/*
* $RCSfile: VecMathUtil.java,v $
*
* Copyright 2004-2008 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
* CA 95054 USA or visit www.sun.com if you need additional information or
* have any questions.
*
* $Revision: 1.5 $
* $Date: 2008/02/28 20:18:51 $
* $State: Exp $
*/
package javax.vecmath;
/**
* Utility vecmath class used when computing the hash code for vecmath objects
* containing float or double values. This fixes Issue 36.
*/
class VecMathUtil {
/**
* Returns the representation of the specified floating-point value according
* to the IEEE 754 floating-point "single format" bit layout, after first
* mapping -0.0 to 0.0. This method is identical to
* Float.floatToIntBits(float) except that an integer value of 0 is returned
* for a floating-point value of -0.0f. This is done for the purpose of
* computing a hash code that satisfies the contract of hashCode() and
* equals(). The equals() method in each vecmath class does a pair-wise "=="
* test on each floating-point field in the class (e.g., x, y, and z for a
* Tuple3f). Since 0.0f == -0.0f returns true, we must also return
* the same hash code for two objects, one of which has a field with a value
* of -0.0f and the other of which has a cooresponding field with a value of
* 0.0f.
*
* @param f
* an input floating-point number
* @return the integer bits representing that floating-point number, after
* first mapping -0.0f to 0.0f
*/
static long floatToIntBits(float f) {
// Check for +0 or -0
if (f == 0.0f) {
return 0;
} else {
return doubleToLongBitsImpl(f);
}
}
/**
* Returns the representation of the specified floating-point value according
* to the IEEE 754 floating-point "double format" bit layout, after first
* mapping -0.0 to 0.0. This method is identical to
* Double.doubleToLongBits(double) except that an integer value of 0L is
* returned for a floating-point value of -0.0. This is done for the purpose
* of computing a hash code that satisfies the contract of hashCode() and
* equals(). The equals() method in each vecmath class does a pair-wise "=="
* test on each floating-point field in the class (e.g., x, y, and z for a
* Tuple3d). Since 0.0 == -0.0 returns true, we must also return the
* same hash code for two objects, one of which has a field with a value of
* -0.0 and the other of which has a cooresponding field with a value of 0.0.
*
* @param d
* an input double precision floating-point number
* @return the integer bits representing that floating-point number, after
* first mapping -0.0f to 0.0f
*/
static long doubleToLongBits(double d) {
// Check for +0 or -0
if (d == 0.0) {
return 0L;
} else {
return doubleToLongBitsImpl(d);
}
}
/**
* Implementation of doubleToLongBits as GWT does not provide that.
* Reference: http://markmail.org/message/mqp52x6lukels2sd
*
* @param v
* @return
*/
private static long doubleToLongBitsImpl(double v) {
if (Double.isNaN(v)) {
// IEEE754, NaN exponent bits all 1s, and mantissa is non-zero
return 0x0FFFl << 51;
}
long sign = (v < 0 ? 0x1l << 63 : 0);
long exponent = 0;
double absV = Math.abs(v);
// IEEE754 infinite numbers, exponent all 1s, mantissa is 0
if (Double.isInfinite(v)) {
exponent = 0x07FFl << 52;
} else {
if (absV == 0.0) {
// IEEE754, exponent is 0, mantissa is zero
// we don't handle negative zero at the moment, it is treated as
// positive zero
exponent = 0l;
} else {
// get an approximation to the exponent
int guess = (int) Math.floor(Math.log(absV) / Math.log(2));
// force it to -1023, 1023 interval (<= -1023 = denorm/zero)
guess = Math.max(-1023, Math.min(guess, 1023));
// divide away exponent guess
double exp = Math.pow(2, guess);
absV = absV / exp;
// while the number is still bigger than a normalized number
// increment exponent guess
while (absV > 2.0) {
guess++;
absV /= 2.0;
}
// if the number is smaller than a normalized number
// decrement exponent
while (absV < 1 && guess > 1024) {
guess--;
absV *= 2;
}
exponent = (guess + 1023l) << 52;
}
}
// if denorm
if (exponent <= 0) {
absV /= 2;
}
// the input value has now been stripped of its exponent
// and is in the range [0,2), we strip off the leading decimal
// and use the remainer as a percentage of the significand value (2^52)
long mantissa = (long) ((absV % 1) * Math.pow(2, 52));
return sign | exponent | (mantissa & 0xfffffffffffffl);
}
/**
* Do not construct an instance of this class.
*/
private VecMathUtil() {
}
}