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mvref_common.c (58277B)


      1 /*
      2 * Copyright (c) 2016, Alliance for Open Media. All rights reserved.
      3 *
      4 * This source code is subject to the terms of the BSD 2 Clause License and
      5 * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
      6 * was not distributed with this source code in the LICENSE file, you can
      7 * obtain it at www.aomedia.org/license/software. If the Alliance for Open
      8 * Media Patent License 1.0 was not distributed with this source code in the
      9 * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
     10 */
     11 
     12 #include <stdlib.h>
     13 
     14 #include "av1/common/mvref_common.h"
     15 #include "av1/common/warped_motion.h"
     16 
     17 // Although we assign 32 bit integers, all the values are strictly under 14
     18 // bits.
     19 static const int div_mult[32] = { 0,    16384, 8192, 5461, 4096, 3276, 2730,
     20                                  2340, 2048,  1820, 1638, 1489, 1365, 1260,
     21                                  1170, 1092,  1024, 963,  910,  862,  819,
     22                                  780,  744,   712,  682,  655,  630,  606,
     23                                  585,  564,   546,  528 };
     24 
     25 // TODO(jingning): Consider the use of lookup table for (num / den)
     26 // altogether.
     27 void av1_get_mv_projection(MV *output, MV ref, int num, int den) {
     28  den = AOMMIN(den, MAX_FRAME_DISTANCE);
     29  num = num > 0 ? AOMMIN(num, MAX_FRAME_DISTANCE)
     30                : AOMMAX(num, -MAX_FRAME_DISTANCE);
     31  const int mv_row =
     32      ROUND_POWER_OF_TWO_SIGNED(ref.row * num * div_mult[den], 14);
     33  const int mv_col =
     34      ROUND_POWER_OF_TWO_SIGNED(ref.col * num * div_mult[den], 14);
     35  const int clamp_max = MV_UPP - 1;
     36  const int clamp_min = MV_LOW + 1;
     37  output->row = (int16_t)clamp(mv_row, clamp_min, clamp_max);
     38  output->col = (int16_t)clamp(mv_col, clamp_min, clamp_max);
     39 }
     40 
     41 void av1_copy_frame_mvs(const AV1_COMMON *const cm,
     42                        const MB_MODE_INFO *const mi, int mi_row, int mi_col,
     43                        int x_mis, int y_mis) {
     44  const int frame_mvs_stride = ROUND_POWER_OF_TWO(cm->mi_params.mi_cols, 1);
     45  MV_REF *frame_mvs =
     46      cm->cur_frame->mvs + (mi_row >> 1) * frame_mvs_stride + (mi_col >> 1);
     47  x_mis = ROUND_POWER_OF_TWO(x_mis, 1);
     48  y_mis = ROUND_POWER_OF_TWO(y_mis, 1);
     49  int w, h;
     50 
     51  for (h = 0; h < y_mis; h++) {
     52    MV_REF *mv = frame_mvs;
     53    for (w = 0; w < x_mis; w++) {
     54      mv->ref_frame = NONE_FRAME;
     55      mv->mv.as_int = 0;
     56 
     57      for (int idx = 0; idx < 2; ++idx) {
     58        MV_REFERENCE_FRAME ref_frame = mi->ref_frame[idx];
     59        if (ref_frame > INTRA_FRAME) {
     60          int8_t ref_idx = cm->ref_frame_side[ref_frame];
     61          if (ref_idx) continue;
     62          if ((abs(mi->mv[idx].as_mv.row) > REFMVS_LIMIT) ||
     63              (abs(mi->mv[idx].as_mv.col) > REFMVS_LIMIT))
     64            continue;
     65          mv->ref_frame = ref_frame;
     66          mv->mv.as_int = mi->mv[idx].as_int;
     67        }
     68      }
     69      mv++;
     70    }
     71    frame_mvs += frame_mvs_stride;
     72  }
     73 }
     74 
     75 static inline void add_ref_mv_candidate(
     76    const MB_MODE_INFO *const candidate, const MV_REFERENCE_FRAME rf[2],
     77    uint8_t *refmv_count, uint8_t *ref_match_count, uint8_t *newmv_count,
     78    CANDIDATE_MV *ref_mv_stack, uint16_t *ref_mv_weight,
     79    int_mv *gm_mv_candidates, const WarpedMotionParams *gm_params,
     80    uint16_t weight) {
     81  if (!is_inter_block(candidate)) return;
     82  assert(weight % 2 == 0);
     83  int index, ref;
     84 
     85  if (rf[1] == NONE_FRAME) {
     86    // single reference frame
     87    for (ref = 0; ref < 2; ++ref) {
     88      if (candidate->ref_frame[ref] == rf[0]) {
     89        const int is_gm_block =
     90            is_global_mv_block(candidate, gm_params[rf[0]].wmtype);
     91        const int_mv this_refmv =
     92            is_gm_block ? gm_mv_candidates[0] : get_block_mv(candidate, ref);
     93        for (index = 0; index < *refmv_count; ++index) {
     94          if (ref_mv_stack[index].this_mv.as_int == this_refmv.as_int) {
     95            ref_mv_weight[index] += weight;
     96            break;
     97          }
     98        }
     99 
    100        // Add a new item to the list.
    101        if (index == *refmv_count && *refmv_count < MAX_REF_MV_STACK_SIZE) {
    102          ref_mv_stack[index].this_mv = this_refmv;
    103          ref_mv_weight[index] = weight;
    104          ++(*refmv_count);
    105        }
    106        if (have_newmv_in_inter_mode(candidate->mode)) ++*newmv_count;
    107        ++*ref_match_count;
    108      }
    109    }
    110  } else {
    111    // compound reference frame
    112    if (candidate->ref_frame[0] == rf[0] && candidate->ref_frame[1] == rf[1]) {
    113      int_mv this_refmv[2];
    114 
    115      for (ref = 0; ref < 2; ++ref) {
    116        if (is_global_mv_block(candidate, gm_params[rf[ref]].wmtype))
    117          this_refmv[ref] = gm_mv_candidates[ref];
    118        else
    119          this_refmv[ref] = get_block_mv(candidate, ref);
    120      }
    121 
    122      for (index = 0; index < *refmv_count; ++index) {
    123        if ((ref_mv_stack[index].this_mv.as_int == this_refmv[0].as_int) &&
    124            (ref_mv_stack[index].comp_mv.as_int == this_refmv[1].as_int)) {
    125          ref_mv_weight[index] += weight;
    126          break;
    127        }
    128      }
    129 
    130      // Add a new item to the list.
    131      if (index == *refmv_count && *refmv_count < MAX_REF_MV_STACK_SIZE) {
    132        ref_mv_stack[index].this_mv = this_refmv[0];
    133        ref_mv_stack[index].comp_mv = this_refmv[1];
    134        ref_mv_weight[index] = weight;
    135        ++(*refmv_count);
    136      }
    137      if (have_newmv_in_inter_mode(candidate->mode)) ++*newmv_count;
    138      ++*ref_match_count;
    139    }
    140  }
    141 }
    142 
    143 static inline void scan_row_mbmi(const AV1_COMMON *cm, const MACROBLOCKD *xd,
    144                                 int mi_col, const MV_REFERENCE_FRAME rf[2],
    145                                 int row_offset, CANDIDATE_MV *ref_mv_stack,
    146                                 uint16_t *ref_mv_weight, uint8_t *refmv_count,
    147                                 uint8_t *ref_match_count, uint8_t *newmv_count,
    148                                 int_mv *gm_mv_candidates, int max_row_offset,
    149                                 int *processed_rows) {
    150  int end_mi = AOMMIN(xd->width, cm->mi_params.mi_cols - mi_col);
    151  end_mi = AOMMIN(end_mi, mi_size_wide[BLOCK_64X64]);
    152  const int width_8x8 = mi_size_wide[BLOCK_8X8];
    153  const int width_16x16 = mi_size_wide[BLOCK_16X16];
    154  int col_offset = 0;
    155  // TODO(jingning): Revisit this part after cb4x4 is stable.
    156  if (abs(row_offset) > 1) {
    157    col_offset = 1;
    158    if ((mi_col & 0x01) && xd->width < width_8x8) --col_offset;
    159  }
    160  const int use_step_16 = (xd->width >= 16);
    161  MB_MODE_INFO **const candidate_mi0 = xd->mi + row_offset * xd->mi_stride;
    162 
    163  for (int i = 0; i < end_mi;) {
    164    const MB_MODE_INFO *const candidate = candidate_mi0[col_offset + i];
    165    const int candidate_bsize = candidate->bsize;
    166    const int n4_w = mi_size_wide[candidate_bsize];
    167    int len = AOMMIN(xd->width, n4_w);
    168    if (use_step_16)
    169      len = AOMMAX(width_16x16, len);
    170    else if (abs(row_offset) > 1)
    171      len = AOMMAX(len, width_8x8);
    172 
    173    uint16_t weight = 2;
    174    if (xd->width >= width_8x8 && xd->width <= n4_w) {
    175      uint16_t inc = AOMMIN(-max_row_offset + row_offset + 1,
    176                            mi_size_high[candidate_bsize]);
    177      // Obtain range used in weight calculation.
    178      weight = AOMMAX(weight, inc);
    179      // Update processed rows.
