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 <assert.h>
#include <stdio.h>
#include <limits.h>

#include "vpx/vpx_encoder.h"
#include "vpx_mem/vpx_mem.h"

#include "vp9/common/vp9_entropymode.h"
#include "vp9/common/vp9_entropymv.h"
#include "vp9/common/vp9_findnearmv.h"
#include "vp9/common/vp9_tile_common.h"
#include "vp9/common/vp9_systemdependent.h"
#include "vp9/common/vp9_pragmas.h"
#include "vp9/common/vp9_seg_common.h"
#include "vp9/common/vp9_pred_common.h"
#include "vp9/common/vp9_entropy.h"
#include "vp9/common/vp9_entropymv.h"
#include "vp9/common/vp9_mvref_common.h"
#include "vp9/common/vp9_treecoder.h"

#include "vp9/encoder/vp9_encodemv.h"
#include "vp9/encoder/vp9_mcomp.h"
#include "vp9/encoder/vp9_bitstream.h"
#include "vp9/encoder/vp9_segmentation.h"
#include "vp9/encoder/vp9_write_bit_buffer.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];
vp9_coeff_stats tree_update_hist_4x4[BLOCK_TYPES];
vp9_coeff_stats tree_update_hist_8x8[BLOCK_TYPES];
vp9_coeff_stats tree_update_hist_16x16[BLOCK_TYPES];
vp9_coeff_stats tree_update_hist_32x32[BLOCK_TYPES];

extern unsigned int active_section;
#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)))

static int update_bits[255];

static INLINE void write_le16(uint8_t *p, int value) {
  p[0] = value;
  p[1] = value >> 8;
}

static INLINE void write_le32(uint8_t *p, int value) {
  p[0] = value;
  p[1] = value >> 8;
  p[2] = value >> 16;
  p[3] = value >> 24;
}

void vp9_encode_unsigned_max(vp9_writer *br, int data, int max) {
  assert(data <= max);
  while (max) {
    vp9_write_bit(br, data & 1);
    data >>= 1;
    max >>= 1;
  }
}

int recenter_nonneg(int v, int m) {
  if (v > (m << 1))
    return v;
  else if (v >= m)
    return ((v - m) << 1);
  else
    return ((m - v) << 1) - 1;
}

static int get_unsigned_bits(unsigned num_values) {
  int cat = 0;
  if ((num_values--) <= 1) return 0;
  while (num_values > 0) {
    cat++;
    num_values >>= 1;
  }
  return cat;
}

void encode_uniform(vp9_writer *w, int v, int n) {
  int l = get_unsigned_bits(n);
  int m;
  if (l == 0)
    return;
  m = (1 << l) - n;
  if (v < m) {
    vp9_write_literal(w, v, l - 1);
  } else {
    vp9_write_literal(w, m + ((v - m) >> 1), l - 1);
    vp9_write_literal(w, (v - m) & 1, 1);
  }
}

int count_uniform(int v, int n) {
  int l = get_unsigned_bits(n);
  int m;
  if (l == 0) return 0;
  m = (1 << l) - n;
  if (v < m)
    return l - 1;
  else
    return l;
}

void encode_term_subexp(vp9_writer *w, int word, int k, int num_syms) {
  int i = 0;
  int mk = 0;
  while (1) {
    int b = (i ? k + i - 1 : k);
    int a = (1 << b);
    if (num_syms <= mk + 3 * a) {
      encode_uniform(w, word - mk, num_syms - mk);
      break;
    } else {
      int t = (word >= mk + a);
      vp9_write_literal(w, t, 1);
      if (t) {
        i = i + 1;
        mk += a;
      } else {
        vp9_write_literal(w, word - mk, b);
        break;
      }
    }
  }
}

int count_term_subexp(int word, int k, int num_syms) {
  int count = 0;
  int i = 0;
  int mk = 0;
  while (1) {
    int b = (i ? k + i - 1 : k);
    int a = (1 << b);
    if (num_syms <= mk + 3 * a) {
      count += count_uniform(word - mk, num_syms - mk);
      break;
    } else {
      int t = (word >= mk + a);
      count++;
      if (t) {
        i = i + 1;
        mk += a;
      } else {
        count += b;
        break;
      }
    }
  }
  return count;
}

static void compute_update_table() {
  int i;
  for (i = 0; i < 255; i++)
    update_bits[i] = 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 = recenter_nonneg(v, m) - 1;
  else
    i = 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 *w,
                                   vp9_prob newp, vp9_prob oldp) {
  int delp = remap_prob(newp, oldp);
  encode_term_subexp(w, 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 *w,
  int n,
  const struct 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(tree, Pnew, bct, num_events, 0);
  n--;

