1 // Copyright 2010 Google Inc. All Rights Reserved.
2 //
3 // Use of this source code is governed by a BSD-style license
4 // that can be found in the COPYING file in the root of the source
5 // tree. An additional intellectual property rights grant can be found
6 // in the file PATENTS. All contributing project authors may
7 // be found in the AUTHORS file in the root of the source tree.
8 // -----------------------------------------------------------------------------
9 //
10 // Boolean decoder
11 //
12 // Author: Skal ([email protected])
13 // Vikas Arora ([email protected])
14
15 #ifndef WEBP_UTILS_BIT_READER_UTILS_H_
16 #define WEBP_UTILS_BIT_READER_UTILS_H_
17
18 #include <assert.h>
19 #ifdef _MSC_VER
20 #include <stdlib.h> // _byteswap_ulong
21 #endif
22 #include "src/dsp/cpu.h"
23 #include "src/webp/types.h"
24
25 // Warning! This macro triggers quite some MACRO wizardry around func signature!
26 #if !defined(BITTRACE)
27 #define BITTRACE 0 // 0 = off, 1 = print bits, 2 = print bytes
28 #endif
29
30 #if (BITTRACE > 0)
31 struct VP8BitReader;
32 extern void BitTrace(const struct VP8BitReader* const br, const char label[]);
33 #define BT_TRACK(br) BitTrace(br, label)
34 #define VP8Get(BR, L) VP8GetValue(BR, 1, L)
35 #else
36 #define BT_TRACK(br)
37 // We'll REMOVE the 'const char label[]' from all signatures and calls (!!):
38 #define VP8GetValue(BR, N, L) VP8GetValue(BR, N)
39 #define VP8Get(BR, L) VP8GetValue(BR, 1, L)
40 #define VP8GetSignedValue(BR, N, L) VP8GetSignedValue(BR, N)
41 #define VP8GetBit(BR, P, L) VP8GetBit(BR, P)
42 #define VP8GetBitAlt(BR, P, L) VP8GetBitAlt(BR, P)
43 #define VP8GetSigned(BR, V, L) VP8GetSigned(BR, V)
44 #endif
45
46 #ifdef __cplusplus
47 extern "C" {
48 #endif
49
50 // The Boolean decoder needs to maintain infinite precision on the value_ field.
51 // However, since range_ is only 8bit, we only need an active window of 8 bits
52 // for value_. Left bits (MSB) gets zeroed and shifted away when value_ falls
53 // below 128, range_ is updated, and fresh bits read from the bitstream are
54 // brought in as LSB. To avoid reading the fresh bits one by one (slow), we
55 // cache BITS of them ahead. The total of (BITS + 8) bits must fit into a
56 // natural register (with type bit_t). To fetch BITS bits from bitstream we
57 // use a type lbit_t.
58 //
59 // BITS can be any multiple of 8 from 8 to 56 (inclusive).
60 // Pick values that fit natural register size.
61
62 #if defined(__i386__) || defined(_M_IX86) // x86 32bit
63 #define BITS 24
64 #elif defined(__x86_64__) || defined(_M_X64) // x86 64bit
65 #define BITS 56
66 #elif defined(__arm__) || defined(_M_ARM) // ARM
67 #define BITS 24
68 #elif WEBP_AARCH64 // ARM 64bit
69 #define BITS 56
70 #elif defined(__mips__) // MIPS
71 #define BITS 24
72 #else // reasonable default
73 #define BITS 24
74 #endif
75
76 //------------------------------------------------------------------------------
77 // Derived types and constants:
78 // bit_t = natural register type for storing 'value_' (which is BITS+8 bits)
79 // range_t = register for 'range_' (which is 8bits only)
80
81 #if (BITS > 24)
82 typedef uint64_t bit_t;
83 #else
84 typedef uint32_t bit_t;
85 #endif
86
87 typedef uint32_t range_t;
88
89 //------------------------------------------------------------------------------
90 // Bitreader
91
92 typedef struct VP8BitReader VP8BitReader;
93 struct VP8BitReader {
94 // boolean decoder (keep the field ordering as is!)
95 bit_t value_; // current value
96 range_t range_; // current range minus 1. In [127, 254] interval.
