1 // Copyright 2011 the V8 project authors. All rights reserved. 2 // Redistribution and use in source and binary forms, with or without 3 // modification, are permitted provided that the following conditions are 4 // met: 5 // 6 // * Redistributions of source code must retain the above copyright 7 // notice, this list of conditions and the following disclaimer. 8 // * Redistributions in binary form must reproduce the above 9 // copyright notice, this list of conditions and the following 10 // disclaimer in the documentation and/or other materials provided 11 // with the distribution. 12 // * Neither the name of Google Inc. nor the names of its 13 // contributors may be used to endorse or promote products derived 14 // from this software without specific prior written permission. 15 // 16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 27 28 #ifndef V8_DIY_FP_H_ 29 #define V8_DIY_FP_H_ 30 31 namespace v8 { 32 namespace internal { 33 34 // This "Do It Yourself Floating Point" class implements a floating-point number 35 // with a uint64 significand and an int exponent. Normalized DiyFp numbers will 36 // have the most significant bit of the significand set. 37 // Multiplication and Subtraction do not normalize their results. 38 // DiyFp are not designed to contain special doubles (NaN and Infinity). 39 class DiyFp { 40 public: 41 static const int kSignificandSize = 64; 42 43 DiyFp() : f_(0), e_(0) {} 44 DiyFp(uint64_t f, int e) : f_(f), e_(e) {} 45 46 // this = this - other. 47 // The exponents of both numbers must be the same and the significand of this 48 // must be bigger than the significand of other. 49 // The result will not be normalized. 50 void Subtract(const DiyFp& other) { 51 ASSERT(e_ == other.e_); 52 ASSERT(f_ >= other.f_); 53 f_ -= other.f_; 54 } 55 56 // Returns a - b. 57 // The exponents of both numbers must be the same and this must be bigger 58 // than other. The result will not be normalized. 59 static DiyFp Minus(const DiyFp& a, const DiyFp& b) { 60 DiyFp result = a; 61 result.Subtract(b); 62 return result; 63 } 64 65 66 // this = this * other. 67 void Multiply(const DiyFp& other); 68 69 // returns a * b; 70 static DiyFp Times(const DiyFp& a, const DiyFp& b) { 71 DiyFp result = a; 72 result.Multiply(b); 73 return result; 74 } 75 76 void Normalize() { 77 ASSERT(f_ != 0); 78 uint64_t f = f_; 79 int e = e_; 80 81 // This method is mainly called for normalizing boundaries. In general 82 // boundaries need to be shifted by 10 bits. We thus optimize for this case. 83 const uint64_t k10MSBits = static_cast<uint64_t>(0x3FF) << 54; 84 while ((f & k10MSBits) == 0) { 85 f <<= 10; 86 e -= 10; 87 } 88 while ((f & kUint64MSB) == 0) { 89 f <<= 1; 90 e--; 91 } 92 f_ = f; 93 e_ = e; 94 } 95 96 static DiyFp Normalize(const DiyFp& a) { 97 DiyFp result = a; 98 result.Normalize(); 99 return result; 100 } 101 102 uint64_t f() const { return f_; } 103 int e() const { return e_; } 104 105 void set_f(uint64_t new_value) { f_ = new_value; } 106 void set_e(int new_value) { e_ = new_value; } 107 108 private: 109 static const uint64_t kUint64MSB = static_cast<uint64_t>(1) << 63; 110 111 uint64_t f_; 112 int e_; 113 }; 114 115 } } // namespace v8::internal 116 117 #endif // V8_DIY_FP_H_ 118
