1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
|
/*
* 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 int shift = vp8_norm[range];
range <<= shift;
value <<= shift;
count -= shift;
}
br->value = value;
br->count = count;
br->range = range;
return bit;
}
static INLINE 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 INLINE 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_
|