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 "vp9/decoder/vp9_treereader.h"
#include "vp9/common/vp9_entropymv.h"
#include "vp9/common/vp9_entropymode.h"
#include "vp9/common/vp9_reconinter.h"
#include "vp9/decoder/vp9_onyxd_int.h"
#include "vp9/common/vp9_findnearmv.h"
#include "vp9/common/vp9_common.h"
#include "vp9/common/vp9_seg_common.h"
#include "vp9/common/vp9_pred_common.h"
#include "vp9/common/vp9_entropy.h"
#include "vp9/decoder/vp9_decodemv.h"
#include "vp9/common/vp9_mvref_common.h"
#if CONFIG_DEBUG
#include <assert.h>
#endif

// #define DEBUG_DEC_MV
#ifdef DEBUG_DEC_MV
int dec_mvcount = 0;
#endif

// #define DEC_DEBUG
#ifdef DEC_DEBUG
extern int dec_debug;
#endif

static B_PREDICTION_MODE read_bmode(vp9_reader *bc, const vp9_prob *p) {
  B_PREDICTION_MODE m = treed_read(bc, vp9_bmode_tree, p);
#if CONFIG_NEWBINTRAMODES
  if (m == B_CONTEXT_PRED - CONTEXT_PRED_REPLACEMENTS)
    m = B_CONTEXT_PRED;
  assert(m < B_CONTEXT_PRED - CONTEXT_PRED_REPLACEMENTS || m == B_CONTEXT_PRED);
#endif
  return m;
}

static B_PREDICTION_MODE read_kf_bmode(vp9_reader *bc, const vp9_prob *p) {
  return (B_PREDICTION_MODE)treed_read(bc, vp9_kf_bmode_tree, p);
}

static MB_PREDICTION_MODE read_ymode(vp9_reader *bc, const vp9_prob *p) {
  return (MB_PREDICTION_MODE)treed_read(bc, vp9_ymode_tree, p);
}

static MB_PREDICTION_MODE read_sb_ymode(vp9_reader *bc, const vp9_prob *p) {
  return (MB_PREDICTION_MODE)treed_read(bc, vp9_sb_ymode_tree, p);
}

static MB_PREDICTION_MODE read_kf_sb_ymode(vp9_reader *bc, const vp9_prob *p) {
  return (MB_PREDICTION_MODE)treed_read(bc, vp9_uv_mode_tree, p);
}

static MB_PREDICTION_MODE read_kf_mb_ymode(vp9_reader *bc, const vp9_prob *p) {
  return (MB_PREDICTION_MODE)treed_read(bc, vp9_kf_ymode_tree, p);
}

static int read_i8x8_mode(vp9_reader *bc, const vp9_prob *p) {
  return treed_read(bc, vp9_i8x8_mode_tree, p);
}

static MB_PREDICTION_MODE read_uv_mode(vp9_reader *bc, const vp9_prob *p) {
  return (MB_PREDICTION_MODE)treed_read(bc, vp9_uv_mode_tree, p);
}

// This function reads the current macro block's segnent id from the bitstream
// It should only be called if a segment map update is indicated.
static void read_mb_segid(vp9_reader *r, MB_MODE_INFO *mi, MACROBLOCKD *xd) {
  if (xd->segmentation_enabled && xd->update_mb_segmentation_map) {
    const vp9_prob *const p = xd->mb_segment_tree_probs;
    mi->segment_id = vp9_read(r, p[0]) ? 2 + vp9_read(r, p[2])
                                       : vp9_read(r, p[1]);
  }
}

// This function reads the current macro block's segnent id from the bitstream
// It should only be called if a segment map update is indicated.
static void read_mb_segid_except(VP9_COMMON *cm,
                                 vp9_reader *r, MB_MODE_INFO *mi,
                                 MACROBLOCKD *xd, int mb_row, int mb_col) {
  const int mb_index = mb_row * cm->mb_cols + mb_col;
  const int pred_seg_id = vp9_get_pred_mb_segid(cm, xd, mb_index);
  const vp9_prob *const p = xd->mb_segment_tree_probs;
  const vp9_prob prob = xd->mb_segment_mispred_tree_probs[pred_seg_id];

  if (xd->segmentation_enabled && xd->update_mb_segmentation_map) {
    mi->segment_id = vp9_read(r, prob)
        ? 2 + (pred_seg_id  < 2 ? vp9_read(r, p[2]) : (pred_seg_id == 2))
        :     (pred_seg_id >= 2 ? vp9_read(r, p[1]) : (pred_seg_id == 0));
  }
}

