vp9_dboolhuff.h 4.33 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_DBOOLHUFF_H_
#define VP9_DECODER_VP9_DBOOLHUFF_H_
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#include <stddef.h>
#include <limits.h>
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#include "vpx_ports/config.h"
#include "vpx_ports/mem.h"
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#include "vpx/vpx_integer.h"
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typedef size_t VP9_BD_VALUE;
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# define VP9_BD_VALUE_SIZE ((int)sizeof(VP9_BD_VALUE)*CHAR_BIT)
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/*This is meant to be a large, positive constant that can still be efficiently
   loaded as an immediate (on platforms like ARM, for example).
  Even relatively modest values like 100 would work fine.*/
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# define VP9_LOTS_OF_BITS (0x40000000)
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typedef struct {
  const unsigned char *user_buffer_end;
  const unsigned char *user_buffer;
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  VP9_BD_VALUE         value;
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  int                  count;
  unsigned int         range;
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} BOOL_DECODER;

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DECLARE_ALIGNED(16, extern const unsigned char, vp9_norm[256]);
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int vp9_start_decode(BOOL_DECODER *br,
                     const unsigned char *source,
                     unsigned int source_sz);
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void vp9_bool_decoder_fill(BOOL_DECODER *br);
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int vp9_decode_uniform(BOOL_DECODER *br, int n);
int vp9_decode_term_subexp(BOOL_DECODER *br, int k, int num_syms);
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int vp9_inv_recenter_nonneg(int v, int m);
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/*The refill loop is used in several places, so define it in a macro to make
   sure they're all consistent.
  An inline function would be cleaner, but has a significant penalty, because
   multiple BOOL_DECODER fields must be modified, and the compiler is not smart
   enough to eliminate the stores to those fields and the subsequent reloads
   from them when inlining the function.*/
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#define VP9DX_BOOL_DECODER_FILL(_count,_value,_bufptr,_bufend) \
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  do \
  { \
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    int shift = VP9_BD_VALUE_SIZE - 8 - ((_count) + 8); \
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    int loop_end, x; \
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    int bits_left = (int)(((_bufend)-(_bufptr))*CHAR_BIT); \
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    \
    x = shift + CHAR_BIT - bits_left; \
    loop_end = 0; \
    if(x >= 0) \
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    { \
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      (_count) += VP9_LOTS_OF_BITS; \
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      loop_end = x; \
      if(!bits_left) break; \
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    } \
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    while(shift >= loop_end) \
    { \
      (_count) += CHAR_BIT; \
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      (_value) |= (VP9_BD_VALUE)*(_bufptr)++ << shift; \
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      shift -= CHAR_BIT; \
    } \
  } \
  while(0) \
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static int decode_bool(BOOL_DECODER *br, int probability) {
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  unsigned int bit = 0;
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  VP9_BD_VALUE value;
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  unsigned int split;
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  VP9_BD_VALUE bigsplit;
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  int count;
  unsigned int range;

  split = 1 + (((br->range - 1) * probability) >> 8);

  if (br->count < 0)
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    vp9_bool_decoder_fill(br);
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  value = br->value;
  count = br->count;

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  bigsplit = (VP9_BD_VALUE)split << (VP9_BD_VALUE_SIZE - 8);
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  range = split;

  if (value >= bigsplit) {
    range = br->range - split;
    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;
  }
  br->value = value;
  br->count = count;
  br->range = range;

  return bit;
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}

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static int decode_value(BOOL_DECODER *br, int bits) {
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  int z = 0;
  int bit;
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  for (bit = bits - 1; bit >= 0; bit--) {
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    z |= (decode_bool(br, 0x80) << bit);
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  }
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  return z;
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}
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static int bool_error(BOOL_DECODER *br) {
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  /* Check if we have reached the end of the buffer.
   *
   * Variable 'count' stores the number of bits in the 'value' buffer, minus
   * 8. The top byte is part of the algorithm, and the remainder is buffered
   * to be shifted into it. So if count == 8, the top 16 bits of 'value' are
   * occupied, 8 for the algorithm and 8 in the buffer.
   *
   * When reading a byte from the user's buffer, count is filled with 8 and
   * one byte is filled into the value buffer. When we reach the end of the
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   * data, count is additionally filled with VP9_LOTS_OF_BITS. So when
   * count == VP9_LOTS_OF_BITS - 1, the user's data has been exhausted.
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   */
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  if ((br->count > VP9_BD_VALUE_SIZE) && (br->count < VP9_LOTS_OF_BITS)) {
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    /* We have tried to decode bits after the end of
     * stream was encountered.
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     */
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    return 1;
  }

  /* No error. */
  return 0;
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}
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extern int vp9_decode_unsigned_max(BOOL_DECODER *br, int max);

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#endif