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) 30 struct VP8BitReader; 31 extern 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 46 extern "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) 81 typedef uint64_t bit_t; 82 #else 83 typedef uint32_t bit_t; 84 #endif 85 86 typedef uint32_t range_t; 87 88 //------------------------------------------------------------------------------ 89 // Bitreader 90 91 typedef struct VP8BitReader VP8BitReader; 92 struct 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. 105 void VP8InitBitReader(VP8BitReader* const br, 106 const uint8_t* const start, size_t size); 107 // Sets the working read buffer. 108 void 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'. 113 void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset); 114 115 // return the next value made of 'num_bits' bits 116 uint32_t VP8GetValue(VP8BitReader* const br, int num_bits, const char label[]); 117 118 // return the next value with sign-extension. 119 int32_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. 137 138 typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit. 139 140 typedef 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; 148 149 void VP8LInitBitReader(VP8LBitReader* const br, 150 const uint8_t* const start, 151 size_t length); 152 153 // Sets a new data buffer. 154 void 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. 161 uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits); 162 163 // Return the prefetched bits, so they can be looked up. 164 static 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. 170 static 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! 179 static 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. 185 extern void VP8LDoFillBitWindow(VP8LBitReader* const br); 186 static 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