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/*
* 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.
*/
#ifndef VP8_DECODER_DBOOLHUFF_H_
#define VP8_DECODER_DBOOLHUFF_H_
#include <stddef.h>
#include <limits.h>
#include "vpx_config.h"
#include "vpx_ports/mem.h"
#include "vpx/vp8dx.h"
#include "vpx/vpx_integer.h"
#ifdef __cplusplus
extern "C" {
#endif
typedef size_t VP8_BD_VALUE;
#define VP8_BD_VALUE_SIZE ((int)sizeof(VP8_BD_VALUE)*CHAR_BIT)
/*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.*/
#define VP8_LOTS_OF_BITS (0x40000000)
typedef struct
{
const unsigned char *user_buffer_end;
const unsigned char *user_buffer;
VP8_BD_VALUE value;
int count;
unsigned int range;
vpx_decrypt_cb decrypt_cb;
void *decrypt_state;
} BOOL_DECODER;
DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]);
int vp8dx_start_decode(BOOL_DECODER *br,
const unsigned char *source,
unsigned int source_sz,
vpx_decrypt_cb decrypt_cb,
void *decrypt_state);
void vp8dx_bool_decoder_fill(BOOL_DECODER *br);
static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {
unsigned int bit = 0;
VP8_BD_VALUE value;
unsigned int split;
VP8_BD_VALUE bigsplit;
int count;
unsigned int range;
split = 1 + (((br->range - 1) * probability) >> 8);
if(br->count < 0)
vp8dx_bool_decoder_fill(br);
value = br->value;
count = br->count;
bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);
range = split;
if (value >= bigsplit)
{
range = br->range - split;
value = value - bigsplit;
bit = 1;
}
{
register unsigned int shift = vp8_norm[range];
range <<= shift;
value <<= shift;
count -= shift;
}
br->value = value;
br->count = count;
br->range = range;
return bit;
}
static int vp8_decode_value(BOOL_DECODER *br, int bits)
{
int z = 0;
int bit;
for (bit = bits - 1; bit >= 0; bit--)
{
z |= (vp8dx_decode_bool(br, 0x80) << bit);
}
return z;
}
static int vp8dx_bool_error(BOOL_DECODER *br)
{
/* 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
* data, count is additionally filled with VP8_LOTS_OF_BITS. So when
* count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
*/
if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS))
{
/* We have tried to decode bits after the end of
* stream was encountered.
*/
return 1;
}
/* No error. */
return 0;
}
#ifdef __cplusplus
} // extern "C"
#endif
#endif // VP8_DECODER_DBOOLHUFF_H_
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