зеркало из https://github.com/mozilla/gecko-dev.git
139 строки
3.7 KiB
C
139 строки
3.7 KiB
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.
|
|
*/
|
|
|
|
|
|
#ifndef DBOOLHUFF_H_
|
|
#define DBOOLHUFF_H_
|
|
|
|
#include <stddef.h>
|
|
#include <limits.h>
|
|
|
|
#include "vpx_config.h"
|
|
#include "vpx_ports/mem.h"
|
|
#include "vpx/vpx_integer.h"
|
|
|
|
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)
|
|
|
|
/*Decrypt n bytes of data from input -> output, using the decrypt_state
|
|
passed in VP8D_SET_DECRYPTOR.
|
|
*/
|
|
typedef void (vp8_decrypt_cb)(void *decrypt_state, const unsigned char *input,
|
|
unsigned char *output, int count);
|
|
|
|
typedef struct
|
|
{
|
|
const unsigned char *user_buffer_end;
|
|
const unsigned char *user_buffer;
|
|
VP8_BD_VALUE value;
|
|
int count;
|
|
unsigned int range;
|
|
vp8_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,
|
|
vp8_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;
|
|
}
|
|
|
|
#endif // DBOOLHUFF_H_
|