aboutsummaryrefslogtreecommitdiffstats
path: root/libavcodec/hevc_cabac.c
blob: ff55b02cc0c26a793c1c406d35e05d9daf8fb6d1 (plain) (blame)
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
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
/*
 * HEVC CABAC decoding
 *
 * Copyright (C) 2012 - 2013 Guillaume Martres
 * Copyright (C) 2012 - 2013 Gildas Cocherel
 *
 * This file is part of Libav.
 *
 * Libav is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * Libav is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "libavutil/attributes.h"
#include "libavutil/common.h"

#include "cabac_functions.h"
#include "hevc.h"

#define CABAC_MAX_BIN 100

/**
 * number of bin by SyntaxElement.
 */
av_unused static const int8_t num_bins_in_se[] = {
     1, // sao_merge_flag
     1, // sao_type_idx
     0, // sao_eo_class
     0, // sao_band_position
     0, // sao_offset_abs
     0, // sao_offset_sign
     0, // end_of_slice_flag
     3, // split_coding_unit_flag
     1, // cu_transquant_bypass_flag
     3, // skip_flag
     3, // cu_qp_delta
     1, // pred_mode
     4, // part_mode
     0, // pcm_flag
     1, // prev_intra_luma_pred_mode
     0, // mpm_idx
     0, // rem_intra_luma_pred_mode
     2, // intra_chroma_pred_mode
     1, // merge_flag
     1, // merge_idx
     5, // inter_pred_idc
     2, // ref_idx_l0
     2, // ref_idx_l1
     2, // abs_mvd_greater0_flag
     2, // abs_mvd_greater1_flag
     0, // abs_mvd_minus2
     0, // mvd_sign_flag
     1, // mvp_lx_flag
     1, // no_residual_data_flag
     3, // split_transform_flag
     2, // cbf_luma
     4, // cbf_cb, cbf_cr
     2, // transform_skip_flag[][]
    18, // last_significant_coeff_x_prefix
    18, // last_significant_coeff_y_prefix
     0, // last_significant_coeff_x_suffix
     0, // last_significant_coeff_y_suffix
     4, // significant_coeff_group_flag
    42, // significant_coeff_flag
    24, // coeff_abs_level_greater1_flag
     6, // coeff_abs_level_greater2_flag
     0, // coeff_abs_level_remaining
     0, // coeff_sign_flag
};

/**
 * Offset to ctxIdx 0 in init_values and states, indexed by SyntaxElement.
 */
static const int elem_offset[sizeof(num_bins_in_se)] = {
      0,
      1,
      2,
      2,
      2,
      2,
      2,
      2,
      5,
      6,
      9,
     12,
     13,
     17,
     17,
     18,
     18,
     18,
     20,
     21,
     22,
     27,
     29,
     31,
     33,
     35,
     35,
     35,
     36,
     37,
     40,
     42,
     46,
     48,
     66,
     84,
     84,
     84,
     88,
    130,
    154,
    160,
    160,
};

