1 // Copyright 2014 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 // Specific inlined methods for boolean decoder [VP8GetBit() ...] 11 // This file should be included by the .c sources that actually need to call 12 // these methods. 13 // 14 // Author: Skal (pascal.massimino (at) gmail.com) 15 16 #ifndef WEBP_UTILS_BIT_READER_INL_H_ 17 #define WEBP_UTILS_BIT_READER_INL_H_ 18 19 #ifdef HAVE_CONFIG_H 20 #include "webp/config.h" 21 #endif 22 23 #ifdef WEBP_FORCE_ALIGNED 24 #include <string.h> // memcpy 25 #endif 26 27 #include "./bit_reader.h" 28 #include "./endian_inl.h" 29 30 #ifdef __cplusplus 31 extern "C" { 32 #endif 33 34 //------------------------------------------------------------------------------ 35 // Derived type lbit_t = natural type for memory I/O 36 37 #if (BITS > 32) 38 typedef uint64_t lbit_t; 39 #elif (BITS > 16) 40 typedef uint32_t lbit_t; 41 #elif (BITS > 8) 42 typedef uint16_t lbit_t; 43 #else 44 typedef uint8_t lbit_t; 45 #endif 46 47 extern const uint8_t kVP8Log2Range[128]; 48 extern const range_t kVP8NewRange[128]; 49 50 // special case for the tail byte-reading 51 void VP8LoadFinalBytes(VP8BitReader* const br); 52 53 //------------------------------------------------------------------------------ 54 // Inlined critical functions 55 56 // makes sure br->value_ has at least BITS bits worth of data 57 static WEBP_INLINE void VP8LoadNewBytes(VP8BitReader* const br) { 58 assert(br != NULL && br->buf_ != NULL); 59 // Read 'BITS' bits at a time if possible. 60 if (br->buf_ + sizeof(lbit_t) <= br->buf_end_) { 61 // convert memory type to register type (with some zero'ing!) 62 bit_t bits; 63 #if defined(WEBP_FORCE_ALIGNED) 64 lbit_t in_bits; 65 memcpy(&in_bits, br->buf_, sizeof(in_bits)); 66 #elif defined(__mips__) && !defined(__mips64) // MIPS 67 // This is needed because of un-aligned read. 68 lbit_t in_bits; 69 lbit_t* p_buf_ = (lbit_t*)br->buf_; 70 __asm__ volatile( 71 ".set push \n\t" 72 ".set at \n\t" 73 ".set macro \n\t" 74 "ulw %[in_bits], 0(%[p_buf_]) \n\t" 75 ".set pop \n\t" 76 : [in_bits]"=r"(in_bits) 77 : [p_buf_]"r"(p_buf_) 78 : "memory", "at" 79 ); 80 #else 81 const lbit_t in_bits = *(const lbit_t*)br->buf_; 82 #endif 83 br->buf_ += BITS >> 3; 84 #if !defined(WORDS_BIGENDIAN) 85 #if (BITS > 32) 86 bits = BSwap64(in_bits); 87 bits >>= 64 - BITS; 88 #elif (BITS >= 24) 89 bits = BSwap32(in_bits); 90 bits >>= (32 - BITS); 91 #elif (BITS == 16) 92 bits = BSwap16(in_bits); 93 #else // BITS == 8 94 bits = (bit_t)in_bits; 95 #endif // BITS > 32 96 #else // WORDS_BIGENDIAN 97 bits = (bit_t)in_bits; 98 if (BITS != 8 * sizeof(bit_t)) bits >>= (8 * sizeof(bit_t) - BITS); 99 #endif 100 br->value_ = bits | (br->value_ << BITS); 101 br->bits_ += BITS; 102 } else { 103 VP8LoadFinalBytes(br); // no need to be inlined 104 } 105 } 106 107 // Read a bit with proba 'prob'. Speed-critical function! 108 static WEBP_INLINE int VP8GetBit(VP8BitReader* const br, int prob) { 109 // Don't move this declaration! It makes a big speed difference to store 110 // 'range' *before* calling VP8LoadNewBytes(), even if this function doesn't 111 // alter br->range_ value. 112 range_t range = br->range_; 113 if (br->bits_ < 0) { 114 VP8LoadNewBytes(br); 115 } 116 { 117 const int pos = br->bits_; 118 const range_t split = (range * prob) >> 8; 119 const range_t value = (range_t)(br->value_ >> pos); 120 #if defined(__arm__) || defined(_M_ARM) // ARM-specific 121 const int bit = ((int)(split - value) >> 31) & 1; 122 if (value > split) { 123 range -= split + 1; 124 br->value_ -= (bit_t)(split + 1) << pos; 125 } else { 126 range = split; 127 } 128 #else // faster version on x86 129 int bit; // Don't use 'const int bit = (value > split);", it's slower. 130 if (value > split) { 131 range -= split + 1; 132 br->value_ -= (bit_t)(split + 1) << pos; 133 bit = 1; 134 } else { 135 range = split; 136 bit = 0; 137 } 138 #endif 139 if (range <= (range_t)0x7e) { 140 const int shift = kVP8Log2Range[range]; 141 range = kVP8NewRange[range]; 142 br->bits_ -= shift; 143 } 144 br->range_ = range; 145 return bit; 146 } 147 } 148 149 // simplified version of VP8GetBit() for prob=0x80 (note shift is always 1 here) 150 static WEBP_INLINE int VP8GetSigned(VP8BitReader* const br, int v) { 151 if (br->bits_ < 0) { 152 VP8LoadNewBytes(br); 153 } 154 { 155 const int pos = br->bits_; 156 const range_t split = br->range_ >> 1; 157 const range_t value = (range_t)(br->value_ >> pos); 158 const int32_t mask = (int32_t)(split - value) >> 31; // -1 or 0 159 br->bits_ -= 1; 160 br->range_ += mask; 161 br->range_ |= 1; 162 br->value_ -= (bit_t)((split + 1) & mask) << pos; 163 return (v ^ mask) - mask; 164 } 165 } 166 167 #ifdef __cplusplus 168 } // extern "C" 169 #endif 170 171 #endif // WEBP_UTILS_BIT_READER_INL_H_ 172
