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// Copyright 2010 the V8 project authors. All rights reserved.
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following
// disclaimer in the documentation and/or other materials provided
// with the distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#ifndef V8_DOUBLE_H_
#define V8_DOUBLE_H_
#include "diy-fp.h"
namespace v8 {
namespace internal {
// We assume that doubles and uint64_t have the same endianness.
static uint64_t double_to_uint64(double d) { return BitCast<uint64_t>(d); }
static double uint64_to_double(uint64_t d64) { return BitCast<double>(d64); }
// Helper functions for doubles.
class Double {
public:
static const uint64_t kSignMask = V8_2PART_UINT64_C(0x80000000, 00000000);
static const uint64_t kExponentMask = V8_2PART_UINT64_C(0x7FF00000, 00000000);
static const uint64_t kSignificandMask =
V8_2PART_UINT64_C(0x000FFFFF, FFFFFFFF);
static const uint64_t kHiddenBit = V8_2PART_UINT64_C(0x00100000, 00000000);
Double() : d64_(0) {}
explicit Double(double d) : d64_(double_to_uint64(d)) {}
explicit Double(uint64_t d64) : d64_(d64) {}
DiyFp AsDiyFp() const {
ASSERT(!IsSpecial());
return DiyFp(Significand(), Exponent());
}
// this->Significand() must not be 0.
DiyFp AsNormalizedDiyFp() const {
uint64_t f = Significand();
int e = Exponent();
ASSERT(f != 0);
// The current double could be a denormal.
while ((f & kHiddenBit) == 0) {
f <<= 1;
e--;
}
// Do the final shifts in one go. Don't forget the hidden bit (the '-1').
f <<= DiyFp::kSignificandSize - kSignificandSize - 1;
e -= DiyFp::kSignificandSize - kSignificandSize - 1;
return DiyFp(f, e);
}
// Returns the double's bit as uint64.
uint64_t AsUint64() const {
return d64_;
}
int Exponent() const {
if (IsDenormal()) return kDenormalExponent;
uint64_t d64 = AsUint64();
int biased_e = static_cast<int>((d64 & kExponentMask) >> kSignificandSize);
return biased_e - kExponentBias;
}
uint64_t Significand() const {
uint64_t d64 = AsUint64();
uint64_t significand = d64 & kSignificandMask;
if (!IsDenormal()) {
return significand + kHiddenBit;
} else {
return significand;
}
}
// Returns true if the double is a denormal.
bool IsDenormal() const {
uint64_t d64 = AsUint64();
return (d64 & kExponentMask) == 0;
}
// We consider denormals not to be special.
// Hence only Infinity and NaN are special.
bool IsSpecial() const {
uint64_t d64 = AsUint64();
return (d64 & kExponentMask) == kExponentMask;
}
bool IsNan() const {
uint64_t d64 = AsUint64();
return ((d64 & kExponentMask) == kExponentMask) &&
((d64 & kSignificandMask) != 0);
}
bool IsInfinite() const {
uint64_t d64 = AsUint64();
return ((d64 & kExponentMask) == kExponentMask) &&
((d64 & kSignificandMask) == 0);
}
int Sign() const {
uint64_t d64 = AsUint64();
return (d64 & kSignMask) == 0? 1: -1;
}
// Returns the two boundaries of this.
// The bigger boundary (m_plus) is normalized. The lower boundary has the same
// exponent as m_plus.
void NormalizedBoundaries(DiyFp* out_m_minus, DiyFp* out_m_plus) const {
DiyFp v = this->AsDiyFp();
bool significand_is_zero = (v.f() == kHiddenBit);
DiyFp m_plus = DiyFp::Normalize(DiyFp((v.f() << 1) + 1, v.e() - 1));
DiyFp m_minus;
if (significand_is_zero && v.e() != kDenormalExponent) {
// The boundary is closer. Think of v = 1000e10 and v- = 9999e9.
// Then the boundary (== (v - v-)/2) is not just at a distance of 1e9 but
// at a distance of 1e8.
// The only exception is for the smallest normal: the largest denormal is
// at the same distance as its successor.
// Note: denormals have the same exponent as the smallest normals.
m_minus = DiyFp((v.f() << 2) - 1, v.e() - 2);
} else {
m_minus = DiyFp((v.f() << 1) - 1, v.e() - 1);
}
m_minus.set_f(m_minus.f() << (m_minus.e() - m_plus.e()));
m_minus.set_e(m_plus.e());
*out_m_plus = m_plus;
*out_m_minus = m_minus;
}
double value() const { return uint64_to_double(d64_); }
private:
static const int kSignificandSize = 52; // Excludes the hidden bit.
static const int kExponentBias = 0x3FF + kSignificandSize;
static const int kDenormalExponent = -kExponentBias + 1;
uint64_t d64_;
};
} } // namespace v8::internal
#endif // V8_DOUBLE_H_
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