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Issue 804005: Revert grisu commits. (Closed) Base URL: http://v8.googlecode.com/svn/branches/bleeding_edge/
Patch Set: Created 10 years, 9 months ago
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1 // Copyright 2010 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,
21 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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_DOUBLE_H_
29 #define V8_DOUBLE_H_
30
31 #include "diy_fp.h"
32
33 namespace v8 {
34 namespace internal {
35
36 // We assume that doubles and uint64_t have the same endianness.
37 static uint64_t double_to_uint64(double d) { return bit_cast<uint64_t>(d); }
38 static double uint64_to_double(uint64_t d64) { return bit_cast<double>(d64); }
39
40 // Helper functions for doubles.
41 class Double {
42 public:
43 static const uint64_t kSignMask = V8_2PART_UINT64_C(0x80000000, 00000000);
44 static const uint64_t kExponentMask = V8_2PART_UINT64_C(0x7FF00000, 00000000);
45 static const uint64_t kSignificandMask =
46 V8_2PART_UINT64_C(0x000FFFFF, FFFFFFFF);
47 static const uint64_t kHiddenBit = V8_2PART_UINT64_C(0x00100000, 00000000);
48
49 Double() : d64_(0.0) {}
50 explicit Double(double d) : d64_(double_to_uint64(d)) {}
51 explicit Double(uint64_t d64) : d64_(d64) {}
52
53 DiyFp AsDiyFp() const {
54 ASSERT(!IsSpecial());
55 return DiyFp(Significand(), Exponent());
56 }
57
58 // this->Significand() must not be 0.
59 DiyFp AsNormalizedDiyFp() const {
60 uint64_t f = Significand();
61 int e = Exponent();
62
63 ASSERT(f != 0);
64
65 // The current double could be a denormal.
66 while ((f & kHiddenBit) == 0) {
67 f <<= 1;
68 e--;
69 }
70 // Do the final shifts in one go. Don't forget the hidden bit (the '-1').
71 f <<= DiyFp::kSignificandSize - kSignificandSize - 1;
72 e -= DiyFp::kSignificandSize - kSignificandSize - 1;
73 return DiyFp(f, e);
74 }
75
76 // Returns the double's bit as uint64.
77 uint64_t AsUint64() const {
78 return d64_;
79 }
80
81 int Exponent() const {
82 if (IsDenormal()) return kDenormalExponent;
83
84 uint64_t d64 = AsUint64();
85 int biased_e = (d64 & kExponentMask) >> kSignificandSize;
86 return biased_e - kExponentBias;
87 }
88
89 uint64_t Significand() const {
90 uint64_t d64 = AsUint64();
91 uint64_t significand = d64 & kSignificandMask;
92 if (!IsDenormal()) {
93 return significand + kHiddenBit;
94 } else {
95 return significand;
96 }
97 }
98
99 // Returns true if the double is a denormal.
100 bool IsDenormal() const {
101 uint64_t d64 = AsUint64();
102 return (d64 & kExponentMask) == 0;
103 }
104
105 // We consider denormals not to be special.
106 // Hence only Infinity and NaN are special.
107 bool IsSpecial() const {
108 uint64_t d64 = AsUint64();
109 return (d64 & kExponentMask) == kExponentMask;
110 }
111
112 bool IsNan() const {
113 uint64_t d64 = AsUint64();
114 return ((d64 & kExponentMask) == kExponentMask) &&
115 ((d64 & kSignificandMask) != 0);
116 }
117
118
119 bool IsInfinite() const {
120 uint64_t d64 = AsUint64();
121 return ((d64 & kExponentMask) == kExponentMask) &&
122 ((d64 & kSignificandMask) == 0);
123 }
124
125
126 int Sign() const {
127 uint64_t d64 = AsUint64();
128 return (d64 & kSignMask) == 0? 1: -1;
129 }
130
131
132 // Returns the two boundaries of this.
133 // The bigger boundary (m_plus) is normalized. The lower boundary has the same
134 // exponent as m_plus.
135 void NormalizedBoundaries(DiyFp* out_m_minus, DiyFp* out_m_plus) const {
136 DiyFp v = this->AsDiyFp();
137 bool significand_is_zero = (v.f() == kHiddenBit);
138 DiyFp m_plus = DiyFp::Normalize(DiyFp((v.f() << 1) + 1, v.e() - 1));
139 DiyFp m_minus;
140 if (significand_is_zero && v.e() != kDenormalExponent) {
141 // The boundary is closer. Think of v = 1000e10 and v- = 9999e9.
142 // Then the boundary (== (v - v-)/2) is not just at a distance of 1e9 but
143 // at a distance of 1e8.
144 // The only exception is for the smallest normal: the largest denormal is
145 // at the same distance as its successor.
146 // Note: denormals have the same exponent as the smallest normals.
147 m_minus = DiyFp((v.f() << 2) - 1, v.e() - 2);
148 } else {
149 m_minus = DiyFp((v.f() << 1) - 1, v.e() - 1);
150 }
151 m_minus.set_f(m_minus.f() << (m_minus.e() - m_plus.e()));
152 m_minus.set_e(m_plus.e());
153 *out_m_plus = m_plus;
154 *out_m_minus = m_minus;
155 }
156
157 double value() const { return uint64_to_double(d64_); }
158
159 private:
160 static const int kSignificandSize = 52; // Excludes the hidden bit.
161 static const int kExponentBias = 0x3FF + kSignificandSize;
162 static const int kDenormalExponent = -kExponentBias + 1;
163
164 uint64_t d64_;
165 };
166
167 } } // namespace v8::internal
168
169 #endif // V8_DOUBLE_H_
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