vp9_bitstream.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/common/vp9_header.h"
#include "vp9/encoder/vp9_encodemv.h"
#include "vp9/common/vp9_entropymode.h"
#include "vp9/common/vp9_findnearmv.h"
#include "vp9/encoder/vp9_mcomp.h"
#include "vp9/common/vp9_systemdependent.h"
#include <assert.h>
#include <stdio.h>
#include <limits.h>
#include "vp9/common/vp9_pragmas.h"
#include "vpx/vpx_encoder.h"
#include "vpx_mem/vpx_mem.h"
#include "vp9/encoder/vp9_bitstream.h"
#include "vp9/encoder/vp9_segmentation.h"

#include "vp9/common/vp9_seg_common.h"
#include "vp9/common/vp9_pred_common.h"
#include "vp9/common/vp9_entropy.h"
#include "vp9/encoder/vp9_encodemv.h"
#include "vp9/common/vp9_entropymv.h"
#include "vp9/common/vp9_mvref_common.h"

#if defined(SECTIONBITS_OUTPUT)
unsigned __int64 Sectionbits[500];
#endif

#ifdef ENTROPY_STATS
int intra_mode_stats[VP9_KF_BINTRAMODES]
                    [VP9_KF_BINTRAMODES]
                    [VP9_KF_BINTRAMODES];
unsigned int tree_update_hist [BLOCK_TYPES]
                              [COEF_BANDS]
                              [PREV_COEF_CONTEXTS]
                              [ENTROPY_NODES][2];
unsigned int hybrid_tree_update_hist [BLOCK_TYPES]
                                     [COEF_BANDS]
                                     [PREV_COEF_CONTEXTS]
                                     [ENTROPY_NODES][2];
unsigned int tree_update_hist_8x8 [BLOCK_TYPES_8X8]
                                  [COEF_BANDS]
                                  [PREV_COEF_CONTEXTS]
                                  [ENTROPY_NODES] [2];
unsigned int hybrid_tree_update_hist_8x8 [BLOCK_TYPES_8X8]
                                         [COEF_BANDS]
                                         [PREV_COEF_CONTEXTS]
                                         [ENTROPY_NODES] [2];
unsigned int tree_update_hist_16x16 [BLOCK_TYPES_16X16]
                                    [COEF_BANDS]
                                    [PREV_COEF_CONTEXTS]
                                    [ENTROPY_NODES] [2];
unsigned int hybrid_tree_update_hist_16x16 [BLOCK_TYPES_16X16]
                                           [COEF_BANDS]
                                           [PREV_COEF_CONTEXTS]
                                           [ENTROPY_NODES] [2];

extern unsigned int active_section;
#endif

#ifdef MODE_STATS
int count_mb_seg[4] = { 0, 0, 0, 0 };
#endif

#define vp9_cost_upd  ((int)(vp9_cost_one(upd) - vp9_cost_zero(upd)) >> 8)
#define vp9_cost_upd256  ((int)(vp9_cost_one(upd) - vp9_cost_zero(upd)))

#define SEARCH_NEWP
static int update_bits[255];

static void compute_update_table() {
  int i;
  for (i = 0; i < 255; i++)
    update_bits[i] = vp9_count_term_subexp(i, SUBEXP_PARAM, 255);
}

static int split_index(int i, int n, int modulus) {
  int max1 = (n - 1 - modulus / 2) / modulus + 1;
  if (i % modulus == modulus / 2) i = i / modulus;
  else i = max1 + i - (i + modulus - modulus / 2) / modulus;
  return i;
}

static int remap_prob(int v, int m) {
  const int n = 256;
  const int modulus = MODULUS_PARAM;
  int i;
  if ((m << 1) <= n)
    i = vp9_recenter_nonneg(v, m) - 1;
  else
    i = vp9_recenter_nonneg(n - 1 - v, n - 1 - m) - 1;

  i = split_index(i, n - 1, modulus);
  return i;
}

static void write_prob_diff_update(vp9_writer *const bc,
                                   vp9_prob newp, vp9_prob oldp) {
  int delp = remap_prob(newp, oldp);
  vp9_encode_term_subexp(bc, delp, SUBEXP_PARAM, 255);
}

