vp9_decodemv.c

/*
  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#include <assert.h>

#include "vp9/common/vp9_common.h"
#include "vp9/common/vp9_entropy.h"
#include "vp9/common/vp9_entropymode.h"
#include "vp9/common/vp9_entropymv.h"
#include "vp9/common/vp9_findnearmv.h"
#include "vp9/common/vp9_mvref_common.h"
#include "vp9/common/vp9_pred_common.h"
#include "vp9/common/vp9_reconinter.h"
#include "vp9/common/vp9_seg_common.h"

#include "vp9/decoder/vp9_decodemv.h"
#include "vp9/decoder/vp9_decodframe.h"
#include "vp9/decoder/vp9_onyxd_int.h"
#include "vp9/decoder/vp9_treereader.h"

static MB_PREDICTION_MODE read_intra_mode(vp9_reader *r, const vp9_prob *p) {
  return (MB_PREDICTION_MODE)treed_read(r, vp9_intra_mode_tree, p);
}

static MB_PREDICTION_MODE read_intra_mode_y(VP9_COMMON *cm, vp9_reader *r,
                                            int size_group) {
  const MB_PREDICTION_MODE y_mode = read_intra_mode(r,
                                        cm->fc.y_mode_prob[size_group]);
  if (!cm->frame_parallel_decoding_mode)
    ++cm->counts.y_mode[size_group][y_mode];
  return y_mode;
}

static MB_PREDICTION_MODE read_intra_mode_uv(VP9_COMMON *cm, vp9_reader *r,
                                             MB_PREDICTION_MODE y_mode) {
  const MB_PREDICTION_MODE uv_mode = read_intra_mode(r,
                                         cm->fc.uv_mode_prob[y_mode]);
  if (!cm->frame_parallel_decoding_mode)
    ++cm->counts.uv_mode[y_mode][uv_mode];
  return uv_mode;
}

static MB_PREDICTION_MODE read_inter_mode(VP9_COMMON *cm, vp9_reader *r,
                                          uint8_t context) {
  const MB_PREDICTION_MODE mode = treed_read(r, vp9_inter_mode_tree,
                                             cm->fc.inter_mode_probs[context]);
  if (!cm->frame_parallel_decoding_mode)
    ++cm->counts.inter_mode[context][inter_mode_offset(mode)];
  return mode;
}

static int read_segment_id(vp9_reader *r, const struct segmentation *seg) {
  return treed_read(r, vp9_segment_tree, seg->tree_probs);
}

static TX_SIZE read_selected_tx_size(VP9_COMMON *cm, MACROBLOCKD *xd,
                                     BLOCK_SIZE bsize, vp9_reader *r) {
  const uint8_t context = vp9_get_pred_context_tx_size(xd);
  const vp9_prob *tx_probs = get_tx_probs(bsize, context, &cm->fc.tx_probs);
  TX_SIZE tx_size = vp9_read(r, tx_probs[0]);
  if (tx_size != TX_4X4 && bsize >= BLOCK_16X16) {
    tx_size += vp9_read(r, tx_probs[1]);
    if (tx_size != TX_8X8 && bsize >= BLOCK_32X32)
      tx_size += vp9_read(r, tx_probs[2]);
  }

  if (!cm->frame_parallel_decoding_mode)
    ++get_tx_counts(bsize, context, &cm->counts.tx)[tx_size];
  return tx_size;
}

static TX_SIZE read_tx_size(VP9_COMMON *const cm, MACROBLOCKD *const xd,
                            TX_MODE tx_mode, BLOCK_SIZE bsize, int allow_select,
                            vp9_reader *r) {
  if (allow_select && tx_mode == TX_MODE_SELECT && bsize >= BLOCK_8X8) {
    return read_selected_tx_size(cm, xd, bsize, r);
  } else {
    const TX_SIZE max_tx_size_block = max_txsize_lookup[bsize];
    const TX_SIZE max_tx_size_txmode = tx_mode_to_biggest_tx_size[tx_mode];
    return MIN(max_tx_size_block, max_tx_size_txmode);
  }
}

static void set_segment_id(VP9_COMMON *cm, BLOCK_SIZE bsize,
                           int mi_row, int mi_col, int segment_id) {
  const int mi_offset = mi_row * cm->mi_cols + mi_col;
  const int bw = 1 << mi_width_log2(bsize);
  const int bh = 1 << mi_height_log2(bsize);
  const int xmis = MIN(cm->mi_cols - mi_col, bw);
  const int ymis = MIN(cm->mi_rows - mi_row, bh);
  int x, y;

