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//******************************************************************************
//
// File: DefaultRandom.java
// Package: edu.rit.util
// Unit: Class edu.rit.util.DefaultRandom
//
// This Java source file is copyright (C) 2008 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ 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 for more details.
//
// Linking this library statically or dynamically with other modules is making a
// combined work based on this library. Thus, the terms and conditions of the
// GNU General Public License cover the whole combination.
//
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent modules, and
// to copy and distribute the resulting executable under terms of your choice,
// provided that you also meet, for each linked independent module, the terms
// and conditions of the license of that module. An independent module is a
// module which is not derived from or based on this library. If you modify this
// library, you may extend this exception to your version of the library, but
// you are not obligated to do so. If you do not wish to do so, delete this
// exception statement from your version.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************
package edu.rit.util;
/**
* Class DefaultRandom provides a default pseudorandom number generator (PRNG)
* designed for use in parallel scientific programming. To create an instance of
* class DefaultRandom, either use the <TT>DefaultRandom()</TT> constructor, or
* use the static <TT>getInstance(long)</TT> method in class {@linkplain
* Random}.
* <P>
* Class DefaultRandom generates random numbers by hashing successive counter
* values. The seed initializes the counter. The hash function is defined in W.
* Press et al., <I>Numerical Recipes: The Art of Scientific Computing, Third
* Edition</I> (Cambridge University Press, 2007), page 352. The hash function
* applied to the counter value <I>i</I> is:
* <P>
* <I>x</I> := 3935559000370003845 * <I>i</I> + 2691343689449507681 (mod 2<SUP>64</SUP>)
* <BR><I>x</I> := <I>x</I> xor (<I>x</I> right-shift 21)
* <BR><I>x</I> := <I>x</I> xor (<I>x</I> left-shift 37)
* <BR><I>x</I> := <I>x</I> xor (<I>x</I> right-shift 4)
* <BR><I>x</I> := 4768777513237032717 * <I>x</I> (mod 2<SUP>64</SUP>)
* <BR><I>x</I> := <I>x</I> xor (<I>x</I> left-shift 20)
* <BR><I>x</I> := <I>x</I> xor (<I>x</I> right-shift 41)
* <BR><I>x</I> := <I>x</I> xor (<I>x</I> left-shift 5)
* <BR>Return <I>x</I>
* <P>
* (The shift and arithmetic operations are all performed on unsigned 64-bit
* numbers.)
*
* @author Alan Kaminsky
* @version 30-Mar-2008
*/
public class DefaultRandom
extends Random
{
// Hidden data members.
// Seed for this PRNG.
private long seed;
// 128 bytes of extra padding to avert cache interference.
private transient long p0, p1, p2, p3, p4, p5, p6, p7;
private transient long p8, p9, pa, pb, pc, pd, pe, pf;
// Exported constructors.
/**
* Construct a new PRNG with the given seed. Any seed value is allowed.
*
* @param seed Seed.
*/
public DefaultRandom
(long seed)
{
setSeed (seed);
}
// Exported operations.
/**
* Set this PRNG's seed. Any seed value is allowed.
*
* @param seed Seed.
*/
public void setSeed
(long seed)
{
this.seed = hash (seed);
}
// Hidden operations.
/**
* Return the next 64-bit pseudorandom value in this PRNG's sequence.
*
* @return Pseudorandom value.
*/
protected long next()
{
++ seed;
return hash (seed);
}
/**
* Return the 64-bit pseudorandom value the given number of positions ahead
* in this PRNG's sequence.
*
* @param skip Number of positions to skip, assumed to be > 0.
*
* @return Pseudorandom value.
*/
protected long next
(long skip)
{
seed += skip;
return hash (seed);
}
/**
* Return the hash of the given value.
*/
private static long hash
(long x)
{
x = 3935559000370003845L * x + 2691343689449507681L;
x = x ^ (x >>> 21);
x = x ^ (x << 37);
x = x ^ (x >>> 4);
x = 4768777513237032717L * x;
x = x ^ (x << 20);
x = x ^ (x >>> 41);
x = x ^ (x << 5);
return x;
}
}
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