1 /*
2 * Copyright (c) 2010 The WebM project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11
12 #ifndef VP8_DECODER_DBOOLHUFF_H_
13 #define VP8_DECODER_DBOOLHUFF_H_
14
15 #include <stddef.h>
16 #include <limits.h>
17
18 #include "./vpx_config.h"
19 #include "vpx_ports/mem.h"
20 #include "vpx/vp8dx.h"
21 #include "vpx/vpx_integer.h"
22
23 #ifdef __cplusplus
24 extern "C" {
25 #endif
26
27 typedef size_t VP8_BD_VALUE;
28
29 #define VP8_BD_VALUE_SIZE ((int)sizeof(VP8_BD_VALUE)*CHAR_BIT)
30
31 /*This is meant to be a large, positive constant that can still be efficiently
32 loaded as an immediate (on platforms like ARM, for example).
33 Even relatively modest values like 100 would work fine.*/
34 #define VP8_LOTS_OF_BITS (0x40000000)
35
36 typedef struct
37 {
38 const unsigned char *user_buffer_end;
39 const unsigned char *user_buffer;
40 VP8_BD_VALUE value;
41 int count;
42 unsigned int range;
43 vpx_decrypt_cb decrypt_cb;
44 void *decrypt_state;
45 } BOOL_DECODER;
46
47 DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]);
48
49 int vp8dx_start_decode(BOOL_DECODER *br,
50 const unsigned char *source,
51 unsigned int source_sz,
52 vpx_decrypt_cb decrypt_cb,
53 void *decrypt_state);
54
55 void vp8dx_bool_decoder_fill(BOOL_DECODER *br);
56
57
vp8dx_decode_bool(BOOL_DECODER * br,int probability)58 static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {
59 unsigned int bit = 0;
60 VP8_BD_VALUE value;
61 unsigned int split;
62 VP8_BD_VALUE bigsplit;
63 int count;
64 unsigned int range;
65
66 split = 1 + (((br->range - 1) * probability) >> 8);
67
68 if(br->count < 0)
69 vp8dx_bool_decoder_fill(br);
70
71 value = br->value;
72 count = br->count;
73
74 bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);
75
76 range = split;
77
78 if (value >= bigsplit)
79 {
80 range = br->range - split;
81 value = value - bigsplit;
82 bit = 1;
83 }
84
85 {
86 register int shift = vp8_norm[range];
87 range <<= shift;
88 value <<= shift;
89 count -= shift;
90 }
91 br->value = value;
92 br->count = count;
93 br->range = range;
94
95 return bit;
96 }
97
vp8_decode_value(BOOL_DECODER * br,int bits)98 static INLINE int vp8_decode_value(BOOL_DECODER *br, int bits)
99 {
100 int z = 0;
101 int bit;
102
103 for (bit = bits - 1; bit >= 0; bit--)
104 {
105 z |= (vp8dx_decode_bool(br, 0x80) << bit);
106 }
107
108 return z;
109 }
110
vp8dx_bool_error(BOOL_DECODER * br)111 static INLINE int vp8dx_bool_error(BOOL_DECODER *br)
112 {
113 /* Check if we have reached the end of the buffer.
114 *
115 * Variable 'count' stores the number of bits in the 'value' buffer, minus
116 * 8. The top byte is part of the algorithm, and the remainder is buffered
117 * to be shifted into it. So if count == 8, the top 16 bits of 'value' are
118 * occupied, 8 for the algorithm and 8 in the buffer.
119 *
120 * When reading a byte from the user's buffer, count is filled with 8 and
121 * one byte is filled into the value buffer. When we reach the end of the
122 * data, count is additionally filled with VP8_LOTS_OF_BITS. So when
123 * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
124 */
125 if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS))
126 {
127 /* We have tried to decode bits after the end of
128 * stream was encountered.
129 */
130 return 1;
131 }
132
133 /* No error. */
134 return 0;
135 }
136
137 #ifdef __cplusplus
138 } // extern "C"
139 #endif
140
141 #endif // VP8_DECODER_DBOOLHUFF_H_
142