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| 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_H_ | |
| 16 #define WEBP_UTILS_BIT_READER_H_ | |
| 17 | |
| 18 #include <assert.h> | |
| 19 #ifdef _MSC_VER | |
| 20 #include <stdlib.h> // _byteswap_ulong | |
| 21 #endif | |
| 22 #include "../webp/types.h" | |
| 23 | |
| 24 #ifdef __cplusplus | |
| 25 extern "C" { | |
| 26 #endif | |
| 27 | |
| 28 // The Boolean decoder needs to maintain infinite precision on the value_ field. | |
| 29 // However, since range_ is only 8bit, we only need an active window of 8 bits | |
| 30 // for value_. Left bits (MSB) gets zeroed and shifted away when value_ falls | |
| 31 // below 128, range_ is updated, and fresh bits read from the bitstream are | |
| 32 // brought in as LSB. To avoid reading the fresh bits one by one (slow), we | |
| 33 // cache BITS of them ahead. The total of (BITS + 8) bits must fit into a | |
| 34 // natural register (with type bit_t). To fetch BITS bits from bitstream we | |
| 35 // use a type lbit_t. | |
| 36 // | |
| 37 // BITS can be any multiple of 8 from 8 to 56 (inclusive). | |
| 38 // Pick values that fit natural register size. | |
| 39 | |
| 40 #if defined(__i386__) || defined(_M_IX86) // x86 32bit | |
| 41 #define BITS 24 | |
| 42 #elif defined(__x86_64__) || defined(_M_X64) // x86 64bit | |
| 43 #define BITS 56 | |
| 44 #elif defined(__arm__) || defined(_M_ARM) // ARM | |
| 45 #define BITS 24 | |
| 46 #elif defined(__aarch64__) // ARM 64bit | |
| 47 #define BITS 56 | |
| 48 #elif defined(__mips__) // MIPS | |
| 49 #define BITS 24 | |
| 50 #else // reasonable default | |
| 51 #define BITS 24 | |
| 52 #endif | |
| 53 | |
| 54 //------------------------------------------------------------------------------ | |
| 55 // Derived types and constants: | |
| 56 // bit_t = natural register type for storing 'value_' (which is BITS+8 bits) | |
| 57 // range_t = register for 'range_' (which is 8bits only) | |
| 58 | |
| 59 #if (BITS > 24) | |
| 60 typedef uint64_t bit_t; | |
| 61 #else | |
| 62 typedef uint32_t bit_t; | |
| 63 #endif | |
| 64 | |
| 65 typedef uint32_t range_t; | |
| 66 | |
| 67 //------------------------------------------------------------------------------ | |
| 68 // Bitreader | |
| 69 | |
| 70 typedef struct VP8BitReader VP8BitReader; | |
| 71 struct VP8BitReader { | |
| 72 // boolean decoder (keep the field ordering as is!) | |
| 73 bit_t value_; // current value | |
| 74 range_t range_; // current range minus 1. In [127, 254] interval. | |
| 75 int bits_; // number of valid bits left | |
| 76 // read buffer | |
| 77 const uint8_t* buf_; // next byte to be read | |
| 78 const uint8_t* buf_end_; // end of read buffer | |
| 79 const uint8_t* buf_max_; // max packed-read position on buffer | |
| 80 int eof_; // true if input is exhausted | |
| 81 }; | |
| 82 | |
| 83 // Initialize the bit reader and the boolean decoder. | |
| 84 void VP8InitBitReader(VP8BitReader* const br, | |
| 85 const uint8_t* const start, size_t size); | |
| 86 // Sets the working read buffer. | |
| 87 void VP8BitReaderSetBuffer(VP8BitReader* const br, | |
| 88 const uint8_t* const start, size_t size); | |
| 89 | |
| 90 // Update internal pointers to displace the byte buffer by the | |
| 91 // relative offset 'offset'. | |
| 92 void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset); | |
| 93 | |
| 94 // return the next value made of 'num_bits' bits | |
| 95 uint32_t VP8GetValue(VP8BitReader* const br, int num_bits); | |
| 96 static WEBP_INLINE uint32_t VP8Get(VP8BitReader* const br) { | |
| 97 return VP8GetValue(br, 1); | |
| 98 } | |
| 99 | |
| 100 // return the next value with sign-extension. | |
