bit_reader_utils.h (7708B)
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 #include <stddef.h> 20 21 #ifdef _MSC_VER 22 #include <stdlib.h> // _byteswap_ulong 23 #endif 24 #include "src/dsp/cpu.h" 25 #include "src/webp/types.h" 26 27 // Warning! This macro triggers quite some MACRO wizardry around func signature! 28 #if !defined(BITTRACE) 29 #define BITTRACE 0 // 0 = off, 1 = print bits, 2 = print bytes 30 #endif 31 32 #if (BITTRACE > 0) 33 struct VP8BitReader; 34 extern void BitTrace(const struct VP8BitReader* const br, const char label[]); 35 #define BT_TRACK(br) BitTrace(br, label) 36 #define VP8Get(BR, L) VP8GetValue(BR, 1, L) 37 #else 38 #define BT_TRACK(br) 39 // We'll REMOVE the 'const char label[]' from all signatures and calls (!!): 40 #define VP8GetValue(BR, N, L) VP8GetValue(BR, N) 41 #define VP8Get(BR, L) VP8GetValue(BR, 1, L) 42 #define VP8GetSignedValue(BR, N, L) VP8GetSignedValue(BR, N) 43 #define VP8GetBit(BR, P, L) VP8GetBit(BR, P) 44 #define VP8GetBitAlt(BR, P, L) VP8GetBitAlt(BR, P) 45 #define VP8GetSigned(BR, V, L) VP8GetSigned(BR, V) 46 #endif 47 48 #ifdef __cplusplus 49 extern "C" { 50 #endif 51 52 // The Boolean decoder needs to maintain infinite precision on the 'value' 53 // field. However, since 'range' is only 8bit, we only need an active window of 54 // 8 bits for 'value". Left bits (MSB) gets zeroed and shifted away when 55 // 'value' falls below 128, 'range' is updated, and fresh bits read from the 56 // bitstream are brought in as LSB. To avoid reading the fresh bits one by one 57 // (slow), we cache BITS of them ahead. The total of (BITS + 8) bits must fit 58 // into a natural register (with type bit_t). To fetch BITS bits from bitstream 59 // we use a type lbit_t. 60 // 61 // BITS can be any multiple of 8 from 8 to 56 (inclusive). 62 // Pick values that fit natural register size. 63 64 #if defined(__i386__) || defined(_M_IX86) // x86 32bit 65 #define BITS 24 66 #elif defined(__x86_64__) || defined(_M_X64) // x86 64bit 67 #define BITS 56 68 #elif defined(__arm__) || defined(_M_ARM) // ARM 69 #define BITS 24 70 #elif WEBP_AARCH64 // ARM 64bit 71 #define BITS 56 72 #elif defined(__mips__) // MIPS 73 #define BITS 24 74 #elif defined(__wasm__) // WASM 75 #define BITS 56 76 #else // reasonable default 77 #define BITS 24 78 #endif 79 80 //------------------------------------------------------------------------------ 81 // Derived types and constants: 82 // bit_t = natural register type for storing 'value' (which is BITS+8 bits) 83 // range_t = register for 'range' (which is 8bits only) 84 85 #if (BITS > 24) 86 typedef uint64_t bit_t; 87 #else 88 typedef uint32_t bit_t; 89 #endif 90 91 typedef uint32_t range_t; 92 93 //------------------------------------------------------------------------------ 94 // Bitreader 95 96 typedef struct VP8BitReader VP8BitReader; 97 struct VP8BitReader { 98 // boolean decoder (keep the field ordering as is!) 99 bit_t value; // current value 100 range_t range; // current range minus 1. In [127, 254] interval. 101 int bits; // number of valid bits left 102 // read buffer 103 const uint8_t* buf; // next byte to be read 104 const uint8_t* buf_end; // end of read buffer 105 const uint8_t* buf_max; // max packed-read position on buffer 106 int eof; // true if input is exhausted 107 }; 108 109 // Initialize the bit reader and the boolean decoder. 110 void VP8InitBitReader(VP8BitReader* const br, 111 const uint8_t* const start, size_t size); 112 // Sets the working read buffer. 113 void VP8BitReaderSetBuffer(VP8BitReader* const br, 114 const uint8_t* const start, size_t size); 115 116 // Update internal pointers to displace the byte buffer by the 117 // relative offset 'offset'. 