  assert(segment_id >= 0 && segment_id < MAX_SEGMENTS);

  for (y = 0; y < ymis; y++)
    for (x = 0; x < xmis; x++)
      cm->last_frame_seg_map[mi_offset + y * cm->mi_cols + x] = segment_id;
}

static int read_intra_segment_id(VP9_COMMON *const cm, MACROBLOCKD *const xd,
                                 int mi_row, int mi_col,
                                 vp9_reader *r) {
  struct segmentation *const seg = &cm->seg;
  const BLOCK_SIZE bsize = xd->mi_8x8[0]->mbmi.sb_type;
  int segment_id;

  if (!seg->enabled)
    return 0;  // Default for disabled segmentation

  if (!seg->update_map)
    return 0;

  segment_id = read_segment_id(r, seg);
  set_segment_id(cm, bsize, mi_row, mi_col, segment_id);
  return segment_id;
}

static int read_inter_segment_id(VP9_COMMON *const cm, MACROBLOCKD *const xd,
                                 int mi_row, int mi_col, vp9_reader *r) {
  struct segmentation *const seg = &cm->seg;
  const BLOCK_SIZE bsize = xd->mi_8x8[0]->mbmi.sb_type;
  int pred_segment_id, segment_id;

  if (!seg->enabled)
    return 0;  // Default for disabled segmentation

  pred_segment_id = vp9_get_segment_id(cm, cm->last_frame_seg_map,
                                       bsize, mi_row, mi_col);
  if (!seg->update_map)
    return pred_segment_id;

  if (seg->temporal_update) {
    const vp9_prob pred_prob = vp9_get_pred_prob_seg_id(seg, xd);
    const int pred_flag = vp9_read(r, pred_prob);
    vp9_set_pred_flag_seg_id(xd, pred_flag);
    segment_id = pred_flag ? pred_segment_id
                           : read_segment_id(r, seg);
  } else {
    segment_id = read_segment_id(r, seg);
  }
  set_segment_id(cm, bsize, mi_row, mi_col, segment_id);
  return segment_id;
}

static int read_skip_coeff(VP9_COMMON *cm, const MACROBLOCKD *xd,
                           int segment_id, vp9_reader *r) {
  if (vp9_segfeature_active(&cm->seg, segment_id, SEG_LVL_SKIP)) {
    return 1;
  } else {
    const int ctx = vp9_get_pred_context_mbskip(xd);
    const int skip = vp9_read(r, cm->fc.mbskip_probs[ctx]);
    if (!cm->frame_parallel_decoding_mode)
      ++cm->counts.mbskip[ctx][skip];
    return skip;
  }
}

static void read_intra_frame_mode_info(VP9_COMMON *const cm,
                                       MACROBLOCKD *const xd,
                                       MODE_INFO *const m,
                                       int mi_row, int mi_col, vp9_reader *r) {
  MB_MODE_INFO *const mbmi = &m->mbmi;
  const BLOCK_SIZE bsize = mbmi->sb_type;
  const MODE_INFO *above_mi = xd->mi_8x8[-cm->mode_info_stride];
  const MODE_INFO *left_mi  = xd->left_available ? xd->mi_8x8[-1] : NULL;

  mbmi->segment_id = read_intra_segment_id(cm, xd, mi_row, mi_col, r);
  mbmi->skip_coeff = read_skip_coeff(cm, xd, mbmi->segment_id, r);
  mbmi->tx_size = read_tx_size(cm, xd, cm->tx_mode, bsize, 1, r);
  mbmi->ref_frame[0] = INTRA_FRAME;
  mbmi->ref_frame[1] = NONE;

  if (bsize >= BLOCK_8X8) {
    const MB_PREDICTION_MODE A = above_block_mode(m, above_mi, 0);
    const MB_PREDICTION_MODE L = left_block_mode(m, left_mi, 0);
    mbmi->mode = read_intra_mode(r, vp9_kf_y_mode_prob[A][L]);
  } else {
    // Only 4x4, 4x8, 8x4 blocks
    const int num_4x4_w = num_4x4_blocks_wide_lookup[bsize];  // 1 or 2
    const int num_4x4_h = num_4x4_blocks_high_lookup[bsize];  // 1 or 2
    int idx, idy;

