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| 1 // Copyright 2010 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 // Simply "emulates" a 128 bit multiplication. | |
| 69 // However: the resulting number only contains 64 bits. The least | |
| 70 // significant 64 bits are only used for rounding the most significant 64 | |
| 71 // bits. | |
| 72 const uint64_t kM32 = 0xFFFFFFFFu; | |
| 73 uint64_t a = f_ >> 32; | |
| 74 uint64_t b = f_ & kM32; | |
| 75 uint64_t c = other.f_ >> 32; | |
| 76 uint64_t d = other.f_ & kM32; | |
| 77 uint64_t ac = a * c; | |
| 78 uint64_t bc = b * c; | |
| 79 uint64_t ad = a * d; | |
| 80 uint64_t bd = b * d; | |
| 81 uint64_t tmp = (bd >> 32) + (ad & kM32) + (bc & kM32); | |
| 82 tmp += 1U << 31; // round | |
| 83 uint64_t result_f = ac + (ad >> 32) + (bc >> 32) + (tmp >> 32); | |
| 84 e_ += other.e_ + 64; | |
| 85 f_ = result_f; | |
| 86 } | |
| 87 | |
| 88 // returns a * b; | |
| 89 static DiyFp Times(const DiyFp& a, const DiyFp& b) { | |
| 90 DiyFp result = a; | |
| 91 result.Multiply(b); | |
| 92 return result; | |
| 93 } | |
| 94 | |
| 95 void Normalize() { | |
| 96 ASSERT(f_ != 0); | |
| 97 uint64_t f = f_; | |
| 98 int e = e_; | |
| 99 | |
| 100 // This method is mainly called for normalizing boundaries. In general | |
| 101 // boundaries need to be shifted by 10 bits. We thus optimize for this case. | |
| 102 const uint64_t k10MSBits = V8_2PART_UINT64_C(0xFFC00000, 00000000); | |
| 103 while ((f & k10MSBits) == 0) { | |
| 104 f <<= 10; | |
| 105 e -= 10; | |
| 106 } | |
| 107 while ((f & kUint64MSB) == 0) { | |
| 108 f <<= 1; | |
| 109 e--; | |
| 110 } | |
| 111 f_ = f; | |
| 112 e_ = e; | |
| 113 } | |
| 114 | |
| 115 static DiyFp Normalize(const DiyFp& a) { | |
| 116 DiyFp result = a; | |
| 117 result.Normalize(); | |
| 118 return result; | |
| 119 } | |
| 120 | |
| 121 uint64_t f() const { return f_; } | |
| 122 int e() const { return e_; } | |
| 123 | |
| 124 void set_f(uint64_t new_value) { f_ = new_value; } | |
| 125 void set_e(int new_value) { e_ = new_value; } | |
| 126 | |
| 127 private: | |
| 128 static const uint64_t kUint64MSB = V8_2PART_UINT64_C(0x80000000, 00000000); | |
| 129 | |
| 130 uint64_t f_; | |
| 131 int e_; | |
| 132 }; | |
| 133 | |
| 134 } } // namespace v8::internal | |
| 135 | |
| 136 #endif // V8_DIY_FP_H_ | |
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