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/mem.h"
19 #include "vpx/vp8dx.h"
20 #include "vpx/vpx_integer.h"
21
22 #ifdef __cplusplus
23 extern "C" {
24 #endif
25
26 typedef size_t VP8_BD_VALUE;
27
28 #define VP8_BD_VALUE_SIZE ((int)sizeof(VP8_BD_VALUE) * CHAR_BIT)
29
30 /*This is meant to be a large, positive constant that can still be efficiently
31 loaded as an immediate (on platforms like ARM, for example).
32 Even relatively modest values like 100 would work fine.*/
33 #define VP8_LOTS_OF_BITS (0x40000000)
34
35 typedef struct {
36 const unsigned char *user_buffer_end;
37 const unsigned char *user_buffer;
38 VP8_BD_VALUE value;
39 int count;
40 unsigned int range;
41 vpx_decrypt_cb decrypt_cb;
42 void *decrypt_state;
43 } BOOL_DECODER;
44
45 DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]);
46
47 int vp8dx_start_decode(BOOL_DECODER *br, const unsigned char *source,
48 unsigned int source_sz, vpx_decrypt_cb decrypt_cb,
49 void *decrypt_state);
50
51 void vp8dx_bool_decoder_fill(BOOL_DECODER *br);
52
vp8dx_decode_bool(BOOL_DECODER * br,int probability)53 static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {
54 unsigned int bit = 0;
55 VP8_BD_VALUE value;
56 unsigned int split;
57 VP8_BD_VALUE bigsplit;
58 int count;
59 unsigned int range;
60
61 split = 1 + (((br->range - 1) * probability) >> 8);
62
63 if (br->count < 0) vp8dx_bool_decoder_fill(br);
64
65 value = br->value;
66 count = br->count;
67
68 bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);
69
70 range = split;
71
72 if (value >= bigsplit) {
73 range = br->range - split;
74 value = value - bigsplit;
75 bit = 1;
76 }
77
78 {
79 const unsigned char shift = vp8_norm[(unsigned char)range];
80 range <<= shift;
81 value <<= shift;
82 count -= shift;
83 }
84 br->value = value;
85 br->count = count;
86 br->range = range;
87
88 return bit;
89 }
90
vp8_decode_value(BOOL_DECODER * br,int bits)91 static INLINE int vp8_decode_value(BOOL_DECODER *br, int bits) {
92 int z = 0;
93 int bit;
94
95 for (bit = bits - 1; bit >= 0; bit--) {
96 z |= (vp8dx_decode_bool(br, 0x80) << bit);
97 }
98
99 return z;
100 }
101
vp8dx_bool_error(BOOL_DECODER * br)102 static INLINE int vp8dx_bool_error(BOOL_DECODER *br) {
103 /* Check if we have reached the end of the buffer.
104 *
105 * Variable 'count' stores the number of bits in the 'value' buffer, minus
106 * 8. The top byte is part of the algorithm, and the remainder is buffered
107 * to be shifted into it. So if count == 8, the top 16 bits of 'value' are
108 * occupied, 8 for the algorithm and 8 in the buffer.
109 *
110 * When reading a byte from the user's buffer, count is filled with 8 and
111 * one byte is filled into the value buffer. When we reach the end of the
112 * data, count is additionally filled with VP8_LOTS_OF_BITS. So when
113 * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
114 */
115 if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS)) {
116 /* We have tried to decode bits after the end of
117 * stream was encountered.
118 */
119 return 1;
120 }
121
122 /* No error. */
123 return 0;
124 }
125
126 #ifdef __cplusplus
127 } // extern "C"
128 #endif
129
130 #endif // VPX_VP8_DECODER_DBOOLHUFF_H_
131