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)
31struct VP8BitReader;
32extern 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
47extern "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)
82typedef uint64_t bit_t;
83#else
84typedef uint32_t bit_t;
85#endif
86
87typedef uint32_t range_t;
88
89//------------------------------------------------------------------------------
90// Bitreader
91
92typedef struct VP8BitReader VP8BitReader;
93struct 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.
106void VP8InitBitReader(VP8BitReader* const br,
107 const uint8_t* const start, size_t size);
108// Sets the working read buffer.
109void 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'.
114void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset);
115
116// return the next value made of 'num_bits' bits
117uint32_t VP8GetValue(VP8BitReader* const br, int num_bits, const char label[]);
118
119// return the next value with sign-extension.
120int32_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
139typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit.
140
141typedef 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
150void VP8LInitBitReader(VP8LBitReader* const br,
151 const uint8_t* const start,
152 size_t length);
153
154// Sets a new data buffer.
155void 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.
162uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits);
163
164// Return the prefetched bits, so they can be looked up.
165static 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.
171static 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!
180static 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.
186extern void VP8LDoFillBitWindow(VP8LBitReader* const br);
187static 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