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 WELL44497b 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 Well44497b extends AbstractWell { 36 37 /** Serializable version identifier. */ 38 private static final long serialVersionUID = 4032007538246675492L; 39 40 /** Number of bits in the pool. */ 41 private static final int K = 44497; 42 43 /** First parameter of the algorithm. */ 44 private static final int M1 = 23; 45 46 /** Second parameter of the algorithm. */ 47 private static final int M2 = 481; 48 49 /** Third parameter of the algorithm. */ 50 private static final int M3 = 229; 51 52 /** Creates a new random number generator. 53 * <p>The instance is initialized using the current time as the 54 * seed.</p> 55 */ Well44497b()56 public Well44497b() { 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 */ Well44497b(int seed)63 public Well44497b(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 */ Well44497b(int[] seed)71 public Well44497b(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 */ Well44497b(long seed)78 public Well44497b(long seed) { 79 super(K, M1, M2, M3, seed); 80 } 81 82 /** {@inheritDoc} */ 83 @Override next(final int bits)84 protected int next(final int bits) { 85 86 // compute raw value given by WELL44497a generator 87 // which is NOT maximally-equidistributed 88 final int indexRm1 = iRm1[index]; 89 final int indexRm2 = iRm2[index]; 90 91 final int v0 = v[index]; 92 final int vM1 = v[i1[index]]; 93 final int vM2 = v[i2[index]]; 94 final int vM3 = v[i3[index]]; 95 96 // the values below include the errata of the original article 97 final int z0 = (0xFFFF8000 & v[indexRm1]) ^ (0x00007FFF & v[indexRm2]); 98 final int z1 = (v0 ^ (v0 << 24)) ^ (vM1 ^ (vM1 >>> 30)); 99 final int z2 = (vM2 ^ (vM2 << 10)) ^ (vM3 << 26); 100 final int z3 = z1 ^ z2; 101 final int z2Prime = ((z2 << 9) ^ (z2 >>> 23)) & 0xfbffffff; 102 final int z2Second = ((z2 & 0x00020000) != 0) ? (z2Prime ^ 0xb729fcec) : z2Prime; 103 int z4 = z0 ^ (z1 ^ (z1 >>> 20)) ^ z2Second ^ z3; 104 105 v[index] = z3; 106 v[indexRm1] = z4; 107 v[indexRm2] &= 0xFFFF8000; 108 index = indexRm1; 109 110 // add Matsumoto-Kurita tempering 111 // to get a maximally-equidistributed generator 112 z4 = z4 ^ ((z4 << 7) & 0x93dd1400); 113 z4 = z4 ^ ((z4 << 15) & 0xfa118000); 114 115 return z4 >>> (32 - bits); 116 117 } 118 119 } 120