#if CONFIG_NEW_MVREF
int vp9_read_mv_ref_id(vp9_reader *r, vp9_prob *ref_id_probs) {
  int ref_index = 0;

  if (vp9_read(r, ref_id_probs[0])) {
    ref_index++;
    if (vp9_read(r, ref_id_probs[1])) {
      ref_index++;
      if (vp9_read(r, ref_id_probs[2]))
        ref_index++;
    }
  }
  return ref_index;
}
#endif

extern const int vp9_i8x8_block[4];
static void kfread_modes(VP9D_COMP *pbi,
                         MODE_INFO *m,
                         int mb_row,
                         int mb_col,
                         BOOL_DECODER* const bc) {
  VP9_COMMON *const cm = &pbi->common;
  MACROBLOCKD *const xd  = &pbi->mb;
  const int mis = pbi->common.mode_info_stride;
  int map_index = mb_row * pbi->common.mb_cols + mb_col;
  MB_PREDICTION_MODE y_mode;

  m->mbmi.ref_frame = INTRA_FRAME;

  // Read the Macroblock segmentation map if it is being updated explicitly
  // this frame (reset to 0 by default).
  m->mbmi.segment_id = 0;
  if (pbi->mb.update_mb_segmentation_map) {
    read_mb_segid(bc, &m->mbmi, &pbi->mb);
    if (m->mbmi.sb_type) {
      const int bw = 1 << mb_width_log2(m->mbmi.sb_type);
      const int bh = 1 << mb_height_log2(m->mbmi.sb_type);
      const int ymbs = MIN(cm->mb_rows - mb_row, bh);
      const int xmbs = MIN(cm->mb_cols - mb_col, bw);
      int x, y;

      for (y = 0; y < ymbs; y++) {
        for (x = 0; x < xmbs; x++) {
          cm->last_frame_seg_map[map_index + x + y * cm->mb_cols] =
              m->mbmi.segment_id;
        }
      }
    } else {
      cm->last_frame_seg_map[map_index] = m->mbmi.segment_id;
    }
  }

  m->mbmi.mb_skip_coeff = 0;
  if (pbi->common.mb_no_coeff_skip &&
      (!vp9_segfeature_active(&pbi->mb, m->mbmi.segment_id, SEG_LVL_SKIP))) {
    m->mbmi.mb_skip_coeff = vp9_read(bc, vp9_get_pred_prob(cm, &pbi->mb,
                                                           PRED_MBSKIP));
  } else {
    m->mbmi.mb_skip_coeff = vp9_segfeature_active(&pbi->mb, m->mbmi.segment_id,
                                                  SEG_LVL_SKIP);
  }

  y_mode = m->mbmi.sb_type ?
      read_kf_sb_ymode(bc,
          pbi->common.sb_kf_ymode_prob[pbi->common.kf_ymode_probs_index]):
      read_kf_mb_ymode(bc,
          pbi->common.kf_ymode_prob[pbi->common.kf_ymode_probs_index]);

  m->mbmi.ref_frame = INTRA_FRAME;

  if ((m->mbmi.mode = y_mode) == B_PRED) {
    int i = 0;
    do {
      const B_PREDICTION_MODE a = above_block_mode(m, i, mis);
      const B_PREDICTION_MODE l = (xd->left_available || (i & 3)) ?
                                  left_block_mode(m, i) : B_DC_PRED;

      m->bmi[i].as_mode.first = read_kf_bmode(bc,
                                              pbi->common.kf_bmode_prob[a][l]);
    } while (++i < 16);
  }

  if ((m->mbmi.mode = y_mode) == I8X8_PRED) {
    int i;
    for (i = 0; i < 4; i++) {
      const int ib = vp9_i8x8_block[i];
      const int mode8x8 = read_i8x8_mode(bc, pbi->common.fc.i8x8_mode_prob);