    180      *processed_rows = inc - row_offset - 1;
    181    }
    182 
    183    add_ref_mv_candidate(candidate, rf, refmv_count, ref_match_count,
    184                         newmv_count, ref_mv_stack, ref_mv_weight,
    185                         gm_mv_candidates, cm->global_motion, len * weight);
    186 
    187    i += len;
    188  }
    189 }
    190 
    191 static inline void scan_col_mbmi(const AV1_COMMON *cm, const MACROBLOCKD *xd,
    192                                 int mi_row, const MV_REFERENCE_FRAME rf[2],
    193                                 int col_offset, CANDIDATE_MV *ref_mv_stack,
    194                                 uint16_t *ref_mv_weight, uint8_t *refmv_count,
    195                                 uint8_t *ref_match_count, uint8_t *newmv_count,
    196                                 int_mv *gm_mv_candidates, int max_col_offset,
    197                                 int *processed_cols) {
    198  int end_mi = AOMMIN(xd->height, cm->mi_params.mi_rows - mi_row);
    199  end_mi = AOMMIN(end_mi, mi_size_high[BLOCK_64X64]);
    200  const int n8_h_8 = mi_size_high[BLOCK_8X8];
    201  const int n8_h_16 = mi_size_high[BLOCK_16X16];
    202  int i;
    203  int row_offset = 0;
    204  if (abs(col_offset) > 1) {
    205    row_offset = 1;
    206    if ((mi_row & 0x01) && xd->height < n8_h_8) --row_offset;
    207  }
    208  const int use_step_16 = (xd->height >= 16);
    209 
    210  for (i = 0; i < end_mi;) {
    211    const MB_MODE_INFO *const candidate =
    212        xd->mi[(row_offset + i) * xd->mi_stride + col_offset];
    213    const int candidate_bsize = candidate->bsize;
    214    const int n4_h = mi_size_high[candidate_bsize];
    215    int len = AOMMIN(xd->height, n4_h);
    216    if (use_step_16)
    217      len = AOMMAX(n8_h_16, len);
    218    else if (abs(col_offset) > 1)
    219      len = AOMMAX(len, n8_h_8);
    220 
    221    int weight = 2;
    222    if (xd->height >= n8_h_8 && xd->height <= n4_h) {
    223      int inc = AOMMIN(-max_col_offset + col_offset + 1,
    224                       mi_size_wide[candidate_bsize]);
    225      // Obtain range used in weight calculation.
    226      weight = AOMMAX(weight, inc);
    227      // Update processed cols.
    228      *processed_cols = inc - col_offset - 1;
    229    }
    230 
    231    add_ref_mv_candidate(candidate, rf, refmv_count, ref_match_count,
    232                         newmv_count, ref_mv_stack, ref_mv_weight,
    233                         gm_mv_candidates, cm->global_motion, len * weight);
    234 
    235    i += len;
    236  }
    237 }
    238 
    239 static inline void scan_blk_mbmi(const AV1_COMMON *cm, const MACROBLOCKD *xd,
    240                                 const int mi_row, const int mi_col,
    241                                 const MV_REFERENCE_FRAME rf[2], int row_offset,
    242                                 int col_offset, CANDIDATE_MV *ref_mv_stack,
    243                                 uint16_t *ref_mv_weight,
    244                                 uint8_t *ref_match_count, uint8_t *newmv_count,
    245                                 int_mv *gm_mv_candidates,
    246                                 uint8_t *refmv_count) {
    247  const TileInfo *const tile = &xd->tile;
    248  POSITION mi_pos;
    249 
    250  mi_pos.row = row_offset;
    251  mi_pos.col = col_offset;
    252 
    253  if (is_inside(tile, mi_col, mi_row, &mi_pos)) {
    254    const MB_MODE_INFO *const candidate =
    255        xd->mi[mi_pos.row * xd->mi_stride + mi_pos.col];
    256    const int len = mi_size_wide[BLOCK_8X8];
    257 
    258    add_ref_mv_candidate(candidate, rf, refmv_count, ref_match_count,
    259                         newmv_count, ref_mv_stack, ref_mv_weight,
    260                         gm_mv_candidates, cm->global_motion, 2 * len);
    261  }  // Analyze a single 8x8 block motion information.
    262 }
    263 
    264 static int has_top_right(const AV1_COMMON *cm, const MACROBLOCKD *xd,
    265                         int mi_row, int mi_col, int bs) {
    266  const int sb_mi_size = mi_size_wide[cm->seq_params->sb_size];
    267  const int mask_row = mi_row & (sb_mi_size - 1);
    268  const int mask_col = mi_col & (sb_mi_size - 1);
    269 
    270  if (bs > mi_size_wide[BLOCK_64X64]) return 0;
    271 
    272  // In a split partition all apart from the bottom right has a top right
    273  int has_tr = !((mask_row & bs) && (mask_col & bs));
    274 
    275  // bs > 0 and bs is a power of 2
    276  assert(bs > 0 && !(bs & (bs - 1)));
    277 
    278  // For each 4x4 group of blocks, when the bottom right is decoded the blocks
    279  // to the right have not been decoded therefore the bottom right does
    280  // not have a top right
    281  while (bs < sb_mi_size) {
    282    if (mask_col & bs) {
    283      if ((mask_col & (2 * bs)) && (mask_row & (2 * bs))) {
    284        has_tr = 0;
    285        break;
    286      }
    287    } else {
    288      break;
    289    }
    290    bs <<= 1;
    291  }
    292 
    293  // In a VERTICAL or VERTICAL_4 partition, all partition before the last one
    294  // always have a top right (as the block above will have been decoded).
    295  if (xd->width < xd->height) {
    296    if (!xd->is_last_vertical_rect) has_tr = 1;
    297  }
    298 
    299  // In a HORIZONTAL or HORIZONTAL_4 partition, partitions after the first one
    300  // never have a top right (as the block to the right won't have been decoded).
    301  if (xd->width > xd->height) {
    302    if (!xd->is_first_horizontal_rect) has_tr = 0;
    303  }
    304 
    305  // The bottom left square of a Vertical A (in the old format) does
    306  // not have a top right as it is decoded before the right hand
    307  // rectangle of the partition
    308  if (xd->mi[0]->partition == PARTITION_VERT_A) {
    309    if (xd->width == xd->height)
    310      if (mask_row & bs) has_tr = 0;
    311  }
    312 
    313  return has_tr;
    314 }
    315 
    316 static int check_sb_border(const int mi_row, const int mi_col,
    317                           const int row_offset, const int col_offset) {
    318  const int sb_mi_size = mi_size_wide[BLOCK_64X64];
    319  const int row = mi_row & (sb_mi_size - 1);
    320  const int col = mi_col & (sb_mi_size - 1);
    321 
    322  if (row + row_offset < 0 || row + row_offset >= sb_mi_size ||
    323      col + col_offset < 0 || col + col_offset >= sb_mi_size)
    324    return 0;
    325 
    326  return 1;
    327 }
    328 
    329 static int add_tpl_ref_mv(const AV1_COMMON *cm, const MACROBLOCKD *xd,
    330                          int mi_row, int mi_col, MV_REFERENCE_FRAME ref_frame,
    331                          int blk_row, int blk_col, int_mv *gm_mv_candidates,
    332                          uint8_t *const refmv_count,
    333                          CANDIDATE_MV ref_mv_stack[MAX_REF_MV_STACK_SIZE],
    334                          uint16_t ref_mv_weight[MAX_REF_MV_STACK_SIZE],
    335                          int16_t *mode_context) {
    336  POSITION mi_pos;
    337  mi_pos.row = (mi_row & 0x01) ? blk_row : blk_row + 1;
    338  mi_pos.col = (mi_col & 0x01) ? blk_col : blk_col + 1;
    339 
    340  if (!is_inside(&xd->tile, mi_col, mi_row, &mi_pos)) return 0;
    341 
    342  const TPL_MV_REF *prev_frame_mvs =
    343      cm->tpl_mvs +
    344      ((mi_row + mi_pos.row) >> 1) * (cm->mi_params.mi_stride >> 1) +
    345      ((mi_col + mi_pos.col) >> 1);
    346  if (prev_frame_mvs->mfmv0.as_int == INVALID_MV) return 0;
    347 
    348  MV_REFERENCE_FRAME rf[2];
    349  av1_set_ref_frame(rf, ref_frame);
    350 
    351  const uint16_t weight_unit = 1;  // mi_size_wide[BLOCK_8X8];
    352  const int cur_frame_index = cm->cur_frame->order_hint;
    353  const RefCntBuffer *const buf_0 = get_ref_frame_buf(cm, rf[0]);
    354  const int frame0_index = buf_0->order_hint;
    355  const int cur_offset_0 = get_relative_dist(&cm->seq_params->order_hint_info,
    356                                             cur_frame_index, frame0_index);
    357  int idx;
    358  const int allow_high_precision_mv = cm->features.allow_high_precision_mv;
    359  const int force_integer_mv = cm->features.cur_frame_force_integer_mv;
    360 
    361  int_mv this_refmv;
    362  av1_get_mv_projection(&this_refmv.as_mv, prev_frame_mvs->mfmv0.as_mv,
    363                        cur_offset_0, prev_frame_mvs->ref_frame_offset);
    364  lower_mv_precision(&this_refmv.as_mv, allow_high_precision_mv,
    365                     force_integer_mv);
    366 
    367  if (rf[1] == NONE_FRAME) {
    368    if (blk_row == 0 && blk_col == 0) {
    369      if (abs(this_refmv.as_mv.row - gm_mv_candidates[0].as_mv.row) >= 16 ||
    370          abs(this_refmv.as_mv.col - gm_mv_candidates[0].as_mv.col) >= 16)
    371        mode_context[ref_frame] |= (1 << GLOBALMV_OFFSET);
    372    }
    373 
    374    for (idx = 0; idx < *refmv_count; ++idx)
    375      if (this_refmv.as_int == ref_mv_stack[idx].this_mv.as_int) break;
    376 
    377    if (idx < *refmv_count) ref_mv_weight[idx] += 2 * weight_unit;
    378 
    379    if (idx == *refmv_count && *refmv_count < MAX_REF_MV_STACK_SIZE) {
    380      ref_mv_stack[idx].this_mv.as_int = this_refmv.as_int;
    381      ref_mv_weight[idx] = 2 * weight_unit;
    382      ++(*refmv_count);
    383    }
    384  } else {
    385    // Process compound inter mode
    386    const RefCntBuffer *const buf_1 = get_ref_frame_buf(cm, rf[1]);
    387    const int frame1_index = buf_1->order_hint;
    388    const int cur_offset_1 = get_relative_dist(&cm->seq_params->order_hint_info,
    389                                               cur_frame_index, frame1_index);
