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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
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
// Ported to Java from Mozilla's version of V8-dtoa by Hannes Wallnoefer.
// The original revision was 67d1049b0bf9 from the mozilla-central tree.
package org.mozilla.javascript.v8dtoa;
// Helper functions for doubles.
public class DoubleHelper {
static final long kSignMask = 0x8000000000000000L;
static final long kExponentMask = 0x7FF0000000000000L;
static final long kSignificandMask = 0x000FFFFFFFFFFFFFL;
static final long kHiddenBit = 0x0010000000000000L;
static DiyFp asDiyFp(long d64) {
assert(!isSpecial(d64));
return new DiyFp(significand(d64), exponent(d64));
}
// this->Significand() must not be 0.
static DiyFp asNormalizedDiyFp(long d64) {
long f = significand(d64);
int e = exponent(d64);
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 new DiyFp(f, e);
}
static int exponent(long d64) {
if (isDenormal(d64)) return kDenormalExponent;
int biased_e = (int)(((d64 & kExponentMask) >>> kSignificandSize) & 0xffffffffL);
return biased_e - kExponentBias;
}
static long significand(long d64) {
long significand = d64 & kSignificandMask;
if (!isDenormal(d64)) {
return significand + kHiddenBit;
} else {
return significand;
}
}
// Returns true if the double is a denormal.
static boolean isDenormal(long d64) {
return (d64 & kExponentMask) == 0L;
}
// We consider denormals not to be special.
// Hence only Infinity and NaN are special.
static boolean isSpecial(long d64) {
return (d64 & kExponentMask) == kExponentMask;
}
static boolean isNan(long d64) {
return ((d64 & kExponentMask) == kExponentMask) &&
((d64 & kSignificandMask) != 0L);
}
static boolean isInfinite(long d64) {
return ((d64 & kExponentMask) == kExponentMask) &&
((d64 & kSignificandMask) == 0L);
}
static int sign(long d64) {
return (d64 & kSignMask) == 0L? 1: -1;
}
// Returns the two boundaries of first argument.
// The bigger boundary (m_plus) is normalized. The lower boundary has the same
// exponent as m_plus.
static void normalizedBoundaries(long d64, DiyFp m_minus, DiyFp m_plus) {
DiyFp v = asDiyFp(d64);
boolean significand_is_zero = (v.f() == kHiddenBit);
m_plus.setF((v.f() << 1) + 1);
m_plus.setE(v.e() - 1);
m_plus.normalize();
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.setF((v.f() << 2) - 1);
m_minus.setE(v.e() - 2);
} else {
m_minus.setF((v.f() << 1) - 1);
m_minus.setE(v.e() - 1);
}
m_minus.setF(m_minus.f() << (m_minus.e() - m_plus.e()));
m_minus.setE(m_plus.e());
}
private static final int kSignificandSize = 52; // Excludes the hidden bit.
private static final int kExponentBias = 0x3FF + kSignificandSize;
private static final int kDenormalExponent = -kExponentBias + 1;
}