    for (idy = 0; idy < 2; idy += num_4x4_h) {
      for (idx = 0; idx < 2; idx += num_4x4_w) {
        const int ib = idy * 2 + idx;
        const MB_PREDICTION_MODE A = above_block_mode(m, above_mi, ib);
        const MB_PREDICTION_MODE L = left_block_mode(m, left_mi, ib);
        const MB_PREDICTION_MODE b_mode = read_intra_mode(r,
                                              vp9_kf_y_mode_prob[A][L]);
        m->bmi[ib].as_mode = b_mode;
        if (num_4x4_h == 2)
          m->bmi[ib + 2].as_mode = b_mode;
        if (num_4x4_w == 2)
          m->bmi[ib + 1].as_mode = b_mode;
      }
    }

    mbmi->mode = m->bmi[3].as_mode;
  }

  mbmi->uv_mode = read_intra_mode(r, vp9_kf_uv_mode_prob[mbmi->mode]);
}

static int read_mv_component(vp9_reader *r,
                             const nmv_component *mvcomp, int usehp) {
  int mag, d, fr, hp;
  const int sign = vp9_read(r, mvcomp->sign);
  const int mv_class = treed_read(r, vp9_mv_class_tree, mvcomp->classes);
  const int class0 = mv_class == MV_CLASS_0;

  // Integer part
  if (class0) {
    d = treed_read(r, vp9_mv_class0_tree, mvcomp->class0);
  } else {
    int i;
    const int n = mv_class + CLASS0_BITS - 1;  // number of bits

    d = 0;
    for (i = 0; i < n; ++i)
      d |= vp9_read(r, mvcomp->bits[i]) << i;
  }

  // Fractional part
  fr = treed_read(r, vp9_mv_fp_tree,
                  class0 ? mvcomp->class0_fp[d] : mvcomp->fp);


  // High precision part (if hp is not used, the default value of the hp is 1)
  hp = usehp ? vp9_read(r, class0 ? mvcomp->class0_hp : mvcomp->hp)
             : 1;

  // Result
  mag = vp9_get_mv_mag(mv_class, (d << 3) | (fr << 1) | hp) + 1;
  return sign ? -mag : mag;
}

static INLINE void read_mv(vp9_reader *r, MV *mv, const MV *ref,
                           const nmv_context *ctx,
                           nmv_context_counts *counts, int allow_hp) {
  const MV_JOINT_TYPE j = treed_read(r, vp9_mv_joint_tree, ctx->joints);
  const int use_hp = allow_hp && vp9_use_mv_hp(ref);
  MV diff = {0, 0};

  if (mv_joint_vertical(j))
    diff.row = read_mv_component(r, &ctx->comps[0], use_hp);

  if (mv_joint_horizontal(j))
    diff.col = read_mv_component(r, &ctx->comps[1], use_hp);

  vp9_inc_mv(&diff, counts);

  mv->row = ref->row + diff.row;
  mv->col = ref->col + diff.col;
}

static COMPPREDMODE_TYPE read_reference_mode(VP9_COMMON *cm,
                                             const MACROBLOCKD *xd,
                                             vp9_reader *r) {
  const int ctx = vp9_get_pred_context_comp_inter_inter(cm, xd);
  const int mode = vp9_read(r, cm->fc.comp_inter_prob[ctx]);
  if (!cm->frame_parallel_decoding_mode)
    ++cm->counts.comp_inter[ctx][mode];
  return mode;  // SINGLE_PREDICTION_ONLY or COMP_PREDICTION_ONLY
}

// Read the referncence frame
static void read_ref_frames(VP9_COMMON *const cm, MACROBLOCKD *const xd,
                            vp9_reader *r,
                            int segment_id, MV_REFERENCE_FRAME ref_frame[2]) {
  FRAME_CONTEXT *const fc = &cm->fc;
  FRAME_COUNTS *const counts = &cm->counts;

  if (vp9_segfeature_active(&cm->seg, segment_id, SEG_LVL_REF_FRAME)) {
    ref_frame[0] = vp9_get_segdata(&cm->seg, segment_id, SEG_LVL_REF_FRAME);
    ref_frame[1] = NONE;
  } else {
    const COMPPREDMODE_TYPE mode = (cm->comp_pred_mode == HYBRID_PREDICTION)
                                      ? read_reference_mode(cm, xd, r)
                                      : cm->comp_pred_mode;

