vp9/decoder/vp9_decodeframe.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 <stdlib.h>  // qsort()

#include "./vp9_rtcd.h"
#include "./vpx_dsp_rtcd.h"
#include "./vpx_scale_rtcd.h"

#include "vpx_dsp/bitreader_buffer.h"
#include "vpx_dsp/bitreader.h"
#include "vpx_dsp/vpx_dsp_common.h"
#include "vpx_mem/vpx_mem.h"
#include "vpx_ports/mem.h"
#include "vpx_ports/mem_ops.h"
#include "vpx_scale/vpx_scale.h"
#include "vpx_util/vpx_thread.h"

#include "vp9/common/vp9_alloccommon.h"
#include "vp9/common/vp9_common.h"
#include "vp9/common/vp9_entropy.h"
#include "vp9/common/vp9_entropymode.h"
#include "vp9/common/vp9_idct.h"
#include "vp9/common/vp9_thread_common.h"
#include "vp9/common/vp9_pred_common.h"
#include "vp9/common/vp9_quant_common.h"
#include "vp9/common/vp9_reconintra.h"
#include "vp9/common/vp9_reconinter.h"
#include "vp9/common/vp9_seg_common.h"
#include "vp9/common/vp9_tile_common.h"

#include "vp9/decoder/vp9_decodeframe.h"
#include "vp9/decoder/vp9_detokenize.h"
#include "vp9/decoder/vp9_decodemv.h"
#include "vp9/decoder/vp9_decoder.h"
#include "vp9/decoder/vp9_dsubexp.h"

#define MAX_VP9_HEADER_SIZE 80

static int is_compound_reference_allowed(const VP9_COMMON *cm) {
  int i;
  for (i = 1; i < REFS_PER_FRAME; ++i)
    if (cm->ref_frame_sign_bias[i + 1] != cm->ref_frame_sign_bias[1])
      return 1;

  return 0;
}

static void setup_compound_reference_mode(VP9_COMMON *cm) {
  if (cm->ref_frame_sign_bias[LAST_FRAME] ==
          cm->ref_frame_sign_bias[GOLDEN_FRAME]) {
    cm->comp_fixed_ref = ALTREF_FRAME;
    cm->comp_var_ref[0] = LAST_FRAME;
    cm->comp_var_ref[1] = GOLDEN_FRAME;
  } else if (cm->ref_frame_sign_bias[LAST_FRAME] ==
                 cm->ref_frame_sign_bias[ALTREF_FRAME]) {
    cm->comp_fixed_ref = GOLDEN_FRAME;
    cm->comp_var_ref[0] = LAST_FRAME;
    cm->comp_var_ref[1] = ALTREF_FRAME;
  } else {
    cm->comp_fixed_ref = LAST_FRAME;
    cm->comp_var_ref[0] = GOLDEN_FRAME;
    cm->comp_var_ref[1] = ALTREF_FRAME;
  }
}

static int read_is_valid(const uint8_t *start, size_t len, const uint8_t *end) {
  return len != 0 && len <= (size_t)(end - start);
}

static int decode_unsigned_max(struct vpx_read_bit_buffer *rb, int max) {
  const int data = vpx_rb_read_literal(rb, get_unsigned_bits(max));
  return data > max ? max : data;
}

static TX_MODE read_tx_mode(vpx_reader *r) {
  TX_MODE tx_mode = vpx_read_literal(r, 2);
  if (tx_mode == ALLOW_32X32)
    tx_mode += vpx_read_bit(r);
  return tx_mode;
}

static void read_tx_mode_probs(struct tx_probs *tx_probs, vpx_reader *r) {
  int i, j;

  for (i = 0; i < TX_SIZE_CONTEXTS; ++i)
    for (j = 0; j < TX_SIZES - 3; ++j)
      vp9_diff_update_prob(r, &tx_probs->p8x8[i][j]);

  for (i = 0; i < TX_SIZE_CONTEXTS; ++i)
    for (j = 0; j < TX_SIZES - 2; ++j)
      vp9_diff_update_prob(r, &tx_probs->p16x16[i][j]);

  for (i = 0; i < TX_SIZE_CONTEXTS; ++i)
    for (j = 0; j < TX_SIZES - 1; ++j)
      vp9_diff_update_prob(r, &tx_probs->p32x32[i][j]);
}

static void read_switchable_interp_probs(FRAME_CONTEXT *fc, vpx_reader *r) {
  int i, j;
  for (j = 0; j < SWITCHABLE_FILTER_CONTEXTS; ++j)
    for (i = 0; i < SWITCHABLE_FILTERS - 1; ++i)
      vp9_diff_update_prob(r, &fc->switchable_interp_prob[j][i]);
}

static void read_inter_mode_probs(FRAME_CONTEXT *fc, vpx_reader *r) {
  int i, j;
  for (i = 0; i < INTER_MODE_CONTEXTS; ++i)
    for (j = 0; j < INTER_MODES - 1; ++j)
      vp9_diff_update_prob(r, &fc->inter_mode_probs[i][j]);
}

static REFERENCE_MODE read_frame_reference_mode(const VP9_COMMON *cm,
                                                vpx_reader *r) {
  if (is_compound_reference_allowed(cm)) {
    return vpx_read_bit(r) ? (vpx_read_bit(r) ? REFERENCE_MODE_SELECT
                                              : COMPOUND_REFERENCE)
                           : SINGLE_REFERENCE;
  } else {
    return SINGLE_REFERENCE;
  }
}

static void read_frame_reference_mode_probs(VP9_COMMON *cm, vpx_reader *r) {
  FRAME_CONTEXT *const fc = cm->fc;
  int i;

  if (cm->reference_mode == REFERENCE_MODE_SELECT)
    for (i = 0; i < COMP_INTER_CONTEXTS; ++i)
      vp9_diff_update_prob(r, &fc->comp_inter_prob[i]);

  if (cm->reference_mode != COMPOUND_REFERENCE)
    for (i = 0; i < REF_CONTEXTS; ++i) {
      vp9_diff_update_prob(r, &fc->single_ref_prob[i][0]);
      vp9_diff_update_prob(r, &fc->single_ref_prob[i][1]);
    }

  if (cm->reference_mode != SINGLE_REFERENCE)
    for (i = 0; i < REF_CONTEXTS; ++i)
      vp9_diff_update_prob(r, &fc->comp_ref_prob[i]);
}

static void update_mv_probs(vpx_prob *p, int n, vpx_reader *r) {
  int i;
  for (i = 0; i < n; ++i)
    if (vpx_read(r, MV_UPDATE_PROB))
      p[i] = (vpx_read_literal(r, 7) << 1) | 1;
}

static void read_mv_probs(nmv_context *ctx, int allow_hp, vpx_reader *r) {
  int i, j;

  update_mv_probs(ctx->joints, MV_JOINTS - 1, r);

  for (i = 0; i < 2; ++i) {
    nmv_component *const comp_ctx = &ctx->comps[i];
    update_mv_probs(&comp_ctx->sign, 1, r);
    update_mv_probs(comp_ctx->classes, MV_CLASSES - 1, r);
    update_mv_probs(comp_ctx->class0, CLASS0_SIZE - 1, r);
    update_mv_probs(comp_ctx->bits, MV_OFFSET_BITS, r);
  }

  for (i = 0; i < 2; ++i) {
    nmv_component *const comp_ctx = &ctx->comps[i];
    for (j = 0; j < CLASS0_SIZE; ++j)
      update_mv_probs(comp_ctx->class0_fp[j], MV_FP_SIZE - 1, r);
    update_mv_probs(comp_ctx->fp, 3, r);
  }

  if (allow_hp) {
    for (i = 0; i < 2; ++i) {
      nmv_component *const comp_ctx = &ctx->comps[i];
      update_mv_probs(&comp_ctx->class0_hp, 1, r);
      update_mv_probs(&comp_ctx->hp, 1, r);
    }
  }
}

static void inverse_transform_block_inter(MACROBLOCKD* xd, int plane,
                                          const TX_SIZE tx_size,
                                          uint8_t *dst, int stride,
                                          int eob) {
  struct macroblockd_plane *const pd = &xd->plane[plane];
  if (eob > 0) {
    tran_low_t *const dqcoeff = pd->dqcoeff;
#if CONFIG_VP9_HIGHBITDEPTH
    if (xd->cur_buf->flags & YV12_FLAG_HIGHBITDEPTH) {
      if (xd->lossless) {
        vp9_highbd_iwht4x4_add(dqcoeff, dst, stride, eob, xd->bd);
      } else {
        switch (tx_size) {
          case TX_4X4:
            vp9_highbd_idct4x4_add(dqcoeff, dst, stride, eob, xd->bd);
            break;
          case TX_8X8:
            vp9_highbd_idct8x8_add(dqcoeff, dst, stride, eob, xd->bd);
            break;
          case TX_16X16:
            vp9_highbd_idct16x16_add(dqcoeff, dst, stride, eob, xd->bd);
            break;
          case TX_32X32:
            vp9_highbd_idct32x32_add(dqcoeff, dst, stride, eob, xd->bd);
            break;
          default:
            assert(0 && "Invalid transform size");
        }
      }
    } else {
      if (xd->lossless) {
        vp9_iwht4x4_add(dqcoeff, dst, stride, eob);
      } else {
        switch (tx_size) {
          case TX_4X4:
            vp9_idct4x4_add(dqcoeff, dst, stride, eob);
            break;
          case TX_8X8:
            vp9_idct8x8_add(dqcoeff, dst, stride, eob);
            break;
          case TX_16X16:
            vp9_idct16x16_add(dqcoeff, dst, stride, eob);
            break;
          case TX_32X32:
            vp9_idct32x32_add(dqcoeff, dst, stride, eob);
            break;
          default:
            assert(0 && "Invalid transform size");
            return;
        }
      }
    }
#else
    if (xd->lossless) {
      vp9_iwht4x4_add(dqcoeff, dst, stride, eob);
    } else {
      switch (tx_size) {
        case TX_4X4:
          vp9_idct4x4_add(dqcoeff, dst, stride, eob);
          break;
        case TX_8X8:
          vp9_idct8x8_add(dqcoeff, dst, stride, eob);
          break;
        case TX_16X16:
          vp9_idct16x16_add(dqcoeff, dst, stride, eob);
          break;
        case TX_32X32:
          vp9_idct32x32_add(dqcoeff, dst, stride, eob);
          break;
        default:
          assert(0 && "Invalid transform size");
          return;
      }
    }
#endif  // CONFIG_VP9_HIGHBITDEPTH

    if (eob == 1) {
      dqcoeff[0] = 0;
    } else {
      if (tx_size <= TX_16X16 && eob <= 10)
        memset(dqcoeff, 0, 4 * (4 << tx_size) * sizeof(dqcoeff[0]));
      else if (tx_size == TX_32X32 && eob <= 34)
        memset(dqcoeff, 0, 256 * sizeof(dqcoeff[0]));
      else
        memset(dqcoeff, 0, (16 << (tx_size << 1)) * sizeof(dqcoeff[0]));
    }
  }
}

