xref: /third_party/node/deps/v8/src/base/numbers/diy-fp.h (revision 1cb0ef41) 
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_BASE_NUMBERS_DIY_FP_H_
6#define V8_BASE_NUMBERS_DIY_FP_H_
7
8#include <stdint.h>
9
10#include "src/base/logging.h"
11#include "src/base/macros.h"
12
13namespace v8 {
14namespace base {
15
16// This "Do It Yourself Floating Point" class implements a floating-point number
17// with a uint64 significand and an int exponent. Normalized DiyFp numbers will
18// have the most significant bit of the significand set.
19// Multiplication and Subtraction do not normalize their results.
20// DiyFp are not designed to contain special doubles (NaN and Infinity).
21class DiyFp {
22 public:
23  static const int kSignificandSize = 64;
24
25  DiyFp() : f_(0), e_(0) {}
26  DiyFp(uint64_t f, int e) : f_(f), e_(e) {}
27
28  // this = this - other.
29  // The exponents of both numbers must be the same and the significand of this
30  // must be bigger than the significand of other.
31  // The result will not be normalized.
32  void Subtract(const DiyFp& other) {
33    DCHECK(e_ == other.e_);
34    DCHECK(f_ >= other.f_);
35    f_ -= other.f_;
36  }
37
38  // Returns a - b.
39  // The exponents of both numbers must be the same and this must be bigger
40  // than other. The result will not be normalized.
41  static DiyFp Minus(const DiyFp& a, const DiyFp& b) {
42    DiyFp result = a;
43    result.Subtract(b);
44    return result;
45  }
46
47  // this = this * other.
48  V8_BASE_EXPORT 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 base
97}  // namespace v8
98
99#endif  // V8_BASE_NUMBERS_DIY_FP_H_
100