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/vpx_integer.h"
21
22#ifdef __cplusplus
23extern "C" {
24#endif
25
26typedef 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/*Decrypt n bytes of data from input -> output, using the decrypt_state
36   passed in VP8D_SET_DECRYPTOR.
37*/
38typedef void (vp8_decrypt_cb)(void *decrypt_state, const unsigned char *input,
39                              unsigned char *output, int count);
40
41typedef struct
42{
43    const unsigned char *user_buffer_end;
44    const unsigned char *user_buffer;
45    VP8_BD_VALUE         value;
46    int                  count;
47    unsigned int         range;
48    vp8_decrypt_cb      *decrypt_cb;
49    void                *decrypt_state;
50} BOOL_DECODER;
51
52DECLARE_ALIGNED(16, extern const unsigned char, vp8_norm[256]);
53
54int vp8dx_start_decode(BOOL_DECODER *br,
55                       const unsigned char *source,
56                       unsigned int source_sz,
57                       vp8_decrypt_cb *decrypt_cb,
58                       void *decrypt_state);
59
60void vp8dx_bool_decoder_fill(BOOL_DECODER *br);
61
62
63static int vp8dx_decode_bool(BOOL_DECODER *br, int probability) {
64    unsigned int bit = 0;
65    VP8_BD_VALUE value;
66    unsigned int split;
67    VP8_BD_VALUE bigsplit;
68    int count;
69    unsigned int range;
70
71    split = 1 + (((br->range - 1) * probability) >> 8);
72
73    if(br->count < 0)
74        vp8dx_bool_decoder_fill(br);
75
76    value = br->value;
77    count = br->count;
78
79    bigsplit = (VP8_BD_VALUE)split << (VP8_BD_VALUE_SIZE - 8);
80
81    range = split;
82
83    if (value >= bigsplit)
84    {
85        range = br->range - split;
86        value = value - bigsplit;
87        bit = 1;
88    }
89
90    {
91        register unsigned int shift = vp8_norm[range];
92        range <<= shift;
93        value <<= shift;
94        count -= shift;
95    }
96    br->value = value;
97    br->count = count;
98    br->range = range;
99
100    return bit;
101}
102
103static int vp8_decode_value(BOOL_DECODER *br, int bits)
104{
105    int z = 0;
106    int bit;
107
108    for (bit = bits - 1; bit >= 0; bit--)
109    {
110        z |= (vp8dx_decode_bool(br, 0x80) << bit);
111    }
112
113    return z;
114}
115
116static int vp8dx_bool_error(BOOL_DECODER *br)
117{
118    /* Check if we have reached the end of the buffer.
119     *
120     * Variable 'count' stores the number of bits in the 'value' buffer, minus
121     * 8. The top byte is part of the algorithm, and the remainder is buffered
122     * to be shifted into it. So if count == 8, the top 16 bits of 'value' are
123     * occupied, 8 for the algorithm and 8 in the buffer.
124     *
125     * When reading a byte from the user's buffer, count is filled with 8 and
126     * one byte is filled into the value buffer. When we reach the end of the
127     * data, count is additionally filled with VP8_LOTS_OF_BITS. So when
128     * count == VP8_LOTS_OF_BITS - 1, the user's data has been exhausted.
129     */
130    if ((br->count > VP8_BD_VALUE_SIZE) && (br->count < VP8_LOTS_OF_BITS))
131    {
132       /* We have tried to decode bits after the end of
133        * stream was encountered.
134        */
135        return 1;
136    }
137
138    /* No error. */
139    return 0;
140}
141
142#ifdef __cplusplus
143}  // extern "C"
144#endif
145
146#endif  // VP8_DECODER_DBOOLHUFF_H_
147