static void inverse_transform_block_intra(MACROBLOCKD* xd, int plane,
                                          const TX_TYPE tx_type,
                                          const TX_SIZE tx_size,
                                          uint8_t *dst, int stride,
                                          int eob) {
  struct macroblockd_plane *const pd = &xd->plane[plane];
  if (eob > 0) {
    tran_low_t *const dqcoeff = pd->dqcoeff;
#if CONFIG_VP9_HIGHBITDEPTH
    if (xd->cur_buf->flags & YV12_FLAG_HIGHBITDEPTH) {
      if (xd->lossless) {
        vp9_highbd_iwht4x4_add(dqcoeff, dst, stride, eob, xd->bd);
      } else {
        switch (tx_size) {
          case TX_4X4:
            vp9_highbd_iht4x4_add(tx_type, dqcoeff, dst, stride, eob, xd->bd);
            break;
          case TX_8X8:
            vp9_highbd_iht8x8_add(tx_type, dqcoeff, dst, stride, eob, xd->bd);
            break;
          case TX_16X16:
            vp9_highbd_iht16x16_add(tx_type, dqcoeff, dst, stride, eob, xd->bd);
            break;
          case TX_32X32:
            vp9_highbd_idct32x32_add(dqcoeff, dst, stride, eob, xd->bd);
            break;
          default:
            assert(0 && "Invalid transform size");
        }
      }
    } else {
      if (xd->lossless) {
        vp9_iwht4x4_add(dqcoeff, dst, stride, eob);
      } else {
        switch (tx_size) {
          case TX_4X4:
            vp9_iht4x4_add(tx_type, dqcoeff, dst, stride, eob);
            break;
          case TX_8X8:
            vp9_iht8x8_add(tx_type, dqcoeff, dst, stride, eob);
            break;
          case TX_16X16:
            vp9_iht16x16_add(tx_type, dqcoeff, dst, stride, eob);
            break;
          case TX_32X32:
            vp9_idct32x32_add(dqcoeff, dst, stride, eob);
            break;
          default:
            assert(0 && "Invalid transform size");
            return;
        }
      }
    }
#else
    if (xd->lossless) {
      vp9_iwht4x4_add(dqcoeff, dst, stride, eob);
    } else {
      switch (tx_size) {
        case TX_4X4:
          vp9_iht4x4_add(tx_type, dqcoeff, dst, stride, eob);
          break;
        case TX_8X8:
          vp9_iht8x8_add(tx_type, dqcoeff, dst, stride, eob);
          break;
        case TX_16X16:
          vp9_iht16x16_add(tx_type, dqcoeff, dst, stride, eob);
          break;
        case TX_32X32:
          vp9_idct32x32_add(dqcoeff, dst, stride, eob);
          break;
        default:
          assert(0 && "Invalid transform size");
          return;
      }
    }
#endif  // CONFIG_VP9_HIGHBITDEPTH

    if (eob == 1) {
      dqcoeff[0] = 0;
    } else {
      if (tx_type == DCT_DCT && tx_size <= TX_16X16 && eob <= 10)
        memset(dqcoeff, 0, 4 * (4 << tx_size) * sizeof(dqcoeff[0]));
      else if (tx_size == TX_32X32 && eob <= 34)
        memset(dqcoeff, 0, 256 * sizeof(dqcoeff[0]));
      else
        memset(dqcoeff, 0, (16 << (tx_size << 1)) * sizeof(dqcoeff[0]));
    }
  }
}

static void predict_and_reconstruct_intra_block(MACROBLOCKD *const xd,
                                                vpx_reader *r,
                                                MODE_INFO *const mi,
                                                int plane,
                                                int row, int col,
                                                TX_SIZE tx_size) {
  struct macroblockd_plane *const pd = &xd->plane[plane];
  PREDICTION_MODE mode = (plane == 0) ? mi->mode : mi->uv_mode;
  uint8_t *dst;
  dst = &pd->dst.buf[4 * row * pd->dst.stride + 4 * col];

  if (mi->sb_type < BLOCK_8X8)
    if (plane == 0)
      mode = xd->mi[0]->bmi[(row << 1) + col].as_mode;

  vp9_predict_intra_block(xd, pd->n4_wl, tx_size, mode,
                          dst, pd->dst.stride, dst, pd->dst.stride,
                          col, row, plane);

  if (!mi->skip) {
    const TX_TYPE tx_type = (plane || xd->lossless) ?
        DCT_DCT : intra_mode_to_tx_type_lookup[mode];
    const scan_order *sc = (plane || xd->lossless) ?
        &vp9_default_scan_orders[tx_size] : &vp9_scan_orders[tx_size][tx_type];
    const int eob = vp9_decode_block_tokens(xd, plane, sc, col, row, tx_size,
                                            r, mi->segment_id);
    inverse_transform_block_intra(xd, plane, tx_type, tx_size,
                                  dst, pd->dst.stride, eob);
  }
}

static int reconstruct_inter_block(MACROBLOCKD *const xd, vpx_reader *r,
                                   MODE_INFO *const mi, int plane,
                                   int row, int col, TX_SIZE tx_size) {
  struct macroblockd_plane *const pd = &xd->plane[plane];
  const scan_order *sc = &vp9_default_scan_orders[tx_size];
  const int eob = vp9_decode_block_tokens(xd, plane, sc, col, row, tx_size, r,
                                          mi->segment_id);

  inverse_transform_block_inter(xd, plane, tx_size,
                            &pd->dst.buf[4 * row * pd->dst.stride + 4 * col],
                            pd->dst.stride, eob);
  return eob;
}

static void build_mc_border(const uint8_t *src, int src_stride,
                            uint8_t *dst, int dst_stride,
                            int x, int y, int b_w, int b_h, int w, int h) {
  // Get a pointer to the start of the real data for this row.
  const uint8_t *ref_row = src - x - y * src_stride;

  if (y >= h)
    ref_row += (h - 1) * src_stride;
  else if (y > 0)
    ref_row += y * src_stride;

  do {
    int right = 0, copy;
    int left = x < 0 ? -x : 0;

    if (left > b_w)
      left = b_w;

    if (x + b_w > w)
      right = x + b_w - w;

    if (right > b_w)
      right = b_w;

    copy = b_w - left - right;

    if (left)
      memset(dst, ref_row[0], left);

    if (copy)
      memcpy(dst + left, ref_row + x + left, copy);

    if (right)
      memset(dst + left + copy, ref_row[w - 1], right);

    dst += dst_stride;
    ++y;

    if (y > 0 && y < h)
      ref_row += src_stride;
  } while (--b_h);
}

#if CONFIG_VP9_HIGHBITDEPTH
static void high_build_mc_border(const uint8_t *src8, int src_stride,
                                 uint16_t *dst, int dst_stride,
                                 int x, int y, int b_w, int b_h,
                                 int w, int h) {
  // Get a pointer to the start of the real data for this row.
  const uint16_t *src = CONVERT_TO_SHORTPTR(src8);
  const uint16_t *ref_row = src - x - y * src_stride;

  if (y >= h)
    ref_row += (h - 1) * src_stride;
  else if (y > 0)
    ref_row += y * src_stride;

  do {
    int right = 0, copy;
    int left = x < 0 ? -x : 0;

    if (left > b_w)
      left = b_w;

    if (x + b_w > w)
      right = x + b_w - w;

    if (right > b_w)
      right = b_w;

    copy = b_w - left - right;

    if (left)
      vpx_memset16(dst, ref_row[0], left);

    if (copy)
      memcpy(dst + left, ref_row + x + left, copy * sizeof(uint16_t));

    if (right)
      vpx_memset16(dst + left + copy, ref_row[w - 1], right);

    dst += dst_stride;
    ++y;

    if (y > 0 && y < h)
      ref_row += src_stride;
  } while (--b_h);
}
#endif  // CONFIG_VP9_HIGHBITDEPTH

#if CONFIG_VP9_HIGHBITDEPTH
static void extend_and_predict(const uint8_t *buf_ptr1, int pre_buf_stride,
                               int x0, int y0, int b_w, int b_h,
                               int frame_width, int frame_height,
                               int border_offset,
                               uint8_t *const dst, int dst_buf_stride,
                               int subpel_x, int subpel_y,
                               const InterpKernel *kernel,
                               const struct scale_factors *sf,
                               MACROBLOCKD *xd,
                               int w, int h, int ref, int xs, int ys) {
  DECLARE_ALIGNED(16, uint16_t, mc_buf_high[80 * 2 * 80 * 2]);
  const uint8_t *buf_ptr;

  if (xd->cur_buf->flags & YV12_FLAG_HIGHBITDEPTH) {
    high_build_mc_border(buf_ptr1, pre_buf_stride, mc_buf_high, b_w,
                         x0, y0, b_w, b_h, frame_width, frame_height);
    buf_ptr = CONVERT_TO_BYTEPTR(mc_buf_high) + border_offset;
  } else {
    build_mc_border(buf_ptr1, pre_buf_stride, (uint8_t *)mc_buf_high, b_w,
                    x0, y0, b_w, b_h, frame_width, frame_height);
    buf_ptr = ((uint8_t *)mc_buf_high) + border_offset;
  }

  if (xd->cur_buf->flags & YV12_FLAG_HIGHBITDEPTH) {
    high_inter_predictor(buf_ptr, b_w, dst, dst_buf_stride, subpel_x,
                         subpel_y, sf, w, h, ref, kernel, xs, ys, xd->bd);
  } else {
    inter_predictor(buf_ptr, b_w, dst, dst_buf_stride, subpel_x,
                    subpel_y, sf, w, h, ref, kernel, xs, ys);
  }
}
#else
static void extend_and_predict(const uint8_t *buf_ptr1, int pre_buf_stride,
                               int x0, int y0, int b_w, int b_h,
                               int frame_width, int frame_height,
                               int border_offset,
                               uint8_t *const dst, int dst_buf_stride,
                               int subpel_x, int subpel_y,
                               const InterpKernel *kernel,
                               const struct scale_factors *sf,
                               int w, int h, int ref, int xs, int ys) {
  DECLARE_ALIGNED(16, uint8_t, mc_buf[80 * 2 * 80 * 2]);
  const uint8_t *buf_ptr;

  build_mc_border(buf_ptr1, pre_buf_stride, mc_buf, b_w,
                  x0, y0, b_w, b_h, frame_width, frame_height);
  buf_ptr = mc_buf + border_offset;

  inter_predictor(buf_ptr, b_w, dst, dst_buf_stride, subpel_x,
                  subpel_y, sf, w, h, ref, kernel, xs, ys);
}
#endif  // CONFIG_VP9_HIGHBITDEPTH

static void dec_build_inter_predictors(VPxWorker *const worker, MACROBLOCKD *xd,
                                       int plane, int bw, int bh, int x,
                                       int y, int w, int h, int mi_x, int mi_y,
                                       const InterpKernel *kernel,
                                       const struct scale_factors *sf,
                                       struct buf_2d *pre_buf,
                                       struct buf_2d *dst_buf, const MV* mv,
                                       RefCntBuffer *ref_frame_buf,
                                       int is_scaled, int ref) {
  struct macroblockd_plane *const pd = &xd->plane[plane];
  uint8_t *const dst = dst_buf->buf + dst_buf->stride * y + x;
  MV32 scaled_mv;
  int xs, ys, x0, y0, x0_16, y0_16, frame_width, frame_height,
      buf_stride, subpel_x, subpel_y;
  uint8_t *ref_frame, *buf_ptr;

  // Get reference frame pointer, width and height.
  if (plane == 0) {
    frame_width = ref_frame_buf->buf.y_crop_width;
    frame_height = ref_frame_buf->buf.y_crop_height;
    ref_frame = ref_frame_buf->buf.y_buffer;
  } else {
    frame_width = ref_frame_buf->buf.uv_crop_width;
    frame_height = ref_frame_buf->buf.uv_crop_height;
    ref_frame = plane == 1 ? ref_frame_buf->buf.u_buffer
                         : ref_frame_buf->buf.v_buffer;
  }

  if (is_scaled) {
    const MV mv_q4 = clamp_mv_to_umv_border_sb(xd, mv, bw, bh,
                                               pd->subsampling_x,
                                               pd->subsampling_y);
    // Co-ordinate of containing block to pixel precision.
    int x_start = (-xd->mb_to_left_edge >> (3 + pd->subsampling_x));
    int y_start = (-xd->mb_to_top_edge >> (3 + pd->subsampling_y));
#if CONFIG_BETTER_HW_COMPATIBILITY
    assert(xd->mi[0]->sb_type != BLOCK_4X8 &&
           xd->mi[0]->sb_type != BLOCK_8X4);
    assert(mv_q4.row == mv->row * (1 << (1 - pd->subsampling_y)) &&
           mv_q4.col == mv->col * (1 << (1 - pd->subsampling_x)));
#endif
    // Co-ordinate of the block to 1/16th pixel precision.
    x0_16 = (x_start + x) << SUBPEL_BITS;
    y0_16 = (y_start + y) << SUBPEL_BITS;

    // Co-ordinate of current block in reference frame
    // to 1/16th pixel precision.
    x0_16 = sf->scale_value_x(x0_16, sf);
    y0_16 = sf->scale_value_y(y0_16, sf);

