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