1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
|
// Copyright 2010 Google Inc. All Rights Reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the COPYING file in the root of the source
// tree. An additional intellectual property rights grant can be found
// in the file PATENTS. All contributing project authors may
// be found in the AUTHORS file in the root of the source tree.
// -----------------------------------------------------------------------------
//
// Boolean decoder
//
// Author: Skal (pascal.massimino@gmail.com)
// Vikas Arora (vikaas.arora@gmail.com)
#ifndef WEBP_UTILS_BIT_READER_UTILS_H_
#define WEBP_UTILS_BIT_READER_UTILS_H_
#include <assert.h>
#ifdef _MSC_VER
#include <stdlib.h> // _byteswap_ulong
#endif
#include "src/webp/types.h"
#ifdef __cplusplus
extern "C" {
#endif
// The Boolean decoder needs to maintain infinite precision on the value_ field.
// However, since range_ is only 8bit, we only need an active window of 8 bits
// for value_. Left bits (MSB) gets zeroed and shifted away when value_ falls
// below 128, range_ is updated, and fresh bits read from the bitstream are
// brought in as LSB. To avoid reading the fresh bits one by one (slow), we
// cache BITS of them ahead. The total of (BITS + 8) bits must fit into a
// natural register (with type bit_t). To fetch BITS bits from bitstream we
// use a type lbit_t.
//
// BITS can be any multiple of 8 from 8 to 56 (inclusive).
// Pick values that fit natural register size.
#if defined(__i386__) || defined(_M_IX86) // x86 32bit
#define BITS 24
#elif defined(__x86_64__) || defined(_M_X64) // x86 64bit
#define BITS 56
#elif defined(__arm__) || defined(_M_ARM) // ARM
#define BITS 24
#elif defined(__aarch64__) // ARM 64bit
#define BITS 56
#elif defined(__mips__) // MIPS
#define BITS 24
#else // reasonable default
#define BITS 24
#endif
//------------------------------------------------------------------------------
// Derived types and constants:
// bit_t = natural register type for storing 'value_' (which is BITS+8 bits)
// range_t = register for 'range_' (which is 8bits only)
#if (BITS > 24)
typedef uint64_t bit_t;
#else
typedef uint32_t bit_t;
#endif
typedef uint32_t range_t;
//------------------------------------------------------------------------------
// Bitreader
typedef struct VP8BitReader VP8BitReader;
struct VP8BitReader {
// boolean decoder (keep the field ordering as is!)
bit_t value_; // current value
range_t range_; // current range minus 1. In [127, 254] interval.
int bits_; // number of valid bits left
// read buffer
const uint8_t* buf_; // next byte to be read
const uint8_t* buf_end_; // end of read buffer
const uint8_t* buf_max_; // max packed-read position on buffer
int eof_; // true if input is exhausted
};
// Initialize the bit reader and the boolean decoder.
void VP8InitBitReader(VP8BitReader* const br,
const uint8_t* const start, size_t size);
// Sets the working read buffer.
void VP8BitReaderSetBuffer(VP8BitReader* const br,
const uint8_t* const start, size_t size);
// Update internal pointers to displace the byte buffer by the
// relative offset 'offset'.
void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset);
// return the next value made of 'num_bits' bits
uint32_t VP8GetValue(VP8BitReader* const br, int num_bits);
static WEBP_INLINE uint32_t VP8Get(VP8BitReader* const br) {
return VP8GetValue(br, 1);
}
// return the next value with sign-extension.
int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits);
// bit_reader_inl.h will implement the following methods:
// static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob)
// static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v)
// and should be included by the .c files that actually need them.
// This is to avoid recompiling the whole library whenever this file is touched,
// and also allowing platform-specific ad-hoc hacks.
// -----------------------------------------------------------------------------
// Bitreader for lossless format
// maximum number of bits (inclusive) the bit-reader can handle:
#define VP8L_MAX_NUM_BIT_READ 24
#define VP8L_LBITS 64 // Number of bits prefetched (= bit-size of vp8l_val_t).
#define VP8L_WBITS 32 // Minimum number of bytes ready after VP8LFillBitWindow.
typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit.
typedef struct {
vp8l_val_t val_; // pre-fetched bits
const uint8_t* buf_; // input byte buffer
size_t len_; // buffer length
size_t pos_; // byte position in buf_
int bit_pos_; // current bit-reading position in val_
int eos_; // true if a bit was read past the end of buffer
} VP8LBitReader;
void VP8LInitBitReader(VP8LBitReader* const br,
const uint8_t* const start,
size_t length);
// Sets a new data buffer.
void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
const uint8_t* const buffer, size_t length);
// Reads the specified number of bits from read buffer.
// Flags an error in case end_of_stream or n_bits is more than the allowed limit
// of VP8L_MAX_NUM_BIT_READ (inclusive).
// Flags eos_ if this read attempt is going to cross the read buffer.
uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits);
// Return the prefetched bits, so they can be looked up.
static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) {
return (uint32_t)(br->val_ >> (br->bit_pos_ & (VP8L_LBITS - 1)));
}
// Returns true if there was an attempt at reading bit past the end of
// the buffer. Doesn't set br->eos_ flag.
static WEBP_INLINE int VP8LIsEndOfStream(const VP8LBitReader* const br) {
assert(br->pos_ <= br->len_);
return br->eos_ || ((br->pos_ == br->len_) && (br->bit_pos_ > VP8L_LBITS));
}
// For jumping over a number of bits in the bit stream when accessed with
// VP8LPrefetchBits and VP8LFillBitWindow.
// This function does *not* set br->eos_, since it's speed-critical.
// Use with extreme care!
static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) {
br->bit_pos_ = val;
}
// Advances the read buffer by 4 bytes to make room for reading next 32 bits.
// Speed critical, but infrequent part of the code can be non-inlined.
extern void VP8LDoFillBitWindow(VP8LBitReader* const br);
static WEBP_INLINE void VP8LFillBitWindow(VP8LBitReader* const br) {
if (br->bit_pos_ >= VP8L_WBITS) VP8LDoFillBitWindow(br);
}
#ifdef __cplusplus
} // extern "C"
#endif
#endif // WEBP_UTILS_BIT_READER_UTILS_H_
|