    // Map the top left corner of the block into the reference frame.
    x0 = sf->scale_value_x(x_start + x, sf);
    y0 = sf->scale_value_y(y_start + y, sf);

    // Scale the MV and incorporate the sub-pixel offset of the block
    // in the reference frame.
    scaled_mv = vp9_scale_mv(&mv_q4, mi_x + x, mi_y + y, sf);
    xs = sf->x_step_q4;
    ys = sf->y_step_q4;
  } else {
    // Co-ordinate of containing block to pixel precision.
    x0 = (-xd->mb_to_left_edge >> (3 + pd->subsampling_x)) + x;
    y0 = (-xd->mb_to_top_edge >> (3 + pd->subsampling_y)) + y;

    // Co-ordinate of the block to 1/16th pixel precision.
    x0_16 = x0 << SUBPEL_BITS;
    y0_16 = y0 << SUBPEL_BITS;

    scaled_mv.row = mv->row * (1 << (1 - pd->subsampling_y));
    scaled_mv.col = mv->col * (1 << (1 - pd->subsampling_x));
    xs = ys = 16;
  }
  subpel_x = scaled_mv.col & SUBPEL_MASK;
  subpel_y = scaled_mv.row & SUBPEL_MASK;

  // Calculate the top left corner of the best matching block in the
  // reference frame.
  x0 += scaled_mv.col >> SUBPEL_BITS;
  y0 += scaled_mv.row >> SUBPEL_BITS;
  x0_16 += scaled_mv.col;
  y0_16 += scaled_mv.row;

  // Get reference block pointer.
  buf_ptr = ref_frame + y0 * pre_buf->stride + x0;
  buf_stride = pre_buf->stride;

  // Do border extension if there is motion or the
  // width/height is not a multiple of 8 pixels.
  if (is_scaled || scaled_mv.col || scaled_mv.row ||
      (frame_width & 0x7) || (frame_height & 0x7)) {
    int y1 = ((y0_16 + (h - 1) * ys) >> SUBPEL_BITS) + 1;

    // Get reference block bottom right horizontal coordinate.
    int x1 = ((x0_16 + (w - 1) * xs) >> SUBPEL_BITS) + 1;
    int x_pad = 0, y_pad = 0;

    if (subpel_x || (sf->x_step_q4 != SUBPEL_SHIFTS)) {
      x0 -= VP9_INTERP_EXTEND - 1;
      x1 += VP9_INTERP_EXTEND;
      x_pad = 1;
    }

    if (subpel_y || (sf->y_step_q4 != SUBPEL_SHIFTS)) {
      y0 -= VP9_INTERP_EXTEND - 1;
      y1 += VP9_INTERP_EXTEND;
      y_pad = 1;
    }

    // Wait until reference block is ready. Pad 7 more pixels as last 7
    // pixels of each superblock row can be changed by next superblock row.
    if (worker != NULL)
      vp9_frameworker_wait(worker, ref_frame_buf,
                           VPXMAX(0, (y1 + 7)) << (plane == 0 ? 0 : 1));

    // Skip border extension if block is inside the frame.
    if (x0 < 0 || x0 > frame_width - 1 || x1 < 0 || x1 > frame_width - 1 ||
        y0 < 0 || y0 > frame_height - 1 || y1 < 0 || y1 > frame_height - 1) {
      // Extend the border.
      const uint8_t *const buf_ptr1 = ref_frame + y0 * buf_stride + x0;
      const int b_w = x1 - x0 + 1;
      const int b_h = y1 - y0 + 1;
      const int border_offset = y_pad * 3 * b_w + x_pad * 3;

      extend_and_predict(buf_ptr1, buf_stride, x0, y0, b_w, b_h,
                         frame_width, frame_height, border_offset,
                         dst, dst_buf->stride,
                         subpel_x, subpel_y,
                         kernel, sf,
#if CONFIG_VP9_HIGHBITDEPTH
                         xd,
#endif
                         w, h, ref, xs, ys);
      return;
    }
  } else {
    // Wait until reference block is ready. Pad 7 more pixels as last 7
    // pixels of each superblock row can be changed by next superblock row.
    if (worker != NULL) {
      const int y1 = (y0_16 + (h - 1) * ys) >> SUBPEL_BITS;
      vp9_frameworker_wait(worker, ref_frame_buf,
                           VPXMAX(0, (y1 + 7)) << (plane == 0 ? 0 : 1));
    }
  }
#if CONFIG_VP9_HIGHBITDEPTH
  if (xd->cur_buf->flags & YV12_FLAG_HIGHBITDEPTH) {
    high_inter_predictor(buf_ptr, buf_stride, dst, dst_buf->stride, subpel_x,
                         subpel_y, sf, w, h, ref, kernel, xs, ys, xd->bd);
  } else {
    inter_predictor(buf_ptr, buf_stride, dst, dst_buf->stride, subpel_x,
                    subpel_y, sf, w, h, ref, kernel, xs, ys);
  }
#else
  inter_predictor(buf_ptr, buf_stride, dst, dst_buf->stride, subpel_x,
                  subpel_y, sf, w, h, ref, kernel, xs, ys);
#endif  // CONFIG_VP9_HIGHBITDEPTH
}

static void dec_build_inter_predictors_sb(VP9Decoder *const pbi,
                                          MACROBLOCKD *xd,
                                          int mi_row, int mi_col) {
  int plane;
  const int mi_x = mi_col * MI_SIZE;
  const int mi_y = mi_row * MI_SIZE;
  const MODE_INFO *mi = xd->mi[0];
  const InterpKernel *kernel = vp9_filter_kernels[mi->interp_filter];
  const BLOCK_SIZE sb_type = mi->sb_type;
  const int is_compound = has_second_ref(mi);
  int ref;
  int is_scaled;
  VPxWorker *const fwo = pbi->frame_parallel_decode ?
      pbi->frame_worker_owner : NULL;

  for (ref = 0; ref < 1 + is_compound; ++ref) {
    const MV_REFERENCE_FRAME frame = mi->ref_frame[ref];
    RefBuffer *ref_buf = &pbi->common.frame_refs[frame - LAST_FRAME];
    const struct scale_factors *const sf = &ref_buf->sf;
    const int idx = ref_buf->idx;
    BufferPool *const pool = pbi->common.buffer_pool;
    RefCntBuffer *const ref_frame_buf = &pool->frame_bufs[idx];

    if (!vp9_is_valid_scale(sf))
      vpx_internal_error(xd->error_info, VPX_CODEC_UNSUP_BITSTREAM,
                         "Reference frame has invalid dimensions");

    is_scaled = vp9_is_scaled(sf);
    vp9_setup_pre_planes(xd, ref, ref_buf->buf, mi_row, mi_col,
                         is_scaled ? sf : NULL);
    xd->block_refs[ref] = ref_buf;

    if (sb_type < BLOCK_8X8) {
      for (plane = 0; plane < MAX_MB_PLANE; ++plane) {
        struct macroblockd_plane *const pd = &xd->plane[plane];
        struct buf_2d *const dst_buf = &pd->dst;
        const int num_4x4_w = pd->n4_w;
        const int num_4x4_h = pd->n4_h;
        const int n4w_x4 = 4 * num_4x4_w;
        const int n4h_x4 = 4 * num_4x4_h;
        struct buf_2d *const pre_buf = &pd->pre[ref];
        int i = 0, x, y;
        for (y = 0; y < num_4x4_h; ++y) {
          for (x = 0; x < num_4x4_w; ++x) {
            const MV mv = average_split_mvs(pd, mi, ref, i++);
            dec_build_inter_predictors(fwo, xd, plane, n4w_x4, n4h_x4,
                                       4 * x, 4 * y, 4, 4, mi_x, mi_y, kernel,
                                       sf, pre_buf, dst_buf, &mv,
                                       ref_frame_buf, is_scaled, ref);
          }
        }
      }
    } else {
      const MV mv = mi->mv[ref].as_mv;
      for (plane = 0; plane < MAX_MB_PLANE; ++plane) {
        struct macroblockd_plane *const pd = &xd->plane[plane];
        struct buf_2d *const dst_buf = &pd->dst;
        const int num_4x4_w = pd->n4_w;
        const int num_4x4_h = pd->n4_h;
        const int n4w_x4 = 4 * num_4x4_w;
        const int n4h_x4 = 4 * num_4x4_h;
        struct buf_2d *const pre_buf = &pd->pre[ref];
        dec_build_inter_predictors(fwo, xd, plane, n4w_x4, n4h_x4,
                                   0, 0, n4w_x4, n4h_x4, mi_x, mi_y, kernel,
                                   sf, pre_buf, dst_buf, &mv,
                                   ref_frame_buf, is_scaled, ref);
      }
    }
  }
}

static INLINE TX_SIZE dec_get_uv_tx_size(const MODE_INFO *mi,
                                         int n4_wl, int n4_hl) {
  // get minimum log2 num4x4s dimension
  const int x = VPXMIN(n4_wl, n4_hl);
  return VPXMIN(mi->tx_size,  x);
}

static INLINE void dec_reset_skip_context(MACROBLOCKD *xd) {
  int i;
  for (i = 0; i < MAX_MB_PLANE; i++) {
    struct macroblockd_plane *const pd = &xd->plane[i];
    memset(pd->above_context, 0, sizeof(ENTROPY_CONTEXT) * pd->n4_w);
    memset(pd->left_context, 0, sizeof(ENTROPY_CONTEXT) * pd->n4_h);
  }
}

static void set_plane_n4(MACROBLOCKD *const xd, int bw, int bh, int bwl,
                         int bhl) {
  int i;
  for (i = 0; i < MAX_MB_PLANE; i++) {
    xd->plane[i].n4_w = (bw << 1) >> xd->plane[i].subsampling_x;
    xd->plane[i].n4_h = (bh << 1) >> xd->plane[i].subsampling_y;
    xd->plane[i].n4_wl = bwl - xd->plane[i].subsampling_x;
    xd->plane[i].n4_hl = bhl - xd->plane[i].subsampling_y;
  }
}

static MODE_INFO *set_offsets(VP9_COMMON *const cm, MACROBLOCKD *const xd,
                              BLOCK_SIZE bsize, int mi_row, int mi_col,
                              int bw, int bh, int x_mis, int y_mis,
                              int bwl, int bhl) {
  const int offset = mi_row * cm->mi_stride + mi_col;
  int x, y;
  const TileInfo *const tile = &xd->tile;

  xd->mi = cm->mi_grid_visible + offset;
  xd->mi[0] = &cm->mi[offset];
  // TODO(slavarnway): Generate sb_type based on bwl and bhl, instead of
  // passing bsize from decode_partition().
  xd->mi[0]->sb_type = bsize;
  for (y = 0; y < y_mis; ++y)
    for (x = !y; x < x_mis; ++x) {
      xd->mi[y * cm->mi_stride + x] = xd->mi[0];
    }

  set_plane_n4(xd, bw, bh, bwl, bhl);

  set_skip_context(xd, mi_row, mi_col);

  // Distance of Mb to the various image edges. These are specified to 8th pel
  // as they are always compared to values that are in 1/8th pel units
  set_mi_row_col(xd, tile, mi_row, bh, mi_col, bw, cm->mi_rows, cm->mi_cols);

  vp9_setup_dst_planes(xd->plane, get_frame_new_buffer(cm), mi_row, mi_col);
  return xd->mi[0];
}

static void decode_block(VP9Decoder *const pbi, MACROBLOCKD *const xd,
                         int mi_row, int mi_col,
                         vpx_reader *r, BLOCK_SIZE bsize,
                         int bwl, int bhl) {
  VP9_COMMON *const cm = &pbi->common;
  const int less8x8 = bsize < BLOCK_8X8;
  const int bw = 1 << (bwl - 1);
  const int bh = 1 << (bhl - 1);
  const int x_mis = VPXMIN(bw, cm->mi_cols - mi_col);
  const int y_mis = VPXMIN(bh, cm->mi_rows - mi_row);