    // FIXME(rbultje) I'm pretty sure this breaks segmentation ref frame coding
    if (mode == COMP_PREDICTION_ONLY) {
      const int idx = cm->ref_frame_sign_bias[cm->comp_fixed_ref];
      const int ctx = vp9_get_pred_context_comp_ref_p(cm, xd);
      const int bit = vp9_read(r, fc->comp_ref_prob[ctx]);
      if (!cm->frame_parallel_decoding_mode)
        ++counts->comp_ref[ctx][bit];
      ref_frame[idx] = cm->comp_fixed_ref;
      ref_frame[!idx] = cm->comp_var_ref[bit];
    } else if (mode == SINGLE_PREDICTION_ONLY) {
      const int ctx0 = vp9_get_pred_context_single_ref_p1(xd);
      const int bit0 = vp9_read(r, fc->single_ref_prob[ctx0][0]);
      if (!cm->frame_parallel_decoding_mode)
        ++counts->single_ref[ctx0][0][bit0];
      if (bit0) {
        const int ctx1 = vp9_get_pred_context_single_ref_p2(xd);
        const int bit1 = vp9_read(r, fc->single_ref_prob[ctx1][1]);
        if (!cm->frame_parallel_decoding_mode)
          ++counts->single_ref[ctx1][1][bit1];
        ref_frame[0] = bit1 ? ALTREF_FRAME : GOLDEN_FRAME;
      } else {
        ref_frame[0] = LAST_FRAME;
      }

      ref_frame[1] = NONE;
    } else {
      assert(!"Invalid prediction mode.");
    }
  }
}


static INLINE INTERPOLATION_TYPE read_switchable_filter_type(
    VP9_COMMON *const cm, MACROBLOCKD *const xd, vp9_reader *r) {
  const int ctx = vp9_get_pred_context_switchable_interp(xd);
  const int type = treed_read(r, vp9_switchable_interp_tree,
                              cm->fc.switchable_interp_prob[ctx]);
  if (!cm->frame_parallel_decoding_mode)
    ++cm->counts.switchable_interp[ctx][type];
  return type;
}

static void read_intra_block_mode_info(VP9_COMMON *const cm, MODE_INFO *mi,
                                       vp9_reader *r) {
  MB_MODE_INFO *const mbmi = &mi->mbmi;
  const BLOCK_SIZE bsize = mi->mbmi.sb_type;

  mbmi->ref_frame[0] = INTRA_FRAME;
  mbmi->ref_frame[1] = NONE;

  if (bsize >= BLOCK_8X8) {
    mbmi->mode = read_intra_mode_y(cm, r, size_group_lookup[bsize]);
  } else {
     // Only 4x4, 4x8, 8x4 blocks
     const int num_4x4_w = num_4x4_blocks_wide_lookup[bsize];  // 1 or 2
     const int num_4x4_h = num_4x4_blocks_high_lookup[bsize];  // 1 or 2
     int idx, idy;

     for (idy = 0; idy < 2; idy += num_4x4_h) {
       for (idx = 0; idx < 2; idx += num_4x4_w) {
         const int ib = idy * 2 + idx;
         const int b_mode = read_intra_mode_y(cm, r, 0);
         mi->bmi[ib].as_mode = b_mode;
         if (num_4x4_h == 2)
           mi->bmi[ib + 2].as_mode = b_mode;
         if (num_4x4_w == 2)
           mi->bmi[ib + 1].as_mode = b_mode;
      }
    }
    mbmi->mode = mi->bmi[3].as_mode;
  }

  mbmi->uv_mode = read_intra_mode_uv(cm, r, mbmi->mode);
}

static INLINE int assign_mv(VP9_COMMON *cm, MB_PREDICTION_MODE mode,
                             int_mv mv[2], int_mv best_mv[2],
                             int_mv nearest_mv[2], int_mv near_mv[2],
                             int is_compound, int allow_hp, vp9_reader *r) {
  int i;
  int ret = 1;