static int prob_diff_update_cost(vp9_prob newp, vp9_prob oldp) {
  int delp = remap_prob(newp, oldp);
  return update_bits[delp] * 256;
}

static void update_mode(
  vp9_writer *const bc,
  int n,
  vp9_token tok               [/* n */],
  vp9_tree tree,
  vp9_prob Pnew               [/* n-1 */],
  vp9_prob Pcur               [/* n-1 */],
  unsigned int bct            [/* n-1 */] [2],
  const unsigned int num_events[/* n */]
) {
  unsigned int new_b = 0, old_b = 0;
  int i = 0;

  vp9_tree_probs_from_distribution(
    n--, tok, tree,
    Pnew, bct, num_events,
    256, 1
  );

  do {
    new_b += cost_branch(bct[i], Pnew[i]);
    old_b += cost_branch(bct[i], Pcur[i]);
  } while (++i < n);

  if (new_b + (n << 8) < old_b) {
    int i = 0;

    vp9_write_bit(bc, 1);

    do {
      const vp9_prob p = Pnew[i];

      vp9_write_literal(bc, Pcur[i] = p ? p : 1, 8);
    } while (++i < n);
  } else
    vp9_write_bit(bc, 0);
}

static void update_mbintra_mode_probs(VP9_COMP* const cpi,
                                      vp9_writer* const bc) {
  VP9_COMMON *const cm = &cpi->common;

  {
    vp9_prob Pnew   [VP9_YMODES - 1];
    unsigned int bct [VP9_YMODES - 1] [2];

    update_mode(
      bc, VP9_YMODES, vp9_ymode_encodings, vp9_ymode_tree,
      Pnew, cm->fc.ymode_prob, bct, (unsigned int *)cpi->ymode_count
    );
#if CONFIG_SUPERBLOCKS
    update_mode(bc, VP9_I32X32_MODES, vp9_sb_ymode_encodings,
                vp9_sb_ymode_tree, Pnew, cm->fc.sb_ymode_prob, bct,
                (unsigned int *)cpi->sb_ymode_count);
#endif
  }
}

static int get_prob(int num, int den) {
  int p;
  if (den <= 0)
    return 128;
  p = (num * 255 + (den >> 1)) / den;
  return clip_prob(p);
}

static int get_binary_prob(int n0, int n1) {
  return get_prob(n0, n0 + n1);
}

void vp9_update_skip_probs(VP9_COMP *cpi) {
  VP9_COMMON *const pc = &cpi->common;
  int k;

  for (k = 0; k < MBSKIP_CONTEXTS; ++k) {
    pc->mbskip_pred_probs[k] = get_binary_prob(cpi->skip_false_count[k],
                                               cpi->skip_true_count[k]);
  }
}

static void update_switchable_interp_probs(VP9_COMP *cpi,
                                           vp9_writer* const bc) {
  VP9_COMMON *const pc = &cpi->common;
  unsigned int branch_ct[32][2];
  int i, j;
  for (j = 0; j <= VP9_SWITCHABLE_FILTERS; ++j) {
    vp9_tree_probs_from_distribution(
        VP9_SWITCHABLE_FILTERS,
        vp9_switchable_interp_encodings, vp9_switchable_interp_tree,
        pc->fc.switchable_interp_prob[j], branch_ct,
        cpi->switchable_interp_count[j], 256, 1);
    for (i = 0; i < VP9_SWITCHABLE_FILTERS - 1; ++i) {
      if (pc->fc.switchable_interp_prob[j][i] < 1)
        pc->fc.switchable_interp_prob[j][i] = 1;
      vp9_write_literal(bc, pc->fc.switchable_interp_prob[j][i], 8);
    }
  }
}

// This function updates the reference frame prediction stats
static void update_refpred_stats(VP9_COMP *cpi) {
  VP9_COMMON *const cm = &cpi->common;
  int i;
  vp9_prob new_pred_probs[PREDICTION_PROBS];
  int old_cost, new_cost;