    390    int_mv comp_refmv;
    391    av1_get_mv_projection(&comp_refmv.as_mv, prev_frame_mvs->mfmv0.as_mv,
    392                          cur_offset_1, prev_frame_mvs->ref_frame_offset);
    393    lower_mv_precision(&comp_refmv.as_mv, allow_high_precision_mv,
    394                       force_integer_mv);
    395 
    396    if (blk_row == 0 && blk_col == 0) {
    397      if (abs(this_refmv.as_mv.row - gm_mv_candidates[0].as_mv.row) >= 16 ||
    398          abs(this_refmv.as_mv.col - gm_mv_candidates[0].as_mv.col) >= 16 ||
    399          abs(comp_refmv.as_mv.row - gm_mv_candidates[1].as_mv.row) >= 16 ||
    400          abs(comp_refmv.as_mv.col - gm_mv_candidates[1].as_mv.col) >= 16)
    401        mode_context[ref_frame] |= (1 << GLOBALMV_OFFSET);
    402    }
    403 
    404    for (idx = 0; idx < *refmv_count; ++idx) {
    405      if (this_refmv.as_int == ref_mv_stack[idx].this_mv.as_int &&
    406          comp_refmv.as_int == ref_mv_stack[idx].comp_mv.as_int)
    407        break;
    408    }
    409 
    410    if (idx < *refmv_count) ref_mv_weight[idx] += 2 * weight_unit;
    411 
    412    if (idx == *refmv_count && *refmv_count < MAX_REF_MV_STACK_SIZE) {
    413      ref_mv_stack[idx].this_mv.as_int = this_refmv.as_int;
    414      ref_mv_stack[idx].comp_mv.as_int = comp_refmv.as_int;
    415      ref_mv_weight[idx] = 2 * weight_unit;
    416      ++(*refmv_count);
    417    }
    418  }
    419 
    420  return 1;
    421 }
    422 
    423 static inline void process_compound_ref_mv_candidate(
    424    const MB_MODE_INFO *const candidate, const AV1_COMMON *const cm,
    425    const MV_REFERENCE_FRAME *const rf, int_mv ref_id[2][2],
    426    int ref_id_count[2], int_mv ref_diff[2][2], int ref_diff_count[2]) {
    427  for (int rf_idx = 0; rf_idx < 2; ++rf_idx) {
    428    MV_REFERENCE_FRAME can_rf = candidate->ref_frame[rf_idx];
    429 
    430    for (int cmp_idx = 0; cmp_idx < 2; ++cmp_idx) {
    431      if (can_rf == rf[cmp_idx] && ref_id_count[cmp_idx] < 2) {
    432        ref_id[cmp_idx][ref_id_count[cmp_idx]] = candidate->mv[rf_idx];
    433        ++ref_id_count[cmp_idx];
    434      } else if (can_rf > INTRA_FRAME && ref_diff_count[cmp_idx] < 2) {
    435        int_mv this_mv = candidate->mv[rf_idx];
    436        if (cm->ref_frame_sign_bias[can_rf] !=
    437            cm->ref_frame_sign_bias[rf[cmp_idx]]) {
    438          this_mv.as_mv.row = -this_mv.as_mv.row;
    439          this_mv.as_mv.col = -this_mv.as_mv.col;
    440        }
    441        ref_diff[cmp_idx][ref_diff_count[cmp_idx]] = this_mv;
    442        ++ref_diff_count[cmp_idx];
    443      }
    444    }
    445  }
    446 }
    447 
    448 static inline void process_single_ref_mv_candidate(
    449    const MB_MODE_INFO *const candidate, const AV1_COMMON *const cm,
    450    MV_REFERENCE_FRAME ref_frame, uint8_t *const refmv_count,
    451    CANDIDATE_MV ref_mv_stack[MAX_REF_MV_STACK_SIZE],
    452    uint16_t ref_mv_weight[MAX_REF_MV_STACK_SIZE]) {
    453  for (int rf_idx = 0; rf_idx < 2; ++rf_idx) {
    454    if (candidate->ref_frame[rf_idx] > INTRA_FRAME) {
    455      int_mv this_mv = candidate->mv[rf_idx];
    456      if (cm->ref_frame_sign_bias[candidate->ref_frame[rf_idx]] !=
    457          cm->ref_frame_sign_bias[ref_frame]) {
    458        this_mv.as_mv.row = -this_mv.as_mv.row;
    459        this_mv.as_mv.col = -this_mv.as_mv.col;
    460      }
    461      int stack_idx;
    462      for (stack_idx = 0; stack_idx < *refmv_count; ++stack_idx) {
    463        const int_mv stack_mv = ref_mv_stack[stack_idx].this_mv;
    464        if (this_mv.as_int == stack_mv.as_int) break;
    465      }
    466 
    467      if (stack_idx == *refmv_count) {
    468        ref_mv_stack[stack_idx].this_mv = this_mv;
    469 
    470        // TODO(jingning): Set an arbitrary small number here. The weight
    471        // doesn't matter as long as it is properly initialized.
    472        ref_mv_weight[stack_idx] = 2;
    473        ++(*refmv_count);
    474      }
    475    }
    476  }
    477 }
    478 
    479 static inline void setup_ref_mv_list(
    480    const AV1_COMMON *cm, const MACROBLOCKD *xd, MV_REFERENCE_FRAME ref_frame,
    481    uint8_t *const refmv_count,
    482    CANDIDATE_MV ref_mv_stack[MAX_REF_MV_STACK_SIZE],
    483    uint16_t ref_mv_weight[MAX_REF_MV_STACK_SIZE],
    484    int_mv mv_ref_list[MAX_MV_REF_CANDIDATES], int_mv *gm_mv_candidates,
    485    int mi_row, int mi_col, int16_t *mode_context) {
    486  const int bs = AOMMAX(xd->width, xd->height);
    487  const int has_tr = has_top_right(cm, xd, mi_row, mi_col, bs);
    488  MV_REFERENCE_FRAME rf[2];
    489 
    490  const TileInfo *const tile = &xd->tile;
    491  int max_row_offset = 0, max_col_offset = 0;
    492  const int row_adj = (xd->height < mi_size_high[BLOCK_8X8]) && (mi_row & 0x01);
    493  const int col_adj = (xd->width < mi_size_wide[BLOCK_8X8]) && (mi_col & 0x01);
    494  int processed_rows = 0;
    495  int processed_cols = 0;
    496 
    497  av1_set_ref_frame(rf, ref_frame);
    498  mode_context[ref_frame] = 0;
    499  *refmv_count = 0;
    500 
    501  // Find valid maximum row/col offset.
    502  if (xd->up_available) {
    503    max_row_offset = -(MVREF_ROW_COLS << 1) + row_adj;
    504 
    505    if (xd->height < mi_size_high[BLOCK_8X8])
    506      max_row_offset = -(2 << 1) + row_adj;
    507 
    508    max_row_offset = find_valid_row_offset(tile, mi_row, max_row_offset);
    509  }
    510 
    511  if (xd->left_available) {
    512    max_col_offset = -(MVREF_ROW_COLS << 1) + col_adj;
    513 
    514    if (xd->width < mi_size_wide[BLOCK_8X8])
    515      max_col_offset = -(2 << 1) + col_adj;
    516 
    517    max_col_offset = find_valid_col_offset(tile, mi_col, max_col_offset);
    518  }
    519 
    520  uint8_t col_match_count = 0;
    521  uint8_t row_match_count = 0;
    522  uint8_t newmv_count = 0;
    523 
    524  // Scan the first above row mode info. row_offset = -1;
    525  if (abs(max_row_offset) >= 1)
    526    scan_row_mbmi(cm, xd, mi_col, rf, -1, ref_mv_stack, ref_mv_weight,
    527                  refmv_count, &row_match_count, &newmv_count, gm_mv_candidates,
    528                  max_row_offset, &processed_rows);
    529  // Scan the first left column mode info. col_offset = -1;
    530  if (abs(max_col_offset) >= 1)
    531    scan_col_mbmi(cm, xd, mi_row, rf, -1, ref_mv_stack, ref_mv_weight,
    532                  refmv_count, &col_match_count, &newmv_count, gm_mv_candidates,
    533                  max_col_offset, &processed_cols);
    534  // Check top-right boundary
    535  if (has_tr)
    536    scan_blk_mbmi(cm, xd, mi_row, mi_col, rf, -1, xd->width, ref_mv_stack,
    537                  ref_mv_weight, &row_match_count, &newmv_count,
    538                  gm_mv_candidates, refmv_count);
    539 
    540  const uint8_t nearest_match = (row_match_count > 0) + (col_match_count > 0);
    541  const uint8_t nearest_refmv_count = *refmv_count;
    542 
    543  // TODO(yunqing): for comp_search, do it for all 3 cases.
    544  for (int idx = 0; idx < nearest_refmv_count; ++idx)
    545    ref_mv_weight[idx] += REF_CAT_LEVEL;
    546 
    547  if (cm->features.allow_ref_frame_mvs) {
    548    int is_available = 0;
    549    const int voffset = AOMMAX(mi_size_high[BLOCK_8X8], xd->height);
    550    const int hoffset = AOMMAX(mi_size_wide[BLOCK_8X8], xd->width);
    551    const int blk_row_end = AOMMIN(xd->height, mi_size_high[BLOCK_64X64]);
    552    const int blk_col_end = AOMMIN(xd->width, mi_size_wide[BLOCK_64X64]);
    553 
    554    const int tpl_sample_pos[3][2] = {
    555      { voffset, -2 },
    556      { voffset, hoffset },
    557      { voffset - 2, hoffset },
    558    };
    559    const int allow_extension = (xd->height >= mi_size_high[BLOCK_8X8]) &&
    560                                (xd->height < mi_size_high[BLOCK_64X64]) &&
    561                                (xd->width >= mi_size_wide[BLOCK_8X8]) &&
    562                                (xd->width < mi_size_wide[BLOCK_64X64]);
    563 
    564    const int step_h = (xd->height >= mi_size_high[BLOCK_64X64])
    565                           ? mi_size_high[BLOCK_16X16]
    566                           : mi_size_high[BLOCK_8X8];
    567    const int step_w = (xd->width >= mi_size_wide[BLOCK_64X64])
    568                           ? mi_size_wide[BLOCK_16X16]
    569                           : mi_size_wide[BLOCK_8X8];
    570 
    571    for (int blk_row = 0; blk_row < blk_row_end; blk_row += step_h) {
    572      for (int blk_col = 0; blk_col < blk_col_end; blk_col += step_w) {
    573        int ret = add_tpl_ref_mv(cm, xd, mi_row, mi_col, ref_frame, blk_row,
    574                                 blk_col, gm_mv_candidates, refmv_count,
    575                                 ref_mv_stack, ref_mv_weight, mode_context);
    576        if (blk_row == 0 && blk_col == 0) is_available = ret;
    577      }
    578    }
    579 
    580    if (is_available == 0) mode_context[ref_frame] |= (1 << GLOBALMV_OFFSET);
    581 
    582    for (int i = 0; i < 3 && allow_extension; ++i) {
    583      const int blk_row = tpl_sample_pos[i][0];
    584      const int blk_col = tpl_sample_pos[i][1];
    585 
    586      if (!check_sb_border(mi_row, mi_col, blk_row, blk_col)) continue;
    587      add_tpl_ref_mv(cm, xd, mi_row, mi_col, ref_frame, blk_row, blk_col,
    588                     gm_mv_candidates, refmv_count, ref_mv_stack, ref_mv_weight,
    589                     mode_context);
    590    }
    591  }
    592 
    593  uint8_t dummy_newmv_count = 0;
    594 
    595  // Scan the second outer area.