  switch (mode) {
    case NEWMV: {
      nmv_context_counts *const mv_counts = cm->frame_parallel_decoding_mode ?
                                            NULL : &cm->counts.mv;
      read_mv(r, &mv[0].as_mv, &best_mv[0].as_mv,
              &cm->fc.nmvc, mv_counts, allow_hp);
      if (is_compound)
        read_mv(r, &mv[1].as_mv, &best_mv[1].as_mv,
                &cm->fc.nmvc, mv_counts, allow_hp);
      for (i = 0; i < 1 + is_compound; ++i) {
        ret = ret && mv[i].as_mv.row < MV_UPP && mv[i].as_mv.row > MV_LOW;
        ret = ret && mv[i].as_mv.col < MV_UPP && mv[i].as_mv.col > MV_LOW;
      }
      break;
    }
    case NEARESTMV: {
      mv[0].as_int = nearest_mv[0].as_int;
      if (is_compound) mv[1].as_int = nearest_mv[1].as_int;
      break;
    }
    case NEARMV: {
      mv[0].as_int = near_mv[0].as_int;
      if (is_compound) mv[1].as_int = near_mv[1].as_int;
      break;
    }
    case ZEROMV: {
      mv[0].as_int = 0;
      if (is_compound) mv[1].as_int = 0;
      break;
    }
    default: {
      return 0;
    }
  }
  return ret;
}

static int read_is_inter_block(VP9_COMMON *const cm, MACROBLOCKD *const xd,
                               int segment_id, vp9_reader *r) {
  if (vp9_segfeature_active(&cm->seg, segment_id, SEG_LVL_REF_FRAME)) {
    return vp9_get_segdata(&cm->seg, segment_id, SEG_LVL_REF_FRAME) !=
           INTRA_FRAME;
  } else {
    const int ctx = vp9_get_pred_context_intra_inter(xd);
    const int is_inter = vp9_read(r, vp9_get_pred_prob_intra_inter(cm, xd));
    if (!cm->frame_parallel_decoding_mode)
      ++cm->counts.intra_inter[ctx][is_inter];
    return is_inter;
  }
}

static void read_inter_block_mode_info(VP9_COMMON *const cm,
                                       MACROBLOCKD *const xd,
                                       const TileInfo *const tile,
                                       MODE_INFO *const mi,
                                       int mi_row, int mi_col, vp9_reader *r) {
  MB_MODE_INFO *const mbmi = &mi->mbmi;
  const BLOCK_SIZE bsize = mbmi->sb_type;
  const int allow_hp = cm->allow_high_precision_mv;

  int_mv nearest[2], nearmv[2], best[2];
  uint8_t inter_mode_ctx;
  MV_REFERENCE_FRAME ref0;
  int is_compound;

  mbmi->uv_mode = DC_PRED;
  read_ref_frames(cm, xd, r, mbmi->segment_id, mbmi->ref_frame);
  ref0 = mbmi->ref_frame[0];
  is_compound = has_second_ref(mbmi);

  vp9_find_mv_refs(cm, xd, tile, mi, xd->last_mi, ref0, mbmi->ref_mvs[ref0],
                   mi_row, mi_col);

  inter_mode_ctx = mbmi->mode_context[ref0];

  if (vp9_segfeature_active(&cm->seg, mbmi->segment_id, SEG_LVL_SKIP)) {
    mbmi->mode = ZEROMV;
    if (bsize < BLOCK_8X8) {
        vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                           "Invalid usage of segement feature on small blocks");
        return;
    }
  } else {
    if (bsize >= BLOCK_8X8)
      mbmi->mode = read_inter_mode(cm, r, inter_mode_ctx);
  }

  // nearest, nearby
  if (bsize < BLOCK_8X8 || mbmi->mode != ZEROMV) {
    vp9_find_best_ref_mvs(xd, allow_hp,
                          mbmi->ref_mvs[ref0], &nearest[0], &nearmv[0]);
    best[0].as_int = nearest[0].as_int;
  }

  if (is_compound) {
    const MV_REFERENCE_FRAME ref1 = mbmi->ref_frame[1];
    vp9_find_mv_refs(cm, xd, tile, mi, xd->last_mi,
                     ref1, mbmi->ref_mvs[ref1], mi_row, mi_col);

    if (bsize < BLOCK_8X8 || mbmi->mode != ZEROMV) {
      vp9_find_best_ref_mvs(xd, allow_hp,
                            mbmi->ref_mvs[ref1], &nearest[1], &nearmv[1]);
      best[1].as_int = nearest[1].as_int;
    }
  }