  MODE_INFO *mi = set_offsets(cm, xd, bsize, mi_row, mi_col,
                              bw, bh, x_mis, y_mis, bwl, bhl);

  if (bsize >= BLOCK_8X8 && (cm->subsampling_x || cm->subsampling_y)) {
    const BLOCK_SIZE uv_subsize =
        ss_size_lookup[bsize][cm->subsampling_x][cm->subsampling_y];
    if (uv_subsize == BLOCK_INVALID)
      vpx_internal_error(xd->error_info,
                         VPX_CODEC_CORRUPT_FRAME, "Invalid block size.");
  }

  vpx_read_mode_info(pbi, xd, mi_row, mi_col, r, x_mis, y_mis);

  if (mi->skip) {
    dec_reset_skip_context(xd);
  }

  if (!is_inter_block(mi)) {
    int plane;
    for (plane = 0; plane < MAX_MB_PLANE; ++plane) {
      const struct macroblockd_plane *const pd = &xd->plane[plane];
      const TX_SIZE tx_size =
          plane ? dec_get_uv_tx_size(mi, pd->n4_wl, pd->n4_hl)
                  : mi->tx_size;
      const int num_4x4_w = pd->n4_w;
      const int num_4x4_h = pd->n4_h;
      const int step = (1 << tx_size);
      int row, col;
      const int max_blocks_wide = num_4x4_w + (xd->mb_to_right_edge >= 0 ?
          0 : xd->mb_to_right_edge >> (5 + pd->subsampling_x));
      const int max_blocks_high = num_4x4_h + (xd->mb_to_bottom_edge >= 0 ?
          0 : xd->mb_to_bottom_edge >> (5 + pd->subsampling_y));

      for (row = 0; row < max_blocks_high; row += step)
        for (col = 0; col < max_blocks_wide; col += step)
          predict_and_reconstruct_intra_block(xd, r, mi, plane,
                                              row, col, tx_size);
    }
  } else {
    // Prediction
    dec_build_inter_predictors_sb(pbi, xd, mi_row, mi_col);

    // Reconstruction
    if (!mi->skip) {
      int eobtotal = 0;
      int plane;

      for (plane = 0; plane < MAX_MB_PLANE; ++plane) {
        const struct macroblockd_plane *const pd = &xd->plane[plane];
        const TX_SIZE tx_size =
            plane ? dec_get_uv_tx_size(mi, pd->n4_wl, pd->n4_hl)
                    : mi->tx_size;
        const int num_4x4_w = pd->n4_w;
        const int num_4x4_h = pd->n4_h;
        const int step = (1 << tx_size);
        int row, col;
        const int max_blocks_wide = num_4x4_w + (xd->mb_to_right_edge >= 0 ?
            0 : xd->mb_to_right_edge >> (5 + pd->subsampling_x));
        const int max_blocks_high = num_4x4_h + (xd->mb_to_bottom_edge >= 0 ?
            0 : xd->mb_to_bottom_edge >> (5 + pd->subsampling_y));

        for (row = 0; row < max_blocks_high; row += step)
          for (col = 0; col < max_blocks_wide; col += step)
            eobtotal += reconstruct_inter_block(xd, r, mi, plane, row, col,
                                                tx_size);
      }

      if (!less8x8 && eobtotal == 0)
        mi->skip = 1;  // skip loopfilter
    }
  }

  xd->corrupted |= vpx_reader_has_error(r);

  if (cm->lf.filter_level) {
    vp9_build_mask(cm, mi, mi_row, mi_col, bw, bh);
  }
}

static INLINE int dec_partition_plane_context(const MACROBLOCKD *xd,
                                              int mi_row, int mi_col,
                                              int bsl) {
  const PARTITION_CONTEXT *above_ctx = xd->above_seg_context + mi_col;
  const PARTITION_CONTEXT *left_ctx = xd->left_seg_context + (mi_row & MI_MASK);
  int above = (*above_ctx >> bsl) & 1 , left = (*left_ctx >> bsl) & 1;

//  assert(bsl >= 0);

  return (left * 2 + above) + bsl * PARTITION_PLOFFSET;
}

static INLINE void dec_update_partition_context(MACROBLOCKD *xd,
                                                int mi_row, int mi_col,
                                                BLOCK_SIZE subsize,
                                                int bw) {
  PARTITION_CONTEXT *const above_ctx = xd->above_seg_context + mi_col;
  PARTITION_CONTEXT *const left_ctx = xd->left_seg_context + (mi_row & MI_MASK);

  // update the partition context at the end notes. set partition bits
  // of block sizes larger than the current one to be one, and partition
  // bits of smaller block sizes to be zero.
  memset(above_ctx, partition_context_lookup[subsize].above, bw);
  memset(left_ctx, partition_context_lookup[subsize].left, bw);
}

static PARTITION_TYPE read_partition(MACROBLOCKD *xd, int mi_row, int mi_col,
                                     vpx_reader *r,
                                     int has_rows, int has_cols, int bsl) {
  const int ctx = dec_partition_plane_context(xd, mi_row, mi_col, bsl);
  const vpx_prob *const probs = get_partition_probs(xd, ctx);
  FRAME_COUNTS *counts = xd->counts;
  PARTITION_TYPE p;

  if (has_rows && has_cols)
    p = (PARTITION_TYPE)vpx_read_tree(r, vp9_partition_tree, probs);
  else if (!has_rows && has_cols)
    p = vpx_read(r, probs[1]) ? PARTITION_SPLIT : PARTITION_HORZ;
  else if (has_rows && !has_cols)
    p = vpx_read(r, probs[2]) ? PARTITION_SPLIT : PARTITION_VERT;
  else
    p = PARTITION_SPLIT;

  if (counts)
    ++counts->partition[ctx][p];

  return p;
}

// TODO(slavarnway): eliminate bsize and subsize in future commits
static void decode_partition(VP9Decoder *const pbi, MACROBLOCKD *const xd,
                             int mi_row, int mi_col,
                             vpx_reader* r, BLOCK_SIZE bsize, int n4x4_l2) {
  VP9_COMMON *const cm = &pbi->common;
  const int n8x8_l2 = n4x4_l2 - 1;
  const int num_8x8_wh = 1 << n8x8_l2;
  const int hbs = num_8x8_wh >> 1;
  PARTITION_TYPE partition;
  BLOCK_SIZE subsize;
  const int has_rows = (mi_row + hbs) < cm->mi_rows;
  const int has_cols = (mi_col + hbs) < cm->mi_cols;

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

  partition = read_partition(xd, mi_row, mi_col, r, has_rows, has_cols,
                             n8x8_l2);
  subsize = subsize_lookup[partition][bsize];  // get_subsize(bsize, partition);
  if (!hbs) {
    // calculate bmode block dimensions (log 2)
    xd->bmode_blocks_wl = 1 >> !!(partition & PARTITION_VERT);
    xd->bmode_blocks_hl = 1 >> !!(partition & PARTITION_HORZ);
    decode_block(pbi, xd, mi_row, mi_col, r, subsize, 1, 1);
  } else {
    switch (partition) {
      case PARTITION_NONE:
        decode_block(pbi, xd, mi_row, mi_col, r, subsize, n4x4_l2, n4x4_l2);
        break;
      case PARTITION_HORZ:
        decode_block(pbi, xd, mi_row, mi_col, r, subsize, n4x4_l2, n8x8_l2);
        if (has_rows)
          decode_block(pbi, xd, mi_row + hbs, mi_col, r, subsize, n4x4_l2,
                       n8x8_l2);
        break;
      case PARTITION_VERT:
        decode_block(pbi, xd, mi_row, mi_col, r, subsize, n8x8_l2, n4x4_l2);
        if (has_cols)
          decode_block(pbi, xd, mi_row, mi_col + hbs, r, subsize, n8x8_l2,
                       n4x4_l2);
        break;
      case PARTITION_SPLIT:
        decode_partition(pbi, xd, mi_row, mi_col, r, subsize, n8x8_l2);
        decode_partition(pbi, xd, mi_row, mi_col + hbs, r, subsize, n8x8_l2);
        decode_partition(pbi, xd, mi_row + hbs, mi_col, r, subsize, n8x8_l2);
        decode_partition(pbi, xd, mi_row + hbs, mi_col + hbs, r, subsize,
                         n8x8_l2);
        break;
      default:
        assert(0 && "Invalid partition type");
    }
  }

  // update partition context
  if (bsize >= BLOCK_8X8 &&
      (bsize == BLOCK_8X8 || partition != PARTITION_SPLIT))
    dec_update_partition_context(xd, mi_row, mi_col, subsize, num_8x8_wh);
}

static void setup_token_decoder(const uint8_t *data,
                                const uint8_t *data_end,
                                size_t read_size,
                                struct vpx_internal_error_info *error_info,
                                vpx_reader *r,
                                vpx_decrypt_cb decrypt_cb,
                                void *decrypt_state) {
  // Validate the calculated partition length. If the buffer
  // described by the partition can't be fully read, then restrict
  // it to the portion that can be (for EC mode) or throw an error.
  if (!read_is_valid(data, read_size, data_end))
    vpx_internal_error(error_info, VPX_CODEC_CORRUPT_FRAME,
                       "Truncated packet or corrupt tile length");

  if (vpx_reader_init(r, data, read_size, decrypt_cb, decrypt_state))
    vpx_internal_error(error_info, VPX_CODEC_MEM_ERROR,
                       "Failed to allocate bool decoder %d", 1);
}

static void read_coef_probs_common(vp9_coeff_probs_model *coef_probs,
                                   vpx_reader *r) {
  int i, j, k, l, m;

  if (vpx_read_bit(r))
    for (i = 0; i < PLANE_TYPES; ++i)
      for (j = 0; j < REF_TYPES; ++j)
        for (k = 0; k < COEF_BANDS; ++k)
          for (l = 0; l < BAND_COEFF_CONTEXTS(k); ++l)
            for (m = 0; m < UNCONSTRAINED_NODES; ++m)
              vp9_diff_update_prob(r, &coef_probs[i][j][k][l][m]);
}

static void read_coef_probs(FRAME_CONTEXT *fc, TX_MODE tx_mode,
                            vpx_reader *r) {
    const TX_SIZE max_tx_size = tx_mode_to_biggest_tx_size[tx_mode];
    TX_SIZE tx_size;
    for (tx_size = TX_4X4; tx_size <= max_tx_size; ++tx_size)
      read_coef_probs_common(fc->coef_probs[tx_size], r);
}

static void setup_segmentation(struct segmentation *seg,
                               struct vpx_read_bit_buffer *rb) {
  int i, j;

  seg->update_map = 0;
  seg->update_data = 0;

  seg->enabled = vpx_rb_read_bit(rb);
  if (!seg->enabled)
    return;

  // Segmentation map update
  seg->update_map = vpx_rb_read_bit(rb);
  if (seg->update_map) {
    for (i = 0; i < SEG_TREE_PROBS; i++)
      seg->tree_probs[i] = vpx_rb_read_bit(rb) ? vpx_rb_read_literal(rb, 8)
                                               : MAX_PROB;

    seg->temporal_update = vpx_rb_read_bit(rb);
    if (seg->temporal_update) {
      for (i = 0; i < PREDICTION_PROBS; i++)
        seg->pred_probs[i] = vpx_rb_read_bit(rb) ? vpx_rb_read_literal(rb, 8)
                                                 : MAX_PROB;
    } else {
      for (i = 0; i < PREDICTION_PROBS; i++)
        seg->pred_probs[i] = MAX_PROB;
    }
  }

  // Segmentation data update
  seg->update_data = vpx_rb_read_bit(rb);
  if (seg->update_data) {
    seg->abs_delta = vpx_rb_read_bit(rb);

    vp9_clearall_segfeatures(seg);

    for (i = 0; i < MAX_SEGMENTS; i++) {
      for (j = 0; j < SEG_LVL_MAX; j++) {
        int data = 0;
        const int feature_enabled = vpx_rb_read_bit(rb);
        if (feature_enabled) {
          vp9_enable_segfeature(seg, i, j);
          data = decode_unsigned_max(rb, vp9_seg_feature_data_max(j));
          if (vp9_is_segfeature_signed(j))
            data = vpx_rb_read_bit(rb) ? -data : data;
        }
        vp9_set_segdata(seg, i, j, data);
      }
    }
  }
}

static void setup_loopfilter(struct loopfilter *lf,
                             struct vpx_read_bit_buffer *rb) {
  lf->filter_level = vpx_rb_read_literal(rb, 6);
  lf->sharpness_level = vpx_rb_read_literal(rb, 3);