      m->bmi[ib + 0].as_mode.first = mode8x8;
      m->bmi[ib + 1].as_mode.first = mode8x8;
      m->bmi[ib + 4].as_mode.first = mode8x8;
      m->bmi[ib + 5].as_mode.first = mode8x8;
    }
  } else {
    m->mbmi.uv_mode = read_uv_mode(bc,
                                   pbi->common.kf_uv_mode_prob[m->mbmi.mode]);
  }

  if (cm->txfm_mode == TX_MODE_SELECT &&
      m->mbmi.mb_skip_coeff == 0 &&
      m->mbmi.mode <= I8X8_PRED) {
    // FIXME(rbultje) code ternary symbol once all experiments are merged
    m->mbmi.txfm_size = vp9_read(bc, cm->prob_tx[0]);
    if (m->mbmi.txfm_size != TX_4X4 && m->mbmi.mode != I8X8_PRED) {
      m->mbmi.txfm_size += vp9_read(bc, cm->prob_tx[1]);
      if (m->mbmi.txfm_size != TX_8X8 && m->mbmi.sb_type >= BLOCK_SIZE_SB32X32)
        m->mbmi.txfm_size += vp9_read(bc, cm->prob_tx[2]);
    }
  } else if (cm->txfm_mode >= ALLOW_32X32 &&
             m->mbmi.sb_type >= BLOCK_SIZE_SB32X32) {
    m->mbmi.txfm_size = TX_32X32;
  } else if (cm->txfm_mode >= ALLOW_16X16 && m->mbmi.mode <= TM_PRED) {
    m->mbmi.txfm_size = TX_16X16;
  } else if (cm->txfm_mode >= ALLOW_8X8 && m->mbmi.mode != B_PRED) {
    m->mbmi.txfm_size = TX_8X8;
  } else {
    m->mbmi.txfm_size = TX_4X4;
  }
}

static int read_nmv_component(vp9_reader *r,
                              int rv,
                              const nmv_component *mvcomp) {
  int mag, d;
  const int sign = vp9_read(r, mvcomp->sign);
  const int mv_class = treed_read(r, vp9_mv_class_tree, mvcomp->classes);

  if (mv_class == MV_CLASS_0) {
    d = treed_read(r, vp9_mv_class0_tree, mvcomp->class0);
  } else {
    int i;
    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;
  }

  mag = vp9_get_mv_mag(mv_class, d << 3);
  return sign ? -(mag + 8) : (mag + 8);
}

static int read_nmv_component_fp(vp9_reader *r,
                                 int v,
                                 int rv,
                                 const nmv_component *mvcomp,
                                 int usehp) {
  const int sign = v < 0;
  int mag = ((sign ? -v : v) - 1) & ~7;  // magnitude - 1
  int offset;
  const int mv_class = vp9_get_mv_class(mag, &offset);
  const int f = mv_class == MV_CLASS_0 ?
      treed_read(r, vp9_mv_fp_tree, mvcomp->class0_fp[offset >> 3]):
      treed_read(r, vp9_mv_fp_tree, mvcomp->fp);

  offset += f << 1;

  if (usehp) {
    const vp9_prob p = mv_class == MV_CLASS_0 ? mvcomp->class0_hp : mvcomp->hp;
    offset += vp9_read(r, p);
  } else {
    offset += 1;  // If hp is not used, the default value of the hp bit is 1
  }
  mag = vp9_get_mv_mag(mv_class, offset);
  return sign ? -(mag + 1) : (mag + 1);
}

static void read_nmv(vp9_reader *r, MV *mv, const MV *ref,
                     const nmv_context *mvctx) {
  const MV_JOINT_TYPE j = treed_read(r, vp9_mv_joint_tree, mvctx->joints);
  mv->row = mv-> col = 0;
  if (j == MV_JOINT_HZVNZ || j == MV_JOINT_HNZVNZ) {
    mv->row = read_nmv_component(r, ref->row, &mvctx->comps[0]);
  }

  if (j == MV_JOINT_HNZVZ || j == MV_JOINT_HNZVNZ) {
    mv->col = read_nmv_component(r, ref->col, &mvctx->comps[1]);
  }
}