  // Set the prediction probability structures to defaults
  if (cm->frame_type == KEY_FRAME) {
    // Set the prediction probabilities to defaults
    cm->ref_pred_probs[0] = 120;
    cm->ref_pred_probs[1] = 80;
    cm->ref_pred_probs[2] = 40;

    vpx_memset(cpi->ref_pred_probs_update, 0,
               sizeof(cpi->ref_pred_probs_update));
  } else {
    // From the prediction counts set the probabilities for each context
    for (i = 0; i < PREDICTION_PROBS; i++) {
      new_pred_probs[i] = get_binary_prob(cpi->ref_pred_count[i][0],
                                          cpi->ref_pred_count[i][1]);

      // Decide whether or not to update the reference frame probs.
      // Returned costs are in 1/256 bit units.
      old_cost =
        (cpi->ref_pred_count[i][0] * vp9_cost_zero(cm->ref_pred_probs[i])) +
        (cpi->ref_pred_count[i][1] * vp9_cost_one(cm->ref_pred_probs[i]));

      new_cost =
        (cpi->ref_pred_count[i][0] * vp9_cost_zero(new_pred_probs[i])) +
        (cpi->ref_pred_count[i][1] * vp9_cost_one(new_pred_probs[i]));

      // Cost saving must be >= 8 bits (2048 in these units)
      if ((old_cost - new_cost) >= 2048) {
        cpi->ref_pred_probs_update[i] = 1;
        cm->ref_pred_probs[i] = new_pred_probs[i];
      } else
        cpi->ref_pred_probs_update[i] = 0;

    }
  }
}

// This function is called to update the mode probability context used to encode
// inter modes. It assumes the branch counts table has already been populated
// prior to the actual packing of the bitstream (in rd stage or dummy pack)
//
// The branch counts table is re-populated during the actual pack stage and in
// the decoder to facilitate backwards update of the context.
static update_mode_probs(VP9_COMMON *cm,
                         int mode_context[INTER_MODE_CONTEXTS][4]) {
  int i, j;
  int (*mv_ref_ct)[4][2];

  vpx_memcpy(mode_context, cm->fc.vp9_mode_contexts,
             sizeof(cm->fc.vp9_mode_contexts));

  mv_ref_ct = cm->fc.mv_ref_ct;

  for (i = 0; i < INTER_MODE_CONTEXTS; i++) {
    for (j = 0; j < 4; j++) {
      int new_prob, count, old_cost, new_cost;

      // Work out cost of coding branches with the old and optimal probability
      old_cost = cost_branch256(mv_ref_ct[i][j], mode_context[i][j]);
      count = mv_ref_ct[i][j][0] + mv_ref_ct[i][j][1];
      new_prob = count > 0 ? (255 * mv_ref_ct[i][j][0]) / count : 128;
      new_prob = (new_prob > 0) ? new_prob : 1;
      new_cost = cost_branch256(mv_ref_ct[i][j], new_prob);

      // If cost saving is >= 14 bits then update the mode probability.
      // This is the approximate net cost of updating one probability given
      // that the no update case ismuch more common than the update case.
      if (new_cost <= (old_cost - (14 << 8))) {
        mode_context[i][j] = new_prob;
      }
    }
  }
}
static void write_ymode(vp9_writer *bc, int m, const vp9_prob *p) {
  write_token(bc, vp9_ymode_tree, p, vp9_ymode_encodings + m);
}

static void kfwrite_ymode(vp9_writer *bc, int m, const vp9_prob *p) {
  write_token(bc, vp9_kf_ymode_tree, p, vp9_kf_ymode_encodings + m);
}

#if CONFIG_SUPERBLOCKS
static void write_sb_ymode(vp9_writer *bc, int m, const vp9_prob *p) {
  write_token(bc, vp9_sb_ymode_tree, p, vp9_sb_ymode_encodings + m);
}

static void sb_kfwrite_ymode(vp9_writer *bc, int m, const vp9_prob *p) {
  write_token(bc, vp9_uv_mode_tree, p, vp9_sb_kf_ymode_encodings + m);
}
#endif

static void write_i8x8_mode(vp9_writer *bc, int m, const vp9_prob *p) {
  write_token(bc, vp9_i8x8_mode_tree, p, vp9_i8x8_mode_encodings + m);
}