  // Read in loop filter deltas applied at the MB level based on mode or ref
  // frame.
  lf->mode_ref_delta_update = 0;

  lf->mode_ref_delta_enabled = vpx_rb_read_bit(rb);
  if (lf->mode_ref_delta_enabled) {
    lf->mode_ref_delta_update = vpx_rb_read_bit(rb);
    if (lf->mode_ref_delta_update) {
      int i;

      for (i = 0; i < MAX_REF_LF_DELTAS; i++)
        if (vpx_rb_read_bit(rb))
          lf->ref_deltas[i] = vpx_rb_read_signed_literal(rb, 6);

      for (i = 0; i < MAX_MODE_LF_DELTAS; i++)
        if (vpx_rb_read_bit(rb))
          lf->mode_deltas[i] = vpx_rb_read_signed_literal(rb, 6);
    }
  }
}

static INLINE int read_delta_q(struct vpx_read_bit_buffer *rb) {
  return vpx_rb_read_bit(rb) ? vpx_rb_read_signed_literal(rb, 4) : 0;
}

static void setup_quantization(VP9_COMMON *const cm, MACROBLOCKD *const xd,
                               struct vpx_read_bit_buffer *rb) {
  cm->base_qindex = vpx_rb_read_literal(rb, QINDEX_BITS);
  cm->y_dc_delta_q = read_delta_q(rb);
  cm->uv_dc_delta_q = read_delta_q(rb);
  cm->uv_ac_delta_q = read_delta_q(rb);
  cm->dequant_bit_depth = cm->bit_depth;
  xd->lossless = cm->base_qindex == 0 &&
                 cm->y_dc_delta_q == 0 &&
                 cm->uv_dc_delta_q == 0 &&
                 cm->uv_ac_delta_q == 0;

#if CONFIG_VP9_HIGHBITDEPTH
  xd->bd = (int)cm->bit_depth;
#endif
}

static void setup_segmentation_dequant(VP9_COMMON *const cm) {
  // Build y/uv dequant values based on segmentation.
  if (cm->seg.enabled) {
    int i;
    for (i = 0; i < MAX_SEGMENTS; ++i) {
      const int qindex = vp9_get_qindex(&cm->seg, i, cm->base_qindex);
      cm->y_dequant[i][0] = vp9_dc_quant(qindex, cm->y_dc_delta_q,
                                         cm->bit_depth);
      cm->y_dequant[i][1] = vp9_ac_quant(qindex, 0, cm->bit_depth);
      cm->uv_dequant[i][0] = vp9_dc_quant(qindex, cm->uv_dc_delta_q,
                                          cm->bit_depth);
      cm->uv_dequant[i][1] = vp9_ac_quant(qindex, cm->uv_ac_delta_q,
                                          cm->bit_depth);
    }
  } else {
    const int qindex = cm->base_qindex;
    // When segmentation is disabled, only the first value is used.  The
    // remaining are don't cares.
    cm->y_dequant[0][0] = vp9_dc_quant(qindex, cm->y_dc_delta_q, cm->bit_depth);
    cm->y_dequant[0][1] = vp9_ac_quant(qindex, 0, cm->bit_depth);
    cm->uv_dequant[0][0] = vp9_dc_quant(qindex, cm->uv_dc_delta_q,
                                        cm->bit_depth);
    cm->uv_dequant[0][1] = vp9_ac_quant(qindex, cm->uv_ac_delta_q,
                                        cm->bit_depth);
  }
}

static INTERP_FILTER read_interp_filter(struct vpx_read_bit_buffer *rb) {
  const INTERP_FILTER literal_to_filter[] = { EIGHTTAP_SMOOTH,
                                              EIGHTTAP,
                                              EIGHTTAP_SHARP,
                                              BILINEAR };
  return vpx_rb_read_bit(rb) ? SWITCHABLE
                             : literal_to_filter[vpx_rb_read_literal(rb, 2)];
}

static void setup_render_size(VP9_COMMON *cm, struct vpx_read_bit_buffer *rb) {
  cm->render_width = cm->width;
  cm->render_height = cm->height;
  if (vpx_rb_read_bit(rb))
    vp9_read_frame_size(rb, &cm->render_width, &cm->render_height);
}

static void resize_mv_buffer(VP9_COMMON *cm) {
  vpx_free(cm->cur_frame->mvs);
  cm->cur_frame->mi_rows = cm->mi_rows;
  cm->cur_frame->mi_cols = cm->mi_cols;
  CHECK_MEM_ERROR(cm, cm->cur_frame->mvs,
                  (MV_REF *)vpx_calloc(cm->mi_rows * cm->mi_cols,
                                       sizeof(*cm->cur_frame->mvs)));
}

static void resize_context_buffers(VP9_COMMON *cm, int width, int height) {
#if CONFIG_SIZE_LIMIT
  if (width > DECODE_WIDTH_LIMIT || height > DECODE_HEIGHT_LIMIT)
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Dimensions of %dx%d beyond allowed size of %dx%d.",
                       width, height, DECODE_WIDTH_LIMIT, DECODE_HEIGHT_LIMIT);
#endif
  if (cm->width != width || cm->height != height) {
    const int new_mi_rows =
        ALIGN_POWER_OF_TWO(height, MI_SIZE_LOG2) >> MI_SIZE_LOG2;
    const int new_mi_cols =
        ALIGN_POWER_OF_TWO(width,  MI_SIZE_LOG2) >> MI_SIZE_LOG2;

    // Allocations in vp9_alloc_context_buffers() depend on individual
    // dimensions as well as the overall size.
    if (new_mi_cols > cm->mi_cols || new_mi_rows > cm->mi_rows) {
      if (vp9_alloc_context_buffers(cm, width, height))
        vpx_internal_error(&cm->error, VPX_CODEC_MEM_ERROR,
                           "Failed to allocate context buffers");
    } else {
      vp9_set_mb_mi(cm, width, height);
    }
    vp9_init_context_buffers(cm);
    cm->width = width;
    cm->height = height;
  }
  if (cm->cur_frame->mvs == NULL || cm->mi_rows > cm->cur_frame->mi_rows ||
      cm->mi_cols > cm->cur_frame->mi_cols) {
    resize_mv_buffer(cm);
  }
}

static void setup_frame_size(VP9_COMMON *cm, struct vpx_read_bit_buffer *rb) {
  int width, height;
  BufferPool *const pool = cm->buffer_pool;
  vp9_read_frame_size(rb, &width, &height);
  resize_context_buffers(cm, width, height);
  setup_render_size(cm, rb);

  lock_buffer_pool(pool);
  if (vpx_realloc_frame_buffer(
          get_frame_new_buffer(cm), cm->width, cm->height,
          cm->subsampling_x, cm->subsampling_y,
#if CONFIG_VP9_HIGHBITDEPTH
          cm->use_highbitdepth,
#endif
          VP9_DEC_BORDER_IN_PIXELS,
          cm->byte_alignment,
          &pool->frame_bufs[cm->new_fb_idx].raw_frame_buffer, pool->get_fb_cb,
          pool->cb_priv)) {
    unlock_buffer_pool(pool);
    vpx_internal_error(&cm->error, VPX_CODEC_MEM_ERROR,
                       "Failed to allocate frame buffer");
  }
  unlock_buffer_pool(pool);

  pool->frame_bufs[cm->new_fb_idx].buf.subsampling_x = cm->subsampling_x;
  pool->frame_bufs[cm->new_fb_idx].buf.subsampling_y = cm->subsampling_y;
  pool->frame_bufs[cm->new_fb_idx].buf.bit_depth = (unsigned int)cm->bit_depth;
  pool->frame_bufs[cm->new_fb_idx].buf.color_space = cm->color_space;
  pool->frame_bufs[cm->new_fb_idx].buf.color_range = cm->color_range;
  pool->frame_bufs[cm->new_fb_idx].buf.render_width  = cm->render_width;
  pool->frame_bufs[cm->new_fb_idx].buf.render_height = cm->render_height;
}

static INLINE int valid_ref_frame_img_fmt(vpx_bit_depth_t ref_bit_depth,
                                          int ref_xss, int ref_yss,
                                          vpx_bit_depth_t this_bit_depth,
                                          int this_xss, int this_yss) {
  return ref_bit_depth == this_bit_depth && ref_xss == this_xss &&
         ref_yss == this_yss;
}

static void setup_frame_size_with_refs(VP9_COMMON *cm,
                                       struct vpx_read_bit_buffer *rb) {
  int width, height;
  int found = 0, i;
  int has_valid_ref_frame = 0;
  BufferPool *const pool = cm->buffer_pool;
  for (i = 0; i < REFS_PER_FRAME; ++i) {
    if (vpx_rb_read_bit(rb)) {
      YV12_BUFFER_CONFIG *const buf = cm->frame_refs[i].buf;
      width = buf->y_crop_width;
      height = buf->y_crop_height;
      found = 1;
      break;
    }
  }

  if (!found)
    vp9_read_frame_size(rb, &width, &height);

  if (width <= 0 || height <= 0)
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Invalid frame size");

  // Check to make sure at least one of frames that this frame references
  // has valid dimensions.
  for (i = 0; i < REFS_PER_FRAME; ++i) {
    RefBuffer *const ref_frame = &cm->frame_refs[i];
    has_valid_ref_frame |= valid_ref_frame_size(ref_frame->buf->y_crop_width,
                                                ref_frame->buf->y_crop_height,
                                                width, height);
  }
  if (!has_valid_ref_frame)
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Referenced frame has invalid size");
  for (i = 0; i < REFS_PER_FRAME; ++i) {
    RefBuffer *const ref_frame = &cm->frame_refs[i];
    if (!valid_ref_frame_img_fmt(
            ref_frame->buf->bit_depth,
            ref_frame->buf->subsampling_x,
            ref_frame->buf->subsampling_y,
            cm->bit_depth,
            cm->subsampling_x,
            cm->subsampling_y))
      vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                         "Referenced frame has incompatible color format");
  }

  resize_context_buffers(cm, width, height);
  setup_render_size(cm, rb);

  lock_buffer_pool(pool);
  if (vpx_realloc_frame_buffer(
          get_frame_new_buffer(cm), cm->width, cm->height,
          cm->subsampling_x, cm->subsampling_y,
#if CONFIG_VP9_HIGHBITDEPTH
          cm->use_highbitdepth,
#endif
          VP9_DEC_BORDER_IN_PIXELS,
          cm->byte_alignment,
          &pool->frame_bufs[cm->new_fb_idx].raw_frame_buffer, pool->get_fb_cb,
          pool->cb_priv)) {
    unlock_buffer_pool(pool);
    vpx_internal_error(&cm->error, VPX_CODEC_MEM_ERROR,
                       "Failed to allocate frame buffer");
  }
  unlock_buffer_pool(pool);

  pool->frame_bufs[cm->new_fb_idx].buf.subsampling_x = cm->subsampling_x;
  pool->frame_bufs[cm->new_fb_idx].buf.subsampling_y = cm->subsampling_y;
  pool->frame_bufs[cm->new_fb_idx].buf.bit_depth = (unsigned int)cm->bit_depth;
  pool->frame_bufs[cm->new_fb_idx].buf.color_space = cm->color_space;
  pool->frame_bufs[cm->new_fb_idx].buf.color_range = cm->color_range;
  pool->frame_bufs[cm->new_fb_idx].buf.render_width  = cm->render_width;
  pool->frame_bufs[cm->new_fb_idx].buf.render_height = cm->render_height;
}

static void setup_tile_info(VP9_COMMON *cm, struct vpx_read_bit_buffer *rb) {
  int min_log2_tile_cols, max_log2_tile_cols, max_ones;
  vp9_get_tile_n_bits(cm->mi_cols, &min_log2_tile_cols, &max_log2_tile_cols);