static void read_nmv_fp(vp9_reader *r, MV *mv, const MV *ref,
                        const nmv_context *mvctx, int usehp) {
  const MV_JOINT_TYPE j = vp9_get_mv_joint(*mv);
  usehp = usehp && vp9_use_nmv_hp(ref);
  if (j == MV_JOINT_HZVNZ || j == MV_JOINT_HNZVNZ) {
    mv->row = read_nmv_component_fp(r, mv->row, ref->row, &mvctx->comps[0],
                                    usehp);
  }
  if (j == MV_JOINT_HNZVZ || j == MV_JOINT_HNZVNZ) {
    mv->col = read_nmv_component_fp(r, mv->col, ref->col, &mvctx->comps[1],
                                    usehp);
  }
  /*
  printf("MV: %d %d REF: %d %d\n", mv->row + ref->row, mv->col + ref->col,
	 ref->row, ref->col);
	 */
}

static void update_nmv(vp9_reader *bc, vp9_prob *const p,
                       const vp9_prob upd_p) {
  if (vp9_read(bc, upd_p)) {
#ifdef LOW_PRECISION_MV_UPDATE
    *p = (vp9_read_literal(bc, 7) << 1) | 1;
#else
    *p = (vp9_read_literal(bc, 8));
#endif
  }
}

static void read_nmvprobs(vp9_reader *bc, nmv_context *mvctx,
                          int usehp) {
  int i, j, k;

#ifdef MV_GROUP_UPDATE
  if (!vp9_read_bit(bc))
    return;
#endif
  for (j = 0; j < MV_JOINTS - 1; ++j)
    update_nmv(bc, &mvctx->joints[j], VP9_NMV_UPDATE_PROB);

  for (i = 0; i < 2; ++i) {
    update_nmv(bc, &mvctx->comps[i].sign, VP9_NMV_UPDATE_PROB);
    for (j = 0; j < MV_CLASSES - 1; ++j)
      update_nmv(bc, &mvctx->comps[i].classes[j], VP9_NMV_UPDATE_PROB);

    for (j = 0; j < CLASS0_SIZE - 1; ++j)
      update_nmv(bc, &mvctx->comps[i].class0[j], VP9_NMV_UPDATE_PROB);

    for (j = 0; j < MV_OFFSET_BITS; ++j)
      update_nmv(bc, &mvctx->comps[i].bits[j], VP9_NMV_UPDATE_PROB);
  }

  for (i = 0; i < 2; ++i) {
    for (j = 0; j < CLASS0_SIZE; ++j)
      for (k = 0; k < 3; ++k)
        update_nmv(bc, &mvctx->comps[i].class0_fp[j][k], VP9_NMV_UPDATE_PROB);

    for (j = 0; j < 3; ++j)
      update_nmv(bc, &mvctx->comps[i].fp[j], VP9_NMV_UPDATE_PROB);
  }

  if (usehp) {
    for (i = 0; i < 2; ++i) {
      update_nmv(bc, &mvctx->comps[i].class0_hp, VP9_NMV_UPDATE_PROB);
      update_nmv(bc, &mvctx->comps[i].hp, VP9_NMV_UPDATE_PROB);
    }
  }
}

// Read the referncence frame
static MV_REFERENCE_FRAME read_ref_frame(VP9D_COMP *pbi,
                                         vp9_reader *const bc,
                                         unsigned char segment_id) {
  MV_REFERENCE_FRAME ref_frame;
  VP9_COMMON *const cm = &pbi->common;
  MACROBLOCKD *const xd = &pbi->mb;

  int seg_ref_count = 0;
  int seg_ref_active = vp9_segfeature_active(xd, segment_id, SEG_LVL_REF_FRAME);

  // If segment coding enabled does the segment allow for more than one
  // possible reference frame
  if (seg_ref_active) {
    seg_ref_count = vp9_check_segref(xd, segment_id, INTRA_FRAME) +
                    vp9_check_segref(xd, segment_id, LAST_FRAME) +
                    vp9_check_segref(xd, segment_id, GOLDEN_FRAME) +
                    vp9_check_segref(xd, segment_id, ALTREF_FRAME);
  }

  // Segment reference frame features not available or allows for
  // multiple reference frame options
  if (!seg_ref_active || seg_ref_count > 1) {
    // Values used in prediction model coding
    MV_REFERENCE_FRAME pred_ref;

    // Get the context probability the prediction flag
    vp9_prob pred_prob = vp9_get_pred_prob(cm, xd, PRED_REF);

    // Read the prediction status flag
    unsigned char prediction_flag = vp9_read(bc, pred_prob);