static void write_uv_mode(vp9_writer *bc, int m, const vp9_prob *p) {
  write_token(bc, vp9_uv_mode_tree, p, vp9_uv_mode_encodings + m);
}


static void write_bmode(vp9_writer *bc, int m, const vp9_prob *p) {
#if CONFIG_NEWBINTRAMODES
  assert(m < B_CONTEXT_PRED - CONTEXT_PRED_REPLACEMENTS || m == B_CONTEXT_PRED);
  if (m == B_CONTEXT_PRED) m -= CONTEXT_PRED_REPLACEMENTS;
#endif
  write_token(bc, vp9_bmode_tree, p, vp9_bmode_encodings + m);
}

static void write_kf_bmode(vp9_writer *bc, int m, const vp9_prob *p) {
  write_token(bc, vp9_kf_bmode_tree, p, vp9_kf_bmode_encodings + m);
}

static void write_split(vp9_writer *bc, int x, const vp9_prob *p) {
  write_token(
    bc, vp9_mbsplit_tree, p, vp9_mbsplit_encodings + x);
}

static int prob_update_savings(const unsigned int *ct,
                               const vp9_prob oldp, const vp9_prob newp,
                               const vp9_prob upd) {
  const int old_b = cost_branch256(ct, oldp);
  const int new_b = cost_branch256(ct, newp);
  const int update_b = 2048 + vp9_cost_upd256;
  return (old_b - new_b - update_b);
}

static int prob_diff_update_savings(const unsigned int *ct,
                                    const vp9_prob oldp, const vp9_prob newp,
                                    const vp9_prob upd) {
  const int old_b = cost_branch256(ct, oldp);
  const int new_b = cost_branch256(ct, newp);
  const int update_b = (newp == oldp ? 0 :
                        prob_diff_update_cost(newp, oldp) + vp9_cost_upd256);
  return (old_b - new_b - update_b);
}

static int prob_diff_update_savings_search(const unsigned int *ct,
                                           const vp9_prob oldp, vp9_prob *bestp,
                                           const vp9_prob upd) {
  const int old_b = cost_branch256(ct, oldp);
  int new_b, update_b, savings, bestsavings, step;
  vp9_prob newp, bestnewp;

  bestsavings = 0;
  bestnewp = oldp;

  step = (*bestp > oldp ? -1 : 1);
  for (newp = *bestp; newp != oldp; newp += step) {
    new_b = cost_branch256(ct, newp);
    update_b = prob_diff_update_cost(newp, oldp) + vp9_cost_upd256;
    savings = old_b - new_b - update_b;
    if (savings > bestsavings) {
      bestsavings = savings;
      bestnewp = newp;
    }
  }
  *bestp = bestnewp;
  return bestsavings;
}

static void vp9_cond_prob_update(vp9_writer *bc, vp9_prob *oldp, vp9_prob upd,
                                 unsigned int *ct) {
  vp9_prob newp;
  int savings;
  newp = get_binary_prob(ct[0], ct[1]);
  savings = prob_update_savings(ct, *oldp, newp, upd);
  if (savings > 0) {
    vp9_write(bc, 1, upd);
    vp9_write_literal(bc, newp, 8);
    *oldp = newp;
  } else {
    vp9_write(bc, 0, upd);
  }
}

static void pack_mb_tokens(vp9_writer* const bc,
                           TOKENEXTRA **tp,
                           const TOKENEXTRA *const stop) {
  unsigned int split;
  unsigned int shift;
  int count = bc->count;
  unsigned int range = bc->range;
  unsigned int lowvalue = bc->lowvalue;
  TOKENEXTRA *p = *tp;

  while (p < stop) {
    const int t = p->Token;
    vp9_token *const a = vp9_coef_encodings + t;
    const vp9_extra_bit_struct *const b = vp9_extra_bits + t;
    int i = 0;
    const unsigned char *pp = p->context_tree;
    int v = a->value;
    int n = a->Len;

    if (t == EOSB_TOKEN)
    {
      ++p;
      break;
    }

    /* skip one or two nodes */
    if (p->skip_eob_node) {
      n -= p->skip_eob_node;
      i = 2 * p->skip_eob_node;
    }