#define CNU 154
/**
 * Indexed by init_type
 */
static const uint8_t init_values[3][HEVC_CONTEXTS] = {
    { // sao_merge_flag
      153,
      // sao_type_idx
      200,
      // split_coding_unit_flag
      139, 141, 157,
      // cu_transquant_bypass_flag
      154,
      // skip_flag
      CNU, CNU, CNU,
      // cu_qp_delta
      154, 154, 154,
      // pred_mode
      CNU,
      // part_mode
      184, CNU, CNU, CNU,
      // prev_intra_luma_pred_mode
      184,
      // intra_chroma_pred_mode
      63, 139,
      // merge_flag
      CNU,
      // merge_idx
      CNU,
      // inter_pred_idc
      CNU, CNU, CNU, CNU, CNU,
      // ref_idx_l0
      CNU, CNU,
      // ref_idx_l1
      CNU, CNU,
      // abs_mvd_greater1_flag
      CNU, CNU,
      // abs_mvd_greater1_flag
      CNU, CNU,
      // mvp_lx_flag
      CNU,
      // no_residual_data_flag
      CNU,
      // split_transform_flag
      153, 138, 138,
      // cbf_luma
      111, 141,
      // cbf_cb, cbf_cr
      94, 138, 182, 154,
      // transform_skip_flag
      139, 139,
      // last_significant_coeff_x_prefix
      110, 110, 124, 125, 140, 153, 125, 127, 140, 109, 111, 143, 127, 111,
       79, 108, 123,  63,
      // last_significant_coeff_y_prefix
      110, 110, 124, 125, 140, 153, 125, 127, 140, 109, 111, 143, 127, 111,
       79, 108, 123,  63,
      // significant_coeff_group_flag
      91, 171, 134, 141,
      // significant_coeff_flag
      111, 111, 125, 110, 110,  94, 124, 108, 124, 107, 125, 141, 179, 153,
      125, 107, 125, 141, 179, 153, 125, 107, 125, 141, 179, 153, 125, 140,
      139, 182, 182, 152, 136, 152, 136, 153, 136, 139, 111, 136, 139, 111,
      // coeff_abs_level_greater1_flag
      140,  92, 137, 138, 140, 152, 138, 139, 153,  74, 149,  92, 139, 107,
      122, 152, 140, 179, 166, 182, 140, 227, 122, 197,
      // coeff_abs_level_greater2_flag
      138, 153, 136, 167, 152, 152, },
    { // sao_merge_flag
      153,
      // sao_type_idx
      185,
      // split_coding_unit_flag
      107, 139, 126,
      // cu_transquant_bypass_flag
      154,
      // skip_flag
      197, 185, 201,
      // cu_qp_delta
      154, 154, 154,
      // pred_mode
      149,
      // part_mode
      154, 139, 154, 154,
      // prev_intra_luma_pred_mode
      154,
      // intra_chroma_pred_mode
      152, 139,
      // merge_flag
      110,
      // merge_idx
      122,
      // inter_pred_idc
      95, 79, 63, 31, 31,
      // ref_idx_l0
      153, 153,
      // ref_idx_l1
      153, 153,
      // abs_mvd_greater1_flag
      140, 198,
      // abs_mvd_greater1_flag
      140, 198,
      // mvp_lx_flag
      168,
      // no_residual_data_flag
      79,
      // split_transform_flag
      124, 138, 94,
      // cbf_luma
      153, 111,
      // cbf_cb, cbf_cr
      149, 107, 167, 154,
      // transform_skip_flag
      139, 139,
      // last_significant_coeff_x_prefix
      125, 110,  94, 110,  95,  79, 125, 111, 110,  78, 110, 111, 111,  95,
       94, 108, 123, 108,
      // last_significant_coeff_y_prefix
      125, 110,  94, 110,  95,  79, 125, 111, 110,  78, 110, 111, 111,  95,
       94, 108, 123, 108,
      // significant_coeff_group_flag
      121, 140, 61, 154,
      // significant_coeff_flag
      155, 154, 139, 153, 139, 123, 123,  63, 153, 166, 183, 140, 136, 153,
      154, 166, 183, 140, 136, 153, 154, 166, 183, 140, 136, 153, 154, 170,
      153, 123, 123, 107, 121, 107, 121, 167, 151, 183, 140, 151, 183, 140,
      // coeff_abs_level_greater1_flag
      154, 196, 196, 167, 154, 152, 167, 182, 182, 134, 149, 136, 153, 121,
      136, 137, 169, 194, 166, 167, 154, 167, 137, 182,
      // coeff_abs_level_greater2_flag
      107, 167, 91, 122, 107, 167, },
    { // sao_merge_flag
      153,
      // sao_type_idx
      160,
      // split_coding_unit_flag
      107, 139, 126,
      // cu_transquant_bypass_flag
      154,
      // skip_flag
      197, 185, 201,
      // cu_qp_delta
      154, 154, 154,
      // pred_mode
      134,
      // part_mode
      154, 139, 154, 154,
      // prev_intra_luma_pred_mode
      183,
      // intra_chroma_pred_mode
      152, 139,
      // merge_flag
      154,
      // merge_idx
      137,
      // inter_pred_idc
      95, 79, 63, 31, 31,
      // ref_idx_l0
      153, 153,
      // ref_idx_l1
      153, 153,
      // abs_mvd_greater1_flag
      169, 198,
      // abs_mvd_greater1_flag
      169, 198,
      // mvp_lx_flag
      168,
      // no_residual_data_flag
      79,
      // split_transform_flag
      224, 167, 122,
      // cbf_luma
      153, 111,
      // cbf_cb, cbf_cr
      149, 92, 167, 154,
      // transform_skip_flag
      139, 139,
      // last_significant_coeff_x_prefix
      125, 110, 124, 110,  95,  94, 125, 111, 111,  79, 125, 126, 111, 111,
       79, 108, 123,  93,
      // last_significant_coeff_y_prefix
      125, 110, 124, 110,  95,  94, 125, 111, 111,  79, 125, 126, 111, 111,
       79, 108, 123,  93,
      // significant_coeff_group_flag
      121, 140, 61, 154,
      // significant_coeff_flag
      170, 154, 139, 153, 139, 123, 123,  63, 124, 166, 183, 140, 136, 153,
      154, 166, 183, 140, 136, 153, 154, 166, 183, 140, 136, 153, 154, 170,
      153, 138, 138, 122, 121, 122, 121, 167, 151, 183, 140, 151, 183, 140,
      // coeff_abs_level_greater1_flag
      154, 196, 167, 167, 154, 152, 167, 182, 182, 134, 149, 136, 153, 121,
      136, 122, 169, 208, 166, 167, 154, 152, 167, 182,
      // coeff_abs_level_greater2_flag
      107, 167, 91, 107, 107, 167, },
};