    // Store the prediction flag.
    vp9_set_pred_flag(xd, PRED_REF, prediction_flag);

    // Get the predicted reference frame.
    pred_ref = vp9_get_pred_ref(cm, xd);

    // If correctly predicted then use the predicted value
    if (prediction_flag) {
      ref_frame = pred_ref;
    } else {
      // decode the explicitly coded value
      vp9_prob mod_refprobs[PREDICTION_PROBS];
      vpx_memcpy(mod_refprobs,
                 cm->mod_refprobs[pred_ref], sizeof(mod_refprobs));

      // If segment coding enabled blank out options that cant occur by
      // setting the branch probability to 0.
      if (seg_ref_active) {
        mod_refprobs[INTRA_FRAME] *=
          vp9_check_segref(xd, segment_id, INTRA_FRAME);
        mod_refprobs[LAST_FRAME] *=
          vp9_check_segref(xd, segment_id, LAST_FRAME);
        mod_refprobs[GOLDEN_FRAME] *=
          vp9_check_segref(xd, segment_id, GOLDEN_FRAME) *
          vp9_check_segref(xd, segment_id, ALTREF_FRAME);
      }

      // Default to INTRA_FRAME (value 0)
      ref_frame = INTRA_FRAME;

      // Do we need to decode the Intra/Inter branch
      if (mod_refprobs[0])
        ref_frame = vp9_read(bc, mod_refprobs[0]);
      else
        ref_frame++;

      if (ref_frame) {
        // Do we need to decode the Last/Gf_Arf branch
        if (mod_refprobs[1])
          ref_frame += vp9_read(bc, mod_refprobs[1]);
        else
          ref_frame++;

        if (ref_frame > 1) {
          // Do we need to decode the GF/Arf branch
          if (mod_refprobs[2]) {
            ref_frame += vp9_read(bc, mod_refprobs[2]);
          } else {
            if (seg_ref_active) {
              ref_frame = pred_ref == GOLDEN_FRAME ||
                          !vp9_check_segref(xd, segment_id, GOLDEN_FRAME)
                              ? ALTREF_FRAME
                              : GOLDEN_FRAME;
            } else {
              ref_frame = pred_ref == GOLDEN_FRAME
                              ? ALTREF_FRAME
                              : GOLDEN_FRAME;
            }
          }
        }
      }
    }
  } else {
    // Segment reference frame features are enabled
    // The reference frame for the mb is considered as correclty predicted
    // if it is signaled at the segment level for the purposes of the
    // common prediction model
    vp9_set_pred_flag(xd, PRED_REF, 1);
    ref_frame = vp9_get_pred_ref(cm, xd);
  }

  return ref_frame;
}

static MB_PREDICTION_MODE read_sb_mv_ref(vp9_reader *bc, const vp9_prob *p) {
  return (MB_PREDICTION_MODE) treed_read(bc, vp9_sb_mv_ref_tree, p);
}

static MB_PREDICTION_MODE read_mv_ref(vp9_reader *bc, const vp9_prob *p) {
  return (MB_PREDICTION_MODE) treed_read(bc, vp9_mv_ref_tree, p);
}

static B_PREDICTION_MODE sub_mv_ref(vp9_reader *bc, const vp9_prob *p) {
  return (B_PREDICTION_MODE) treed_read(bc, vp9_sub_mv_ref_tree, p);
}

#ifdef VPX_MODE_COUNT
unsigned int vp9_mv_cont_count[5][4] = {
  { 0, 0, 0, 0 },
  { 0, 0, 0, 0 },
  { 0, 0, 0, 0 },
  { 0, 0, 0, 0 },
  { 0, 0, 0, 0 }
};
#endif

static const unsigned char mbsplit_fill_count[4] = { 8, 8, 4, 1 };
static const unsigned char mbsplit_fill_offset[4][16] = {
  { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10, 11, 12, 13, 14, 15 },
  { 0,  1,  4,  5,  8,  9, 12, 13,  2,  3,   6,  7, 10, 11, 14, 15 },
  { 0,  1,  4,  5,  2,  3,  6,  7,  8,  9,  12, 13, 10, 11, 14, 15 },
  { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9,  10, 11, 12, 13, 14, 15 }
};