  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(w, 1);

    do {
      const vp9_prob p = Pnew[i];

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

  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);
}

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_interp_tree,
        pc->fc.switchable_interp_prob[j], branch_ct,
        cpi->switchable_interp_count[j], 0);
    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_prob(bc, pc->fc.switchable_interp_prob[j][i]);
    }
  }
}

// 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) {
    // From the prediction counts set the probabilities for each context
    for (i = 0; i < PREDICTION_PROBS; i++) {
      const int c0 = cpi->ref_pred_count[i][0];
      const int c1 = cpi->ref_pred_count[i][1];

      new_pred_probs[i] = get_binary_prob(c0, c1);

      // Decide whether or not to update the reference frame probs.
      // Returned costs are in 1/256 bit units.
      old_cost = c0 * vp9_cost_zero(cm->ref_pred_probs[i]) +
                 c1 * vp9_cost_one(cm->ref_pred_probs[i]);

      new_cost = c0 * vp9_cost_zero(new_pred_probs[i]) +
                 c1 * 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 void update_inter_mode_probs(VP9_COMMON *cm,
                                    int mode_context[INTER_MODE_CONTEXTS][4]) {
  int i, j;
  unsigned int (*mv_ref_ct)[4][2] = cm->fc.mv_ref_ct;

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

  for (i = 0; i < INTER_MODE_CONTEXTS; i++) {
    for (j = 0; j < 4; j++) {
      int new_prob, 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]);
      new_prob = get_binary_prob(mv_ref_ct[i][j][0], mv_ref_ct[i][j][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);
}

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);
}

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_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 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_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 int prob_diff_update_savings_search_model(const unsigned int *ct,
                                                 const vp9_prob *oldp,
                                                 vp9_prob *bestp,
                                                 const vp9_prob upd,
                                                 int b, int r) {
  int i, old_b, new_b, update_b, savings, bestsavings, step;
  int newp;
  vp9_prob bestnewp, newplist[ENTROPY_NODES], oldplist[ENTROPY_NODES];
  vp9_model_to_full_probs(oldp, oldplist);
  vpx_memcpy(newplist, oldp, sizeof(vp9_prob) * UNCONSTRAINED_NODES);
  for (i = UNCONSTRAINED_NODES, old_b = 0; i < ENTROPY_NODES; ++i)
    old_b += cost_branch256(ct + 2 * i, oldplist[i]);
  old_b += cost_branch256(ct + 2 * PIVOT_NODE, oldplist[PIVOT_NODE]);

  bestsavings = 0;
  bestnewp = oldp[PIVOT_NODE];

  step = (*bestp > oldp[PIVOT_NODE] ? -1 : 1);
  newp = *bestp;
  for (; newp != oldp[PIVOT_NODE]; newp += step) {
    if (newp < 1 || newp > 255) continue;
    newplist[PIVOT_NODE] = newp;
    vp9_model_to_full_probs(newplist, newplist);
    for (i = UNCONSTRAINED_NODES, new_b = 0; i < ENTROPY_NODES; ++i)
      new_b += cost_branch256(ct + 2 * i, newplist[i]);
    new_b += cost_branch256(ct + 2 * PIVOT_NODE, newplist[PIVOT_NODE]);
    update_b = prob_diff_update_cost(newp, oldp[PIVOT_NODE]) +
        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_prob(bc, newp);
    *oldp = newp;
  } else {
    vp9_write(bc, 0, upd);
  }
}

static void pack_mb_tokens(vp9_writer* const bc,
                           TOKENEXTRA **tp,
                           const TOKENEXTRA *const stop) {
  TOKENEXTRA *p = *tp;

  while (p < stop) {
    const int t = p->token;
    const struct vp9_token *const a = vp9_coef_encodings + t;
    const vp9_extra_bit *const b = vp9_extra_bits + t;
    int i = 0;
    const vp9_prob *pp;
    int v = a->value;
    int n = a->len;
    int ncount = n;
    vp9_prob probs[ENTROPY_NODES];

    if (t == EOSB_TOKEN) {
      ++p;
      break;
    }
    if (t >= TWO_TOKEN) {
      vp9_model_to_full_probs(p->context_tree, probs);
      pp = probs;
    } else {
      pp = p->context_tree;
    }
    assert(pp != 0);