| 101 int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits); | |
| 102 | |
| 103 // bit_reader_inl.h will implement the following methods: | |
| 104 // static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) | |
| 105 // static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) | |
| 106 // and should be included by the .c files that actually need them. | |
| 107 // This is to avoid recompiling the whole library whenever this file is touched, | |
| 108 // and also allowing platform-specific ad-hoc hacks. | |
| 109 | |
| 110 // ----------------------------------------------------------------------------- | |
| 111 // Bitreader for lossless format | |
| 112 | |
| 113 // maximum number of bits (inclusive) the bit-reader can handle: | |
| 114 #define VP8L_MAX_NUM_BIT_READ 24 | |
| 115 | |
| 116 #define VP8L_LBITS 64 // Number of bits prefetched (= bit-size of vp8l_val_t). | |
| 117 #define VP8L_WBITS 32 // Minimum number of bytes ready after VP8LFillBitWindow. | |
| 118 | |
| 119 typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit. | |
| 120 | |
| 121 typedef struct { | |
| 122 vp8l_val_t val_; // pre-fetched bits | |
| 123 const uint8_t* buf_; // input byte buffer | |
| 124 size_t len_; // buffer length | |
| 125 size_t pos_; // byte position in buf_ | |
| 126 int bit_pos_; // current bit-reading position in val_ | |
| 127 int eos_; // true if a bit was read past the end of buffer | |
| 128 } VP8LBitReader; | |
| 129 | |
| 130 void VP8LInitBitReader(VP8LBitReader* const br, | |
| 131 const uint8_t* const start, | |
| 132 size_t length); | |
| 133 | |
| 134 // Sets a new data buffer. | |
| 135 void VP8LBitReaderSetBuffer(VP8LBitReader* const br, | |
| 136 const uint8_t* const buffer, size_t length); | |
| 137 | |
| 138 // Reads the specified number of bits from read buffer. | |
| 139 // Flags an error in case end_of_stream or n_bits is more than the allowed limit | |
| 140 // of VP8L_MAX_NUM_BIT_READ (inclusive). | |
| 141 // Flags eos_ if this read attempt is going to cross the read buffer. | |
| 142 uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits); | |
| 143 | |
| 144 // Return the prefetched bits, so they can be looked up. | |
| 145 static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) { | |
| 146 return (uint32_t)(br->val_ >> (br->bit_pos_ & (VP8L_LBITS - 1))); | |
| 147 } | |
| 148 | |
| 149 // Returns true if there was an attempt at reading bit past the end of | |
| 150 // the buffer. Doesn't set br->eos_ flag. | |
| 151 static WEBP_INLINE int VP8LIsEndOfStream(const VP8LBitReader* const br) { | |
| 152 assert(br->pos_ <= br->len_); | |
| 153 return br->eos_ || ((br->pos_ == br->len_) && (br->bit_pos_ > VP8L_LBITS)); | |
| 154 } | |
| 155 | |
| 156 // For jumping over a number of bits in the bit stream when accessed with | |
| 157 // VP8LPrefetchBits and VP8LFillBitWindow. | |
| 158 static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) { | |
| 159 br->bit_pos_ = val; | |
| 160 br->eos_ = VP8LIsEndOfStream(br); | |
| 161 } | |
| 162 | |
| 163 // Advances the read buffer by 4 bytes to make room for reading next 32 bits. | |
| 164 // Speed critical, but infrequent part of the code can be non-inlined. | |
| 165 extern void VP8LDoFillBitWindow(VP8LBitReader* const br); | |
| 166 static WEBP_INLINE void VP8LFillBitWindow(VP8LBitReader* const br) { | |
| 167 if (br->bit_pos_ >= VP8L_WBITS) VP8LDoFillBitWindow(br); | |
| 168 } | |
| 169 | |
| 170 #ifdef __cplusplus | |
| 171 } // extern "C" | |
| 172 #endif | |
| 173 | |
| 174 #endif /* WEBP_UTILS_BIT_READER_H_ */ | |
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Chromium Code Reviews
Issue 2651883004:
libwebp-0.6.0-rc1 (Closed)
