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 VP8_DECODER_DBOOLHUFF_H_
13#define VP8_DECODER_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/vp8dx.h"
21#include "vpx/vpx_integer.h"
22
23#ifdef __cplusplus
24extern "C" {
25#endif
26
27typedef 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
36typedef struct
37{
38    const unsigned char *user_buffer_end;
39    const unsigned char *user_buffer;
40    VP8_BD_VALUE         value;
41    int                  count;
42    unsigned int         range;
43    vpx_decrypt_cb       decrypt_cb;
44    void                *decrypt_state;
45} BOOL_DECODER;
46
47DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]);
48
49int vp8dx_start_decode(BOOL_DECODER *br,
50                       const unsigned char *source,
51                       unsigned int source_sz,
52                       vpx_decrypt_cb decrypt_cb,
53                       void *decrypt_state);
54
55void vp8dx_bool_decoder_fill(BOOL_DECODER *br);
56
57
58static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {
59    unsigned int bit = 0;
60    VP8_BD_VALUE value;
61    unsigned int split;
62    VP8_BD_VALUE bigsplit;
63    int count;
64    unsigned int range;
65
66    split = 1 + (((br->range - 1) * probability) >> 8);
67
68    if(br->count < 0)
69        vp8dx_bool_decoder_fill(br);
70
71    value = br->value;
72    count = br->count;
73
74    bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);
75
76    range = split;
77
78    if (value >= bigsplit)
79    {
80        range = br->range - split;
81        value = value - bigsplit;
82        bit = 1;
83    }
84
85    {
86        register unsigned int shift = vp8_norm[range];
87        range <<= shift;
88        value <<= shift;
89        count -= shift;
90    }
91    br->value = value;
92    br->count = count;
93    br->range = range;
94
95    return bit;
96}
97
98static int vp8_decode_value(BOOL_DECODER *br, int bits)
99{
100    int z = 0;
101    int bit;
102
103    for (bit = bits - 1; bit >= 0; bit--)
104    {
105        z |= (vp8dx_decode_bool(br, 0x80) << bit);
106    }
107
108    return z;
109}
110
111static int vp8dx_bool_error(BOOL_DECODER *br)
112{
113    /* Check if we have reached the end of the buffer.
114     *
115     * Variable 'count' stores the number of bits in the 'value' buffer, minus
116     * 8. The top byte is part of the algorithm, and the remainder is buffered
117     * to be shifted into it. So if count == 8, the top 16 bits of 'value' are
118     * occupied, 8 for the algorithm and 8 in the buffer.
119     *
120     * When reading a byte from the user's buffer, count is filled with 8 and
121     * one byte is filled into the value buffer. When we reach the end of the
122     * data, count is additionally filled with VP8_LOTS_OF_BITS. So when
123     * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
124     */
125    if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS))
126    {
127       /* We have tried to decode bits after the end of
128        * stream was encountered.
129        */
130        return 1;
131    }
132
133    /* No error. */
134    return 0;
135}
136
137#ifdef __cplusplus
138}  // extern "C"
139#endif
140
141#endif  // VP8_DECODER_DBOOLHUFF_H_
142