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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.
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     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
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     26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     27 
     28 #ifndef DOUBLE_CONVERSION_DIY_FP_H_
     29 #define DOUBLE_CONVERSION_DIY_FP_H_
     30 
     31 #include "utils.h"
     32 
     33 namespace WTF {
     34 
     35 namespace double_conversion {
     36 
     37     // This "Do It Yourself Floating Point" class implements a floating-point number
     38     // with a uint64 significand and an int exponent. Normalized DiyFp numbers will
     39     // have the most significant bit of the significand set.
     40     // Multiplication and Subtraction do not normalize their results.
     41     // DiyFp are not designed to contain special doubles (NaN and Infinity).
     42     class DiyFp {
     43     public:
     44         static const int kSignificandSize = 64;
     45 
     46         DiyFp() : f_(0), e_(0) {}
     47         DiyFp(uint64_t f, int e) : f_(f), e_(e) {}
     48 
     49         // this = this - other.
     50         // The exponents of both numbers must be the same and the significand of this
     51         // must be bigger than the significand of other.
     52         // The result will not be normalized.
     53         void Subtract(const DiyFp& other) {
     54             ASSERT(e_ == other.e_);
     55             ASSERT(f_ >= other.f_);
     56             f_ -= other.f_;
     57         }
     58 
     59         // Returns a - b.
     60         // The exponents of both numbers must be the same and this must be bigger
     61         // than other. The result will not be normalized.
     62         static DiyFp Minus(const DiyFp& a, const DiyFp& b) {
     63             DiyFp result = a;
     64             result.Subtract(b);
     65             return result;
     66         }
     67 
     68 
     69         // this = this * other.
     70         void Multiply(const DiyFp& other);
     71 
     72         // returns a * b;
     73         static DiyFp Times(const DiyFp& a, const DiyFp& b) {
     74             DiyFp result = a;
     75             result.Multiply(b);
     76             return result;
     77         }
     78 
     79         void Normalize() {
     80             ASSERT(f_ != 0);
     81             uint64_t f = f_;
     82             int e = e_;
     83 
     84             // This method is mainly called for normalizing boundaries. In general
     85             // boundaries need to be shifted by 10 bits. We thus optimize for this case.
     86             const uint64_t k10MSBits = UINT64_2PART_C(0xFFC00000, 00000000);
     87             while ((f & k10MSBits) == 0) {
     88                 f <<= 10;
     89                 e -= 10;
     90             }
     91             while ((f & kUint64MSB) == 0) {
     92                 f <<= 1;
     93                 e--;
     94             }
     95             f_ = f;
     96             e_ = e;
     97         }
     98 
     99         static DiyFp Normalize(const DiyFp& a) {
    100             DiyFp result = a;
    101             result.Normalize();
    102             return result;
    103         }
    104 
    105         uint64_t f() const { return f_; }
    106         int e() const { return e_; }
    107 
    108         void set_f(uint64_t new_value) { f_ = new_value; }
    109         void set_e(int new_value) { e_ = new_value; }
    110 
    111     private:
    112         static const uint64_t kUint64MSB = UINT64_2PART_C(0x80000000, 00000000);
    113 
    114         uint64_t f_;
    115         int e_;
    116     };
    117 
    118 }  // namespace double_conversion
    119 
    120 } // namespace WTF
    121 
    122 #endif  // DOUBLE_CONVERSION_DIY_FP_H_
    123