third_party/WebKit/Source/wtf/dtoa/diy-fp.h

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  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_