void ff_hevc_save_states(HEVCContext *s, int ctb_addr_ts)
{
    if (s->pps->entropy_coding_sync_enabled_flag &&
        (ctb_addr_ts % s->sps->ctb_width == 2 ||
         (s->sps->ctb_width == 2 &&
          ctb_addr_ts % s->sps->ctb_width == 0))) {
        memcpy(s->cabac_state, s->HEVClc.cabac_state, HEVC_CONTEXTS);
    }
}

static void load_states(HEVCContext *s)
{
    memcpy(s->HEVClc.cabac_state, s->cabac_state, HEVC_CONTEXTS);
}

static void cabac_reinit(HEVCLocalContext *lc)
{
    skip_bytes(&lc->cc, 0);
}

static void cabac_init_decoder(HEVCContext *s)
{
    GetBitContext *gb = &s->HEVClc.gb;
    skip_bits(gb, 1);
    align_get_bits(gb);
    ff_init_cabac_decoder(&s->HEVClc.cc,
                          gb->buffer + get_bits_count(gb) / 8,
                          (get_bits_left(gb) + 7) / 8);
}

static void cabac_init_state(HEVCContext *s)
{
    int init_type = 2 - s->sh.slice_type;
    int i;

    if (s->sh.cabac_init_flag && s->sh.slice_type != I_SLICE)
        init_type ^= 3;

    for (i = 0; i < HEVC_CONTEXTS; i++) {
        int init_value = init_values[init_type][i];
        int m = (init_value >> 4) * 5 - 45;
        int n = ((init_value & 15) << 3) - 16;
        int pre = 2 * (((m * av_clip_c(s->sh.slice_qp, 0, 51)) >> 4) + n) - 127;

        pre ^= pre >> 31;
        if (pre > 124)
            pre = 124 + (pre & 1);
        s->HEVClc.cabac_state[i] = pre;
    }
}

void ff_hevc_cabac_init(HEVCContext *s, int ctb_addr_ts)
{
    if (ctb_addr_ts == s->pps->ctb_addr_rs_to_ts[s->sh.slice_ctb_addr_rs]) {
        cabac_init_decoder(s);
        if (s->sh.dependent_slice_segment_flag == 0 ||
            (s->pps->tiles_enabled_flag &&
             s->pps->tile_id[ctb_addr_ts] != s->pps->tile_id[ctb_addr_ts - 1]))
            cabac_init_state(s);

        if (!s->sh.first_slice_in_pic_flag &&
            s->pps->entropy_coding_sync_enabled_flag) {
            if (ctb_addr_ts % s->sps->ctb_width == 0) {
                if (s->sps->ctb_width == 1)
                    cabac_init_state(s);
                else if (s->sh.dependent_slice_segment_flag == 1)
                    load_states(s);
            }
        }
    } else {
        if (s->pps->tiles_enabled_flag &&
            s->pps->tile_id[ctb_addr_ts] != s->pps->tile_id[ctb_addr_ts - 1]) {
            cabac_reinit(&s->HEVClc);
            cabac_init_state(s);
        }
        if (s->pps->entropy_coding_sync_enabled_flag) {
            if (ctb_addr_ts % s->sps->ctb_width == 0) {
                get_cabac_terminate(&s->HEVClc.cc);
                cabac_reinit(&s->HEVClc);

                if (s->sps->ctb_width == 1)
                    cabac_init_state(s);
                else
                    load_states(s);
            }
        }
    }
}