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

    do {
      const int bb = (v >> --n) & 1;
      vp9_write(bc, bb, pp[i >> 1]);
      i = vp9_coef_tree[i + bb];
      ncount--;
    } while (n && ncount);

    if (b->base_val) {
      const int e = p->extra, l = b->len;

      if (l) {
        const unsigned char *pb = 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;
          vp9_write(bc, bb, pb[i >> 1]);
          i = b->tree[i + bb];
        } while (n);
      }

      vp9_write_bit(bc, e & 1);
    }
    ++p;
  }

  *tp = p;
}

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);
}

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);
}

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);
}


// 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) {
  if (xd->segmentation_enabled && xd->update_mb_segmentation_map)
    treed_write(bc, vp9_segment_tree, xd->mb_segment_tree_probs,
                mi->segment_id, 3);
}

// 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 *cpi, MODE_INFO *m,
                                vp9_writer *bc, int mi_row, int mi_col) {
  VP9_COMMON *const pc = &cpi->common;
  const nmv_context *nmvc = &pc->fc.nmvc;
  MACROBLOCK *const x = &cpi->mb;
  MACROBLOCKD *const xd = &x->e_mbd;
  const int mis = pc->mode_info_stride;
  MB_MODE_INFO *const mi = &m->mbmi;
  const MV_REFERENCE_FRAME rf = mi->ref_frame;
  const MB_PREDICTION_MODE mode = mi->mode;
  const int segment_id = mi->segment_id;
  int skip_coeff;

  xd->prev_mode_info_context = pc->prev_mi + (m - pc->mi);
  x->partition_info = x->pi + (m - pc->mi);

#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) {
      unsigned char prediction_flag = vp9_get_pred_flag(xd, PRED_SEG_ID);
      vp9_prob 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);
    }
  }

  if (vp9_segfeature_active(xd, segment_id, SEG_LVL_SKIP)) {
    skip_coeff = 1;
  } else {
    skip_coeff = m->mbmi.mb_skip_coeff;
    vp9_write(bc, skip_coeff,
              vp9_get_pred_prob(pc, xd, PRED_MBSKIP));
  }

  // Encode the reference frame.
  encode_ref_frame(bc, pc, xd, segment_id, rf);

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

    if (m->mbmi.sb_type >= BLOCK_SIZE_SB8X8)
      write_sb_ymode(bc, mode, pc->fc.sb_ymode_prob);

    if (m->mbmi.sb_type < BLOCK_SIZE_SB8X8) {
      int idx, idy;
      int bw = 1 << b_width_log2(mi->sb_type);
      int bh = 1 << b_height_log2(mi->sb_type);
      for (idy = 0; idy < 2; idy += bh)
        for (idx = 0; idx < 2; idx += bw)
          write_sb_ymode(bc, m->bmi[idy * 2 + idx].as_mode.first,
                         pc->fc.sb_ymode_prob);
    }
    write_uv_mode(bc, mi->uv_mode,
                  pc->fc.uv_mode_prob[mode]);
  } else {
    vp9_prob mv_ref_p[VP9_MVREFS - 1];

    vp9_mv_ref_probs(&cpi->common, mv_ref_p, mi->mb_mode_context[rf]);

#ifdef ENTROPY_STATS
    active_section = 3;
#endif

    // If segment skip is not enabled code the mode.
    if (!vp9_segfeature_active(xd, segment_id, SEG_LVL_SKIP)) {
      if (mi->sb_type >= BLOCK_SIZE_SB8X8)
        write_sb_mv_ref(bc, mode, mv_ref_p);
      vp9_accum_mv_refs(&cpi->common, mode, mi->mb_mode_context[rf]);
    }

    if (is_inter_mode(mode)) {
      if (cpi->common.mcomp_filter_type == SWITCHABLE) {
        write_token(bc, vp9_switchable_interp_tree,
                    vp9_get_pred_probs(&cpi->common, xd,
                                       PRED_SWITCHABLE_INTERP),
                    vp9_switchable_interp_encodings +
                    vp9_switchable_interp_map[mi->interp_filter]);
      } else {
        assert(mi->interp_filter == cpi->common.mcomp_filter_type);
      }
    }

