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 DBOOLHUFF_H_
13 #define DBOOLHUFF_H_
14
15 #include <stdint.h>
16 #include <stddef.h>
17 #include <limits.h>
18 #include <glib.h>
19
20 typedef size_t VP8_BD_VALUE;
21
22 #define VP8_BD_VALUE_SIZE ((int)sizeof(VP8_BD_VALUE)*CHAR_BIT)
23
24 /*This is meant to be a large, positive constant that can still be efficiently
25 loaded as an immediate (on platforms like ARM, for example).
26 Even relatively modest values like 100 would work fine.*/
27 #define VP8_LOTS_OF_BITS (0x40000000)
28
29 /*Decrypt n bytes of data from input -> output, using the decrypt_state
30 passed in VP8D_SET_DECRYPTOR.
31 */
32 typedef void (vp8_decrypt_cb)(void *decrypt_state, const unsigned char *input,
33 unsigned char *output, int count);
34
35 typedef struct
36 {
37 const unsigned char *user_buffer_end;
38 const unsigned char *user_buffer;
39 VP8_BD_VALUE value;
40 int count;
41 unsigned int range;
42 vp8_decrypt_cb *decrypt_cb;
43 void *decrypt_state;
44 } BOOL_DECODER;
45
46 G_GNUC_INTERNAL
47 extern const unsigned char vp8_norm[256];
48
49 G_GNUC_INTERNAL
50 int vp8dx_start_decode(BOOL_DECODER *br,
51 const unsigned char *source,
52 unsigned int source_sz,
53 vp8_decrypt_cb *decrypt_cb,
54 void *decrypt_state);
55
56 G_GNUC_INTERNAL
57 void vp8dx_bool_decoder_fill(BOOL_DECODER *br);
58
59
vp8dx_decode_bool(BOOL_DECODER * br,int probability)60 static inline int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {
61 unsigned int bit = 0;
62 VP8_BD_VALUE value;
63 unsigned int split;
64 VP8_BD_VALUE bigsplit;
65 int count;
66 unsigned int range;
67
68 split = 1 + (((br->range - 1) * probability) >> 8);
69
70 if(br->count < 0)
71 vp8dx_bool_decoder_fill(br);
72
73 value = br->value;
74 count = br->count;
75
76 bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);
77
78 range = split;
79
80 if (value >= bigsplit)
81 {
82 range = br->range - split;
83 value = value - bigsplit;
84 bit = 1;
85 }
86
87 {
88 register unsigned int shift = vp8_norm[range];
89 range <<= shift;
90 value <<= shift;
91 count -= shift;
92 }
93 br->value = value;
94 br->count = count;
95 br->range = range;
96
97 return bit;
98 }
99
vp8_decode_value(BOOL_DECODER * br,int bits)100 static inline int vp8_decode_value(BOOL_DECODER *br, int bits)
101 {
102 int z = 0;
103 int bit;
104
105 for (bit = bits - 1; bit >= 0; bit--)
106 {
107 z |= (vp8dx_decode_bool(br, 0x80) << bit);
108 }
109
110 return z;
111 }
112
vp8dx_bool_error(BOOL_DECODER * br)113 static inline int vp8dx_bool_error(BOOL_DECODER *br)
114 {
115 /* Check if we have reached the end of the buffer.
116 *
117 * Variable 'count' stores the number of bits in the 'value' buffer, minus
118 * 8. The top byte is part of the algorithm, and the remainder is buffered
119 * to be shifted into it. So if count == 8, the top 16 bits of 'value' are
120 * occupied, 8 for the algorithm and 8 in the buffer.
121 *
122 * When reading a byte from the user's buffer, count is filled with 8 and
123 * one byte is filled into the value buffer. When we reach the end of the
124 * data, count is additionally filled with VP8_LOTS_OF_BITS. So when
125 * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
126 */
127 if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS))
128 {
129 /* We have tried to decode bits after the end of
130 * stream was encountered.
131 */
132 return 1;
133 }
134
135 /* No error. */
136 return 0;
137 }
138
139 #endif // DBOOLHUFF_H_
140