#define GET_CABAC(ctx) get_cabac(&s->HEVClc.cc, &s->HEVClc.cabac_state[ctx])

int ff_hevc_sao_merge_flag_decode(HEVCContext *s)
{
    return GET_CABAC(elem_offset[SAO_MERGE_FLAG]);
}

int ff_hevc_sao_type_idx_decode(HEVCContext *s)
{
    if (!GET_CABAC(elem_offset[SAO_TYPE_IDX]))
        return 0;

    if (!get_cabac_bypass(&s->HEVClc.cc))
        return SAO_BAND;
    return SAO_EDGE;
}

int ff_hevc_sao_band_position_decode(HEVCContext *s)
{
    int i;
    int value = get_cabac_bypass(&s->HEVClc.cc);

    for (i = 0; i < 4; i++)
        value = (value << 1) | get_cabac_bypass(&s->HEVClc.cc);
    return value;
}

int ff_hevc_sao_offset_abs_decode(HEVCContext *s)
{
    int i = 0;
    int length = (1 << (FFMIN(s->sps->bit_depth, 10) - 5)) - 1;

    while (i < length && get_cabac_bypass(&s->HEVClc.cc))
        i++;
    return i;
}

int ff_hevc_sao_offset_sign_decode(HEVCContext *s)
{
    return get_cabac_bypass(&s->HEVClc.cc);
}

int ff_hevc_sao_eo_class_decode(HEVCContext *s)
{
    int ret = get_cabac_bypass(&s->HEVClc.cc) << 1;
    ret    |= get_cabac_bypass(&s->HEVClc.cc);
    return ret;
}

int ff_hevc_end_of_slice_flag_decode(HEVCContext *s)
{
    return get_cabac_terminate(&s->HEVClc.cc);
}

int ff_hevc_cu_transquant_bypass_flag_decode(HEVCContext *s)
{
    return GET_CABAC(elem_offset[CU_TRANSQUANT_BYPASS_FLAG]);
}

int ff_hevc_skip_flag_decode(HEVCContext *s, int x0, int y0, int x_cb, int y_cb)
{
    int min_cb_width = s->sps->min_cb_width;
    int inc = 0;
    int x0b = x0 & ((1 << s->sps->log2_ctb_size) - 1);
    int y0b = y0 & ((1 << s->sps->log2_ctb_size) - 1);

    if (s->HEVClc.ctb_left_flag || x0b)
        inc = !!SAMPLE_CTB(s->skip_flag, x_cb - 1, y_cb);
    if (s->HEVClc.ctb_up_flag || y0b)
        inc += !!SAMPLE_CTB(s->skip_flag, x_cb, y_cb - 1);

    return GET_CABAC(elem_offset[SKIP_FLAG] + inc);
}

int ff_hevc_cu_qp_delta_abs(HEVCContext *s)
{
    int prefix_val = 0;
    int suffix_val = 0;
    int inc = 0;

    while (prefix_val < 5 && GET_CABAC(elem_offset[CU_QP_DELTA] + inc)) {
        prefix_val++;
        inc = 1;
    }
    if (prefix_val >= 5) {
        int k = 0;
        while (k < CABAC_MAX_BIN && get_cabac_bypass(&s->HEVClc.cc)) {
            suffix_val += 1 << k;
            k++;
        }
        if (k == CABAC_MAX_BIN)
            av_log(s->avctx, AV_LOG_ERROR, "CABAC_MAX_BIN : %d\n", k);

        while (k--)
            suffix_val += get_cabac_bypass(&s->HEVClc.cc) << k;
    }
    return prefix_val + suffix_val;
}

int ff_hevc_cu_qp_delta_sign_flag(HEVCContext *s)
{
    return get_cabac_bypass(&s->HEVClc.cc);
}

int ff_hevc_pred_mode_decode(HEVCContext *s)
{
    return GET_CABAC(elem_offset[PRED_MODE_FLAG]);
}

int ff_hevc_split_coding_unit_flag_decode(HEVCContext *s, int ct_depth, int x0, int y0)
{
    int inc = 0, depth_left = 0, depth_top = 0;
    int x0b  = x0 & ((1 << s->sps->log2_ctb_size) - 1);
    int y0b  = y0 & ((1 << s->sps->log2_ctb_size) - 1);
    int x_cb = x0 >> s->sps->log2_min_cb_size;
    int y_cb = y0 >> s->sps->log2_min_cb_size;

