1 //****************************************************************************** 2 // 3 // File: DefaultRandom.java 4 // Package: edu.rit.util 5 // Unit: Class edu.rit.util.DefaultRandom 6 // 7 // This Java source file is copyright (C) 2008 by Alan Kaminsky. All rights 8 // reserved. For further information, contact the author, Alan Kaminsky, at 9 // ark@cs.rit.edu. 10 // 11 // This Java source file is part of the Parallel Java Library ("PJ"). PJ is free 12 // software; you can redistribute it and/or modify it under the terms of the GNU 13 // General Public License as published by the Free Software Foundation; either 14 // version 3 of the License, or (at your option) any later version. 15 // 16 // PJ is distributed in the hope that it will be useful, but WITHOUT ANY 17 // WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR 18 // A PARTICULAR PURPOSE. See the GNU General Public License for more details. 19 // 20 // Linking this library statically or dynamically with other modules is making a 21 // combined work based on this library. Thus, the terms and conditions of the GNU 22 // General Public License cover the whole combination. 23 // 24 // As a special exception, the copyright holders of this library give you 25 // permission to link this library with independent modules to produce an 26 // executable, regardless of the license terms of these independent modules, and 27 // to copy and distribute the resulting executable under terms of your choice, 28 // provided that you also meet, for each linked independent module, the terms 29 // and conditions of the license of that module. An independent module is a module 30 // which is not derived from or based on this library. If you modify this library, 31 // you may extend this exception to your version of the library, but you are not 32 // obligated to do so. If you do not wish to do so, delete this exception 33 // statement from your version. 34 // 35 // A copy of the GNU General Public License is provided in the file gpl.txt. You 36 // may also obtain a copy of the GNU General Public License on the World Wide 37 // Web at http://www.gnu.org/licenses/gpl.html. 38 // 39 //****************************************************************************** 40 package edu.rit.util; 41 42 import java.io.Serial; 43 44 /** 45 * Class DefaultRandom provides a default pseudorandom number generator (PRNG) 46 * designed for use in parallel scientific programming. To create an instance of 47 * class DefaultRandom, either use the <code>DefaultRandom()</code> constructor, or 48 * use the static <code>getInstance(long)</code> method in class {@linkplain 49 * Random}. 50 * <P> 51 * Class DefaultRandom generates random numbers by hashing successive counter 52 * values. The seed initializes the counter. The hash function is defined in W. 53 * Press et al., <I>Numerical Recipes: The Art of Scientific Computing, Third 54 * Edition</I> (Cambridge University Press, 2007), page 352. The hash function 55 * applied to the counter value <I>i</I> is: 56 * <P> 57 * <I>x</I> := 3935559000370003845 * <I>i</I> + 2691343689449507681 (mod 58 * 2<SUP>64</SUP>) 59 * <BR><I>x</I> := <I>x</I> xor (<I>x</I> right-shift 21) 60 * <BR><I>x</I> := <I>x</I> xor (<I>x</I> left-shift 37) 61 * <BR><I>x</I> := <I>x</I> xor (<I>x</I> right-shift 4) 62 * <BR><I>x</I> := 4768777513237032717 * <I>x</I> (mod 2<SUP>64</SUP>) 63 * <BR><I>x</I> := <I>x</I> xor (<I>x</I> left-shift 20) 64 * <BR><I>x</I> := <I>x</I> xor (<I>x</I> right-shift 41) 65 * <BR><I>x</I> := <I>x</I> xor (<I>x</I> left-shift 5) 66 * <BR>Return <I>x</I> 67 * <P> 68 * (The shift and arithmetic operations are all performed on unsigned 64-bit 69 * numbers.) 70 * 71 * @author Alan Kaminsky 72 * @version 30-Mar-2008 73 */ 74 public class DefaultRandom 75 extends Random { 76 77 @Serial 78 private static final long serialVersionUID = 1L; 79 80 // Hidden data members. 81 // Seed for this PRNG. 82 private long seed; 83 84 // 128 bytes of extra padding to avert cache interference. 85 private transient long p0, p1, p2, p3, p4, p5, p6, p7; 86 private transient long p8, p9, pa, pb, pc, pd, pe, pf; 87 88 // Exported constructors. 89 /** 90 * Construct a new PRNG with the given seed. Any seed value is allowed. 91 * 92 * @param seed Seed. 93 */ 94 public DefaultRandom(long seed) { 95 setSeed(seed); 96 } 97 98 // Exported operations. 99 /** 100 * {@inheritDoc} 101 * 102 * Set this PRNG's seed. Any seed value is allowed. 103 */ 104 public void setSeed(long seed) { 105 this.seed = hash(seed); 106 } 107 108 // Hidden operations. 109 /** 110 * Return the next 64-bit pseudorandom value in this PRNG's sequence. 111 * 112 * @return Pseudorandom value. 113 */ 114 protected long next() { 115 ++seed; 116 return hash(seed); 117 } 118 119 /** 120 * {@inheritDoc} 121 * 122 * Return the 64-bit pseudorandom value the given number of positions ahead 123 * in this PRNG's sequence. 124 */ 125 protected long next(long skip) { 126 seed += skip; 127 return hash(seed); 128 } 129 130 /** 131 * Return the hash of the given value. 132 */ 133 private static long hash(long x) { 134 x = 3935559000370003845L * x + 2691343689449507681L; 135 x = x ^ (x >>> 21); 136 x = x ^ (x << 37); 137 x = x ^ (x >>> 4); 138 x = 4768777513237032717L * x; 139 x = x ^ (x << 20); 140 x = x ^ (x >>> 41); 141 x = x ^ (x << 5); 142 return x; 143 } 144 145 }