    do {
      const int bb = (v >> --n) & 1;
      split = 1 + (((range - 1) * pp[i >> 1]) >> 8);
      i = vp9_coef_tree[i + bb];

      if (bb) {
        lowvalue += split;
        range = range - split;
      } else {
        range = split;
      }

      shift = vp9_norm[range];
      range <<= shift;
      count += shift;

      if (count >= 0) {
        int offset = shift - count;

        if ((lowvalue << (offset - 1)) & 0x80000000) {
          int x = bc->pos - 1;

          while (x >= 0 && bc->buffer[x] == 0xff) {
            bc->buffer[x] = (unsigned char)0;
            x--;
          }

          bc->buffer[x] += 1;
        }

        bc->buffer[bc->pos++] = (lowvalue >> (24 - offset));
        lowvalue <<= offset;
        shift = count;
        lowvalue &= 0xffffff;
        count -= 8;
      }

      lowvalue <<= shift;
    } while (n);


    if (b->base_val) {
      const int e = p->Extra, L = b->Len;

      if (L) {
        const unsigned char *pp = b->prob;
        int v = e >> 1;
        int n = L;              /* number of bits in v, assumed nonzero */
        int i = 0;

        do {
          const int bb = (v >> --n) & 1;
          split = 1 + (((range - 1) * pp[i >> 1]) >> 8);
          i = b->tree[i + bb];

          if (bb) {
            lowvalue += split;
            range = range - split;
          } else {
            range = split;
          }

          shift = vp9_norm[range];
          range <<= shift;
          count += shift;

          if (count >= 0) {
            int offset = shift - count;

            if ((lowvalue << (offset - 1)) & 0x80000000) {
              int x = bc->pos - 1;

              while (x >= 0 && bc->buffer[x] == 0xff) {
                bc->buffer[x] = (unsigned char)0;
                x--;
              }

              bc->buffer[x] += 1;
            }

            bc->buffer[bc->pos++] = (lowvalue >> (24 - offset));
            lowvalue <<= offset;
            shift = count;
            lowvalue &= 0xffffff;
            count -= 8;
          }

          lowvalue <<= shift;
        } while (n);
      }


      {

        split = (range + 1) >> 1;

        if (e & 1) {
          lowvalue += split;
          range = range - split;
        } else {
          range = split;
        }

        range <<= 1;

        if ((lowvalue & 0x80000000)) {
          int x = bc->pos - 1;

          while (x >= 0 && bc->buffer[x] == 0xff) {
            bc->buffer[x] = (unsigned char)0;
            x--;
          }

          bc->buffer[x] += 1;

        }

        lowvalue  <<= 1;

        if (!++count) {
          count = -8;
          bc->buffer[bc->pos++] = (lowvalue >> 24);
          lowvalue &= 0xffffff;
        }
      }

    }
    ++p;
  }

  bc->count = count;
  bc->lowvalue = lowvalue;
  bc->range = range;
  *tp = p;
}

static void write_partition_size(unsigned char *cx_data, int size) {
  signed char csize;

  csize = size & 0xff;
  *cx_data = csize;
  csize = (size >> 8) & 0xff;
  *(cx_data + 1) = csize;
  csize = (size >> 16) & 0xff;
  *(cx_data + 2) = csize;

}

static void write_mv_ref
(
  vp9_writer *bc, MB_PREDICTION_MODE m, const vp9_prob *p
) {
#if CONFIG_DEBUG
  assert(NEARESTMV <= m  &&  m <= SPLITMV);
#endif
  write_token(bc, vp9_mv_ref_tree, p,
              vp9_mv_ref_encoding_array - NEARESTMV + m);
}