    if (s->HEVClc.ctb_left_flag || x0b)
        depth_left = s->tab_ct_depth[(y_cb) * s->sps->min_cb_width + x_cb - 1];
    if (s->HEVClc.ctb_up_flag || y0b)
        depth_top = s->tab_ct_depth[(y_cb - 1) * s->sps->min_cb_width + x_cb];

    inc += (depth_left > ct_depth);
    inc += (depth_top  > ct_depth);

    return GET_CABAC(elem_offset[SPLIT_CODING_UNIT_FLAG] + inc);
}

int ff_hevc_part_mode_decode(HEVCContext *s, int log2_cb_size)
{
    if (GET_CABAC(elem_offset[PART_MODE])) // 1
        return PART_2Nx2N;
    if (log2_cb_size == s->sps->log2_min_cb_size) {
        if (s->HEVClc.cu.pred_mode == MODE_INTRA) // 0
            return PART_NxN;
        if (GET_CABAC(elem_offset[PART_MODE] + 1)) // 01
            return PART_2NxN;
        if (log2_cb_size == 3) // 00
            return PART_Nx2N;
        if (GET_CABAC(elem_offset[PART_MODE] + 2)) // 001
            return PART_Nx2N;
        return PART_NxN; // 000
    }

    if (!s->sps->amp_enabled_flag) {
        if (GET_CABAC(elem_offset[PART_MODE] + 1)) // 01
            return PART_2NxN;
        return PART_Nx2N;
    }

    if (GET_CABAC(elem_offset[PART_MODE] + 1)) { // 01X, 01XX
        if (GET_CABAC(elem_offset[PART_MODE] + 3)) // 011
            return PART_2NxN;
        if (get_cabac_bypass(&s->HEVClc.cc)) // 0101
            return PART_2NxnD;
        return PART_2NxnU; // 0100
    }

    if (GET_CABAC(elem_offset[PART_MODE] + 3)) // 001
        return PART_Nx2N;
    if (get_cabac_bypass(&s->HEVClc.cc)) // 0001
        return PART_nRx2N;
    return PART_nLx2N;  // 0000
}

int ff_hevc_pcm_flag_decode(HEVCContext *s)
{
    return get_cabac_terminate(&s->HEVClc.cc);
}

int ff_hevc_prev_intra_luma_pred_flag_decode(HEVCContext *s)
{
    return GET_CABAC(elem_offset[PREV_INTRA_LUMA_PRED_FLAG]);
}

int ff_hevc_mpm_idx_decode(HEVCContext *s)
{
    int i = 0;
    while (i < 2 && get_cabac_bypass(&s->HEVClc.cc))
        i++;
    return i;
}

int ff_hevc_rem_intra_luma_pred_mode_decode(HEVCContext *s)
{
    int i;
    int value = get_cabac_bypass(&s->HEVClc.cc);

    for (i = 0; i < 4; i++)
        value = (value << 1) | get_cabac_bypass(&s->HEVClc.cc);
    return value;
}

int ff_hevc_intra_chroma_pred_mode_decode(HEVCContext *s)
{
    int ret;
    if (!GET_CABAC(elem_offset[INTRA_CHROMA_PRED_MODE]))
        return 4;

    ret  = get_cabac_bypass(&s->HEVClc.cc) << 1;
    ret |= get_cabac_bypass(&s->HEVClc.cc);
    return ret;
}

int ff_hevc_merge_idx_decode(HEVCContext *s)
{
    int i = GET_CABAC(elem_offset[MERGE_IDX]);

    if (i != 0) {
        while (i < s->sh.max_num_merge_cand-1 && get_cabac_bypass(&s->HEVClc.cc))
            i++;
    }
    return i;
}

int ff_hevc_merge_flag_decode(HEVCContext *s)
{
    return GET_CABAC(elem_offset[MERGE_FLAG]);
}

int ff_hevc_inter_pred_idc_decode(HEVCContext *s, int nPbW, int nPbH)
{
    if (nPbW + nPbH == 12)
        return GET_CABAC(elem_offset[INTER_PRED_IDC] + 4);
    if (GET_CABAC(elem_offset[INTER_PRED_IDC] + s->HEVClc.ct.depth))
        return PRED_BI;