    596  scan_blk_mbmi(cm, xd, mi_row, mi_col, rf, -1, -1, ref_mv_stack, ref_mv_weight,
    597                &row_match_count, &dummy_newmv_count, gm_mv_candidates,
    598                refmv_count);
    599 
    600  for (int idx = 2; idx <= MVREF_ROW_COLS; ++idx) {
    601    const int row_offset = -(idx << 1) + 1 + row_adj;
    602    const int col_offset = -(idx << 1) + 1 + col_adj;
    603 
    604    if (abs(row_offset) <= abs(max_row_offset) &&
    605        abs(row_offset) > processed_rows)
    606      scan_row_mbmi(cm, xd, mi_col, rf, row_offset, ref_mv_stack, ref_mv_weight,
    607                    refmv_count, &row_match_count, &dummy_newmv_count,
    608                    gm_mv_candidates, max_row_offset, &processed_rows);
    609 
    610    if (abs(col_offset) <= abs(max_col_offset) &&
    611        abs(col_offset) > processed_cols)
    612      scan_col_mbmi(cm, xd, mi_row, rf, col_offset, ref_mv_stack, ref_mv_weight,
    613                    refmv_count, &col_match_count, &dummy_newmv_count,
    614                    gm_mv_candidates, max_col_offset, &processed_cols);
    615  }
    616 
    617  const uint8_t ref_match_count = (row_match_count > 0) + (col_match_count > 0);
    618 
    619  switch (nearest_match) {
    620    case 0:
    621      if (ref_match_count >= 1) mode_context[ref_frame] |= 1;
    622      if (ref_match_count == 1)
    623        mode_context[ref_frame] |= (1 << REFMV_OFFSET);
    624      else if (ref_match_count >= 2)
    625        mode_context[ref_frame] |= (2 << REFMV_OFFSET);
    626      break;
    627    case 1:
    628      mode_context[ref_frame] |= (newmv_count > 0) ? 2 : 3;
    629      if (ref_match_count == 1)
    630        mode_context[ref_frame] |= (3 << REFMV_OFFSET);
    631      else if (ref_match_count >= 2)
    632        mode_context[ref_frame] |= (4 << REFMV_OFFSET);
    633      break;
    634    case 2:
    635    default:
    636      if (newmv_count >= 1)
    637        mode_context[ref_frame] |= 4;
    638      else
    639        mode_context[ref_frame] |= 5;
    640 
    641      mode_context[ref_frame] |= (5 << REFMV_OFFSET);
    642      break;
    643  }
    644 
    645  // Rank the likelihood and assign nearest and near mvs.
    646  int len = nearest_refmv_count;
    647  while (len > 0) {
    648    int nr_len = 0;
    649    for (int idx = 1; idx < len; ++idx) {
    650      if (ref_mv_weight[idx - 1] < ref_mv_weight[idx]) {
    651        const CANDIDATE_MV tmp_mv = ref_mv_stack[idx - 1];
    652        const uint16_t tmp_ref_mv_weight = ref_mv_weight[idx - 1];
    653        ref_mv_stack[idx - 1] = ref_mv_stack[idx];
    654        ref_mv_stack[idx] = tmp_mv;
    655        ref_mv_weight[idx - 1] = ref_mv_weight[idx];
    656        ref_mv_weight[idx] = tmp_ref_mv_weight;
    657        nr_len = idx;
    658      }
    659    }
    660    len = nr_len;
    661  }
    662 
    663  len = *refmv_count;
    664  while (len > nearest_refmv_count) {
    665    int nr_len = nearest_refmv_count;
    666    for (int idx = nearest_refmv_count + 1; idx < len; ++idx) {
    667      if (ref_mv_weight[idx - 1] < ref_mv_weight[idx]) {
    668        const CANDIDATE_MV tmp_mv = ref_mv_stack[idx - 1];
    669        const uint16_t tmp_ref_mv_weight = ref_mv_weight[idx - 1];
    670        ref_mv_stack[idx - 1] = ref_mv_stack[idx];
    671        ref_mv_stack[idx] = tmp_mv;
    672        ref_mv_weight[idx - 1] = ref_mv_weight[idx];
    673        ref_mv_weight[idx] = tmp_ref_mv_weight;
    674        nr_len = idx;
    675      }
    676    }
    677    len = nr_len;
    678  }
    679 
    680  int mi_width = AOMMIN(mi_size_wide[BLOCK_64X64], xd->width);
    681  mi_width = AOMMIN(mi_width, cm->mi_params.mi_cols - mi_col);
    682  int mi_height = AOMMIN(mi_size_high[BLOCK_64X64], xd->height);
    683  mi_height = AOMMIN(mi_height, cm->mi_params.mi_rows - mi_row);
    684  const int mi_size = AOMMIN(mi_width, mi_height);
    685  if (rf[1] > NONE_FRAME) {
    686    // TODO(jingning, yunqing): Refactor and consolidate the compound and
    687    // single reference frame modes. Reduce unnecessary redundancy.
    688    if (*refmv_count < MAX_MV_REF_CANDIDATES) {
    689      int_mv ref_id[2][2], ref_diff[2][2];
    690      int ref_id_count[2] = { 0 }, ref_diff_count[2] = { 0 };
    691 
    692      for (int idx = 0; abs(max_row_offset) >= 1 && idx < mi_size;) {
    693        const MB_MODE_INFO *const candidate = xd->mi[-xd->mi_stride + idx];
    694        process_compound_ref_mv_candidate(
    695            candidate, cm, rf, ref_id, ref_id_count, ref_diff, ref_diff_count);
    696        idx += mi_size_wide[candidate->bsize];
    697      }
    698 
    699      for (int idx = 0; abs(max_col_offset) >= 1 && idx < mi_size;) {
    700        const MB_MODE_INFO *const candidate = xd->mi[idx * xd->mi_stride - 1];
    701        process_compound_ref_mv_candidate(
    702            candidate, cm, rf, ref_id, ref_id_count, ref_diff, ref_diff_count);
    703        idx += mi_size_high[candidate->bsize];
    704      }
    705 
    706      // Build up the compound mv predictor
    707      int_mv comp_list[MAX_MV_REF_CANDIDATES][2];
    708 
    709      for (int idx = 0; idx < 2; ++idx) {
    710        int comp_idx = 0;
    711        for (int list_idx = 0;
    712             list_idx < ref_id_count[idx] && comp_idx < MAX_MV_REF_CANDIDATES;
    713             ++list_idx, ++comp_idx)
    714          comp_list[comp_idx][idx] = ref_id[idx][list_idx];
    715        for (int list_idx = 0;
    716             list_idx < ref_diff_count[idx] && comp_idx < MAX_MV_REF_CANDIDATES;
    717             ++list_idx, ++comp_idx)
    718          comp_list[comp_idx][idx] = ref_diff[idx][list_idx];
    719        for (; comp_idx < MAX_MV_REF_CANDIDATES; ++comp_idx)
    720          comp_list[comp_idx][idx] = gm_mv_candidates[idx];
    721      }
    722 
    723      if (*refmv_count) {
    724        assert(*refmv_count == 1);
    725        if (comp_list[0][0].as_int == ref_mv_stack[0].this_mv.as_int &&
    726            comp_list[0][1].as_int == ref_mv_stack[0].comp_mv.as_int) {
    727          ref_mv_stack[*refmv_count].this_mv = comp_list[1][0];
    728          ref_mv_stack[*refmv_count].comp_mv = comp_list[1][1];
    729        } else {
    730          ref_mv_stack[*refmv_count].this_mv = comp_list[0][0];
    731          ref_mv_stack[*refmv_count].comp_mv = comp_list[0][1];
    732        }
    733        ref_mv_weight[*refmv_count] = 2;
    734        ++*refmv_count;
    735      } else {
    736        for (int idx = 0; idx < MAX_MV_REF_CANDIDATES; ++idx) {
    737          ref_mv_stack[*refmv_count].this_mv = comp_list[idx][0];
    738          ref_mv_stack[*refmv_count].comp_mv = comp_list[idx][1];
    739          ref_mv_weight[*refmv_count] = 2;
    740          ++*refmv_count;
    741        }
    742      }
    743    }
    744 
    745    assert(*refmv_count >= 2);
    746 
    747    for (int idx = 0; idx < *refmv_count; ++idx) {
    748      clamp_mv_ref(&ref_mv_stack[idx].this_mv.as_mv, xd->width << MI_SIZE_LOG2,
    749                   xd->height << MI_SIZE_LOG2, xd);
    750      clamp_mv_ref(&ref_mv_stack[idx].comp_mv.as_mv, xd->width << MI_SIZE_LOG2,
    751                   xd->height << MI_SIZE_LOG2, xd);
    752    }
    753  } else {
    754    // Handle single reference frame extension
    755    for (int idx = 0; abs(max_row_offset) >= 1 && idx < mi_size &&
    756                      *refmv_count < MAX_MV_REF_CANDIDATES;) {
    757      const MB_MODE_INFO *const candidate = xd->mi[-xd->mi_stride + idx];
