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_DSP_BITREADER_H_
12 #define VPX_DSP_BITREADER_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 #include "vpx_dsp/prob.h"
22
23 #ifdef __cplusplus
24 extern "C" {
25 #endif
26
27 typedef size_t BD_VALUE;
28
29 #define BD_VALUE_SIZE ((int)sizeof(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 LOTS_OF_BITS 0x40000000
35
36 typedef struct {
37 // Be careful when reordering this struct, it may impact the cache negatively.
38 BD_VALUE value;
39 unsigned int range;
40 int count;
41 const uint8_t *buffer_end;
42 const uint8_t *buffer;
43 vpx_decrypt_cb decrypt_cb;
44 void *decrypt_state;
45 uint8_t clear_buffer[sizeof(BD_VALUE) + 1];
46 } vpx_reader;
47
48 int vpx_reader_init(vpx_reader *r,
49 const uint8_t *buffer,
50 size_t size,
51 vpx_decrypt_cb decrypt_cb,
52 void *decrypt_state);
53
54 void vpx_reader_fill(vpx_reader *r);
55
56 const uint8_t *vpx_reader_find_end(vpx_reader *r);
57
vpx_reader_has_error(vpx_reader * r)58 static INLINE int vpx_reader_has_error(vpx_reader *r) {
59 // Check if we have reached the end of the buffer.
60 //
61 // Variable 'count' stores the number of bits in the 'value' buffer, minus
62 // 8. The top byte is part of the algorithm, and the remainder is buffered
63 // to be shifted into it. So if count == 8, the top 16 bits of 'value' are
64 // occupied, 8 for the algorithm and 8 in the buffer.
65 //
66 // When reading a byte from the user's buffer, count is filled with 8 and
67 // one byte is filled into the value buffer. When we reach the end of the
68 // data, count is additionally filled with LOTS_OF_BITS. So when
69 // count == LOTS_OF_BITS - 1, the user's data has been exhausted.
70 //
71 // 1 if we have tried to decode bits after the end of stream was encountered.
72 // 0 No error.
73 return r->count > BD_VALUE_SIZE && r->count < LOTS_OF_BITS;
74 }
75
vpx_read(vpx_reader * r,int prob)76 static INLINE int vpx_read(vpx_reader *r, int prob) {
77 unsigned int bit = 0;
78 BD_VALUE value;
79 BD_VALUE bigsplit;
80 int count;
81 unsigned int range;
82 unsigned int split = (r->range * prob + (256 - prob)) >> CHAR_BIT;
83
84 if (r->count < 0)
85 vpx_reader_fill(r);
86
87 value = r->value;
88 count = r->count;
89
90 bigsplit = (BD_VALUE)split << (BD_VALUE_SIZE - CHAR_BIT);
91
92 range = split;
93
94 if (value >= bigsplit) {
95 range = r->range - split;
96 value = value - bigsplit;
97 bit = 1;
98 }
99
100 {
101 register unsigned int shift = vpx_norm[range];
102 range <<= shift;
103 value <<= shift;
104 count -= shift;
105 }
106 r->value = value;
107 r->count = count;
108 r->range = range;
109
110 return bit;
111 }
112
vpx_read_bit(vpx_reader * r)113 static INLINE int vpx_read_bit(vpx_reader *r) {
114 return vpx_read(r, 128); // vpx_prob_half
115 }
116
vpx_read_literal(vpx_reader * r,int bits)117 static INLINE int vpx_read_literal(vpx_reader *r, int bits) {
118 int literal = 0, bit;
119
120 for (bit = bits - 1; bit >= 0; bit--)
121 literal |= vpx_read_bit(r) << bit;
122
123 return literal;
124 }
125
vpx_read_tree(vpx_reader * r,const vpx_tree_index * tree,const vpx_prob * probs)126 static INLINE int vpx_read_tree(vpx_reader *r, const vpx_tree_index *tree,
127 const vpx_prob *probs) {
128 vpx_tree_index i = 0;
129
130 while ((i = tree[i + vpx_read(r, probs[i >> 1])]) > 0)
131 continue;
132
133 return -i;
134 }
135
136 #ifdef __cplusplus
137 } // extern "C"
138 #endif
139
140 #endif // VPX_DSP_BITREADER_H_
141