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#include "src/base/macros.h"
12
13namespace v8 {
14namespace internal {
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
48 // this = this * other.
49 V8_EXPORT_PRIVATE void Multiply(const DiyFp& other);
50
51 // returns a * b;
52 static DiyFp Times(const DiyFp& a, const DiyFp& b) {
53 DiyFp result = a;
54 result.Multiply(b);
55 return result;
56 }
57
58 void Normalize() {
59 DCHECK_NE(f_, 0);
60 uint64_t f = f_;
61 int e = e_;
62
63 // This method is mainly called for normalizing boundaries. In general
64 // boundaries need to be shifted by 10 bits. We thus optimize for this case.
65 const uint64_t k10MSBits = static_cast<uint64_t>(0x3FF) << 54;
66 while ((f & k10MSBits) == 0) {
67 f <<= 10;
68 e -= 10;
69 }
70 while ((f & kUint64MSB) == 0) {
71 f <<= 1;
72 e--;
73 }
74 f_ = f;
75 e_ = e;
76 }
77
78 static DiyFp Normalize(const DiyFp& a) {
79 DiyFp result = a;
80 result.Normalize();
81 return result;
82 }
83
84 uint64_t f() const { return f_; }
85 int e() const { return e_; }
86
87 void set_f(uint64_t new_value) { f_ = new_value; }
88 void set_e(int new_value) { e_ = new_value; }
89
90 private:
91 static const uint64_t kUint64MSB = static_cast<uint64_t>(1) << 63;
92
93 uint64_t f_;
94 int e_;
95};
96
97} // namespace internal
98} // namespace v8
99
100#endif // V8_DIY_FP_H_
101