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 (pascal.massimino@gmail.com)
13 // Vikas Arora (vikaas.arora@gmail.com)
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 #elif defined(__wasm__) // WASM
73 #define BITS 56
74 #else // reasonable default
75 #define BITS 24
76 #endif
77
78 //------------------------------------------------------------------------------
79 // Derived types and constants:
80 // bit_t = natural register type for storing 'value_' (which is BITS+8 bits)
81 // range_t = register for 'range_' (which is 8bits only)
82
83 #if (BITS > 24)
84 typedef uint64_t bit_t;
85 #else
86 typedef uint32_t bit_t;
87 #endif
88
89 typedef uint32_t range_t;
90
91 //------------------------------------------------------------------------------
92 // Bitreader
93
94 typedef struct VP8BitReader VP8BitReader;
95 struct VP8BitReader {
96 // boolean decoder (keep the field ordering as is!)
97 bit_t value_; // current value
98 range_t range_; // current range minus 1. In [127, 254] interval.
99 int bits_; // number of valid bits left
100 // read buffer
101 const uint8_t* buf_; // next byte to be read
102 const uint8_t* buf_end_; // end of read buffer
103 const uint8_t* buf_max_; // max packed-read position on buffer
104 int eof_; // true if input is exhausted
105 };
106
107 // Initialize the bit reader and the boolean decoder.
108 void VP8InitBitReader(VP8BitReader* const br,
109 const uint8_t* const start, size_t size);
110 // Sets the working read buffer.
111 void VP8BitReaderSetBuffer(VP8BitReader* const br,
112 const uint8_t* const start, size_t size);
113
114 // Update internal pointers to displace the byte buffer by the
115 // relative offset 'offset'.
116 void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset);
117
118 // return the next value made of 'num_bits' bits
119 uint32_t VP8GetValue(VP8BitReader* const br, int num_bits, const char label[]);
120
121 // return the next value with sign-extension.
122 int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits,
123 const char label[]);
124
125 // bit_reader_inl.h will implement the following methods:
126 // static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob, ...)
127 // static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v, ...)
128 // and should be included by the .c files that actually need them.
129 // This is to avoid recompiling the whole library whenever this file is touched,
130 // and also allowing platform-specific ad-hoc hacks.
131
132 // -----------------------------------------------------------------------------
133 // Bitreader for lossless format
134
135 // maximum number of bits (inclusive) the bit-reader can handle:
136 #define VP8L_MAX_NUM_BIT_READ 24
137
138 #define VP8L_LBITS 64 // Number of bits prefetched (= bit-size of vp8l_val_t).
139 #define VP8L_WBITS 32 // Minimum number of bytes ready after VP8LFillBitWindow.
140
141 typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit.
142
143 typedef struct {
144 vp8l_val_t val_; // pre-fetched bits
145 const uint8_t* buf_; // input byte buffer
146 size_t len_; // buffer length
147 size_t pos_; // byte position in buf_
148 int bit_pos_; // current bit-reading position in val_
149 int eos_; // true if a bit was read past the end of buffer
150 } VP8LBitReader;
151
152 void VP8LInitBitReader(VP8LBitReader* const br,
153 const uint8_t* const start,
154 size_t length);
155
156 // Sets a new data buffer.
157 void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
158 const uint8_t* const buffer, size_t length);
159
160 // Reads the specified number of bits from read buffer.
161 // Flags an error in case end_of_stream or n_bits is more than the allowed limit
162 // of VP8L_MAX_NUM_BIT_READ (inclusive).
163 // Flags eos_ if this read attempt is going to cross the read buffer.
164 uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits);
165
166 // Return the prefetched bits, so they can be looked up.
VP8LPrefetchBits(VP8LBitReader * const br)167 static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) {
168 return (uint32_t)(br->val_ >> (br->bit_pos_ & (VP8L_LBITS - 1)));
169 }
170
171 // Returns true if there was an attempt at reading bit past the end of
172 // the buffer. Doesn't set br->eos_ flag.
VP8LIsEndOfStream(const VP8LBitReader * const br)173 static WEBP_INLINE int VP8LIsEndOfStream(const VP8LBitReader* const br) {
174 assert(br->pos_ <= br->len_);
175 return br->eos_ || ((br->pos_ == br->len_) && (br->bit_pos_ > VP8L_LBITS));
176 }
177
178 // For jumping over a number of bits in the bit stream when accessed with
179 // VP8LPrefetchBits and VP8LFillBitWindow.
180 // This function does *not* set br->eos_, since it's speed-critical.
181 // Use with extreme care!
VP8LSetBitPos(VP8LBitReader * const br,int val)182 static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) {
183 br->bit_pos_ = val;
184 }
185
186 // Advances the read buffer by 4 bytes to make room for reading next 32 bits.
187 // Speed critical, but infrequent part of the code can be non-inlined.
188 extern void VP8LDoFillBitWindow(VP8LBitReader* const br);
VP8LFillBitWindow(VP8LBitReader * const br)189 static WEBP_INLINE void VP8LFillBitWindow(VP8LBitReader* const br) {
190 if (br->bit_pos_ >= VP8L_WBITS) VP8LDoFillBitWindow(br);
191 }
192
193 #ifdef __cplusplus
194 } // extern "C"
195 #endif
196
197 #endif // WEBP_UTILS_BIT_READER_UTILS_H_
198