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1 // Copyright 2011 the V8 project authors. All rights reserved.
2 // Redistribution and use in source and binary forms, with or without
3 // modification, are permitted provided that the following conditions are
4 // met:
5 //
6 //     * Redistributions of source code must retain the above copyright
7 //       notice, this list of conditions and the following disclaimer.
8 //     * Redistributions in binary form must reproduce the above
9 //       copyright notice, this list of conditions and the following
10 //       disclaimer in the documentation and/or other materials provided
11 //       with the distribution.
12 //     * Neither the name of Google Inc. nor the names of its
13 //       contributors may be used to endorse or promote products derived
14 //       from this software without specific prior written permission.
15 //
16 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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22 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 
28 #ifndef V8_DIY_FP_H_
29 #define V8_DIY_FP_H_
30 
31 namespace v8 {
32 namespace 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).
39 class DiyFp {
40  public:
41   static const int kSignificandSize = 64;
42 
DiyFp()43   DiyFp() : f_(0), e_(0) {}
DiyFp(uint64_t f,int e)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.
Subtract(const DiyFp & other)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.
Minus(const DiyFp & a,const DiyFp & b)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;
Times(const DiyFp & a,const DiyFp & b)70   static DiyFp Times(const DiyFp& a, const DiyFp& b) {
71     DiyFp result = a;
72     result.Multiply(b);
73     return result;
74   }
75 
Normalize()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 
Normalize(const DiyFp & a)96   static DiyFp Normalize(const DiyFp& a) {
97     DiyFp result = a;
98     result.Normalize();
99     return result;
100   }
101 
f()102   uint64_t f() const { return f_; }
e()103   int e() const { return e_; }
104 
set_f(uint64_t new_value)105   void set_f(uint64_t new_value) { f_ = new_value; }
set_e(int 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