    758      process_single_ref_mv_candidate(candidate, cm, ref_frame, refmv_count,
    759                                      ref_mv_stack, ref_mv_weight);
    760      idx += mi_size_wide[candidate->bsize];
    761    }
    762 
    763    for (int idx = 0; abs(max_col_offset) >= 1 && idx < mi_size &&
    764                      *refmv_count < MAX_MV_REF_CANDIDATES;) {
    765      const MB_MODE_INFO *const candidate = xd->mi[idx * xd->mi_stride - 1];
    766      process_single_ref_mv_candidate(candidate, cm, ref_frame, refmv_count,
    767                                      ref_mv_stack, ref_mv_weight);
    768      idx += mi_size_high[candidate->bsize];
    769    }
    770 
    771    for (int idx = 0; idx < *refmv_count; ++idx) {
    772      clamp_mv_ref(&ref_mv_stack[idx].this_mv.as_mv, xd->width << MI_SIZE_LOG2,
    773                   xd->height << MI_SIZE_LOG2, xd);
    774    }
    775 
    776    if (mv_ref_list != NULL) {
    777      for (int idx = *refmv_count; idx < MAX_MV_REF_CANDIDATES; ++idx)
    778        mv_ref_list[idx].as_int = gm_mv_candidates[0].as_int;
    779 
    780      for (int idx = 0; idx < AOMMIN(MAX_MV_REF_CANDIDATES, *refmv_count);
    781           ++idx) {
    782        mv_ref_list[idx].as_int = ref_mv_stack[idx].this_mv.as_int;
    783      }
    784    }
    785  }
    786 }
    787 
    788 void av1_find_mv_refs(const AV1_COMMON *cm, const MACROBLOCKD *xd,
    789                      MB_MODE_INFO *mi, MV_REFERENCE_FRAME ref_frame,
    790                      uint8_t ref_mv_count[MODE_CTX_REF_FRAMES],
    791                      CANDIDATE_MV ref_mv_stack[][MAX_REF_MV_STACK_SIZE],
    792                      uint16_t ref_mv_weight[][MAX_REF_MV_STACK_SIZE],
    793                      int_mv mv_ref_list[][MAX_MV_REF_CANDIDATES],
    794                      int_mv *global_mvs, int16_t *mode_context) {
    795  const int mi_row = xd->mi_row;
    796  const int mi_col = xd->mi_col;
    797  int_mv gm_mv[2];
    798 
    799  if (ref_frame == INTRA_FRAME) {
    800    gm_mv[0].as_int = gm_mv[1].as_int = 0;
    801    if (global_mvs != NULL) {
    802      global_mvs[ref_frame].as_int = INVALID_MV;
    803    }
    804  } else {
    805    const BLOCK_SIZE bsize = mi->bsize;
    806    const int allow_high_precision_mv = cm->features.allow_high_precision_mv;
    807    const int force_integer_mv = cm->features.cur_frame_force_integer_mv;
    808    if (ref_frame < REF_FRAMES) {
    809      gm_mv[0] = gm_get_motion_vector(&cm->global_motion[ref_frame],
    810                                      allow_high_precision_mv, bsize, mi_col,
    811                                      mi_row, force_integer_mv);
    812      gm_mv[1].as_int = 0;
    813      if (global_mvs != NULL) global_mvs[ref_frame] = gm_mv[0];
    814    } else {
    815      MV_REFERENCE_FRAME rf[2];
    816      av1_set_ref_frame(rf, ref_frame);
    817      gm_mv[0] = gm_get_motion_vector(&cm->global_motion[rf[0]],
    818                                      allow_high_precision_mv, bsize, mi_col,
    819                                      mi_row, force_integer_mv);
    820      gm_mv[1] = gm_get_motion_vector(&cm->global_motion[rf[1]],
    821                                      allow_high_precision_mv, bsize, mi_col,
    822                                      mi_row, force_integer_mv);
    823    }
    824  }
    825 
    826  setup_ref_mv_list(cm, xd, ref_frame, &ref_mv_count[ref_frame],
    827                    ref_mv_stack[ref_frame], ref_mv_weight[ref_frame],
    828                    mv_ref_list ? mv_ref_list[ref_frame] : NULL, gm_mv, mi_row,
    829                    mi_col, mode_context);
    830 }
    831 
    832 void av1_find_best_ref_mvs(int allow_hp, int_mv *mvlist, int_mv *nearest_mv,
    833                           int_mv *near_mv, int is_integer) {
    834  int i;
    835  // Make sure all the candidates are properly clamped etc
    836  for (i = 0; i < MAX_MV_REF_CANDIDATES; ++i) {
    837    lower_mv_precision(&mvlist[i].as_mv, allow_hp, is_integer);
    838  }
    839  *nearest_mv = mvlist[0];
    840  *near_mv = mvlist[1];
    841 }
    842 
    843 void av1_setup_frame_buf_refs(AV1_COMMON *cm) {
    844  cm->cur_frame->order_hint = cm->current_frame.order_hint;
    845  cm->cur_frame->display_order_hint = cm->current_frame.display_order_hint;
    846  cm->cur_frame->pyramid_level = cm->current_frame.pyramid_level;
    847  cm->cur_frame->filter_level[0] = -1;
    848  cm->cur_frame->filter_level[1] = -1;
    849  MV_REFERENCE_FRAME ref_frame;
    850  for (ref_frame = LAST_FRAME; ref_frame <= ALTREF_FRAME; ++ref_frame) {
    851    const RefCntBuffer *const buf = get_ref_frame_buf(cm, ref_frame);
    852    if (buf != NULL) {
    853      cm->cur_frame->ref_order_hints[ref_frame - LAST_FRAME] = buf->order_hint;
    854      cm->cur_frame->ref_display_order_hint[ref_frame - LAST_FRAME] =
    855          buf->display_order_hint;
    856    }
    857  }
    858 }
    859 
    860 void av1_setup_frame_sign_bias(AV1_COMMON *cm) {
    861  MV_REFERENCE_FRAME ref_frame;
    862  for (ref_frame = LAST_FRAME; ref_frame <= ALTREF_FRAME; ++ref_frame) {
    863    const RefCntBuffer *const buf = get_ref_frame_buf(cm, ref_frame);
    864    if (cm->seq_params->order_hint_info.enable_order_hint && buf != NULL) {
    865      const int ref_order_hint = buf->order_hint;
    866      cm->ref_frame_sign_bias[ref_frame] =
    867          (get_relative_dist(&cm->seq_params->order_hint_info, ref_order_hint,
    868                             (int)cm->current_frame.order_hint) <= 0)
    869              ? 0
    870              : 1;
    871    } else {
    872      cm->ref_frame_sign_bias[ref_frame] = 0;
    873    }
    874  }
    875 }
    876 
    877 #define MAX_OFFSET_WIDTH 64
    878 #define MAX_OFFSET_HEIGHT 0
    879 
    880 static int get_block_position(AV1_COMMON *cm, int *mi_r, int *mi_c, int blk_row,
    881                              int blk_col, MV mv, int sign_bias) {
    882  const int base_blk_row = (blk_row >> 3) << 3;
    883  const int base_blk_col = (blk_col >> 3) << 3;
    884 
    885  const int row_offset = (mv.row >= 0) ? (mv.row >> (4 + MI_SIZE_LOG2))
    886                                       : -((-mv.row) >> (4 + MI_SIZE_LOG2));
    887 
    888  const int col_offset = (mv.col >= 0) ? (mv.col >> (4 + MI_SIZE_LOG2))
    889                                       : -((-mv.col) >> (4 + MI_SIZE_LOG2));
    890 
    891  const int row =
    892      (sign_bias == 1) ? blk_row - row_offset : blk_row + row_offset;
    893  const int col =
    894      (sign_bias == 1) ? blk_col - col_offset : blk_col + col_offset;
    895 
    896  if (row < 0 || row >= (cm->mi_params.mi_rows >> 1) || col < 0 ||
    897      col >= (cm->mi_params.mi_cols >> 1))
    898    return 0;
    899 
    900  if (row < base_blk_row - (MAX_OFFSET_HEIGHT >> 3) ||
    901      row >= base_blk_row + 8 + (MAX_OFFSET_HEIGHT >> 3) ||
    902      col < base_blk_col - (MAX_OFFSET_WIDTH >> 3) ||
    903      col >= base_blk_col + 8 + (MAX_OFFSET_WIDTH >> 3))
    904    return 0;
    905 
    906  *mi_r = row;
    907  *mi_c = col;
    908 
    909  return 1;
    910 }
    911 
    912 // Note: motion_filed_projection finds motion vectors of current frame's
    913 // reference frame, and projects them to current frame. To make it clear,
    914 // let's call current frame's reference frame as start frame.
    915 // Call Start frame's reference frames as reference frames.
    916 // Call ref_offset as frame distances between start frame and its reference
    917 // frames.