    return GET_CABAC(elem_offset[INTER_PRED_IDC] + 4);
}

int ff_hevc_ref_idx_lx_decode(HEVCContext *s, int num_ref_idx_lx)
{
    int i = 0;
    int max = num_ref_idx_lx - 1;
    int max_ctx = FFMIN(max, 2);

    while (i < max_ctx && GET_CABAC(elem_offset[REF_IDX_L0] + i))
        i++;
    if (i == 2) {
        while (i < max && get_cabac_bypass(&s->HEVClc.cc))
            i++;
    }

    return i;
}

int ff_hevc_mvp_lx_flag_decode(HEVCContext *s)
{
    return GET_CABAC(elem_offset[MVP_LX_FLAG]);
}

int ff_hevc_no_residual_syntax_flag_decode(HEVCContext *s)
{
    return GET_CABAC(elem_offset[NO_RESIDUAL_DATA_FLAG]);
}

int ff_hevc_abs_mvd_greater0_flag_decode(HEVCContext *s)
{
    return GET_CABAC(elem_offset[ABS_MVD_GREATER0_FLAG]);
}

int ff_hevc_abs_mvd_greater1_flag_decode(HEVCContext *s)
{
    return GET_CABAC(elem_offset[ABS_MVD_GREATER1_FLAG] + 1);
}

int ff_hevc_mvd_decode(HEVCContext *s)
{
    int ret = 2;
    int k = 1;

    while (k < CABAC_MAX_BIN && get_cabac_bypass(&s->HEVClc.cc)) {
        ret += 1 << k;
        k++;
    }
    if (k == CABAC_MAX_BIN)
        av_log(s->avctx, AV_LOG_ERROR, "CABAC_MAX_BIN : %d\n", k);
    while (k--)
        ret += get_cabac_bypass(&s->HEVClc.cc) << k;
    return get_cabac_bypass_sign(&s->HEVClc.cc, -ret);
}

int ff_hevc_mvd_sign_flag_decode(HEVCContext *s)
{
    return get_cabac_bypass_sign(&s->HEVClc.cc, -1);
}

int ff_hevc_split_transform_flag_decode(HEVCContext *s, int log2_trafo_size)
{
    return GET_CABAC(elem_offset[SPLIT_TRANSFORM_FLAG] + 5 - log2_trafo_size);
}

int ff_hevc_cbf_cb_cr_decode(HEVCContext *s, int trafo_depth)
{
    return GET_CABAC(elem_offset[CBF_CB_CR] + trafo_depth);
}

int ff_hevc_cbf_luma_decode(HEVCContext *s, int trafo_depth)
{
    return GET_CABAC(elem_offset[CBF_LUMA] + !trafo_depth);
}

int ff_hevc_transform_skip_flag_decode(HEVCContext *s, int c_idx)
{
    return GET_CABAC(elem_offset[TRANSFORM_SKIP_FLAG] + !!c_idx);
}

#define LAST_SIG_COEFF(elem)                                                    \
    int i = 0;                                                                  \
    int max = (log2_size << 1) - 1;                                             \
    int ctx_offset, ctx_shift;                                                  \
                                                                                \
    if (c_idx == 0) {                                                           \
        ctx_offset = 3 * (log2_size - 2)  + ((log2_size - 1) >> 2);             \
        ctx_shift = (log2_size + 1) >> 2;                                       \
    } else {                                                                    \
        ctx_offset = 15;                                                        \
        ctx_shift = log2_size - 2;                                              \
    }                                                                           \
    while (i < max &&                                                           \
           GET_CABAC(elem_offset[elem] + (i >> ctx_shift) + ctx_offset))        \
        i++;                                                                    \
    return i;

int ff_hevc_last_significant_coeff_x_prefix_decode(HEVCContext *s, int c_idx,
                                                   int log2_size)
{
    LAST_SIG_COEFF(LAST_SIGNIFICANT_COEFF_X_PREFIX)
}

int ff_hevc_last_significant_coeff_y_prefix_decode(HEVCContext *s, int c_idx,
                                                   int log2_size)
{
    LAST_SIG_COEFF(LAST_SIGNIFICANT_COEFF_Y_PREFIX)
}

int ff_hevc_last_significant_coeff_suffix_decode(HEVCContext *s,
                                                 int last_significant_coeff_prefix)
{
    int i;
    int length = (last_significant_coeff_prefix >> 1) - 1;
    int value = get_cabac_bypass(&s->HEVClc.cc);