#if CONFIG_SUPERBLOCKS
static void write_sb_mv_ref(vp9_writer *bc, MB_PREDICTION_MODE m,
                            const vp9_prob *p) {
#if CONFIG_DEBUG
  assert(NEARESTMV <= m  &&  m < SPLITMV);
#endif
  write_token(bc, vp9_sb_mv_ref_tree, p,
              vp9_sb_mv_ref_encoding_array - NEARESTMV + m);
}
#endif

static void write_sub_mv_ref
(
  vp9_writer *bc, B_PREDICTION_MODE m, const vp9_prob *p
) {
#if CONFIG_DEBUG
  assert(LEFT4X4 <= m  &&  m <= NEW4X4);
#endif
  write_token(bc, vp9_sub_mv_ref_tree, p,
              vp9_sub_mv_ref_encoding_array - LEFT4X4 + m);
}

static void write_nmv(vp9_writer *bc, const MV *mv, const int_mv *ref,
                      const nmv_context *nmvc, int usehp) {
  MV e;
  e.row = mv->row - ref->as_mv.row;
  e.col = mv->col - ref->as_mv.col;

  vp9_encode_nmv(bc, &e, &ref->as_mv, nmvc);
  vp9_encode_nmv_fp(bc, &e, &ref->as_mv, nmvc, usehp);
}

#if CONFIG_NEW_MVREF
static void vp9_write_mv_ref_id(vp9_writer *w,
                                vp9_prob * ref_id_probs,
                                int mv_ref_id) {
  // Encode the index for the MV reference.
  switch (mv_ref_id) {
    case 0:
      vp9_write(w, 0, ref_id_probs[0]);
      break;
    case 1:
      vp9_write(w, 1, ref_id_probs[0]);
      vp9_write(w, 0, ref_id_probs[1]);
      break;
    case 2:
      vp9_write(w, 1, ref_id_probs[0]);
      vp9_write(w, 1, ref_id_probs[1]);
      vp9_write(w, 0, ref_id_probs[2]);
      break;
    case 3:
      vp9_write(w, 1, ref_id_probs[0]);
      vp9_write(w, 1, ref_id_probs[1]);
      vp9_write(w, 1, ref_id_probs[2]);
      break;

      // TRAP.. This should not happen
    default:
      assert(0);
      break;
  }
}
#endif

// This function writes the current macro block's segnment id to the bitstream
// It should only be called if a segment map update is indicated.
static void write_mb_segid(vp9_writer *bc,
                           const MB_MODE_INFO *mi, const MACROBLOCKD *xd) {
  // Encode the MB segment id.
  int seg_id = mi->segment_id;
#if CONFIG_SUPERBLOCKS
  if (mi->encoded_as_sb) {
    if (xd->mb_to_right_edge >= 0)
      seg_id = seg_id && xd->mode_info_context[1].mbmi.segment_id;
    if (xd->mb_to_bottom_edge >= 0) {
      seg_id = seg_id &&
               xd->mode_info_context[xd->mode_info_stride].mbmi.segment_id;
      if (xd->mb_to_right_edge >= 0)
        seg_id = seg_id &&
                xd->mode_info_context[xd->mode_info_stride + 1].mbmi.segment_id;
    }
  }
#endif
  if (xd->segmentation_enabled && xd->update_mb_segmentation_map) {
    switch (seg_id) {
      case 0:
        vp9_write(bc, 0, xd->mb_segment_tree_probs[0]);
        vp9_write(bc, 0, xd->mb_segment_tree_probs[1]);
        break;
      case 1:
        vp9_write(bc, 0, xd->mb_segment_tree_probs[0]);
        vp9_write(bc, 1, xd->mb_segment_tree_probs[1]);
        break;
      case 2:
        vp9_write(bc, 1, xd->mb_segment_tree_probs[0]);
        vp9_write(bc, 0, xd->mb_segment_tree_probs[2]);
        break;
      case 3:
        vp9_write(bc, 1, xd->mb_segment_tree_probs[0]);
        vp9_write(bc, 1, xd->mb_segment_tree_probs[2]);
        break;

        // TRAP.. This should not happen
      default:
        vp9_write(bc, 0, xd->mb_segment_tree_probs[0]);
        vp9_write(bc, 0, xd->mb_segment_tree_probs[1]);
        break;
    }
  }
}

// This function encodes the reference frame
static void encode_ref_frame(vp9_writer *const bc,
                             VP9_COMMON *const cm,
                             MACROBLOCKD *xd,
                             int segment_id,
                             MV_REFERENCE_FRAME rf) {
  int seg_ref_active;
  int seg_ref_count = 0;
  seg_ref_active = vp9_segfeature_active(xd,
                                         segment_id,
                                         SEG_LVL_REF_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);
  }