  // columns
  max_ones = max_log2_tile_cols - min_log2_tile_cols;
  cm->log2_tile_cols = min_log2_tile_cols;
  while (max_ones-- && vpx_rb_read_bit(rb))
    cm->log2_tile_cols++;

  if (cm->log2_tile_cols > 6)
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Invalid number of tile columns");

  // rows
  cm->log2_tile_rows = vpx_rb_read_bit(rb);
  if (cm->log2_tile_rows)
    cm->log2_tile_rows += vpx_rb_read_bit(rb);
}

// Reads the next tile returning its size and adjusting '*data' accordingly
// based on 'is_last'.
static void get_tile_buffer(const uint8_t *const data_end,
                            int is_last,
                            struct vpx_internal_error_info *error_info,
                            const uint8_t **data,
                            vpx_decrypt_cb decrypt_cb, void *decrypt_state,
                            TileBuffer *buf) {
  size_t size;

  if (!is_last) {
    if (!read_is_valid(*data, 4, data_end))
      vpx_internal_error(error_info, VPX_CODEC_CORRUPT_FRAME,
                         "Truncated packet or corrupt tile length");

    if (decrypt_cb) {
      uint8_t be_data[4];
      decrypt_cb(decrypt_state, *data, be_data, 4);
      size = mem_get_be32(be_data);
    } else {
      size = mem_get_be32(*data);
    }
    *data += 4;

    if (size > (size_t)(data_end - *data))
      vpx_internal_error(error_info, VPX_CODEC_CORRUPT_FRAME,
                         "Truncated packet or corrupt tile size");
  } else {
    size = data_end - *data;
  }

  buf->data = *data;
  buf->size = size;

  *data += size;
}

static void get_tile_buffers(VP9Decoder *pbi,
                             const uint8_t *data, const uint8_t *data_end,
                             int tile_cols, int tile_rows,
                             TileBuffer (*tile_buffers)[1 << 6]) {
  int r, c;

  for (r = 0; r < tile_rows; ++r) {
    for (c = 0; c < tile_cols; ++c) {
      const int is_last = (r == tile_rows - 1) && (c == tile_cols - 1);
      TileBuffer *const buf = &tile_buffers[r][c];
      buf->col = c;
      get_tile_buffer(data_end, is_last, &pbi->common.error, &data,
                      pbi->decrypt_cb, pbi->decrypt_state, buf);
    }
  }
}

static const uint8_t *decode_tiles(VP9Decoder *pbi,
                                   const uint8_t *data,
                                   const uint8_t *data_end) {
  VP9_COMMON *const cm = &pbi->common;
  const VPxWorkerInterface *const winterface = vpx_get_worker_interface();
  const int aligned_cols = mi_cols_aligned_to_sb(cm->mi_cols);
  const int tile_cols = 1 << cm->log2_tile_cols;
  const int tile_rows = 1 << cm->log2_tile_rows;
  TileBuffer tile_buffers[4][1 << 6];
  int tile_row, tile_col;
  int mi_row, mi_col;
  TileData *tile_data = NULL;

  if (cm->lf.filter_level && !cm->skip_loop_filter &&
      pbi->lf_worker.data1 == NULL) {
    CHECK_MEM_ERROR(cm, pbi->lf_worker.data1,
                    vpx_memalign(32, sizeof(LFWorkerData)));
    pbi->lf_worker.hook = (VPxWorkerHook)vp9_loop_filter_worker;
    if (pbi->max_threads > 1 && !winterface->reset(&pbi->lf_worker)) {
      vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
                         "Loop filter thread creation failed");
    }
  }

  if (cm->lf.filter_level && !cm->skip_loop_filter) {
    LFWorkerData *const lf_data = (LFWorkerData*)pbi->lf_worker.data1;
    // Be sure to sync as we might be resuming after a failed frame decode.
    winterface->sync(&pbi->lf_worker);
    vp9_loop_filter_data_reset(lf_data, get_frame_new_buffer(cm), cm,
                               pbi->mb.plane);
  }

  assert(tile_rows <= 4);
  assert(tile_cols <= (1 << 6));

  // Note: this memset assumes above_context[0], [1] and [2]
  // are allocated as part of the same buffer.
  memset(cm->above_context, 0,
         sizeof(*cm->above_context) * MAX_MB_PLANE * 2 * aligned_cols);

  memset(cm->above_seg_context, 0,
         sizeof(*cm->above_seg_context) * aligned_cols);

  vp9_reset_lfm(cm);

  get_tile_buffers(pbi, data, data_end, tile_cols, tile_rows, tile_buffers);

  if (pbi->tile_data == NULL ||
      (tile_cols * tile_rows) != pbi->total_tiles) {
    vpx_free(pbi->tile_data);
    CHECK_MEM_ERROR(
        cm,
        pbi->tile_data,
        vpx_memalign(32, tile_cols * tile_rows * (sizeof(*pbi->tile_data))));
    pbi->total_tiles = tile_rows * tile_cols;
  }

  // Load all tile information into tile_data.
  for (tile_row = 0; tile_row < tile_rows; ++tile_row) {
    for (tile_col = 0; tile_col < tile_cols; ++tile_col) {
      const TileBuffer *const buf = &tile_buffers[tile_row][tile_col];
      tile_data = pbi->tile_data + tile_cols * tile_row + tile_col;
      tile_data->cm = cm;
      tile_data->xd = pbi->mb;
      tile_data->xd.corrupted = 0;
      tile_data->xd.counts = cm->frame_parallel_decoding_mode ?
                             NULL : &cm->counts;
      vp9_zero(tile_data->dqcoeff);
      vp9_tile_init(&tile_data->xd.tile, tile_data->cm, tile_row, tile_col);
      setup_token_decoder(buf->data, data_end, buf->size, &cm->error,
                          &tile_data->bit_reader, pbi->decrypt_cb,
                          pbi->decrypt_state);
      vp9_init_macroblockd(cm, &tile_data->xd, tile_data->dqcoeff);
    }
  }

  for (tile_row = 0; tile_row < tile_rows; ++tile_row) {
    TileInfo tile;
    vp9_tile_set_row(&tile, cm, tile_row);
    for (mi_row = tile.mi_row_start; mi_row < tile.mi_row_end;
         mi_row += MI_BLOCK_SIZE) {
      for (tile_col = 0; tile_col < tile_cols; ++tile_col) {
        const int col = pbi->inv_tile_order ?
                        tile_cols - tile_col - 1 : tile_col;
        tile_data = pbi->tile_data + tile_cols * tile_row + col;
        vp9_tile_set_col(&tile, tile_data->cm, col);
        vp9_zero(tile_data->xd.left_context);
        vp9_zero(tile_data->xd.left_seg_context);
        for (mi_col = tile.mi_col_start; mi_col < tile.mi_col_end;
             mi_col += MI_BLOCK_SIZE) {
          decode_partition(pbi, &tile_data->xd, mi_row,
                           mi_col, &tile_data->bit_reader, BLOCK_64X64, 4);
        }
        pbi->mb.corrupted |= tile_data->xd.corrupted;
        if (pbi->mb.corrupted)
            vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                               "Failed to decode tile data");
      }
      // Loopfilter one row.
      if (cm->lf.filter_level && !cm->skip_loop_filter) {
        const int lf_start = mi_row - MI_BLOCK_SIZE;
        LFWorkerData *const lf_data = (LFWorkerData*)pbi->lf_worker.data1;

        // delay the loopfilter by 1 macroblock row.
        if (lf_start < 0) continue;

        // decoding has completed: finish up the loop filter in this thread.
        if (mi_row + MI_BLOCK_SIZE >= cm->mi_rows) continue;

        winterface->sync(&pbi->lf_worker);
        lf_data->start = lf_start;
        lf_data->stop = mi_row;
        if (pbi->max_threads > 1) {
          winterface->launch(&pbi->lf_worker);
        } else {
          winterface->execute(&pbi->lf_worker);
        }
      }
      // After loopfiltering, the last 7 row pixels in each superblock row may
      // still be changed by the longest loopfilter of the next superblock
      // row.
      if (pbi->frame_parallel_decode)
        vp9_frameworker_broadcast(pbi->cur_buf,
                                  mi_row << MI_BLOCK_SIZE_LOG2);
    }
  }

  // Loopfilter remaining rows in the frame.
  if (cm->lf.filter_level && !cm->skip_loop_filter) {
    LFWorkerData *const lf_data = (LFWorkerData*)pbi->lf_worker.data1;
    winterface->sync(&pbi->lf_worker);
    lf_data->start = lf_data->stop;
    lf_data->stop = cm->mi_rows;
    winterface->execute(&pbi->lf_worker);
  }

  // Get last tile data.
  tile_data = pbi->tile_data + tile_cols * tile_rows - 1;

  if (pbi->frame_parallel_decode)
    vp9_frameworker_broadcast(pbi->cur_buf, INT_MAX);
  return vpx_reader_find_end(&tile_data->bit_reader);
}

// On entry 'tile_data->data_end' points to the end of the input frame, on exit
// it is updated to reflect the bitreader position of the final tile column if
// present in the tile buffer group or NULL otherwise.
static int tile_worker_hook(TileWorkerData *const tile_data,
                            VP9Decoder *const pbi) {
  TileInfo *volatile tile = &tile_data->xd.tile;
  const int final_col = (1 << pbi->common.log2_tile_cols) - 1;
  const uint8_t *volatile bit_reader_end = NULL;
  volatile int n = tile_data->buf_start;
  tile_data->error_info.setjmp = 1;

  if (setjmp(tile_data->error_info.jmp)) {
    tile_data->error_info.setjmp = 0;
    tile_data->xd.corrupted = 1;
    tile_data->data_end = NULL;
    return 0;
  }

  tile_data->xd.error_info = &tile_data->error_info;
  tile_data->xd.corrupted = 0;

  do {
    int mi_row, mi_col;
    const TileBuffer *const buf = pbi->tile_buffers + n;
    vp9_zero(tile_data->dqcoeff);
    vp9_tile_init(tile, &pbi->common, 0, buf->col);
    setup_token_decoder(buf->data, tile_data->data_end, buf->size,
                        &tile_data->error_info, &tile_data->bit_reader,
                        pbi->decrypt_cb, pbi->decrypt_state);
    vp9_init_macroblockd(&pbi->common, &tile_data->xd, tile_data->dqcoeff);

    for (mi_row = tile->mi_row_start; mi_row < tile->mi_row_end;
         mi_row += MI_BLOCK_SIZE) {
      vp9_zero(tile_data->xd.left_context);
      vp9_zero(tile_data->xd.left_seg_context);
      for (mi_col = tile->mi_col_start; mi_col < tile->mi_col_end;
           mi_col += MI_BLOCK_SIZE) {
        decode_partition(pbi, &tile_data->xd, mi_row, mi_col,
                         &tile_data->bit_reader, BLOCK_64X64, 4);
      }
    }

    if (buf->col == final_col) {
      bit_reader_end = vpx_reader_find_end(&tile_data->bit_reader);
    }
  } while (!tile_data->xd.corrupted && ++n <= tile_data->buf_end);

  tile_data->data_end = bit_reader_end;
  return !tile_data->xd.corrupted;
}

// sorts in descending order
static int compare_tile_buffers(const void *a, const void *b) {
  const TileBuffer *const buf1 = (const TileBuffer*)a;
  const TileBuffer *const buf2 = (const TileBuffer*)b;
  return (int)(buf2->size - buf1->size);
}

static const uint8_t *decode_tiles_mt(VP9Decoder *pbi,
                                      const uint8_t *data,
                                      const uint8_t *data_end) {
  VP9_COMMON *const cm = &pbi->common;
  const VPxWorkerInterface *const winterface = vpx_get_worker_interface();
  const uint8_t *bit_reader_end = NULL;
  const int aligned_mi_cols = mi_cols_aligned_to_sb(cm->mi_cols);
  const int tile_cols = 1 << cm->log2_tile_cols;
  const int tile_rows = 1 << cm->log2_tile_rows;
  const int num_workers = VPXMIN(pbi->max_threads, tile_cols);
  int n;

  assert(tile_cols <= (1 << 6));
  assert(tile_rows == 1);
  (void)tile_rows;

  if (pbi->num_tile_workers == 0) {
    const int num_threads = pbi->max_threads;
    CHECK_MEM_ERROR(cm, pbi->tile_workers,
                    vpx_malloc(num_threads * sizeof(*pbi->tile_workers)));
    // Ensure tile data offsets will be properly aligned. This may fail on
    // platforms without DECLARE_ALIGNED().
    assert((sizeof(*pbi->tile_worker_data) % 16) == 0);
    CHECK_MEM_ERROR(cm, pbi->tile_worker_data,
                    vpx_memalign(32, num_threads *
                                 sizeof(*pbi->tile_worker_data)));
    for (n = 0; n < num_threads; ++n) {
      VPxWorker *const worker = &pbi->tile_workers[n];
      ++pbi->num_tile_workers;

      winterface->init(worker);
      if (n < num_threads - 1 && !winterface->reset(worker)) {
        vpx_internal_error(&cm->error, VPX_CODEC_ERROR,
                           "Tile decoder thread creation failed");
      }
    }
  }

