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/webp/types.h"
23
24// Warning! This macro triggers quite some MACRO wizardry around func signature!
25#if !defined(BITTRACE)
26#define BITTRACE 0 // 0 = off, 1 = print bits, 2 = print bytes
27#endif
28
29#if (BITTRACE > 0)
30struct VP8BitReader;
31extern void BitTrace(const struct VP8BitReader* const br, const char label[]);
32#define BT_TRACK(br) BitTrace(br, label)
33#define VP8Get(BR, L) VP8GetValue(BR, 1, L)
34#else
35#define BT_TRACK(br)
36// We'll REMOVE the 'const char label[]' from all signatures and calls (!!):
37#define VP8GetValue(BR, N, L) VP8GetValue(BR, N)
38#define VP8Get(BR, L) VP8GetValue(BR, 1, L)
39#define VP8GetSignedValue(BR, N, L) VP8GetSignedValue(BR, N)
40#define VP8GetBit(BR, P, L) VP8GetBit(BR, P)
41#define VP8GetBitAlt(BR, P, L) VP8GetBitAlt(BR, P)
42#define VP8GetSigned(BR, V, L) VP8GetSigned(BR, V)
43#endif
44
45#ifdef __cplusplus
46extern "C" {
47#endif
48
49// The Boolean decoder needs to maintain infinite precision on the value_ field.
50// However, since range_ is only 8bit, we only need an active window of 8 bits
51// for value_. Left bits (MSB) gets zeroed and shifted away when value_ falls
52// below 128, range_ is updated, and fresh bits read from the bitstream are
53// brought in as LSB. To avoid reading the fresh bits one by one (slow), we
54// cache BITS of them ahead. The total of (BITS + 8) bits must fit into a
55// natural register (with type bit_t). To fetch BITS bits from bitstream we
56// use a type lbit_t.
57//
58// BITS can be any multiple of 8 from 8 to 56 (inclusive).
59// Pick values that fit natural register size.
60
61#if defined(__i386__) || defined(_M_IX86) // x86 32bit
62#define BITS 24
63#elif defined(__x86_64__) || defined(_M_X64) // x86 64bit
64#define BITS 56
65#elif defined(__arm__) || defined(_M_ARM) // ARM
66#define BITS 24
67#elif defined(__aarch64__) // ARM 64bit
68#define BITS 56
69#elif defined(__mips__) // MIPS
70#define BITS 24
71#else // reasonable default
72#define BITS 24
73#endif
74
75//------------------------------------------------------------------------------
76// Derived types and constants:
77// bit_t = natural register type for storing 'value_' (which is BITS+8 bits)
78// range_t = register for 'range_' (which is 8bits only)
79
80#if (BITS > 24)
81typedef uint64_t bit_t;
82#else
83typedef uint32_t bit_t;
84#endif
85
86typedef uint32_t range_t;
87
88//------------------------------------------------------------------------------
89// Bitreader
90
91typedef struct VP8BitReader VP8BitReader;
92struct VP8BitReader {
93 // boolean decoder (keep the field ordering as is!)
94 bit_t value_; // current value
95 range_t range_; // current range minus 1. In [127, 254] interval.
96 int bits_; // number of valid bits left
97 // read buffer
98 const uint8_t* buf_; // next byte to be read
99 const uint8_t* buf_end_; // end of read buffer
100 const uint8_t* buf_max_; // max packed-read position on buffer
101 int eof_; // true if input is exhausted
102};
103
104// Initialize the bit reader and the boolean decoder.
105void VP8InitBitReader(VP8BitReader* const br,
106 const uint8_t* const start, size_t size);
107// Sets the working read buffer.
108void VP8BitReaderSetBuffer(VP8BitReader* const br,
109 const uint8_t* const start, size_t size);
110
111// Update internal pointers to displace the byte buffer by the
112// relative offset 'offset'.
113void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset);
114
115// return the next value made of 'num_bits' bits
116uint32_t VP8GetValue(VP8BitReader* const br, int num_bits, const char label[]);
117
118// return the next value with sign-extension.
119int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits,
120 const char label[]);
121
122// bit_reader_inl.h will implement the following methods:
123// static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob, ...)
124// static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v, ...)
125// and should be included by the .c files that actually need them.
126// This is to avoid recompiling the whole library whenever this file is touched,
127// and also allowing platform-specific ad-hoc hacks.
128
129// -----------------------------------------------------------------------------
130// Bitreader for lossless format
131
132// maximum number of bits (inclusive) the bit-reader can handle:
133#define VP8L_MAX_NUM_BIT_READ 24
134
135#define VP8L_LBITS 64 // Number of bits prefetched (= bit-size of vp8l_val_t).
136#define VP8L_WBITS 32 // Minimum number of bytes ready after VP8LFillBitWindow.
137
138typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit.
139
140typedef struct {
141 vp8l_val_t val_; // pre-fetched bits
142 const uint8_t* buf_; // input byte buffer
143 size_t len_; // buffer length
144 size_t pos_; // byte position in buf_
145 int bit_pos_; // current bit-reading position in val_
146 int eos_; // true if a bit was read past the end of buffer
147} VP8LBitReader;
148
149void VP8LInitBitReader(VP8LBitReader* const br,
150 const uint8_t* const start,
151 size_t length);
152
153// Sets a new data buffer.
154void VP8LBitReaderSetBuffer(VP8LBitReader* const br,
155 const uint8_t* const buffer, size_t length);
156
157// Reads the specified number of bits from read buffer.
158// Flags an error in case end_of_stream or n_bits is more than the allowed limit
159// of VP8L_MAX_NUM_BIT_READ (inclusive).
160// Flags eos_ if this read attempt is going to cross the read buffer.
161uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits);
162
163// Return the prefetched bits, so they can be looked up.
164static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) {
165 return (uint32_t)(br->val_ >> (br->bit_pos_ & (VP8L_LBITS - 1)));
166}
167
168// Returns true if there was an attempt at reading bit past the end of
169// the buffer. Doesn't set br->eos_ flag.
170static WEBP_INLINE int VP8LIsEndOfStream(const VP8LBitReader* const br) {
171 assert(br->pos_ <= br->len_);
172 return br->eos_ || ((br->pos_ == br->len_) && (br->bit_pos_ > VP8L_LBITS));
173}
174
175// For jumping over a number of bits in the bit stream when accessed with
176// VP8LPrefetchBits and VP8LFillBitWindow.
177// This function does *not* set br->eos_, since it's speed-critical.
178// Use with extreme care!
179static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) {
180 br->bit_pos_ = val;
181}
182
183// Advances the read buffer by 4 bytes to make room for reading next 32 bits.
184// Speed critical, but infrequent part of the code can be non-inlined.
185extern void VP8LDoFillBitWindow(VP8LBitReader* const br);
186static WEBP_INLINE void VP8LFillBitWindow(VP8LBitReader* const br) {
187 if (br->bit_pos_ >= VP8L_WBITS) VP8LDoFillBitWindow(br);
188}
189
190#ifdef __cplusplus
191} // extern "C"
192#endif
193
194#endif // WEBP_UTILS_BIT_READER_UTILS_H_
195