  // If segment level coding of this signal is disabled...
  // or the segment allows multiple reference frame options
  if (!seg_ref_active || (seg_ref_count > 1)) {
    // Values used in prediction model coding
    unsigned char prediction_flag;
    vp9_prob pred_prob;
    MV_REFERENCE_FRAME pred_rf;

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

    // Get the predicted value.
    pred_rf = vp9_get_pred_ref(cm, xd);

    // Did the chosen reference frame match its predicted value.
    prediction_flag =
      (xd->mode_info_context->mbmi.ref_frame == pred_rf);

    vp9_set_pred_flag(xd, PRED_REF, prediction_flag);
    vp9_write(bc, prediction_flag, pred_prob);

    // If not predicted correctly then code value explicitly
    if (!prediction_flag) {
      vp9_prob mod_refprobs[PREDICTION_PROBS];

      vpx_memcpy(mod_refprobs,
                 cm->mod_refprobs[pred_rf], 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));
      }

      if (mod_refprobs[0]) {
        vp9_write(bc, (rf != INTRA_FRAME), mod_refprobs[0]);
      }

      // Inter coded
      if (rf != INTRA_FRAME) {
        if (mod_refprobs[1]) {
          vp9_write(bc, (rf != LAST_FRAME), mod_refprobs[1]);
        }

        if (rf != LAST_FRAME) {
          if (mod_refprobs[2]) {
            vp9_write(bc, (rf != GOLDEN_FRAME), mod_refprobs[2]);
          }
        }
      }
    }
  }

  // if using the prediction mdoel we have nothing further to do because
  // the reference frame is fully coded by the segment
}

// Update the probabilities used to encode reference frame data
static void update_ref_probs(VP9_COMP *const cpi) {
  VP9_COMMON *const cm = &cpi->common;

  const int *const rfct = cpi->count_mb_ref_frame_usage;
  const int rf_intra = rfct[INTRA_FRAME];
  const int rf_inter = rfct[LAST_FRAME] +
                       rfct[GOLDEN_FRAME] + rfct[ALTREF_FRAME];

  cm->prob_intra_coded = get_binary_prob(rf_intra, rf_inter);
  cm->prob_last_coded = get_prob(rfct[LAST_FRAME], rf_inter);
  cm->prob_gf_coded = get_binary_prob(rfct[GOLDEN_FRAME], rfct[ALTREF_FRAME]);

  // Compute a modified set of probabilities to use when prediction of the
  // reference frame fails
  vp9_compute_mod_refprobs(cm);
}

static void pack_inter_mode_mvs(VP9_COMP *const cpi, vp9_writer *const bc) {
  VP9_COMMON *const pc = &cpi->common;
  const nmv_context *nmvc = &pc->fc.nmvc;
  MACROBLOCK *x = &cpi->mb;
  MACROBLOCKD *xd = &cpi->mb.e_mbd;
  MODE_INFO *m;
  MODE_INFO *prev_m;
  TOKENEXTRA *tok = cpi->tok;
  TOKENEXTRA *tok_end = tok + cpi->tok_count;

  const int mis = pc->mode_info_stride;
  int mb_row, mb_col;
  int row, col;

  // Values used in prediction model coding
  vp9_prob pred_prob;
  unsigned char prediction_flag;

  int row_delta[4] = { 0, +1,  0, -1};
  int col_delta[4] = { +1, -1, +1, +1};

  cpi->mb.partition_info = cpi->mb.pi;

  mb_row = 0;
  for (row = 0; row < pc->mb_rows; row += 2) {
    m = pc->mi + row * mis;
    prev_m = pc->prev_mi + row * mis;

    mb_col = 0;
    for (col = 0; col < pc->mb_cols; col += 2) {
      int i;