    918 static int motion_field_projection(AV1_COMMON *cm,
    919                                   MV_REFERENCE_FRAME start_frame, int dir) {
    920  TPL_MV_REF *tpl_mvs_base = cm->tpl_mvs;
    921  int ref_offset[REF_FRAMES] = { 0 };
    922 
    923  const RefCntBuffer *const start_frame_buf =
    924      get_ref_frame_buf(cm, start_frame);
    925  if (start_frame_buf == NULL) return 0;
    926 
    927  if (start_frame_buf->frame_type == KEY_FRAME ||
    928      start_frame_buf->frame_type == INTRA_ONLY_FRAME)
    929    return 0;
    930 
    931  if (start_frame_buf->mi_rows != cm->mi_params.mi_rows ||
    932      start_frame_buf->mi_cols != cm->mi_params.mi_cols)
    933    return 0;
    934 
    935  const int start_frame_order_hint = start_frame_buf->order_hint;
    936  const unsigned int *const ref_order_hints =
    937      &start_frame_buf->ref_order_hints[0];
    938  const int cur_order_hint = cm->cur_frame->order_hint;
    939  int start_to_current_frame_offset = get_relative_dist(
    940      &cm->seq_params->order_hint_info, start_frame_order_hint, cur_order_hint);
    941 
    942  for (MV_REFERENCE_FRAME rf = LAST_FRAME; rf <= INTER_REFS_PER_FRAME; ++rf) {
    943    ref_offset[rf] = get_relative_dist(&cm->seq_params->order_hint_info,
    944                                       start_frame_order_hint,
    945                                       ref_order_hints[rf - LAST_FRAME]);
    946  }
    947 
    948  if (dir == 2) start_to_current_frame_offset = -start_to_current_frame_offset;
    949 
    950  MV_REF *mv_ref_base = start_frame_buf->mvs;
    951  const int mvs_rows = (cm->mi_params.mi_rows + 1) >> 1;
    952  const int mvs_cols = (cm->mi_params.mi_cols + 1) >> 1;
    953 
    954  for (int blk_row = 0; blk_row < mvs_rows; ++blk_row) {
    955    for (int blk_col = 0; blk_col < mvs_cols; ++blk_col) {
    956      MV_REF *mv_ref = &mv_ref_base[blk_row * mvs_cols + blk_col];
    957      MV fwd_mv = mv_ref->mv.as_mv;
    958 
    959      if (mv_ref->ref_frame > INTRA_FRAME) {
    960        int_mv this_mv;
    961        int mi_r, mi_c;
    962        const int ref_frame_offset = ref_offset[mv_ref->ref_frame];
    963 
    964        int pos_valid =
    965            abs(ref_frame_offset) <= MAX_FRAME_DISTANCE &&
    966            ref_frame_offset > 0 &&
    967            abs(start_to_current_frame_offset) <= MAX_FRAME_DISTANCE;
    968 
    969        if (pos_valid) {
    970          av1_get_mv_projection(&this_mv.as_mv, fwd_mv,
    971                                start_to_current_frame_offset,
    972                                ref_frame_offset);
    973          pos_valid = get_block_position(cm, &mi_r, &mi_c, blk_row, blk_col,
    974                                         this_mv.as_mv, dir >> 1);
    975        }
    976 
    977        if (pos_valid) {
    978          const int mi_offset = mi_r * (cm->mi_params.mi_stride >> 1) + mi_c;
    979 
    980          tpl_mvs_base[mi_offset].mfmv0.as_mv.row = fwd_mv.row;
    981          tpl_mvs_base[mi_offset].mfmv0.as_mv.col = fwd_mv.col;
    982          tpl_mvs_base[mi_offset].ref_frame_offset = ref_frame_offset;
    983        }
    984      }
    985    }
    986  }
    987 
    988  return 1;
    989 }
    990 
    991 // cm->ref_frame_side is calculated here, and will be used in
    992 // av1_copy_frame_mvs() to affect how mvs are copied.
    993 void av1_calculate_ref_frame_side(AV1_COMMON *cm) {
    994  const OrderHintInfo *const order_hint_info = &cm->seq_params->order_hint_info;
    995 
    996  memset(cm->ref_frame_side, 0, sizeof(cm->ref_frame_side));
    997  if (!order_hint_info->enable_order_hint) return;
    998 
    999  const int cur_order_hint = cm->cur_frame->order_hint;
   1000 
   1001  for (int ref_frame = LAST_FRAME; ref_frame <= ALTREF_FRAME; ref_frame++) {
   1002    const RefCntBuffer *const buf = get_ref_frame_buf(cm, ref_frame);
   1003    int order_hint = 0;
   1004 
   1005    if (buf != NULL) order_hint = buf->order_hint;
   1006 
   1007    if (get_relative_dist(order_hint_info, order_hint, cur_order_hint) > 0)
   1008      cm->ref_frame_side[ref_frame] = 1;
   1009    else if (order_hint == cur_order_hint)
   1010      cm->ref_frame_side[ref_frame] = -1;
   1011  }
   1012 }
   1013 
   1014 void av1_setup_motion_field(AV1_COMMON *cm) {
   1015  const OrderHintInfo *const order_hint_info = &cm->seq_params->order_hint_info;
   1016 
   1017  if (!order_hint_info->enable_order_hint) return;
   1018 
   1019  TPL_MV_REF *tpl_mvs_base = cm->tpl_mvs;
   1020  int size = ((cm->mi_params.mi_rows + MAX_MIB_SIZE) >> 1) *
   1021             (cm->mi_params.mi_stride >> 1);
   1022  for (int idx = 0; idx < size; ++idx) {
   1023    tpl_mvs_base[idx].mfmv0.as_int = INVALID_MV;
   1024    tpl_mvs_base[idx].ref_frame_offset = 0;
   1025  }
   1026 
   1027  const int cur_order_hint = cm->cur_frame->order_hint;
   1028  const RefCntBuffer *ref_buf[INTER_REFS_PER_FRAME];
   1029  int ref_order_hint[INTER_REFS_PER_FRAME];
   1030 
   1031  for (int ref_frame = LAST_FRAME; ref_frame <= ALTREF_FRAME; ref_frame++) {
   1032    const int ref_idx = ref_frame - LAST_FRAME;
   1033    const RefCntBuffer *const buf = get_ref_frame_buf(cm, ref_frame);
   1034    int order_hint = 0;
   1035 
   1036    if (buf != NULL) order_hint = buf->order_hint;
   1037 
   1038    ref_buf[ref_idx] = buf;
   1039    ref_order_hint[ref_idx] = order_hint;
   1040  }
   1041 
   1042  int ref_stamp = MFMV_STACK_SIZE - 1;
   1043 
   1044  if (ref_buf[LAST_FRAME - LAST_FRAME] != NULL) {
   1045    const int alt_of_lst_order_hint =
   1046        ref_buf[LAST_FRAME - LAST_FRAME]
   1047            ->ref_order_hints[ALTREF_FRAME - LAST_FRAME];
   1048 
   1049    const int is_lst_overlay =
   1050        (alt_of_lst_order_hint == ref_order_hint[GOLDEN_FRAME - LAST_FRAME]);
   1051    if (!is_lst_overlay) motion_field_projection(cm, LAST_FRAME, 2);
   1052    --ref_stamp;
   1053  }
   1054 
   1055  if (get_relative_dist(order_hint_info,
   1056                        ref_order_hint[BWDREF_FRAME - LAST_FRAME],
   1057                        cur_order_hint) > 0) {
   1058    if (motion_field_projection(cm, BWDREF_FRAME, 0)) --ref_stamp;
   1059  }
   1060 
   1061  if (get_relative_dist(order_hint_info,
   1062                        ref_order_hint[ALTREF2_FRAME - LAST_FRAME],
   1063                        cur_order_hint) > 0) {
   1064    if (motion_field_projection(cm, ALTREF2_FRAME, 0)) --ref_stamp;
   1065  }
   1066 
   1067  if (get_relative_dist(order_hint_info,
   1068                        ref_order_hint[ALTREF_FRAME - LAST_FRAME],
   1069                        cur_order_hint) > 0 &&
   1070      ref_stamp >= 0)
   1071    if (motion_field_projection(cm, ALTREF_FRAME, 0)) --ref_stamp;
   1072 
   1073  if (ref_stamp >= 0) motion_field_projection(cm, LAST2_FRAME, 2);
   1074 }
   1075 
   1076 static inline void record_samples(const MB_MODE_INFO *mbmi, int *pts,
   1077                                  int *pts_inref, int row_offset, int sign_r,
   1078                                  int col_offset, int sign_c) {
   1079  const int bw = block_size_wide[mbmi->bsize];
   1080  const int bh = block_size_high[mbmi->bsize];
   1081  const int x = col_offset * MI_SIZE + sign_c * bw / 2 - 1;
   1082  const int y = row_offset * MI_SIZE + sign_r * bh / 2 - 1;
   1083 
   1084  pts[0] = GET_MV_SUBPEL(x);
   1085  pts[1] = GET_MV_SUBPEL(y);
   1086  pts_inref[0] = pts[0] + mbmi->mv[0].as_mv.col;
   1087  pts_inref[1] = pts[1] + mbmi->mv[0].as_mv.row;
   1088 }
   1089 
   1090 // Select samples according to the motion vector difference.
   1091 uint8_t av1_selectSamples(MV *mv, int *pts, int *pts_inref, int len,
   1092                          BLOCK_SIZE bsize) {
   1093  const int bw = block_size_wide[bsize];
   1094  const int bh = block_size_high[bsize];
   1095  const int thresh = clamp(AOMMAX(bw, bh), 16, 112);
   1096  uint8_t ret = 0;
   1097  assert(len <= LEAST_SQUARES_SAMPLES_MAX);
   1098 
   1099  // Only keep the samples with MV differences within threshold.
   1100  for (int i = 0; i < len; ++i) {
   1101    const int diff = abs(pts_inref[2 * i] - pts[2 * i] - mv->col) +
   1102                     abs(pts_inref[2 * i + 1] - pts[2 * i + 1] - mv->row);
   1103    if (diff > thresh) continue;
   1104    if (ret != i) {
   1105      memcpy(pts + 2 * ret, pts + 2 * i, 2 * sizeof(pts[0]));
   1106      memcpy(pts_inref + 2 * ret, pts_inref + 2 * i, 2 * sizeof(pts_inref[0]));
   1107    }
   1108    ++ret;
   1109  }
   1110  // Keep at least 1 sample.
   1111  return AOMMAX(ret, 1);
   1112 }
   1113 
   1114 // Note: Samples returned are at 1/8-pel precision
   1115 // Sample are the neighbor block center point's coordinates relative to the
   1116 // left-top pixel of current block.
   1117 uint8_t av1_findSamples(const AV1_COMMON *cm, MACROBLOCKD *xd, int *pts,
   1118                        int *pts_inref) {
   1119  const MB_MODE_INFO *const mbmi0 = xd->mi[0];
   1120  const int ref_frame = mbmi0->ref_frame[0];
   1121  const int up_available = xd->up_available;
   1122  const int left_available = xd->left_available;
   1123  uint8_t np = 0;
   1124  int do_tl = 1;
   1125  int do_tr = 1;
   1126  const int mi_stride = xd->mi_stride;
   1127  const int mi_row = xd->mi_row;
   1128  const int mi_col = xd->mi_col;
   1129 
   1130  // scan the nearest above rows
   1131  if (up_available) {
   1132    const int mi_row_offset = -1;
   1133    const MB_MODE_INFO *mbmi = xd->mi[mi_row_offset * mi_stride];
   1134    uint8_t superblock_width = mi_size_wide[mbmi->bsize];
   1135 
   1136    if (xd->width <= superblock_width) {
   1137      // Handle "current block width <= above block width" case.