    for (i = 1; i < length; i++)
        value = (value << 1) | get_cabac_bypass(&s->HEVClc.cc);
    return value;
}

int ff_hevc_significant_coeff_group_flag_decode(HEVCContext *s, int c_idx, int ctx_cg)
{
    int inc;

    inc = FFMIN(ctx_cg, 1) + (c_idx>0 ? 2 : 0);

    return GET_CABAC(elem_offset[SIGNIFICANT_COEFF_GROUP_FLAG] + inc);
}

int ff_hevc_significant_coeff_flag_decode(HEVCContext *s, int c_idx, int x_c, int y_c,
                                          int log2_trafo_size, int scan_idx, int prev_sig)
{
    static const uint8_t ctx_idx_map[] = {
        0, 1, 4, 5, 2, 3, 4, 5, 6, 6, 8, 8, 7, 7, 8, 8
    };
    int x_cg = x_c >> 2;
    int y_cg = y_c >> 2;
    int sig_ctx, inc;

    if (x_c + y_c == 0) {
        sig_ctx = 0;
    } else if (log2_trafo_size == 2) {
        sig_ctx = ctx_idx_map[(y_c << 2) + x_c];
    } else {
        switch (prev_sig) {
        case 0: {
                int x_off = x_c & 3;
                int y_off = y_c & 3;
                sig_ctx   = ((x_off + y_off) == 0) ? 2 : ((x_off + y_off) <= 2) ? 1 : 0;
            }
            break;
        case 1:
            sig_ctx = 2 - FFMIN(y_c & 3, 2);
            break;
        case 2:
            sig_ctx = 2 - FFMIN(x_c & 3, 2);
            break;
        default:
            sig_ctx = 2;
        }

        if (c_idx == 0 && (x_cg > 0 || y_cg > 0))
            sig_ctx += 3;

        if (log2_trafo_size == 3) {
            sig_ctx += (scan_idx == SCAN_DIAG) ? 9 : 15;
        } else {
            sig_ctx += c_idx ? 12 : 21;
        }
    }

    if (c_idx == 0)
        inc = sig_ctx;
    else
        inc = sig_ctx + 27;

    return GET_CABAC(elem_offset[SIGNIFICANT_COEFF_FLAG] + inc);
}

int ff_hevc_coeff_abs_level_greater1_flag_decode(HEVCContext *s, int c_idx, int inc)
{

    if (c_idx > 0)
        inc += 16;

    return GET_CABAC(elem_offset[COEFF_ABS_LEVEL_GREATER1_FLAG] + inc);
}

int ff_hevc_coeff_abs_level_greater2_flag_decode(HEVCContext *s, int c_idx, int inc)
{
    if (c_idx > 0)
        inc += 4;

    return GET_CABAC(elem_offset[COEFF_ABS_LEVEL_GREATER2_FLAG] + inc);
}

int ff_hevc_coeff_abs_level_remaining(HEVCContext *s, int base_level, int rc_rice_param)
{
    int prefix = 0;
    int suffix = 0;
    int last_coeff_abs_level_remaining;
    int i;

    while (prefix < CABAC_MAX_BIN && get_cabac_bypass(&s->HEVClc.cc))
        prefix++;
    if (prefix == CABAC_MAX_BIN)
        av_log(s->avctx, AV_LOG_ERROR, "CABAC_MAX_BIN : %d\n", prefix);
    if (prefix < 3) {
        for (i = 0; i < rc_rice_param; i++)
            suffix = (suffix << 1) | get_cabac_bypass(&s->HEVClc.cc);
        last_coeff_abs_level_remaining = (prefix << rc_rice_param) + suffix;
    } else {
        int prefix_minus3 = prefix - 3;
        for (i = 0; i < prefix_minus3 + rc_rice_param; i++)
            suffix = (suffix << 1) | get_cabac_bypass(&s->HEVClc.cc);
        last_coeff_abs_level_remaining = (((1 << prefix_minus3) + 3 - 1)
                                              << rc_rice_param) + suffix;
    }
    return last_coeff_abs_level_remaining;
}

int ff_hevc_coeff_sign_flag(HEVCContext *s, uint8_t nb)
{
    int i;
    int ret = 0;

    for (i = 0; i < nb; i++)
        ret = (ret << 1) | get_cabac_bypass(&s->HEVClc.cc);
    return ret;
}