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 #ifndef VPX_VP8_DECODER_DBOOLHUFF_H_
12 #define VPX_VP8_DECODER_DBOOLHUFF_H_
13
14 #include <stddef.h>
15 #include <limits.h>
16
17 #include "./vpx_config.h"
18 #include "vpx_ports/compiler_attributes.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 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 vpx_decrypt_cb decrypt_cb;
43 void *decrypt_state;
44 } BOOL_DECODER;
45
46 DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]);
47
48 int vp8dx_start_decode(BOOL_DECODER *br, const unsigned char *source,
49 unsigned int source_sz, vpx_decrypt_cb decrypt_cb,
50 void *decrypt_state);
51
52 void vp8dx_bool_decoder_fill(BOOL_DECODER *br);
53
vp8dx_decode_bool(BOOL_DECODER * br,int probability)54 static VPX_NO_UNSIGNED_SHIFT_CHECK int vp8dx_decode_bool(BOOL_DECODER *br,
55 int probability) {
56 unsigned int bit = 0;
57 VP8_BD_VALUE value;
58 unsigned int split;
59 VP8_BD_VALUE bigsplit;
60 int count;
61 unsigned int range;
62
63 split = 1 + (((br->range - 1) * probability) >> 8);
64
65 if (br->count < 0) vp8dx_bool_decoder_fill(br);
66
67 value = br->value;
68 count = br->count;
69
70 bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);
71
72 range = split;
73
74 if (value >= bigsplit) {
75 range = br->range - split;
76 value = value - bigsplit;
77 bit = 1;
78 }
79
80 {
81 const unsigned char shift = vp8_norm[(unsigned char)range];
82 range <<= shift;
83 value <<= shift;
84 count -= shift;
85 }
86 br->value = value;
87 br->count = count;
88 br->range = range;
89
90 return bit;
91 }
92
vp8_decode_value(BOOL_DECODER * br,int bits)93 static INLINE int vp8_decode_value(BOOL_DECODER *br, int bits) {
94 int z = 0;
95 int bit;
96
97 for (bit = bits - 1; bit >= 0; bit--) {
98 z |= (vp8dx_decode_bool(br, 0x80) << bit);
99 }
100
101 return z;
102 }
103
vp8dx_bool_error(BOOL_DECODER * br)104 static INLINE int vp8dx_bool_error(BOOL_DECODER *br) {
105 /* Check if we have reached the end of the buffer.
106 *
107 * Variable 'count' stores the number of bits in the 'value' buffer, minus
108 * 8. The top byte is part of the algorithm, and the remainder is buffered
109 * to be shifted into it. So if count == 8, the top 16 bits of 'value' are
110 * occupied, 8 for the algorithm and 8 in the buffer.
111 *
112 * When reading a byte from the user's buffer, count is filled with 8 and
113 * one byte is filled into the value buffer. When we reach the end of the
114 * data, count is additionally filled with VP8_LOTS_OF_BITS. So when
115 * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
116 */
117 if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS)) {
118 /* We have tried to decode bits after the end of
119 * stream was encountered.
120 */
121 return 1;
122 }
123
124 /* No error. */
125 return 0;
126 }
127
128 #ifdef __cplusplus
129 } // extern "C"
130 #endif
131
132 #endif // VPX_VP8_DECODER_DBOOLHUFF_H_
133