static void read_switchable_interp_probs(VP9D_COMP* const pbi,
                                         BOOL_DECODER* const bc) {
  VP9_COMMON *const cm = &pbi->common;
  int i, j;
  for (j = 0; j < VP9_SWITCHABLE_FILTERS + 1; ++j) {
    for (i = 0; i < VP9_SWITCHABLE_FILTERS - 1; ++i) {
      cm->fc.switchable_interp_prob[j][i] = vp9_read_prob(bc);
    }
  }
  //printf("DECODER: %d %d\n", cm->fc.switchable_interp_prob[0],
  //cm->fc.switchable_interp_prob[1]);
}

static void mb_mode_mv_init(VP9D_COMP *pbi, vp9_reader *bc) {
  VP9_COMMON *const cm = &pbi->common;
  nmv_context *const nmvc = &pbi->common.fc.nmvc;
  MACROBLOCKD *const xd = &pbi->mb;

  if (cm->frame_type == KEY_FRAME) {
    if (!cm->kf_ymode_probs_update)
      cm->kf_ymode_probs_index = vp9_read_literal(bc, 3);
  } else {
    if (cm->mcomp_filter_type == SWITCHABLE)
      read_switchable_interp_probs(pbi, bc);
#if CONFIG_COMP_INTERINTRA_PRED
    if (cm->use_interintra) {
      if (vp9_read(bc, VP9_UPD_INTERINTRA_PROB))
        cm->fc.interintra_prob = vp9_read_prob(bc);
    }
#endif
    // Decode the baseline probabilities for decoding reference frame
    cm->prob_intra_coded = vp9_read_prob(bc);
    cm->prob_last_coded  = vp9_read_prob(bc);
    cm->prob_gf_coded    = vp9_read_prob(bc);

    // Computes a modified set of probabilities for use when reference
    // frame prediction fails.
    vp9_compute_mod_refprobs(cm);

    cm->comp_pred_mode = vp9_read_bit(bc);
    if (cm->comp_pred_mode)
      cm->comp_pred_mode += vp9_read_bit(bc);

    if (cm->comp_pred_mode == HYBRID_PREDICTION) {
      int i;
      for (i = 0; i < COMP_PRED_CONTEXTS; i++)
        cm->prob_comppred[i] = vp9_read_prob(bc);
    }

    if (vp9_read_bit(bc)) {
      int i;
      for (i = 0; i < VP9_YMODES - 1; ++i)
        cm->fc.ymode_prob[i] = vp9_read_prob(bc);
    }

    if (vp9_read_bit(bc)) {
      int i;
      for (i = 0; i < VP9_I32X32_MODES - 1; ++i)
        cm->fc.sb_ymode_prob[i] = vp9_read_prob(bc);
    }

    read_nmvprobs(bc, nmvc, xd->allow_high_precision_mv);
  }
}

// This function either reads the segment id for the current macroblock from
// the bitstream or if the value is temporally predicted asserts the predicted
// value
static void read_mb_segment_id(VP9D_COMP *pbi,
                               int mb_row, int mb_col,
                               BOOL_DECODER* const bc) {
  VP9_COMMON *const cm = &pbi->common;
  MACROBLOCKD *const xd = &pbi->mb;
  MODE_INFO *mi = xd->mode_info_context;
  MB_MODE_INFO *mbmi = &mi->mbmi;
  int mb_index = mb_row * pbi->common.mb_cols + mb_col;

  if (xd->segmentation_enabled) {
    if (xd->update_mb_segmentation_map) {
      // Is temporal coding of the segment id for this mb enabled.
      if (cm->temporal_update) {
        // Get the context based probability for reading the
        // prediction status flag
        vp9_prob pred_prob = vp9_get_pred_prob(cm, xd, PRED_SEG_ID);

        // Read the prediction status flag
        unsigned char seg_pred_flag = vp9_read(bc, pred_prob);

        // Store the prediction flag.
        vp9_set_pred_flag(xd, PRED_SEG_ID, seg_pred_flag);

