vp9_reader.h 2.32 KB
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/*
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 *  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
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 *
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 *  Use of this source code is governed by a BSD-style license
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 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
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 *  in the file PATENTS.  All contributing project authors may
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 *  be found in the AUTHORS file in the root of the source tree.
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 */

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#ifndef VP9_DECODER_VP9_READER_H_
#define VP9_DECODER_VP9_READER_H_
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#include <stddef.h>
#include <limits.h>
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#include "./vpx_config.h"
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#include "vpx_ports/mem.h"
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#include "vpx/vpx_integer.h"
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#include "vp9/common/vp9_prob.h"
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#ifdef __cplusplus
extern "C" {
#endif

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typedef size_t BD_VALUE;

#define BD_VALUE_SIZE ((int)sizeof(BD_VALUE) * CHAR_BIT)

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typedef struct {
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  const uint8_t *buffer_end;
  const uint8_t *buffer;
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  BD_VALUE value;
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  int count;
  unsigned int range;
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} vp9_reader;
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int vp9_reader_init(vp9_reader *r, const uint8_t *buffer, size_t size);
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void vp9_reader_fill(vp9_reader *r);
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int vp9_reader_has_error(vp9_reader *r);

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const uint8_t *vp9_reader_find_end(vp9_reader *r);
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static int vp9_read(vp9_reader *r, int prob) {
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  unsigned int bit = 0;
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  BD_VALUE value;
  BD_VALUE bigsplit;
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  int count;
  unsigned int range;
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  unsigned int split = (r->range * prob + (256 - prob)) >> CHAR_BIT;
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  if (r->count < 0)
    vp9_reader_fill(r);
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  value = r->value;
  count = r->count;
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  bigsplit = (BD_VALUE)split << (BD_VALUE_SIZE - CHAR_BIT);
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  range = split;

  if (value >= bigsplit) {
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    range = r->range - split;
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    value = value - bigsplit;
    bit = 1;
  }

  {
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    register unsigned int shift = vp9_norm[range];
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    range <<= shift;
    value <<= shift;
    count -= shift;
  }
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  r->value = value;
  r->count = count;
  r->range = range;
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  return bit;
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}

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static int vp9_read_bit(vp9_reader *r) {
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  return vp9_read(r, 128);  // vp9_prob_half
}

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static int vp9_read_literal(vp9_reader *r, int bits) {
  int literal = 0, bit;
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  for (bit = bits - 1; bit >= 0; bit--)
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    literal |= vp9_read_bit(r) << bit;
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  return literal;
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}
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static int vp9_read_tree(vp9_reader *r, const vp9_tree_index *tree,
                         const vp9_prob *probs) {
  vp9_tree_index i = 0;

  while ((i = tree[i + vp9_read(r, probs[i >> 1])]) > 0)
    continue;

  return -i;
}
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#ifdef __cplusplus
}  // extern "C"
#endif

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#endif  // VP9_DECODER_VP9_READER_H_