  // Reset tile decoding hook
  for (n = 0; n < num_workers; ++n) {
    VPxWorker *const worker = &pbi->tile_workers[n];
    TileWorkerData *const tile_data = &pbi->tile_worker_data[n];
    winterface->sync(worker);
    tile_data->xd = pbi->mb;
    tile_data->xd.counts =
        cm->frame_parallel_decoding_mode ? NULL : &tile_data->counts;
    worker->hook = (VPxWorkerHook)tile_worker_hook;
    worker->data1 = tile_data;
    worker->data2 = pbi;
  }

  // Note: this memset assumes above_context[0], [1] and [2]
  // are allocated as part of the same buffer.
  memset(cm->above_context, 0,
         sizeof(*cm->above_context) * MAX_MB_PLANE * 2 * aligned_mi_cols);
  memset(cm->above_seg_context, 0,
         sizeof(*cm->above_seg_context) * aligned_mi_cols);

  vp9_reset_lfm(cm);

  // Load tile data into tile_buffers
  get_tile_buffers(pbi, data, data_end, tile_cols, tile_rows,
                   &pbi->tile_buffers);

  // Sort the buffers based on size in descending order.
  qsort(pbi->tile_buffers, tile_cols, sizeof(pbi->tile_buffers[0]),
        compare_tile_buffers);

  if (num_workers == tile_cols) {
    // Rearrange the tile buffers such that the largest, and
    // presumably the most difficult, tile will be decoded in the main thread.
    // This should help minimize the number of instances where the main thread
    // is waiting for a worker to complete.
    const TileBuffer largest = pbi->tile_buffers[0];
    memmove(pbi->tile_buffers, pbi->tile_buffers + 1,
            (tile_cols - 1) * sizeof(pbi->tile_buffers[0]));
    pbi->tile_buffers[tile_cols - 1] = largest;
  } else {
    int start = 0, end = tile_cols - 2;
    TileBuffer tmp;

    // Interleave the tiles to distribute the load between threads, assuming a
    // larger tile implies it is more difficult to decode.
    while (start < end) {
      tmp = pbi->tile_buffers[start];
      pbi->tile_buffers[start] = pbi->tile_buffers[end];
      pbi->tile_buffers[end] = tmp;
      start += 2;
      end -= 2;
    }
  }

  // Initialize thread frame counts.
  if (!cm->frame_parallel_decoding_mode) {
    for (n = 0; n < num_workers; ++n) {
      TileWorkerData *const tile_data =
          (TileWorkerData*)pbi->tile_workers[n].data1;
      vp9_zero(tile_data->counts);
    }
  }

  {
    const int base = tile_cols / num_workers;
    const int remain = tile_cols % num_workers;
    int buf_start = 0;

    for (n = 0; n < num_workers; ++n) {
      const int count = base + (remain + n) / num_workers;
      VPxWorker *const worker = &pbi->tile_workers[n];
      TileWorkerData *const tile_data = (TileWorkerData*)worker->data1;

      tile_data->buf_start = buf_start;
      tile_data->buf_end = buf_start + count - 1;
      tile_data->data_end = data_end;
      buf_start += count;

      worker->had_error = 0;
      if (n == num_workers - 1) {
        assert(tile_data->buf_end == tile_cols - 1);
        winterface->execute(worker);
      } else {
        winterface->launch(worker);
      }
    }

    for (; n > 0; --n) {
      VPxWorker *const worker = &pbi->tile_workers[n - 1];
      TileWorkerData *const tile_data = (TileWorkerData*)worker->data1;
      // TODO(jzern): The tile may have specific error data associated with
      // its vpx_internal_error_info which could be propagated to the main info
      // in cm. Additionally once the threads have been synced and an error is
      // detected, there's no point in continuing to decode tiles.
      pbi->mb.corrupted |= !winterface->sync(worker);
      if (!bit_reader_end) bit_reader_end = tile_data->data_end;
    }
  }

  // Accumulate thread frame counts.
  if (!cm->frame_parallel_decoding_mode) {
    for (n = 0; n < num_workers; ++n) {
      TileWorkerData *const tile_data =
          (TileWorkerData*)pbi->tile_workers[n].data1;
      vp9_accumulate_frame_counts(&cm->counts, &tile_data->counts, 1);
    }
  }

  assert(bit_reader_end || pbi->mb.corrupted);
  return bit_reader_end;
}

static void error_handler(void *data) {
  VP9_COMMON *const cm = (VP9_COMMON *)data;
  vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME, "Truncated packet");
}

static void read_bitdepth_colorspace_sampling(
    VP9_COMMON *cm, struct vpx_read_bit_buffer *rb) {
  if (cm->profile >= PROFILE_2) {
    cm->bit_depth = vpx_rb_read_bit(rb) ? VPX_BITS_12 : VPX_BITS_10;
#if CONFIG_VP9_HIGHBITDEPTH
    cm->use_highbitdepth = 1;
#endif
  } else {
    cm->bit_depth = VPX_BITS_8;
#if CONFIG_VP9_HIGHBITDEPTH
    cm->use_highbitdepth = 0;
#endif
  }
  cm->color_space = vpx_rb_read_literal(rb, 3);
  if (cm->color_space != VPX_CS_SRGB) {
    cm->color_range = (vpx_color_range_t)vpx_rb_read_bit(rb);
    if (cm->profile == PROFILE_1 || cm->profile == PROFILE_3) {
      cm->subsampling_x = vpx_rb_read_bit(rb);
      cm->subsampling_y = vpx_rb_read_bit(rb);
      if (cm->subsampling_x == 1 && cm->subsampling_y == 1)
        vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                           "4:2:0 color not supported in profile 1 or 3");
      if (vpx_rb_read_bit(rb))
        vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                           "Reserved bit set");
    } else {
      cm->subsampling_y = cm->subsampling_x = 1;
    }
  } else {
    cm->color_range = VPX_CR_FULL_RANGE;
    if (cm->profile == PROFILE_1 || cm->profile == PROFILE_3) {
      // Note if colorspace is SRGB then 4:4:4 chroma sampling is assumed.
      // 4:2:2 or 4:4:0 chroma sampling is not allowed.
      cm->subsampling_y = cm->subsampling_x = 0;
      if (vpx_rb_read_bit(rb))
        vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                           "Reserved bit set");
    } else {
      vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                         "4:4:4 color not supported in profile 0 or 2");
    }
  }
}

static size_t read_uncompressed_header(VP9Decoder *pbi,
                                       struct vpx_read_bit_buffer *rb) {
  VP9_COMMON *const cm = &pbi->common;
  BufferPool *const pool = cm->buffer_pool;
  RefCntBuffer *const frame_bufs = pool->frame_bufs;
  int i, mask, ref_index = 0;
  size_t sz;

  cm->last_frame_type = cm->frame_type;
  cm->last_intra_only = cm->intra_only;

  if (vpx_rb_read_literal(rb, 2) != VP9_FRAME_MARKER)
      vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                         "Invalid frame marker");

  cm->profile = vp9_read_profile(rb);
#if CONFIG_VP9_HIGHBITDEPTH
  if (cm->profile >= MAX_PROFILES)
    vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                       "Unsupported bitstream profile");
#else
  if (cm->profile >= PROFILE_2)
    vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                       "Unsupported bitstream profile");
#endif

  cm->show_existing_frame = vpx_rb_read_bit(rb);
  if (cm->show_existing_frame) {
    // Show an existing frame directly.
    const int frame_to_show = cm->ref_frame_map[vpx_rb_read_literal(rb, 3)];
    lock_buffer_pool(pool);
    if (frame_to_show < 0 || frame_bufs[frame_to_show].ref_count < 1) {
      unlock_buffer_pool(pool);
      vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                         "Buffer %d does not contain a decoded frame",
                         frame_to_show);
    }

    ref_cnt_fb(frame_bufs, &cm->new_fb_idx, frame_to_show);
    unlock_buffer_pool(pool);
    pbi->refresh_frame_flags = 0;
    cm->lf.filter_level = 0;
    cm->show_frame = 1;

    if (pbi->frame_parallel_decode) {
      for (i = 0; i < REF_FRAMES; ++i)
        cm->next_ref_frame_map[i] = cm->ref_frame_map[i];
    }
    return 0;
  }

  cm->frame_type = (FRAME_TYPE) vpx_rb_read_bit(rb);
  cm->show_frame = vpx_rb_read_bit(rb);
  cm->error_resilient_mode = vpx_rb_read_bit(rb);

  if (cm->frame_type == KEY_FRAME) {
    if (!vp9_read_sync_code(rb))
      vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                         "Invalid frame sync code");

    read_bitdepth_colorspace_sampling(cm, rb);
    pbi->refresh_frame_flags = (1 << REF_FRAMES) - 1;

    for (i = 0; i < REFS_PER_FRAME; ++i) {
      cm->frame_refs[i].idx = INVALID_IDX;
      cm->frame_refs[i].buf = NULL;
    }

    setup_frame_size(cm, rb);
    if (pbi->need_resync) {
      memset(&cm->ref_frame_map, -1, sizeof(cm->ref_frame_map));
      pbi->need_resync = 0;
    }
  } else {
    cm->intra_only = cm->show_frame ? 0 : vpx_rb_read_bit(rb);

    cm->reset_frame_context = cm->error_resilient_mode ?
        0 : vpx_rb_read_literal(rb, 2);

    if (cm->intra_only) {
      if (!vp9_read_sync_code(rb))
        vpx_internal_error(&cm->error, VPX_CODEC_UNSUP_BITSTREAM,
                           "Invalid frame sync code");
      if (cm->profile > PROFILE_0) {
        read_bitdepth_colorspace_sampling(cm, rb);
      } else {
        // NOTE: The intra-only frame header does not include the specification
        // of either the color format or color sub-sampling in profile 0. VP9
        // specifies that the default color format should be YUV 4:2:0 in this
        // case (normative).
        cm->color_space = VPX_CS_BT_601;
        cm->color_range = VPX_CR_STUDIO_RANGE;
        cm->subsampling_y = cm->subsampling_x = 1;
        cm->bit_depth = VPX_BITS_8;
#if CONFIG_VP9_HIGHBITDEPTH
        cm->use_highbitdepth = 0;
#endif
      }

      pbi->refresh_frame_flags = vpx_rb_read_literal(rb, REF_FRAMES);
      setup_frame_size(cm, rb);
      if (pbi->need_resync) {
        memset(&cm->ref_frame_map, -1, sizeof(cm->ref_frame_map));
        pbi->need_resync = 0;
      }
    } else if (pbi->need_resync != 1) {  /* Skip if need resync */
      pbi->refresh_frame_flags = vpx_rb_read_literal(rb, REF_FRAMES);
      for (i = 0; i < REFS_PER_FRAME; ++i) {
        const int ref = vpx_rb_read_literal(rb, REF_FRAMES_LOG2);
        const int idx = cm->ref_frame_map[ref];
        RefBuffer *const ref_frame = &cm->frame_refs[i];
        ref_frame->idx = idx;
        ref_frame->buf = &frame_bufs[idx].buf;
        cm->ref_frame_sign_bias[LAST_FRAME + i] = vpx_rb_read_bit(rb);
      }

