)
{
    int bitcount = count_bits (maxcode);
    uint32_t extras = (1L << bitcount) - maxcode - 1, code;

    if (!bitcount)
        return 0;

    getbits (&code, bitcount - 1, bs);
    code &= (1L << (bitcount - 1)) - 1;

    if (code >= extras) {
        code = (code << 1) - extras;

        if (getbit (bs))
            ++code;
    }

    return code;
}

void send_words (int32_t *buffer, int nsamples, uint32_t flags,
                 struct words_data *w, Bitstream *bs)
{
    register struct entropy_data *c = w->c;

    if (!(flags & MONO_FLAG))
        nsamples *= 2;

    while (nsamples--) {
        int32_t value = *buffer++;
        int sign = (value < 0) ? 1 : 0;
        uint32_t ones_count, low, high;

        if (!(flags & MONO_FLAG))
            c = w->c + (~nsamples & 1);

        if (!(w->c [0].median [0] & ~1) && !w->holding_zero && !(w->c [1].median [0] & ~1)) {
            if (w->zeros_acc) {
                if (value)
                    flush_word (w, bs);
                else {
                    w->zeros_acc++;
                    continue;
                }
            }
            else if (value) {
                putbit_0 (bs);
            }
            else {
                CLEAR (w->c [0].median);
                CLEAR (w->c [1].median);
                w->zeros_acc = 1;
                continue;
            }
        }

        if (sign)
            value = ~value;

        if ((unsigned int32_t) value < GET_MED (0)) {
            ones_count = low = 0;
            high = GET_MED (0) - 1;
            DEC_MED0 ();
        }
        else {
            low = GET_MED (0);
            INC_MED0 ();

            if (value - low < GET_MED (1)) {
                ones_count = 1;
                high = low + GET_MED (1) - 1;
                DEC_MED1 ();
            }
            else {
                low += GET_MED (1);
                INC_MED1 ();

                if (value - low < GET_MED (2)) {
                    ones_count = 2;
                    high = low + GET_MED (2) - 1;
                    DEC_MED2 ();
                }
                else {
                    ones_count = 2 + (value - low) / GET_MED (2);
                    low += (ones_count - 2) * GET_MED (2);
                    high = low + GET_MED (2) - 1;
                    INC_MED2 ();
                }
            }
        }

        if (w->holding_zero) {
            if (ones_count)
                w->holding_one++;

            flush_word (w, bs);

            if (ones_count) {
                w->holding_zero = 1;
                ones_count--;
            }
            else
                w->holding_zero = 0;
        }
        else
            w->holding_zero = 1;

        w->holding_one = ones_count * 2;

        if (high != low) {  
            uint32_t maxcode = high - low, code = value - low;
            int bitcount = count_bits (maxcode);
            uint32_t extras = (1L << bitcount) - maxcode - 1;

            if (code < extras) {
                w->pend_data |= code << w->pend_count;
                w->pend_count += bitcount - 1;
            }
            else {
                w->pend_data |= ((code + extras) >> 1) << w->pend_count;
                w->pend_count += bitcount - 1;
                w->pend_data |= ((code + extras) & 1) << w->pend_count++;
            }
        }

        w->pend_data |= ((int32_t) sign << w->pend_count++);

        if (!w->holding_zero)
            flush_word (w, bs);
    }
}

// Used by send_word() and send_word_lossless() to actually send most the
// accumulated data onto the bitstream. This is also called directly from
// clients when all words have been sent.

void flush_word (struct words_data *w, Bitstream *bs)
{
    int cbits;

    if (w->zeros_acc) {
        cbits = count_bits (w->zeros_acc);

        while (cbits--) {
            putbit_1 (bs);
        }

        putbit_0 (bs);

        while (w->zeros_acc > 1) {
            putbit (w->zeros_acc & 1, bs);
            w->zeros_acc >>= 1;
        }

        w->zeros_acc = 0;
    }

    if (w->holding_one) {
        if (w->holding_one >= LIMIT_ONES) {
            putbits ((1L << LIMIT_ONES) - 1, LIMIT_ONES + 1, bs);
            w->holding_one -= LIMIT_ONES;
            cbits = count_bits (w->holding_one);

            while (cbits--) {
                putbit_1 (bs);
            }

            putbit_0 (bs);

            while (w->holding_one > 1) {
                putbit (w->holding_one & 1, bs);
                w->holding_one >>= 1;
            }

            w->holding_zero = 0;
        }
        else
            putbits ((1L << w->holding_one) - 1, w->holding_one, bs);

        w->holding_one = 0;
    }

    if (w->holding_zero) {
        putbit_0 (bs);
        w->holding_zero = 0;
    }

    if (w->pend_count) {

        while (w->pend_count > 24) {
            putbit (w->pend_data & 1, bs);
            w->pend_data >>= 1;
            w->pend_count--;
        }

        putbits (w->pend_data, w->pend_count, bs);
        w->pend_data = w->pend_count = 0;
    }
}

// The concept of a base 2 logarithm is used in many parts of WavPack. It is
// a way of sufficiently accurately representing 32-bit signed and unsigned
// values storing only 16 bits (actually fewer). It is also used in the hybrid
// mode for quickly comparing the relative magnitude of large values (i.e.
// division) and providing smooth exponentials using only addition.

// These are not strict logarithms in that they become linear around zero and
// can therefore represent both zero and negative values. They have 8 bits
// of precision and in "roundtrip" conversions the total error never exceeds 1
// part in 225 except for the cases of +/-115 and +/-195 (which error by 1).


// This function returns the log2 for the specified 32-bit unsigned value.
// The maximum value allowed is about 0xff800000 and returns 8447.

static int mylog2 (unsigned int32_t avalue)
{
    int dbits;

    if ((avalue += avalue >> 9) < (1 << 8)) {
        dbits = nbits_table [avalue];
        return (dbits << 8) + log2_table [(avalue << (9 - dbits)) & 0xff];
    }
    else {
        if (avalue < (1L << 16))
            dbits = nbits_table [avalue >> 8] + 8;
        else if (avalue < (1L << 24))
            dbits = nbits_table [avalue >> 16] + 16;
        else
            dbits = nbits_table [avalue >> 24] + 24;

        return (dbits << 8) + log2_table [(avalue >> (dbits - 9)) & 0xff];
    }
}

// This function returns the log2 for the specified 32-bit signed value.
// All input values are valid and the return values are in the range of
// +/- 8192.

int log2s (int32_t value)
{
    return (value < 0) ? -mylog2 (-value) : mylog2 (value);
}

// This function returns the original integer represented by the supplied
// logarithm (at least within the provided accuracy). The log is signed,
// but since a full 32-bit value is returned this can be used for unsigned
// conversions as well (i.e. the input range is -8192 to +8447).

int32_t exp2s (int log)
{
    uint32_t value;

    if (log < 0)
        return -exp2s (-log);

    value = exp2_table [log & 0xff] | 0x100;

    if ((log >>= 8) <= 9)
        return value >> (9 - log);
    else
        return value << (log - 9);
}

// These two functions convert internal weights (which are normally +/-1024)
// to and from an 8-bit signed character version for storage in metadata. The
// weights are clipped here in the case that they are outside that range.

signed char store_weight (int weight)
{
    if (weight > 1024)
        weight = 1024;
    else if (weight < -1024)
        weight = -1024;

    if (weight > 0)
        weight -= (weight + 64) >> 7;

    return (weight + 4) >> 3;
}

int restore_weight (signed char weight)
{
    int result;

    if ((result = (int) weight << 3) > 0)
        result += (result + 64) >> 7;

    return result;
}