   1138      const int col_offset = -mi_col % superblock_width;
   1139 
   1140      if (col_offset < 0) do_tl = 0;
   1141      if (col_offset + superblock_width > xd->width) do_tr = 0;
   1142 
   1143      if (mbmi->ref_frame[0] == ref_frame && mbmi->ref_frame[1] == NONE_FRAME) {
   1144        record_samples(mbmi, pts, pts_inref, 0, -1, col_offset, 1);
   1145        pts += 2;
   1146        pts_inref += 2;
   1147        if (++np >= LEAST_SQUARES_SAMPLES_MAX) return LEAST_SQUARES_SAMPLES_MAX;
   1148      }
   1149    } else {
   1150      // Handle "current block width > above block width" case.
   1151      for (int i = 0; i < AOMMIN(xd->width, cm->mi_params.mi_cols - mi_col);
   1152           i += superblock_width) {
   1153        mbmi = xd->mi[i + mi_row_offset * mi_stride];
   1154        superblock_width = mi_size_wide[mbmi->bsize];
   1155 
   1156        if (mbmi->ref_frame[0] == ref_frame &&
   1157            mbmi->ref_frame[1] == NONE_FRAME) {
   1158          record_samples(mbmi, pts, pts_inref, 0, -1, i, 1);
   1159          pts += 2;
   1160          pts_inref += 2;
   1161          if (++np >= LEAST_SQUARES_SAMPLES_MAX)
   1162            return LEAST_SQUARES_SAMPLES_MAX;
   1163        }
   1164      }
   1165    }
   1166  }
   1167  assert(np <= LEAST_SQUARES_SAMPLES_MAX);
   1168 
   1169  // scan the nearest left columns
   1170  if (left_available) {
   1171    const int mi_col_offset = -1;
   1172    const MB_MODE_INFO *mbmi = xd->mi[mi_col_offset];
   1173    uint8_t superblock_height = mi_size_high[mbmi->bsize];
   1174 
   1175    if (xd->height <= superblock_height) {
   1176      // Handle "current block height <= above block height" case.
   1177      const int row_offset = -mi_row % superblock_height;
   1178 
   1179      if (row_offset < 0) do_tl = 0;
   1180 
   1181      if (mbmi->ref_frame[0] == ref_frame && mbmi->ref_frame[1] == NONE_FRAME) {
   1182        record_samples(mbmi, pts, pts_inref, row_offset, 1, 0, -1);
   1183        pts += 2;
   1184        pts_inref += 2;
   1185        np++;
   1186        if (np >= LEAST_SQUARES_SAMPLES_MAX) return LEAST_SQUARES_SAMPLES_MAX;
   1187      }
   1188    } else {
   1189      // Handle "current block height > above block height" case.
   1190      for (int i = 0; i < AOMMIN(xd->height, cm->mi_params.mi_rows - mi_row);
   1191           i += superblock_height) {
   1192        mbmi = xd->mi[mi_col_offset + i * mi_stride];
   1193        superblock_height = mi_size_high[mbmi->bsize];
   1194 
   1195        if (mbmi->ref_frame[0] == ref_frame &&
   1196            mbmi->ref_frame[1] == NONE_FRAME) {
   1197          record_samples(mbmi, pts, pts_inref, i, 1, 0, -1);
   1198          pts += 2;
   1199          pts_inref += 2;
   1200          if (++np >= LEAST_SQUARES_SAMPLES_MAX)
   1201            return LEAST_SQUARES_SAMPLES_MAX;
   1202        }
   1203      }
   1204    }
   1205  }
   1206  assert(np <= LEAST_SQUARES_SAMPLES_MAX);
   1207 
   1208  // Top-left block
   1209  if (do_tl && left_available && up_available) {
   1210    const int mi_row_offset = -1;
   1211    const int mi_col_offset = -1;
   1212    MB_MODE_INFO *mbmi = xd->mi[mi_col_offset + mi_row_offset * mi_stride];
   1213 
   1214    if (mbmi->ref_frame[0] == ref_frame && mbmi->ref_frame[1] == NONE_FRAME) {
   1215      record_samples(mbmi, pts, pts_inref, 0, -1, 0, -1);
   1216      pts += 2;
   1217      pts_inref += 2;
   1218      if (++np >= LEAST_SQUARES_SAMPLES_MAX) return LEAST_SQUARES_SAMPLES_MAX;
   1219    }
   1220  }
   1221  assert(np <= LEAST_SQUARES_SAMPLES_MAX);
   1222 
   1223  // Top-right block
   1224  if (do_tr &&
   1225      has_top_right(cm, xd, mi_row, mi_col, AOMMAX(xd->width, xd->height))) {
   1226    const POSITION trb_pos = { -1, xd->width };
   1227    const TileInfo *const tile = &xd->tile;
   1228    if (is_inside(tile, mi_col, mi_row, &trb_pos)) {
   1229      const int mi_row_offset = -1;
   1230      const int mi_col_offset = xd->width;
   1231      const MB_MODE_INFO *mbmi =
   1232          xd->mi[mi_col_offset + mi_row_offset * mi_stride];
   1233 
   1234      if (mbmi->ref_frame[0] == ref_frame && mbmi->ref_frame[1] == NONE_FRAME) {
   1235        record_samples(mbmi, pts, pts_inref, 0, -1, xd->width, 1);
   1236        if (++np >= LEAST_SQUARES_SAMPLES_MAX) return LEAST_SQUARES_SAMPLES_MAX;
   1237      }
   1238    }
   1239  }
   1240  assert(np <= LEAST_SQUARES_SAMPLES_MAX);
   1241 
   1242  return np;
   1243 }
   1244 
   1245 void av1_setup_skip_mode_allowed(AV1_COMMON *cm) {
   1246  const OrderHintInfo *const order_hint_info = &cm->seq_params->order_hint_info;
   1247  SkipModeInfo *const skip_mode_info = &cm->current_frame.skip_mode_info;
   1248 
   1249  skip_mode_info->skip_mode_allowed = 0;
   1250  skip_mode_info->ref_frame_idx_0 = INVALID_IDX;
   1251  skip_mode_info->ref_frame_idx_1 = INVALID_IDX;
   1252 
   1253  if (!order_hint_info->enable_order_hint || frame_is_intra_only(cm) ||
   1254      cm->current_frame.reference_mode == SINGLE_REFERENCE)
   1255    return;
   1256 
   1257  const int cur_order_hint = cm->current_frame.order_hint;
   1258  int ref_order_hints[2] = { -1, INT_MAX };
   1259  int ref_idx[2] = { INVALID_IDX, INVALID_IDX };
   1260 
   1261  // Identify the nearest forward and backward references.
   1262  for (int i = 0; i < INTER_REFS_PER_FRAME; ++i) {
   1263    const RefCntBuffer *const buf = get_ref_frame_buf(cm, LAST_FRAME + i);
   1264    if (buf == NULL) continue;
   1265 
   1266    const int ref_order_hint = buf->order_hint;
   1267    if (get_relative_dist(order_hint_info, ref_order_hint, cur_order_hint) <
   1268        0) {
   1269      // Forward reference
   1270      if (ref_order_hints[0] == -1 ||
   1271          get_relative_dist(order_hint_info, ref_order_hint,
   1272                            ref_order_hints[0]) > 0) {
   1273        ref_order_hints[0] = ref_order_hint;
   1274        ref_idx[0] = i;
   1275      }
   1276    } else if (get_relative_dist(order_hint_info, ref_order_hint,
   1277                                 cur_order_hint) > 0) {
   1278      // Backward reference
   1279      if (ref_order_hints[1] == INT_MAX ||
   1280          get_relative_dist(order_hint_info, ref_order_hint,
   1281                            ref_order_hints[1]) < 0) {
   1282        ref_order_hints[1] = ref_order_hint;
   1283        ref_idx[1] = i;
   1284      }
   1285    }
   1286  }
   1287 
   1288  if (ref_idx[0] != INVALID_IDX && ref_idx[1] != INVALID_IDX) {
   1289    // == Bi-directional prediction ==
   1290    skip_mode_info->skip_mode_allowed = 1;
   1291    skip_mode_info->ref_frame_idx_0 = AOMMIN(ref_idx[0], ref_idx[1]);
   1292    skip_mode_info->ref_frame_idx_1 = AOMMAX(ref_idx[0], ref_idx[1]);
   1293  } else if (ref_idx[0] != INVALID_IDX && ref_idx[1] == INVALID_IDX) {
   1294    // == Forward prediction only ==
   1295    // Identify the second nearest forward reference.
   1296    ref_order_hints[1] = -1;
   1297    for (int i = 0; i < INTER_REFS_PER_FRAME; ++i) {
   1298      const RefCntBuffer *const buf = get_ref_frame_buf(cm, LAST_FRAME + i);
   1299      if (buf == NULL) continue;
   1300 
   1301      const int ref_order_hint = buf->order_hint;
   1302      if ((ref_order_hints[0] != -1 &&
   1303           get_relative_dist(order_hint_info, ref_order_hint,
   1304                             ref_order_hints[0]) < 0) &&
   1305          (ref_order_hints[1] == -1 ||
   1306           get_relative_dist(order_hint_info, ref_order_hint,
   1307                             ref_order_hints[1]) > 0)) {
   1308        // Second closest forward reference
   1309        ref_order_hints[1] = ref_order_hint;
   1310        ref_idx[1] = i;
   1311      }
   1312    }
   1313    if (ref_order_hints[1] != -1) {
   1314      skip_mode_info->skip_mode_allowed = 1;
   1315      skip_mode_info->ref_frame_idx_0 = AOMMIN(ref_idx[0], ref_idx[1]);
   1316      skip_mode_info->ref_frame_idx_1 = AOMMAX(ref_idx[0], ref_idx[1]);
   1317    }
   1318  }
   1319 }
   1320 
   1321 typedef struct {
   1322  int map_idx;        // frame map index
   1323  RefCntBuffer *buf;  // frame buffer
   1324  int sort_idx;       // index based on the offset to be used for sorting
   1325 } REF_FRAME_INFO;
   1326 
   1327 // Compares the sort_idx fields. If they are equal, then compares the map_idx
   1328 // fields to break the tie. This ensures a stable sort.
