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