    // does the feature use compound prediction or not
    // (if not specified at the frame/segment level)
    if (cpi->common.comp_pred_mode == HYBRID_PREDICTION) {
      vp9_write(bc, mi->second_ref_frame > INTRA_FRAME,
                vp9_get_pred_prob(pc, xd, PRED_COMP));
    }

    switch (mode) { /* new, split require MVs */
      case NEWMV:
#ifdef ENTROPY_STATS
        active_section = 5;
#endif
        vp9_encode_mv(bc,
                      &mi->mv[0].as_mv, &mi->best_mv.as_mv,
                      nmvc, xd->allow_high_precision_mv);

        if (mi->second_ref_frame > 0)
          vp9_encode_mv(bc,
                        &mi->mv[1].as_mv, &mi->best_second_mv.as_mv,
                        nmvc, xd->allow_high_precision_mv);
        break;
      case SPLITMV: {
        int j;
        B_PREDICTION_MODE blockmode;
        int_mv blockmv;
        int k = -1;  /* first block in subset j */
        int mv_contz;
        int_mv leftmv, abovemv;
        int bwl = b_width_log2(mi->sb_type), bw = 1 << bwl;
        int bhl = b_height_log2(mi->sb_type), bh = 1 << bhl;
        int idx, idy;
        for (idy = 0; idy < 2; idy += bh) {
          for (idx = 0; idx < 2; idx += bw) {
            j = idy * 2 + idx;
            blockmode = cpi->mb.partition_info->bmi[j].mode;
            blockmv = cpi->mb.partition_info->bmi[j].mv;
            k = j;
            leftmv.as_int = left_block_mv(xd, m, k);
            abovemv.as_int = above_block_mv(m, k, mis);
            mv_contz = vp9_mv_cont(&leftmv, &abovemv);

            write_sub_mv_ref(bc, blockmode,
                             cpi->common.fc.sub_mv_ref_prob[mv_contz]);
            cpi->sub_mv_ref_count[mv_contz][blockmode - LEFT4X4]++;
            if (blockmode == NEW4X4) {
#ifdef ENTROPY_STATS
              active_section = 11;
#endif
              vp9_encode_mv(bc, &blockmv.as_mv, &mi->best_mv.as_mv,
                            nmvc, xd->allow_high_precision_mv);

              if (mi->second_ref_frame > 0)
                vp9_encode_mv(bc,
                              &cpi->mb.partition_info->bmi[j].second_mv.as_mv,
                              &mi->best_second_mv.as_mv,
                              nmvc, xd->allow_high_precision_mv);
            }
          }
        }

#ifdef MODE_STATS
        ++count_mb_seg[mi->partitioning];
#endif
        break;
      }
      default:
        break;
    }
  }

  if (mi->sb_type >= BLOCK_SIZE_SB8X8 && pc->txfm_mode == TX_MODE_SELECT &&
      !(rf != INTRA_FRAME &&
        (skip_coeff || vp9_segfeature_active(xd, segment_id, SEG_LVL_SKIP)))) {
    TX_SIZE sz = mi->txfm_size;
    // FIXME(rbultje) code ternary symbol once all experiments are merged
    vp9_write(bc, sz != TX_4X4, pc->prob_tx[0]);
    if (mi->sb_type >= BLOCK_SIZE_MB16X16 && sz != TX_4X4) {
      vp9_write(bc, sz != TX_8X8, pc->prob_tx[1]);
      if (mi->sb_type >= BLOCK_SIZE_SB32X32 && sz != TX_8X8)
        vp9_write(bc, sz != TX_16X16, pc->prob_tx[2]);
    }
  }
}

static void write_mb_modes_kf(const VP9_COMP *cpi,
                              MODE_INFO *m,
                              vp9_writer *bc, int mi_row, int mi_col) {
  const VP9_COMMON *const c = &cpi->common;
  const MACROBLOCKD *const xd = &cpi->mb.e_mbd;
  const int ym = m->mbmi.mode;
  const int mis = c->mode_info_stride;
  const int segment_id = m->mbmi.segment_id;
  int skip_coeff;

  if (xd->update_mb_segmentation_map)
    write_mb_segid(bc, &m->mbmi, xd);

  if (vp9_segfeature_active(xd, segment_id, SEG_LVL_SKIP)) {
    skip_coeff = 1;
  } else {
    skip_coeff = m->mbmi.mb_skip_coeff;
    vp9_write(bc, skip_coeff, vp9_get_pred_prob(c, xd, PRED_MBSKIP));
  }

  if (m->mbmi.sb_type >= BLOCK_SIZE_SB8X8) {
    const B_PREDICTION_MODE A = above_block_mode(m, 0, mis);
    const B_PREDICTION_MODE L = xd->left_available ?
                                 left_block_mode(m, 0) : DC_PRED;
    write_kf_bmode(bc, ym, c->kf_bmode_prob[A][L]);
  }

