```/* <![CDATA[ */
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef V8_DIY_FP_H_
6#define V8_DIY_FP_H_
7
8namespace v8 {
9namespace internal {
10
11// This "Do It Yourself Floating Point" class implements a floating-point number
12// with a uint64 significand and an int exponent. Normalized DiyFp numbers will
13// have the most significant bit of the significand set.
14// Multiplication and Subtraction do not normalize their results.
15// DiyFp are not designed to contain special doubles (NaN and Infinity).
16class DiyFp {
17 public:
18  static const int kSignificandSize = 64;
19
20  DiyFp() : f_(0), e_(0) {}
21  DiyFp(uint64_t f, int e) : f_(f), e_(e) {}
22
23  // this = this - other.
24  // The exponents of both numbers must be the same and the significand of this
25  // must be bigger than the significand of other.
26  // The result will not be normalized.
27  void Subtract(const DiyFp& other) {
28    DCHECK(e_ == other.e_);
29    DCHECK(f_ >= other.f_);
30    f_ -= other.f_;
31  }
32
33  // Returns a - b.
34  // The exponents of both numbers must be the same and this must be bigger
35  // than other. The result will not be normalized.
36  static DiyFp Minus(const DiyFp& a, const DiyFp& b) {
37    DiyFp result = a;
38    result.Subtract(b);
39    return result;
40  }
41
42
43  // this = this * other.
44  void Multiply(const DiyFp& other);
45
46  // returns a * b;
47  static DiyFp Times(const DiyFp& a, const DiyFp& b) {
48    DiyFp result = a;
49    result.Multiply(b);
50    return result;
51  }
52
53  void Normalize() {
54    DCHECK(f_ != 0);
55    uint64_t f = f_;
56    int e = e_;
57
58    // This method is mainly called for normalizing boundaries. In general
59    // boundaries need to be shifted by 10 bits. We thus optimize for this case.
60    const uint64_t k10MSBits = static_cast<uint64_t>(0x3FF) << 54;
61    while ((f & k10MSBits) == 0) {
62      f <<= 10;
63      e -= 10;
64    }
65    while ((f & kUint64MSB) == 0) {
66      f <<= 1;
67      e--;
68    }
69    f_ = f;
70    e_ = e;
71  }
72
73  static DiyFp Normalize(const DiyFp& a) {
74    DiyFp result = a;
75    result.Normalize();
76    return result;
77  }
78
79  uint64_t f() const { return f_; }
80  int e() const { return e_; }
81
82  void set_f(uint64_t new_value) { f_ = new_value; }
83  void set_e(int new_value) { e_ = new_value; }
84
85 private:
86  static const uint64_t kUint64MSB = static_cast<uint64_t>(1) << 63;
87
88  uint64_t f_;
89  int e_;
90};
91
92} }  // namespace v8::internal
93
94#endif  // V8_DIY_FP_H_
95```