V8 API Reference, 7.2.502.16 (for Deno 0.2.4)
diy-fp.h
1 // Copyright 2011 the V8 project authors. All rights reserved.
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 
8 #include <stdint.h>
9 
10 #include "src/base/logging.h"
11 
12 namespace v8 {
13 namespace internal {
14 
15 // This "Do It Yourself Floating Point" class implements a floating-point number
16 // with a uint64 significand and an int exponent. Normalized DiyFp numbers will
17 // have the most significant bit of the significand set.
18 // Multiplication and Subtraction do not normalize their results.
19 // DiyFp are not designed to contain special doubles (NaN and Infinity).
20 class DiyFp {
21  public:
22  static const int kSignificandSize = 64;
23 
24  DiyFp() : f_(0), e_(0) {}
25  DiyFp(uint64_t f, int e) : f_(f), e_(e) {}
26 
27  // this = this - other.
28  // The exponents of both numbers must be the same and the significand of this
29  // must be bigger than the significand of other.
30  // The result will not be normalized.
31  void Subtract(const DiyFp& other) {
32  DCHECK(e_ == other.e_);
33  DCHECK(f_ >= other.f_);
34  f_ -= other.f_;
35  }
36 
37  // Returns a - b.
38  // The exponents of both numbers must be the same and this must be bigger
39  // than other. The result will not be normalized.
40  static DiyFp Minus(const DiyFp& a, const DiyFp& b) {
41  DiyFp result = a;
42  result.Subtract(b);
43  return result;
44  }
45 
46 
47  // this = this * other.
48  void Multiply(const DiyFp& other);
49 
50  // returns a * b;
51  static DiyFp Times(const DiyFp& a, const DiyFp& b) {
52  DiyFp result = a;
53  result.Multiply(b);
54  return result;
55  }
56 
57  void Normalize() {
58  DCHECK_NE(f_, 0);
59  uint64_t f = f_;
60  int e = e_;
61 
62  // This method is mainly called for normalizing boundaries. In general
63  // boundaries need to be shifted by 10 bits. We thus optimize for this case.
64  const uint64_t k10MSBits = static_cast<uint64_t>(0x3FF) << 54;
65  while ((f & k10MSBits) == 0) {
66  f <<= 10;
67  e -= 10;
68  }
69  while ((f & kUint64MSB) == 0) {
70  f <<= 1;
71  e--;
72  }
73  f_ = f;
74  e_ = e;
75  }
76 
77  static DiyFp Normalize(const DiyFp& a) {
78  DiyFp result = a;
79  result.Normalize();
80  return result;
81  }
82 
83  uint64_t f() const { return f_; }
84  int e() const { return e_; }
85 
86  void set_f(uint64_t new_value) { f_ = new_value; }
87  void set_e(int new_value) { e_ = new_value; }
88 
89  private:
90  static const uint64_t kUint64MSB = static_cast<uint64_t>(1) << 63;
91 
92  uint64_t f_;
93  int e_;
94 };
95 
96 } // namespace internal
97 } // namespace v8
98 
99 #endif // V8_DIY_FP_H_
Definition: libplatform.h:13