118 void VP8RemapBitReader(VP8BitReader* const br, ptrdiff_t offset); 119 120 // return the next value made of 'num_bits' bits 121 uint32_t VP8GetValue(VP8BitReader* const br, int num_bits, const char label[]); 122 123 // return the next value with sign-extension. 124 int32_t VP8GetSignedValue(VP8BitReader* const br, int num_bits, 125 const char label[]); 126 127 // bit_reader_inl.h will implement the following methods: 128 // static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob, ...) 129 // static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v, ...) 130 // and should be included by the .c files that actually need them. 131 // This is to avoid recompiling the whole library whenever this file is touched, 132 // and also allowing platform-specific ad-hoc hacks. 133 134 // ----------------------------------------------------------------------------- 135 // Bitreader for lossless format 136 137 // maximum number of bits (inclusive) the bit-reader can handle: 138 #define VP8L_MAX_NUM_BIT_READ 24 139 140 #define VP8L_LBITS 64 // Number of bits prefetched (= bit-size of vp8l_val_t). 141 #define VP8L_WBITS 32 // Minimum number of bytes ready after VP8LFillBitWindow. 142 143 typedef uint64_t vp8l_val_t; // right now, this bit-reader can only use 64bit. 144 145 typedef struct { 146 vp8l_val_t val; // pre-fetched bits 147 const uint8_t* buf; // input byte buffer 148 size_t len; // buffer length 149 size_t pos; // byte position in buf 150 int bit_pos; // current bit-reading position in val 151 int eos; // true if a bit was read past the end of buffer 152 } VP8LBitReader; 153 154 void VP8LInitBitReader(VP8LBitReader* const br, 155 const uint8_t* const start, 156 size_t length); 157 158 // Sets a new data buffer. 159 void VP8LBitReaderSetBuffer(VP8LBitReader* const br, 160 const uint8_t* const buffer, size_t length); 161 162 // Reads the specified number of bits from read buffer. 163 // Flags an error in case end_of_stream or n_bits is more than the allowed limit 164 // of VP8L_MAX_NUM_BIT_READ (inclusive). 165 // Flags 'eos' if this read attempt is going to cross the read buffer. 166 uint32_t VP8LReadBits(VP8LBitReader* const br, int n_bits); 167 168 // Return the prefetched bits, so they can be looked up. 169 static WEBP_INLINE uint32_t VP8LPrefetchBits(VP8LBitReader* const br) { 170 return (uint32_t)(br->val >> (br->bit_pos & (VP8L_LBITS - 1))); 171 } 172 173 // Returns true if there was an attempt at reading bit past the end of 174 // the buffer. Doesn't set br->eos flag. 175 static WEBP_INLINE int VP8LIsEndOfStream(const VP8LBitReader* const br) { 176 assert(br->pos <= br->len); 177 return br->eos || ((br->pos == br->len) && (br->bit_pos > VP8L_LBITS)); 178 } 179 180 // For jumping over a number of bits in the bit stream when accessed with 181 // VP8LPrefetchBits and VP8LFillBitWindow. 182 // This function does *not* set br->eos, since it's speed-critical. 183 // Use with extreme care! 184 static WEBP_INLINE void VP8LSetBitPos(VP8LBitReader* const br, int val) { 185 br->bit_pos = val; 186 } 187 188 // Advances the read buffer by 4 bytes to make room for reading next 32 bits. 189 // Speed critical, but infrequent part of the code can be non-inlined. 190 extern void VP8LDoFillBitWindow(VP8LBitReader* const br); 191 static WEBP_INLINE void VP8LFillBitWindow(VP8LBitReader* const br) { 192 if (br->bit_pos >= VP8L_WBITS) VP8LDoFillBitWindow(br); 193 } 194 195 #ifdef __cplusplus 196 } // extern "C" 197 #endif 198 199 #endif // WEBP_UTILS_BIT_READER_UTILS_H_