        // If the value is flagged as correctly predicted
        // then use the predicted value
        if (seg_pred_flag) {
          mbmi->segment_id = vp9_get_pred_mb_segid(cm, xd, mb_index);
        } else {
          // Decode it explicitly
          read_mb_segid_except(cm, bc, mbmi, xd, mb_row, mb_col);
        }
      } else {
        // Normal unpredicted coding mode
        read_mb_segid(bc, mbmi, xd);
      }

      if (mbmi->sb_type) {
        const int bw = 1 << mb_width_log2(mbmi->sb_type);
        const int bh = 1 << mb_height_log2(mbmi->sb_type);
        const int ymbs = MIN(cm->mb_rows - mb_row, bh);
        const int xmbs = MIN(cm->mb_cols - mb_col, bw);
        int x, y;

        for (y = 0; y < ymbs; y++) {
          for (x = 0; x < xmbs; x++) {
            cm->last_frame_seg_map[mb_index + x + y * cm->mb_cols] =
                mbmi->segment_id;
          }
        }
      } else {
        cm->last_frame_seg_map[mb_index] = mbmi->segment_id;
      }
    } else {
      if (mbmi->sb_type) {
        const int bw = 1 << mb_width_log2(mbmi->sb_type);
        const int bh = 1 << mb_height_log2(mbmi->sb_type);
        const int ymbs = MIN(cm->mb_rows - mb_row, bh);
        const int xmbs = MIN(cm->mb_cols - mb_col, bw);
        unsigned segment_id = -1;
        int x, y;

        for (y = 0; y < ymbs; y++) {
          for (x = 0; x < xmbs; x++) {
            segment_id = MIN(segment_id,
                cm->last_frame_seg_map[mb_index + x + y * cm->mb_cols]);
          }
        }
        mbmi->segment_id = segment_id;
      } else {
        mbmi->segment_id = cm->last_frame_seg_map[mb_index];
      }
    }
  } else {
    // The encoder explicitly sets the segment_id to 0
    // when segmentation is disabled
    mbmi->segment_id = 0;
  }
}


static INLINE void assign_and_clamp_mv(int_mv *dst, const int_mv *src,
                                       int mb_to_left_edge,
                                       int mb_to_right_edge,
                                       int mb_to_top_edge,
                                       int mb_to_bottom_edge) {
  dst->as_int = src->as_int;
  clamp_mv(dst, mb_to_left_edge, mb_to_right_edge, mb_to_top_edge,
           mb_to_bottom_edge);
}

static INLINE void process_mv(BOOL_DECODER* bc, MV *mv, MV *ref,
                              nmv_context *nmvc, nmv_context_counts *mvctx,
                              int usehp) {
  read_nmv(bc, mv, ref, nmvc);
  read_nmv_fp(bc, mv, ref, nmvc, usehp);
  vp9_increment_nmv(mv, ref, mvctx, usehp);
  mv->row += ref->row;
  mv->col += ref->col;
}

static INLINE INTERPOLATIONFILTERTYPE read_switchable_filter_type(
    VP9D_COMP *pbi, BOOL_DECODER* bc) {
  const int index = treed_read(bc,
                               vp9_switchable_interp_tree,
                               vp9_get_pred_probs(&pbi->common, &pbi->mb,
                                                  PRED_SWITCHABLE_INTERP));
  return vp9_switchable_interp[index];
}

static void read_mb_modes_mv(VP9D_COMP *pbi, MODE_INFO *mi, MB_MODE_INFO *mbmi,
                             MODE_INFO *prev_mi,
                             int mb_row, int mb_col,
                             BOOL_DECODER* const bc) {
  VP9_COMMON *const cm = &pbi->common;
  nmv_context *const nmvc = &pbi->common.fc.nmvc;
  const int mis = pbi->common.mode_info_stride;
  MACROBLOCKD *const xd = &pbi->mb;

  int_mv *const mv = &mbmi->mv[0];
  const int bw = 1 << mb_width_log2(mi->mbmi.sb_type);
  const int bh = 1 << mb_height_log2(mi->mbmi.sb_type);

  const int use_prev_in_find_mv_refs = cm->width == cm->last_width &&
                                       cm->height == cm->last_height &&
                                       !cm->error_resilient_mode;

  int mb_to_left_edge, mb_to_right_edge, mb_to_top_edge, mb_to_bottom_edge;

  mbmi->need_to_clamp_mvs = 0;
  mbmi->need_to_clamp_secondmv = 0;
  mbmi->second_ref_frame = NONE;

