FFmpeg/libavcodec/hevc_cabac.c

/*
 * 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"
#include "hevcdec.h"

#define CABAC_MAX_BIN 31

/**
 * number of bin by SyntaxElement.
 */
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->ps.pps->entropy_coding_sync_enabled_flag &&
        (ctb_addr_ts % s->ps.sps->ctb_width == 2 ||
         (s->ps.sps->ctb_width == 2 &&
          ctb_addr_ts % s->ps.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 != HEVC_SLICE_I)
        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(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->ps.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->ps.pps->tiles_enabled_flag &&
             s->ps.pps->tile_id[ctb_addr_ts] != s->ps.pps->tile_id[ctb_addr_ts - 1]))
            cabac_init_state(s);

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

                if (s->ps.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->ps.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->ps.sps->min_cb_width;
    int inc = 0;
    int x0b = x0 & ((1 << s->ps.sps->log2_ctb_size) - 1);
    int y0b = y0 & ((1 << s->ps.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->ps.sps->log2_ctb_size) - 1);
    int y0b  = y0 & ((1 << s->ps.sps->log2_ctb_size) - 1);
    int x_cb = x0 >> s->ps.sps->log2_min_cb_size;
    int y_cb = y0 >> s->ps.sps->log2_min_cb_size;

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