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_VPX_DSP_BITREADER_H_
12 #define VPX_VPX_DSP_BITREADER_H_
13
14 #include <stddef.h>
15 #include <stdio.h>
16 #include <limits.h>
17
18 #include "./vpx_config.h"
19 #include "vpx_ports/mem.h"
20 #include "vpx/vp8dx.h"
21 #include "vpx/vpx_integer.h"
22 #include "vpx_dsp/prob.h"
23 #if CONFIG_BITSTREAM_DEBUG
24 #include "vpx_util/vpx_debug_util.h"
25 #endif // CONFIG_BITSTREAM_DEBUG
26
27 #ifdef __cplusplus
28 extern "C" {
29 #endif
30
31 typedef size_t BD_VALUE;
32
33 #define BD_VALUE_SIZE ((int)sizeof(BD_VALUE) * CHAR_BIT)
34
35 // This is meant to be a large, positive constant that can still be efficiently
36 // loaded as an immediate (on platforms like ARM, for example).
37 // Even relatively modest values like 100 would work fine.
38 #define LOTS_OF_BITS 0x40000000
39
40 typedef struct {
41 // Be careful when reordering this struct, it may impact the cache negatively.
42 BD_VALUE value;
43 unsigned int range;
44 int count;
45 const uint8_t *buffer_end;
46 const uint8_t *buffer;
47 vpx_decrypt_cb decrypt_cb;
48 void *decrypt_state;
49 uint8_t clear_buffer[sizeof(BD_VALUE) + 1];
50 } vpx_reader;
51
52 int vpx_reader_init(vpx_reader *r, const uint8_t *buffer, size_t size,
53 vpx_decrypt_cb decrypt_cb, void *decrypt_state);
54
55 void vpx_reader_fill(vpx_reader *r);
56
57 const uint8_t *vpx_reader_find_end(vpx_reader *r);
58
vpx_reader_has_error(vpx_reader * r)59 static INLINE int vpx_reader_has_error(vpx_reader *r) {
60 // Check if we have reached the end of the buffer.
61 //
62 // Variable 'count' stores the number of bits in the 'value' buffer, minus
63 // 8. The top byte is part of the algorithm, and the remainder is buffered
64 // to be shifted into it. So if count == 8, the top 16 bits of 'value' are
65 // occupied, 8 for the algorithm and 8 in the buffer.
66 //
67 // When reading a byte from the user's buffer, count is filled with 8 and
68 // one byte is filled into the value buffer. When we reach the end of the
69 // data, count is additionally filled with LOTS_OF_BITS. So when
70 // count == LOTS_OF_BITS - 1, the user's data has been exhausted.
71 //
72 // 1 if we have tried to decode bits after the end of stream was encountered.
73 // 0 No error.
74 return r->count > BD_VALUE_SIZE && r->count < LOTS_OF_BITS;
75 }
76
vpx_read(vpx_reader * r,int prob)77 static INLINE int vpx_read(vpx_reader *r, int prob) {
78 unsigned int bit = 0;
79 BD_VALUE value;
80 BD_VALUE bigsplit;
81 int count;
82 unsigned int range;
83 unsigned int split = (r->range * prob + (256 - prob)) >> CHAR_BIT;
84
85 if (r->count < 0) 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 const unsigned char shift = vpx_norm[(unsigned char)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 #if CONFIG_BITSTREAM_DEBUG
111 {
112 const int queue_r = bitstream_queue_get_read();
113 const int frame_idx = bitstream_queue_get_frame_read();
114 int ref_result, ref_prob;
115 bitstream_queue_pop(&ref_result, &ref_prob);
116 if ((int)bit != ref_result) {
117 fprintf(stderr,
118 "\n *** [bit] result error, frame_idx_r %d bit %d ref_result %d "
119 "queue_r %d\n",
120 frame_idx, bit, ref_result, queue_r);
121
122 assert(0);
123 }
124 if (prob != ref_prob) {
125 fprintf(stderr,
126 "\n *** [bit] prob error, frame_idx_r %d prob %d ref_prob %d "
127 "queue_r %d\n",
128 frame_idx, prob, ref_prob, queue_r);
129
130 assert(0);
131 }
132 }
133 #endif
134
135 return bit;
136 }
137
vpx_read_bit(vpx_reader * r)138 static INLINE int vpx_read_bit(vpx_reader *r) {
139 return vpx_read(r, 128); // vpx_prob_half
140 }
141
vpx_read_literal(vpx_reader * r,int bits)142 static INLINE int vpx_read_literal(vpx_reader *r, int bits) {
143 int literal = 0, bit;
144
145 for (bit = bits - 1; bit >= 0; bit--) literal |= vpx_read_bit(r) << bit;
146
147 return literal;
148 }
149
vpx_read_tree(vpx_reader * r,const vpx_tree_index * tree,const vpx_prob * probs)150 static INLINE int vpx_read_tree(vpx_reader *r, const vpx_tree_index *tree,
151 const vpx_prob *probs) {
152 vpx_tree_index i = 0;
153
154 while ((i = tree[i + vpx_read(r, probs[i >> 1])]) > 0) continue;
155
156 return -i;
157 }
158
159 #ifdef __cplusplus
160 } // extern "C"
161 #endif
162
163 #endif // VPX_VPX_DSP_BITREADER_H_
164