  mbmi->interp_filter = (cm->mcomp_filter_type == SWITCHABLE)
                      ? read_switchable_filter_type(cm, xd, r)
                      : cm->mcomp_filter_type;

  if (bsize < BLOCK_8X8) {
    const int num_4x4_w = num_4x4_blocks_wide_lookup[bsize];  // 1 or 2
    const int num_4x4_h = num_4x4_blocks_high_lookup[bsize];  // 1 or 2
    int idx, idy;
    int b_mode;
    for (idy = 0; idy < 2; idy += num_4x4_h) {
      for (idx = 0; idx < 2; idx += num_4x4_w) {
        int_mv block[2];
        const int j = idy * 2 + idx;
        b_mode = read_inter_mode(cm, r, inter_mode_ctx);

        if (b_mode == NEARESTMV || b_mode == NEARMV) {
          vp9_append_sub8x8_mvs_for_idx(cm, xd, tile, &nearest[0],
                                        &nearmv[0], j, 0,
                                        mi_row, mi_col);

          if (is_compound)
            vp9_append_sub8x8_mvs_for_idx(cm, xd, tile, &nearest[1],
                                          &nearmv[1], j, 1,
                                          mi_row, mi_col);
        }

        if (!assign_mv(cm, b_mode, block, best, nearest, nearmv,
                       is_compound, allow_hp, r)) {
          xd->corrupted |= 1;
          break;
        };


        mi->bmi[j].as_mv[0].as_int = block[0].as_int;
        if (is_compound)
          mi->bmi[j].as_mv[1].as_int = block[1].as_int;

        if (num_4x4_h == 2)
          mi->bmi[j + 2] = mi->bmi[j];
        if (num_4x4_w == 2)
          mi->bmi[j + 1] = mi->bmi[j];
      }
    }

    mi->mbmi.mode = b_mode;

    mbmi->mv[0].as_int = mi->bmi[3].as_mv[0].as_int;
    mbmi->mv[1].as_int = mi->bmi[3].as_mv[1].as_int;
  } else {
    xd->corrupted |= !assign_mv(cm, mbmi->mode, mbmi->mv,
                                best, nearest, nearmv,
                                is_compound, allow_hp, r);
  }
}

static void read_inter_frame_mode_info(VP9_COMMON *const cm,
                                       MACROBLOCKD *const xd,
                                       const TileInfo *const tile,
                                       MODE_INFO *const mi,
                                       int mi_row, int mi_col, vp9_reader *r) {
  MB_MODE_INFO *const mbmi = &mi->mbmi;
  int inter_block;

  mbmi->mv[0].as_int = 0;
  mbmi->mv[1].as_int = 0;
  mbmi->segment_id = read_inter_segment_id(cm, xd, mi_row, mi_col, r);
  mbmi->skip_coeff = read_skip_coeff(cm, xd, mbmi->segment_id, r);
  inter_block = read_is_inter_block(cm, xd, mbmi->segment_id, r);
  mbmi->tx_size = read_tx_size(cm, xd, cm->tx_mode, mbmi->sb_type,
                               !mbmi->skip_coeff || !inter_block, r);

  if (inter_block)
    read_inter_block_mode_info(cm, xd, tile, mi, mi_row, mi_col, r);
  else
    read_intra_block_mode_info(cm, mi, r);
}

void vp9_read_mode_info(VP9_COMMON *cm, MACROBLOCKD *xd,
                        const TileInfo *const tile,
                        int mi_row, int mi_col, vp9_reader *r) {
  MODE_INFO *const mi = xd->mi_8x8[0];
  const BLOCK_SIZE bsize = mi->mbmi.sb_type;
  const int bw = 1 << mi_width_log2(bsize);
  const int bh = 1 << mi_height_log2(bsize);
  const int y_mis = MIN(bh, cm->mi_rows - mi_row);
  const int x_mis = MIN(bw, cm->mi_cols - mi_col);
  int x, y, z;

  if (frame_is_intra_only(cm))
    read_intra_frame_mode_info(cm, xd, mi, mi_row, mi_col, r);
  else
    read_inter_frame_mode_info(cm, xd, tile, mi, mi_row, mi_col, r);

  for (y = 0, z = 0; y < y_mis; y++, z += cm->mode_info_stride) {
    for (x = !y; x < x_mis; x++) {
      xd->mi_8x8[z + x] = mi;
    }
  }
}