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 WELL512a 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 Well512a extends AbstractWell { 36 37 /** Serializable version identifier. */ 38 private static final long serialVersionUID = -6104179812103820574L; 39 40 /** Number of bits in the pool. */ 41 private static final int K = 512; 42 43 /** First parameter of the algorithm. */ 44 private static final int M1 = 13; 45 46 /** Second parameter of the algorithm. */ 47 private static final int M2 = 9; 48 49 /** Third parameter of the algorithm. */ 50 private static final int M3 = 5; 51 52 /** Creates a new random number generator. 53 * <p>The instance is initialized using the current time as the 54 * seed.</p> 55 */ Well512a()56 public Well512a() { 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 */ Well512a(int seed)63 public Well512a(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 */ Well512a(int[] seed)71 public Well512a(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 */ Well512a(long seed)78 public Well512a(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 final int indexRm1 = iRm1[index]; 87 88 final int vi = v[index]; 89 final int vi1 = v[i1[index]]; 90 final int vi2 = v[i2[index]]; 91 final int z0 = v[indexRm1]; 92 93 // the values below include the errata of the original article 94 final int z1 = (vi ^ (vi << 16)) ^ (vi1 ^ (vi1 << 15)); 95 final int z2 = vi2 ^ (vi2 >>> 11); 96 final int z3 = z1 ^ z2; 97 final int z4 = (z0 ^ (z0 << 2)) ^ (z1 ^ (z1 << 18)) ^ (z2 << 28) ^ (z3 ^ ((z3 << 5) & 0xda442d24)); 98 99 v[index] = z3; 100 v[indexRm1] = z4; 101 index = indexRm1; 102 103 return z4 >>> (32 - bits); 104 105 } 106 107 } 108