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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
33namespace WTF {
34
35namespace 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