      // Process the 4 MBs in the order:
      // top-left, top-right, bottom-left, bottom-right
#if CONFIG_SUPERBLOCKS
      vp9_write(bc, m->mbmi.encoded_as_sb, pc->sb_coded);
#endif
      for (i = 0; i < 4; i++) {
        MB_MODE_INFO *mi;
        MV_REFERENCE_FRAME rf;
        MV_REFERENCE_FRAME sec_ref_frame;
        MB_PREDICTION_MODE mode;
        int segment_id, skip_coeff;

        int dy = row_delta[i];
        int dx = col_delta[i];
        int offset_extended = dy * mis + dx;

        if ((mb_row >= pc->mb_rows) || (mb_col >= pc->mb_cols)) {
          // MB lies outside frame, move on
          mb_row += dy;
          mb_col += dx;
          m += offset_extended;
          prev_m += offset_extended;
          cpi->mb.partition_info += offset_extended;
          continue;
        }

        mi = &m->mbmi;
        rf = mi->ref_frame;
        sec_ref_frame = mi->second_ref_frame;
        mode = mi->mode;
        segment_id = mi->segment_id;

        // 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
        xd->mb_to_left_edge = -((mb_col * 16) << 3);
        xd->mb_to_top_edge = -((mb_row * 16)) << 3;

#if CONFIG_SUPERBLOCKS
        if (mi->encoded_as_sb) {
          xd->mb_to_right_edge = ((pc->mb_cols - 2 - mb_col) * 16) << 3;
          xd->mb_to_bottom_edge = ((pc->mb_rows - 2 - mb_row) * 16) << 3;
        } else {
#endif
          xd->mb_to_right_edge = ((pc->mb_cols - 1 - mb_col) * 16) << 3;
          xd->mb_to_bottom_edge = ((pc->mb_rows - 1 - mb_row) * 16) << 3;
#if CONFIG_SUPERBLOCKS
        }
#endif

        // Make sure the MacroBlockD mode info pointer is set correctly
        xd->mode_info_context = m;
        xd->prev_mode_info_context = prev_m;

#ifdef ENTROPY_STATS
        active_section = 9;
#endif
        if (cpi->mb.e_mbd.update_mb_segmentation_map) {
          // Is temporal coding of the segment map enabled
          if (pc->temporal_update) {
            prediction_flag = vp9_get_pred_flag(xd, PRED_SEG_ID);
            pred_prob = vp9_get_pred_prob(pc, xd, PRED_SEG_ID);

            // Code the segment id prediction flag for this mb
            vp9_write(bc, prediction_flag, pred_prob);

            // If the mb segment id wasn't predicted code explicitly
            if (!prediction_flag)
              write_mb_segid(bc, mi, &cpi->mb.e_mbd);
          } else {
            // Normal unpredicted coding
            write_mb_segid(bc, mi, &cpi->mb.e_mbd);
          }
        }

        skip_coeff = 1;
        if (pc->mb_no_coeff_skip &&
            (!vp9_segfeature_active(xd, segment_id, SEG_LVL_EOB) ||
             (vp9_get_segdata(xd, segment_id, SEG_LVL_EOB) != 0))) {
          skip_coeff = mi->mb_skip_coeff;
#if CONFIG_SUPERBLOCKS
          if (mi->encoded_as_sb) {
            skip_coeff &= m[1].mbmi.mb_skip_coeff;
            skip_coeff &= m[mis].mbmi.mb_skip_coeff;
            skip_coeff &= m[mis + 1].mbmi.mb_skip_coeff;
          }
#endif
          vp9_write(bc, skip_coeff,
                    vp9_get_pred_prob(pc, xd, PRED_MBSKIP));
        }

        // Encode the reference frame.
        if (!vp9_segfeature_active(xd, segment_id, SEG_LVL_MODE)
            || vp9_get_segdata(xd, segment_id, SEG_LVL_MODE) >= NEARESTMV) {
          encode_ref_frame(bc, pc, xd, segment_id, rf);
        } else {
          assert(rf == INTRA_FRAME);
        }

        if (rf == INTRA_FRAME) {
#ifdef ENTROPY_STATS
          active_section = 6;
#endif

          if (!vp9_segfeature_active(xd, segment_id, SEG_LVL_MODE)) {
#if CONFIG_SUPERBLOCKS
            if (m->mbmi.encoded_as_sb)
              write_sb_ymode(bc, mode, pc->fc.sb_ymode_prob);
            else
#endif
            write_ymode(bc, mode, pc->fc.ymode_prob);
          }
          if (mode == B_PRED) {
            int j = 0;
#if CONFIG_COMP_INTRA_PRED