      setup_frame_size_with_refs(cm, rb);

      cm->allow_high_precision_mv = vpx_rb_read_bit(rb);
      cm->interp_filter = read_interp_filter(rb);

      for (i = 0; i < REFS_PER_FRAME; ++i) {
        RefBuffer *const ref_buf = &cm->frame_refs[i];
#if CONFIG_VP9_HIGHBITDEPTH
        vp9_setup_scale_factors_for_frame(&ref_buf->sf,
                                          ref_buf->buf->y_crop_width,
                                          ref_buf->buf->y_crop_height,
                                          cm->width, cm->height,
                                          cm->use_highbitdepth);
#else
        vp9_setup_scale_factors_for_frame(&ref_buf->sf,
                                          ref_buf->buf->y_crop_width,
                                          ref_buf->buf->y_crop_height,
                                          cm->width, cm->height);
#endif
      }
    }
  }
#if CONFIG_VP9_HIGHBITDEPTH
  get_frame_new_buffer(cm)->bit_depth = cm->bit_depth;
#endif
  get_frame_new_buffer(cm)->color_space = cm->color_space;
  get_frame_new_buffer(cm)->color_range = cm->color_range;
  get_frame_new_buffer(cm)->render_width  = cm->render_width;
  get_frame_new_buffer(cm)->render_height = cm->render_height;

  if (pbi->need_resync) {
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Keyframe / intra-only frame required to reset decoder"
                       " state");
  }

  if (!cm->error_resilient_mode) {
    cm->refresh_frame_context = vpx_rb_read_bit(rb);
    cm->frame_parallel_decoding_mode = vpx_rb_read_bit(rb);
    if (!cm->frame_parallel_decoding_mode)
      vp9_zero(cm->counts);
  } else {
    cm->refresh_frame_context = 0;
    cm->frame_parallel_decoding_mode = 1;
  }

  // This flag will be overridden by the call to vp9_setup_past_independence
  // below, forcing the use of context 0 for those frame types.
  cm->frame_context_idx = vpx_rb_read_literal(rb, FRAME_CONTEXTS_LOG2);

  // Generate next_ref_frame_map.
  lock_buffer_pool(pool);
  for (mask = pbi->refresh_frame_flags; mask; mask >>= 1) {
    if (mask & 1) {
      cm->next_ref_frame_map[ref_index] = cm->new_fb_idx;
      ++frame_bufs[cm->new_fb_idx].ref_count;
    } else {
      cm->next_ref_frame_map[ref_index] = cm->ref_frame_map[ref_index];
    }
    // Current thread holds the reference frame.
    if (cm->ref_frame_map[ref_index] >= 0)
      ++frame_bufs[cm->ref_frame_map[ref_index]].ref_count;
    ++ref_index;
  }

  for (; ref_index < REF_FRAMES; ++ref_index) {
    cm->next_ref_frame_map[ref_index] = cm->ref_frame_map[ref_index];
    // Current thread holds the reference frame.
    if (cm->ref_frame_map[ref_index] >= 0)
      ++frame_bufs[cm->ref_frame_map[ref_index]].ref_count;
  }
  unlock_buffer_pool(pool);
  pbi->hold_ref_buf = 1;

  if (frame_is_intra_only(cm) || cm->error_resilient_mode)
    vp9_setup_past_independence(cm);

  setup_loopfilter(&cm->lf, rb);
  setup_quantization(cm, &pbi->mb, rb);
  setup_segmentation(&cm->seg, rb);
  setup_segmentation_dequant(cm);

  setup_tile_info(cm, rb);
  sz = vpx_rb_read_literal(rb, 16);

  if (sz == 0)
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Invalid header size");

  return sz;
}

static int read_compressed_header(VP9Decoder *pbi, const uint8_t *data,
                                  size_t partition_size) {
  VP9_COMMON *const cm = &pbi->common;
  MACROBLOCKD *const xd = &pbi->mb;
  FRAME_CONTEXT *const fc = cm->fc;
  vpx_reader r;
  int k;

  if (vpx_reader_init(&r, data, partition_size, pbi->decrypt_cb,
                      pbi->decrypt_state))
    vpx_internal_error(&cm->error, VPX_CODEC_MEM_ERROR,
                       "Failed to allocate bool decoder 0");

  cm->tx_mode = xd->lossless ? ONLY_4X4 : read_tx_mode(&r);
  if (cm->tx_mode == TX_MODE_SELECT)
    read_tx_mode_probs(&fc->tx_probs, &r);
  read_coef_probs(fc, cm->tx_mode, &r);

  for (k = 0; k < SKIP_CONTEXTS; ++k)
    vp9_diff_update_prob(&r, &fc->skip_probs[k]);

  if (!frame_is_intra_only(cm)) {
    nmv_context *const nmvc = &fc->nmvc;
    int i, j;

    read_inter_mode_probs(fc, &r);

    if (cm->interp_filter == SWITCHABLE)
      read_switchable_interp_probs(fc, &r);

    for (i = 0; i < INTRA_INTER_CONTEXTS; i++)
      vp9_diff_update_prob(&r, &fc->intra_inter_prob[i]);

    cm->reference_mode = read_frame_reference_mode(cm, &r);
    if (cm->reference_mode != SINGLE_REFERENCE)
      setup_compound_reference_mode(cm);
    read_frame_reference_mode_probs(cm, &r);

    for (j = 0; j < BLOCK_SIZE_GROUPS; j++)
      for (i = 0; i < INTRA_MODES - 1; ++i)
        vp9_diff_update_prob(&r, &fc->y_mode_prob[j][i]);

    for (j = 0; j < PARTITION_CONTEXTS; ++j)
      for (i = 0; i < PARTITION_TYPES - 1; ++i)
        vp9_diff_update_prob(&r, &fc->partition_prob[j][i]);

    read_mv_probs(nmvc, cm->allow_high_precision_mv, &r);
  }

  return vpx_reader_has_error(&r);
}

static struct vpx_read_bit_buffer *init_read_bit_buffer(
    VP9Decoder *pbi,
    struct vpx_read_bit_buffer *rb,
    const uint8_t *data,
    const uint8_t *data_end,
    uint8_t clear_data[MAX_VP9_HEADER_SIZE]) {
  rb->bit_offset = 0;
  rb->error_handler = error_handler;
  rb->error_handler_data = &pbi->common;
  if (pbi->decrypt_cb) {
    const int n = (int)VPXMIN(MAX_VP9_HEADER_SIZE, data_end - data);
    pbi->decrypt_cb(pbi->decrypt_state, data, clear_data, n);
    rb->bit_buffer = clear_data;
    rb->bit_buffer_end = clear_data + n;
  } else {
    rb->bit_buffer = data;
    rb->bit_buffer_end = data_end;
  }
  return rb;
}

//------------------------------------------------------------------------------

int vp9_read_sync_code(struct vpx_read_bit_buffer *const rb) {
  return vpx_rb_read_literal(rb, 8) == VP9_SYNC_CODE_0 &&
         vpx_rb_read_literal(rb, 8) == VP9_SYNC_CODE_1 &&
         vpx_rb_read_literal(rb, 8) == VP9_SYNC_CODE_2;
}

void vp9_read_frame_size(struct vpx_read_bit_buffer *rb,
                         int *width, int *height) {
  *width = vpx_rb_read_literal(rb, 16) + 1;
  *height = vpx_rb_read_literal(rb, 16) + 1;
}

BITSTREAM_PROFILE vp9_read_profile(struct vpx_read_bit_buffer *rb) {
  int profile = vpx_rb_read_bit(rb);
  profile |= vpx_rb_read_bit(rb) << 1;
  if (profile > 2)
    profile += vpx_rb_read_bit(rb);
  return (BITSTREAM_PROFILE) profile;
}

void vp9_decode_frame(VP9Decoder *pbi,
                      const uint8_t *data, const uint8_t *data_end,
                      const uint8_t **p_data_end) {
  VP9_COMMON *const cm = &pbi->common;
  MACROBLOCKD *const xd = &pbi->mb;
  struct vpx_read_bit_buffer rb;
  int context_updated = 0;
  uint8_t clear_data[MAX_VP9_HEADER_SIZE];
  const size_t first_partition_size = read_uncompressed_header(pbi,
      init_read_bit_buffer(pbi, &rb, data, data_end, clear_data));
  const int tile_rows = 1 << cm->log2_tile_rows;
  const int tile_cols = 1 << cm->log2_tile_cols;
  YV12_BUFFER_CONFIG *const new_fb = get_frame_new_buffer(cm);
  xd->cur_buf = new_fb;

  if (!first_partition_size) {
    // showing a frame directly
    *p_data_end = data + (cm->profile <= PROFILE_2 ? 1 : 2);
    return;
  }

  data += vpx_rb_bytes_read(&rb);
  if (!read_is_valid(data, first_partition_size, data_end))
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Truncated packet or corrupt header length");

  cm->use_prev_frame_mvs = !cm->error_resilient_mode &&
                           cm->width == cm->last_width &&
                           cm->height == cm->last_height &&
                           !cm->last_intra_only &&
                           cm->last_show_frame &&
                           (cm->last_frame_type != KEY_FRAME);

  vp9_setup_block_planes(xd, cm->subsampling_x, cm->subsampling_y);

  *cm->fc = cm->frame_contexts[cm->frame_context_idx];
  if (!cm->fc->initialized)
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Uninitialized entropy context.");

  xd->corrupted = 0;
  new_fb->corrupted = read_compressed_header(pbi, data, first_partition_size);
  if (new_fb->corrupted)
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Decode failed. Frame data header is corrupted.");

  if (cm->lf.filter_level && !cm->skip_loop_filter) {
    vp9_loop_filter_frame_init(cm, cm->lf.filter_level);
  }

  // If encoded in frame parallel mode, frame context is ready after decoding
  // the frame header.
  if (pbi->frame_parallel_decode && cm->frame_parallel_decoding_mode) {
    VPxWorker *const worker = pbi->frame_worker_owner;
    FrameWorkerData *const frame_worker_data = worker->data1;
    if (cm->refresh_frame_context) {
      context_updated = 1;
      cm->frame_contexts[cm->frame_context_idx] = *cm->fc;
    }
    vp9_frameworker_lock_stats(worker);
    pbi->cur_buf->row = -1;
    pbi->cur_buf->col = -1;
    frame_worker_data->frame_context_ready = 1;
    // Signal the main thread that context is ready.
    vp9_frameworker_signal_stats(worker);
    vp9_frameworker_unlock_stats(worker);
  }

  if (pbi->max_threads > 1 && tile_rows == 1 && tile_cols > 1) {
    // Multi-threaded tile decoder
    *p_data_end = decode_tiles_mt(pbi, data + first_partition_size, data_end);
    if (!xd->corrupted) {
      if (!cm->skip_loop_filter) {
        // If multiple threads are used to decode tiles, then we use those
        // threads to do parallel loopfiltering.
        vp9_loop_filter_frame_mt(new_fb, cm, pbi->mb.plane,
                                 cm->lf.filter_level, 0, 0, pbi->tile_workers,
                                 pbi->num_tile_workers, &pbi->lf_row_sync);
      }
    } else {
      vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                         "Decode failed. Frame data is corrupted.");
    }
  } else {
    *p_data_end = decode_tiles(pbi, data + first_partition_size, data_end);
  }

  if (!xd->corrupted) {
    if (!cm->error_resilient_mode && !cm->frame_parallel_decoding_mode) {
      vp9_adapt_coef_probs(cm);

      if (!frame_is_intra_only(cm)) {
        vp9_adapt_mode_probs(cm);
        vp9_adapt_mv_probs(cm, cm->allow_high_precision_mv);
      }
    }
  } else {
    vpx_internal_error(&cm->error, VPX_CODEC_CORRUPT_FRAME,
                       "Decode failed. Frame data is corrupted.");
  }

  // Non frame parallel update frame context here.
  if (cm->refresh_frame_context && !context_updated)
    cm->frame_contexts[cm->frame_context_idx] = *cm->fc;
}