97 int bits_; // number of valid bits left
98 // read buffer
99 const uint8_t* buf_; // next byte to be read
100 const uint8_t* buf_end_; // end of read buffer
101 const uint8_t* buf_max_; // max packed-read position on buffer
102 int eof_; // true if input is exhausted
103 };
104
105 // Initialize the bit reader and the boolean decoder.
106 void VP8InitBitReader(VP8BitReader* const br,
107 const uint8_t* const start, size_t size);
108 // Sets the working read buffer.
109 void VP8BitReaderSetBuffer(VP8BitReader* const br,
110 const uint8_t* const start, size_t size);
111
112 // Update internal pointers to displace the byte buffer by the
113 // relative offset 'offset'.
114 void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset);
115
116 // return the next value made of 'num_bits' bits
117 uint32_t VP8GetValue(VP8BitReader* const br, int num_bits, const char label[]);
118
119 // return the next value with sign-extension.
120 int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits,
121 const char label[]);
122
123 // bit_reader_inl.h will implement the following methods:
124 // static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob, ...)
125 // static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v, ...)
126 // and should be included by the .c files that actually need them.
127 // This is to avoid recompiling the whole library whenever this file is touched,
128 // and also allowing platform-specific ad-hoc hacks.
129
130 // -----------------------------------------------------------------------------
131 // Bitreader for lossless format
132
133 // maximum number of bits (inclusive) the bit-reader can handle:
134 #define VP8L_MAX_NUM_BIT_READ 24
135
136 #define VP8L_LBITS 64 // Number of bits prefetched (= bit-size of vp8l_val_t).
137 #define VP8L_WBITS 32 // Minimum number of bytes ready after VP8LFillBitWindow.
138
139 typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit.
140
141 typedef struct {
142 vp8l_val_t val_; // pre-fetched bits
143 const uint8_t* buf_; // input byte buffer
144 size_t len_; // buffer length
145 size_t pos_; // byte position in buf_
146 int bit_pos_; // current bit-reading position in val_
147 int eos_; // true if a bit was read past the end of buffer
148 } VP8LBitReader;
149
150 void VP8LInitBitReader(VP8LBitReader* const br,
151 const uint8_t* const start,
152 size_t length);
153
154 // Sets a new data buffer.
155 void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
156 const uint8_t* const buffer, size_t length);
157
158 // Reads the specified number of bits from read buffer.
159 // Flags an error in case end_of_stream or n_bits is more than the allowed limit
160 // of VP8L_MAX_NUM_BIT_READ (inclusive).
161 // Flags eos_ if this read attempt is going to cross the read buffer.
162 uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits);
163
164 // Return the prefetched bits, so they can be looked up.
VP8LPrefetchBits(VP8LBitReader * const br)165 static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) {
166 return (uint32_t)(br->val_ >> (br->bit_pos_ & (VP8L_LBITS - 1)));
167 }
168
169 // Returns true if there was an attempt at reading bit past the end of
170 // the buffer. Doesn't set br->eos_ flag.
VP8LIsEndOfStream(const VP8LBitReader * const br)171 static WEBP_INLINE int VP8LIsEndOfStream(const VP8LBitReader* const br) {
172 assert(br->pos_ <= br->len_);
173 return br->eos_ || ((br->pos_ == br->len_) && (br->bit_pos_ > VP8L_LBITS));
174 }
175
176 // For jumping over a number of bits in the bit stream when accessed with
177 // VP8LPrefetchBits and VP8LFillBitWindow.
178 // This function does *not* set br->eos_, since it's speed-critical.
179 // Use with extreme care!
VP8LSetBitPos(VP8LBitReader * const br,int val)180 static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) {
181 br->bit_pos_ = val;
182 }
183
184 // Advances the read buffer by 4 bytes to make room for reading next 32 bits.
185 // Speed critical, but infrequent part of the code can be non-inlined.
186 extern void VP8LDoFillBitWindow(VP8LBitReader* const br);
VP8LFillBitWindow(VP8LBitReader * const br)187 static WEBP_INLINE void VP8LFillBitWindow(VP8LBitReader* const br) {
188 if (br->bit_pos_ >= VP8L_WBITS) VP8LDoFillBitWindow(br);
189 }
190
191 #ifdef __cplusplus
192 } // extern "C"
193 #endif
194
195 #endif // WEBP_UTILS_BIT_READER_UTILS_H_
196