  if (m->mbmi.sb_type < BLOCK_SIZE_SB8X8) {
    int idx, idy;
    int bw = 1 << b_width_log2(m->mbmi.sb_type);
    int bh = 1 << b_height_log2(m->mbmi.sb_type);
    for (idy = 0; idy < 2; idy += bh) {
      for (idx = 0; idx < 2; idx += bw) {
        int i = idy * 2 + idx;
        const B_PREDICTION_MODE A = above_block_mode(m, i, mis);
        const B_PREDICTION_MODE L = (xd->left_available || idx) ?
                                     left_block_mode(m, i) : DC_PRED;
        write_kf_bmode(bc, m->bmi[i].as_mode.first,
                       c->kf_bmode_prob[A][L]);
      }
    }
  }

  write_uv_mode(bc, m->mbmi.uv_mode, c->kf_uv_mode_prob[ym]);

  if (m->mbmi.sb_type >= BLOCK_SIZE_SB8X8 && c->txfm_mode == TX_MODE_SELECT) {
    TX_SIZE sz = m->mbmi.txfm_size;
    // FIXME(rbultje) code ternary symbol once all experiments are merged
    vp9_write(bc, sz != TX_4X4, c->prob_tx[0]);
    if (m->mbmi.sb_type >= BLOCK_SIZE_MB16X16 && sz != TX_4X4) {
      vp9_write(bc, sz != TX_8X8, c->prob_tx[1]);
      if (m->mbmi.sb_type >= BLOCK_SIZE_SB32X32 && sz != TX_8X8)
        vp9_write(bc, sz != TX_16X16, c->prob_tx[2]);
    }
  }
}

static void write_modes_b(VP9_COMP *cpi, MODE_INFO *m, vp9_writer *bc,
                          TOKENEXTRA **tok, TOKENEXTRA *tok_end,
                          int mi_row, int mi_col) {
  VP9_COMMON *const cm = &cpi->common;
  MACROBLOCKD *const xd = &cpi->mb.e_mbd;

  if (m->mbmi.sb_type < BLOCK_SIZE_SB8X8)
    if (xd->ab_index > 0)
      return;
  xd->mode_info_context = m;
  set_mi_row_col(&cpi->common, xd, mi_row,
                 1 << mi_height_log2(m->mbmi.sb_type),
                 mi_col, 1 << mi_width_log2(m->mbmi.sb_type));
  if (cm->frame_type == KEY_FRAME) {
    write_mb_modes_kf(cpi, m, bc, mi_row, mi_col);
#ifdef ENTROPY_STATS
    active_section = 8;
#endif
  } else {
    pack_inter_mode_mvs(cpi, m, bc, mi_row, mi_col);
#ifdef ENTROPY_STATS
    active_section = 1;
#endif
  }

  assert(*tok < tok_end);
  pack_mb_tokens(bc, tok, tok_end);
}

static void write_modes_sb(VP9_COMP *cpi, MODE_INFO *m, vp9_writer *bc,
                           TOKENEXTRA **tok, TOKENEXTRA *tok_end,
                           int mi_row, int mi_col,
                           BLOCK_SIZE_TYPE bsize) {
  VP9_COMMON *const cm = &cpi->common;
  MACROBLOCKD *xd = &cpi->mb.e_mbd;
  const int mis = cm->mode_info_stride;
  int bwl, bhl;
  int bsl = b_width_log2(bsize);
  int bs = (1 << bsl) / 4;  // mode_info step for subsize
  int n;
  PARTITION_TYPE partition;
  BLOCK_SIZE_TYPE subsize;

  if (mi_row >= cm->mi_rows || mi_col >= cm->mi_cols)
    return;

  bwl = b_width_log2(m->mbmi.sb_type);
  bhl = b_height_log2(m->mbmi.sb_type);

  // parse the partition type
  if ((bwl == bsl) && (bhl == bsl))
    partition = PARTITION_NONE;
  else if ((bwl == bsl) && (bhl < bsl))
    partition = PARTITION_HORZ;
  else if ((bwl < bsl) && (bhl == bsl))
    partition = PARTITION_VERT;
  else if ((bwl < bsl) && (bhl < bsl))
    partition = PARTITION_SPLIT;
  else
    assert(0);

  if (bsize < BLOCK_SIZE_SB8X8)
    if (xd->ab_index > 0)
      return;

  if (bsize >= BLOCK_SIZE_SB8X8) {
    int pl;
    xd->left_seg_context = cm->left_seg_context + (mi_row & MI_MASK);
    xd->above_seg_context = cm->above_seg_context + mi_col;
    pl = partition_plane_context(xd, bsize);
    // encode the partition information
    write_token(bc, vp9_partition_tree, cm->fc.partition_prob[pl],
                vp9_partition_encodings + partition);
  }

  subsize = get_subsize(bsize, partition);