   1329 static int compare_ref_frame_info(const void *arg_a, const void *arg_b) {
   1330  const REF_FRAME_INFO *info_a = (REF_FRAME_INFO *)arg_a;
   1331  const REF_FRAME_INFO *info_b = (REF_FRAME_INFO *)arg_b;
   1332 
   1333  const int sort_idx_diff = info_a->sort_idx - info_b->sort_idx;
   1334  if (sort_idx_diff != 0) return sort_idx_diff;
   1335  return info_a->map_idx - info_b->map_idx;
   1336 }
   1337 
   1338 static inline void set_ref_frame_info(int *remapped_ref_idx, int frame_idx,
   1339                                      REF_FRAME_INFO *ref_info) {
   1340  assert(frame_idx >= 0 && frame_idx < INTER_REFS_PER_FRAME);
   1341 
   1342  remapped_ref_idx[frame_idx] = ref_info->map_idx;
   1343 }
   1344 
   1345 void av1_set_frame_refs(AV1_COMMON *const cm, int *remapped_ref_idx,
   1346                        int lst_map_idx, int gld_map_idx) {
   1347  int lst_frame_sort_idx = -1;
   1348  int gld_frame_sort_idx = -1;
   1349 
   1350  assert(cm->seq_params->order_hint_info.enable_order_hint);
   1351  assert(cm->seq_params->order_hint_info.order_hint_bits_minus_1 >= 0);
   1352  const int cur_order_hint = (int)cm->current_frame.order_hint;
   1353  const int cur_frame_sort_idx =
   1354      1 << cm->seq_params->order_hint_info.order_hint_bits_minus_1;
   1355 
   1356  REF_FRAME_INFO ref_frame_info[REF_FRAMES];
   1357  int ref_flag_list[INTER_REFS_PER_FRAME] = { 0, 0, 0, 0, 0, 0, 0 };
   1358 
   1359  for (int i = 0; i < REF_FRAMES; ++i) {
   1360    const int map_idx = i;
   1361 
   1362    ref_frame_info[i].map_idx = map_idx;
   1363    ref_frame_info[i].sort_idx = -1;
   1364 
   1365    RefCntBuffer *const buf = cm->ref_frame_map[map_idx];
   1366    ref_frame_info[i].buf = buf;
   1367 
   1368    if (buf == NULL) continue;
   1369    // If this assertion fails, there is a reference leak.
   1370    assert(buf->ref_count > 0);
   1371 
   1372    const int offset = (int)buf->order_hint;
   1373    ref_frame_info[i].sort_idx =
   1374        (offset == -1) ? -1
   1375                       : cur_frame_sort_idx +
   1376                             get_relative_dist(&cm->seq_params->order_hint_info,
   1377                                               offset, cur_order_hint);
   1378    assert(ref_frame_info[i].sort_idx >= -1);
   1379 
   1380    if (map_idx == lst_map_idx) lst_frame_sort_idx = ref_frame_info[i].sort_idx;
   1381    if (map_idx == gld_map_idx) gld_frame_sort_idx = ref_frame_info[i].sort_idx;
   1382  }
   1383 
   1384  // Confirm both LAST_FRAME and GOLDEN_FRAME are valid forward reference
   1385  // frames.
   1386  if (lst_frame_sort_idx == -1 || lst_frame_sort_idx >= cur_frame_sort_idx) {
   1387    aom_internal_error(cm->error, AOM_CODEC_CORRUPT_FRAME,
   1388                       "Inter frame requests a look-ahead frame as LAST");
   1389  }
   1390  if (gld_frame_sort_idx == -1 || gld_frame_sort_idx >= cur_frame_sort_idx) {
   1391    aom_internal_error(cm->error, AOM_CODEC_CORRUPT_FRAME,
   1392                       "Inter frame requests a look-ahead frame as GOLDEN");
   1393  }
   1394 
   1395  // Sort ref frames based on their frame_offset values.
   1396  qsort(ref_frame_info, REF_FRAMES, sizeof(REF_FRAME_INFO),
   1397        compare_ref_frame_info);
   1398 
   1399  // Identify forward and backward reference frames.
   1400  // Forward  reference: offset < order_hint
   1401  // Backward reference: offset >= order_hint
   1402  int fwd_start_idx = 0, fwd_end_idx = REF_FRAMES - 1;
   1403 
   1404  for (int i = 0; i < REF_FRAMES; i++) {
   1405    if (ref_frame_info[i].sort_idx == -1) {
   1406      fwd_start_idx++;
   1407      continue;
   1408    }
   1409 
   1410    if (ref_frame_info[i].sort_idx >= cur_frame_sort_idx) {
   1411      fwd_end_idx = i - 1;
   1412      break;
   1413    }
   1414  }
   1415 
   1416  int bwd_start_idx = fwd_end_idx + 1;
   1417  int bwd_end_idx = REF_FRAMES - 1;
   1418 
   1419  // === Backward Reference Frames ===
   1420 
   1421  // == ALTREF_FRAME ==
   1422  if (bwd_start_idx <= bwd_end_idx) {
   1423    set_ref_frame_info(remapped_ref_idx, ALTREF_FRAME - LAST_FRAME,
   1424                       &ref_frame_info[bwd_end_idx]);
   1425    ref_flag_list[ALTREF_FRAME - LAST_FRAME] = 1;
   1426    bwd_end_idx--;
   1427  }
   1428 
   1429  // == BWDREF_FRAME ==
   1430  if (bwd_start_idx <= bwd_end_idx) {
   1431    set_ref_frame_info(remapped_ref_idx, BWDREF_FRAME - LAST_FRAME,
   1432                       &ref_frame_info[bwd_start_idx]);
   1433    ref_flag_list[BWDREF_FRAME - LAST_FRAME] = 1;
   1434    bwd_start_idx++;
   1435  }
   1436 
   1437  // == ALTREF2_FRAME ==
   1438  if (bwd_start_idx <= bwd_end_idx) {
   1439    set_ref_frame_info(remapped_ref_idx, ALTREF2_FRAME - LAST_FRAME,
   1440                       &ref_frame_info[bwd_start_idx]);
   1441    ref_flag_list[ALTREF2_FRAME - LAST_FRAME] = 1;
   1442  }
   1443 
   1444  // === Forward Reference Frames ===
   1445 
   1446  for (int i = fwd_start_idx; i <= fwd_end_idx; ++i) {
   1447    // == LAST_FRAME ==
   1448    if (ref_frame_info[i].map_idx == lst_map_idx) {
   1449      set_ref_frame_info(remapped_ref_idx, LAST_FRAME - LAST_FRAME,
   1450                         &ref_frame_info[i]);
   1451      ref_flag_list[LAST_FRAME - LAST_FRAME] = 1;
   1452    }
   1453 
   1454    // == GOLDEN_FRAME ==
   1455    if (ref_frame_info[i].map_idx == gld_map_idx) {
   1456      set_ref_frame_info(remapped_ref_idx, GOLDEN_FRAME - LAST_FRAME,
   1457                         &ref_frame_info[i]);
   1458      ref_flag_list[GOLDEN_FRAME - LAST_FRAME] = 1;
   1459    }
   1460  }
   1461 
   1462  assert(ref_flag_list[LAST_FRAME - LAST_FRAME] == 1 &&
   1463         ref_flag_list[GOLDEN_FRAME - LAST_FRAME] == 1);
   1464 
   1465  // == LAST2_FRAME ==
   1466  // == LAST3_FRAME ==
   1467  // == BWDREF_FRAME ==
   1468  // == ALTREF2_FRAME ==
   1469  // == ALTREF_FRAME ==
   1470 
   1471  // Set up the reference frames in the anti-chronological order.
   1472  static const MV_REFERENCE_FRAME ref_frame_list[INTER_REFS_PER_FRAME - 2] = {
   1473    LAST2_FRAME, LAST3_FRAME, BWDREF_FRAME, ALTREF2_FRAME, ALTREF_FRAME
   1474  };
   1475 
   1476  int ref_idx;
   1477  for (ref_idx = 0; ref_idx < (INTER_REFS_PER_FRAME - 2); ref_idx++) {
   1478    const MV_REFERENCE_FRAME ref_frame = ref_frame_list[ref_idx];
   1479 
   1480    if (ref_flag_list[ref_frame - LAST_FRAME] == 1) continue;
   1481 
   1482    while (fwd_start_idx <= fwd_end_idx &&
   1483           (ref_frame_info[fwd_end_idx].map_idx == lst_map_idx ||
   1484            ref_frame_info[fwd_end_idx].map_idx == gld_map_idx)) {
   1485      fwd_end_idx--;
   1486    }
   1487    if (fwd_start_idx > fwd_end_idx) break;
   1488 
   1489    set_ref_frame_info(remapped_ref_idx, ref_frame - LAST_FRAME,
   1490                       &ref_frame_info[fwd_end_idx]);
   1491    ref_flag_list[ref_frame - LAST_FRAME] = 1;
   1492 
   1493    fwd_end_idx--;
   1494  }
   1495 
   1496  // Assign all the remaining frame(s), if any, to the earliest reference
   1497  // frame.
   1498  for (; ref_idx < (INTER_REFS_PER_FRAME - 2); ref_idx++) {
   1499    const MV_REFERENCE_FRAME ref_frame = ref_frame_list[ref_idx];
   1500    if (ref_flag_list[ref_frame - LAST_FRAME] == 1) continue;
   1501    set_ref_frame_info(remapped_ref_idx, ref_frame - LAST_FRAME,
   1502                       &ref_frame_info[fwd_start_idx]);
   1503    ref_flag_list[ref_frame - LAST_FRAME] = 1;
   1504  }
   1505 
   1506  for (int i = 0; i < INTER_REFS_PER_FRAME; i++) {
   1507    assert(ref_flag_list[i] == 1);
   1508  }
   1509 }