  // Make sure the MACROBLOCKD mode info pointer is pointed at the
  // correct entry for the current macroblock.
  xd->mode_info_context = mi;
  xd->prev_mode_info_context = prev_mi;

  // Distance of Mb to the various image edges.
  // These specified to 8th pel as they are always compared to MV values
  // that are in 1/8th pel units
  set_mb_row(cm, xd, mb_row, bh);
  set_mb_col(cm, xd, mb_col, bw);

  mb_to_top_edge = xd->mb_to_top_edge - LEFT_TOP_MARGIN;
  mb_to_bottom_edge = xd->mb_to_bottom_edge + RIGHT_BOTTOM_MARGIN;
  mb_to_left_edge = xd->mb_to_left_edge - LEFT_TOP_MARGIN;
  mb_to_right_edge = xd->mb_to_right_edge + RIGHT_BOTTOM_MARGIN;

  // Read the macroblock segment id.
  read_mb_segment_id(pbi, mb_row, mb_col, bc);

  if (pbi->common.mb_no_coeff_skip &&
      (!vp9_segfeature_active(xd, mbmi->segment_id, SEG_LVL_SKIP))) {
    // Read the macroblock coeff skip flag if this feature is in use,
    // else default to 0
    mbmi->mb_skip_coeff = vp9_read(bc, vp9_get_pred_prob(cm, xd, PRED_MBSKIP));
  } else {
    mbmi->mb_skip_coeff = vp9_segfeature_active(xd, mbmi->segment_id,
                                                SEG_LVL_SKIP);
  }

  // Read the reference frame
  mbmi->ref_frame = read_ref_frame(pbi, bc, mbmi->segment_id);

  // if (pbi->common.current_video_frame == 1)
  //   printf("ref frame: %d [%d %d]\n", mbmi->ref_frame, mb_row, mb_col);

  // If reference frame is an Inter frame
  if (mbmi->ref_frame) {
    int_mv nearest, nearby, best_mv;
    int_mv nearest_second, nearby_second, best_mv_second;
    vp9_prob mv_ref_p[VP9_MVREFS - 1];

    const MV_REFERENCE_FRAME ref_frame = mbmi->ref_frame;
    struct scale_factors *sf0 = &xd->scale_factor[0];
    struct scale_factors *sf_uv0 = &xd->scale_factor_uv[0];
    *sf0 = cm->active_ref_scale[mbmi->ref_frame - 1];

    {
      const int use_prev_in_find_best_ref = sf0->x_num == sf0->x_den &&
                                            sf0->y_num == sf0->y_den &&
                                            !cm->error_resilient_mode &&
                                            !cm->frame_parallel_decoding_mode;

      // Select the appropriate reference frame for this MB
      const int ref_fb_idx = cm->active_ref_idx[ref_frame - 1];

      setup_pred_block(&xd->pre, &cm->yv12_fb[ref_fb_idx],
                       mb_row, mb_col, sf0, sf_uv0);

#ifdef DEC_DEBUG
      if (dec_debug)
        printf("%d %d\n", xd->mode_info_context->mbmi.mv[0].as_mv.row,
               xd->mode_info_context->mbmi.mv[0].as_mv.col);
#endif
      vp9_find_mv_refs(cm, xd, mi, use_prev_in_find_mv_refs ? prev_mi : NULL,
                       ref_frame, mbmi->ref_mvs[ref_frame],
                       cm->ref_frame_sign_bias);

      vp9_mv_ref_probs(cm, mv_ref_p, mbmi->mb_mode_context[ref_frame]);

      // If the segment level skip mode enabled
      if (vp9_segfeature_active(xd, mbmi->segment_id, SEG_LVL_SKIP)) {
        mbmi->mode = ZEROMV;
      } else {
        mbmi->mode = mbmi->sb_type ? read_sb_mv_ref(bc, mv_ref_p)
                                   : read_mv_ref(bc, mv_ref_p);
        vp9_accum_mv_refs(cm, mbmi->mode, mbmi->mb_mode_context[ref_frame]);
      }

      if (mbmi->mode != ZEROMV) {
        vp9_find_best_ref_mvs(xd,
                              use_prev_in_find_best_ref ? xd->pre.y_buffer
                                                        : NULL,
                              xd->pre.y_stride,
                              mbmi->ref_mvs[ref_frame],
                              &nearest, &nearby);