1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17 package org.apache.commons.math.random; 18 19 20 /** This class implements the WELL19937a pseudo-random number generator 21 * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto. 22 23 * <p>This generator is described in a paper by François Panneton, 24 * Pierre L'Ecuyer and Makoto Matsumoto <a 25 * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved 26 * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM 27 * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper 28 * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.</p> 29 30 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a> 31 * @version $Revision: 1003892 $ $Date: 2010-10-02 23:28:56 +0200 (sam. 02 oct. 2010) $ 32 * @since 2.2 33 34 */ 35 public class Well19937a extends AbstractWell { 36 37 /** Serializable version identifier. */ 38 private static final long serialVersionUID = -7462102162223815419L; 39 40 /** Number of bits in the pool. */ 41 private static final int K = 19937; 42 43 /** First parameter of the algorithm. */ 44 private static final int M1 = 70; 45 46 /** Second parameter of the algorithm. */ 47 private static final int M2 = 179; 48 49 /** Third parameter of the algorithm. */ 50 private static final int M3 = 449; 51 52 /** Creates a new random number generator. 53 * <p>The instance is initialized using the current time as the 54 * seed.</p> 55 */ 56 public Well19937a() { 57 super(K, M1, M2, M3); 58 } 59 60 /** Creates a new random number generator using a single int seed. 61 * @param seed the initial seed (32 bits integer) 62 */ 63 public Well19937a(int seed) { 64 super(K, M1, M2, M3, seed); 65 } 66 67 /** Creates a new random number generator using an int array seed. 68 * @param seed the initial seed (32 bits integers array), if null 69 * the seed of the generator will be related to the current time 70 */ 71 public Well19937a(int[] seed) { 72 super(K, M1, M2, M3, seed); 73 } 74 75 /** Creates a new random number generator using a single long seed. 76 * @param seed the initial seed (64 bits integer) 77 */ 78 public Well19937a(long seed) { 79 super(K, M1, M2, M3, seed); 80 } 81 82 /** {@inheritDoc} */ 83 @Override 84 protected int next(final int bits) { 85 86 final int indexRm1 = iRm1[index]; 87 final int indexRm2 = iRm2[index]; 88 89 final int v0 = v[index]; 90 final int vM1 = v[i1[index]]; 91 final int vM2 = v[i2[index]]; 92 final int vM3 = v[i3[index]]; 93 94 final int z0 = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]); 95 final int z1 = (v0 ^ (v0 << 25)) ^ (vM1 ^ (vM1 >>> 27)); 96 final int z2 = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1)); 97 final int z3 = z1 ^ z2; 98 final int z4 = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21)); 99 100 v[index] = z3; 101 v[indexRm1] = z4; 102 v[indexRm2] &= 0x80000000; 103 index = indexRm1; 104 105 return z4 >>> (32 - bits); 106 107 } 108 } 109
