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