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27
28#ifndef V8_DIY_FP_H_
29#define V8_DIY_FP_H_
30
31namespace v8 {
32namespace internal {
33
34// This "Do It Yourself Floating Point" class implements a floating-point number
35// with a uint64 significand and an int exponent. Normalized DiyFp numbers will
36// have the most significant bit of the significand set.
37// Multiplication and Subtraction do not normalize their results.
38// DiyFp are not designed to contain special doubles (NaN and Infinity).
39class DiyFp {
40 public:
41  static const int kSignificandSize = 64;
42
43  DiyFp() : f_(0), e_(0) {}
44  DiyFp(uint64_t f, int e) : f_(f), e_(e) {}
45
46  // this = this - other.
47  // The exponents of both numbers must be the same and the significand of this
48  // must be bigger than the significand of other.
49  // The result will not be normalized.
50  void Subtract(const DiyFp& other) {
51    ASSERT(e_ == other.e_);
52    ASSERT(f_ >= other.f_);
53    f_ -= other.f_;
54  }
55
56  // Returns a - b.
57  // The exponents of both numbers must be the same and this must be bigger
58  // than other. The result will not be normalized.
59  static DiyFp Minus(const DiyFp& a, const DiyFp& b) {
60    DiyFp result = a;
61    result.Subtract(b);
62    return result;
63  }
64
65
66  // this = this * other.
67  void Multiply(const DiyFp& other);
68
69  // returns a * b;
70  static DiyFp Times(const DiyFp& a, const DiyFp& b) {
71    DiyFp result = a;
72    result.Multiply(b);
73    return result;
74  }
75
76  void Normalize() {
77    ASSERT(f_ != 0);
78    uint64_t f = f_;
79    int e = e_;
80
81    // This method is mainly called for normalizing boundaries. In general
82    // boundaries need to be shifted by 10 bits. We thus optimize for this case.
83    const uint64_t k10MSBits = static_cast<uint64_t>(0x3FF) << 54;
84    while ((f & k10MSBits) == 0) {
85      f <<= 10;
86      e -= 10;
87    }
88    while ((f & kUint64MSB) == 0) {
89      f <<= 1;
90      e--;
91    }
92    f_ = f;
93    e_ = e;
94  }
95
96  static DiyFp Normalize(const DiyFp& a) {
97    DiyFp result = a;
98    result.Normalize();
99    return result;
100  }
101
102  uint64_t f() const { return f_; }
103  int e() const { return e_; }
104
105  void set_f(uint64_t new_value) { f_ = new_value; }
106  void set_e(int new_value) { e_ = new_value; }
107
108 private:
109  static const uint64_t kUint64MSB = static_cast<uint64_t>(1) << 63;
110
111  uint64_t f_;
112  int e_;
113};
114
115} }  // namespace v8::internal
116
117#endif  // V8_DIY_FP_H_
118