001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.commons.rng.core.source32; 018 019/** 020 * This class implements the WELL19937a pseudo-random number generator 021 * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto. 022 * <p> 023 * This generator is described in a paper by François Panneton, 024 * Pierre L'Ecuyer and Makoto Matsumoto 025 * <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf"> 026 * Improved Long-Period Generators Based on Linear Recurrences Modulo 2</a> 027 * ACM Transactions on Mathematical Software, 32, 1 (2006). 028 * The errata for the paper are in 029 * <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>. 030 * </p> 031 * 032 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a> 033 * @since 1.0 034 */ 035public class Well19937a extends AbstractWell { 036 /** Number of bits in the pool. */ 037 private static final int K = 19937; 038 /** First parameter of the algorithm. */ 039 private static final int M1 = 70; 040 /** Second parameter of the algorithm. */ 041 private static final int M2 = 179; 042 /** Third parameter of the algorithm. */ 043 private static final int M3 = 449; 044 /** The indirection index table. */ 045 private static final IndexTable TABLE = new IndexTable(K, M1, M2, M3); 046 047 /** 048 * Creates a new random number generator. 049 * 050 * @param seed Initial seed. 051 */ 052 public Well19937a(int[] seed) { 053 super(K, seed); 054 } 055 056 /** {@inheritDoc} */ 057 @Override 058 public int next() { 059 final int indexRm1 = TABLE.getIndexPred(index); 060 final int indexRm2 = TABLE.getIndexPred2(index); 061 062 final int v0 = v[index]; 063 final int vM1 = v[TABLE.getIndexM1(index)]; 064 final int vM2 = v[TABLE.getIndexM2(index)]; 065 final int vM3 = v[TABLE.getIndexM3(index)]; 066 067 final int z0 = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]); 068 final int z1 = (v0 ^ (v0 << 25)) ^ (vM1 ^ (vM1 >>> 27)); 069 final int z2 = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1)); 070 final int z3 = z1 ^ z2; 071 final int z4 = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21)); 072 073 v[index] = z3; 074 v[indexRm1] = z4; 075 v[indexRm2] &= 0x80000000; 076 index = indexRm1; 077 078 return z4; 079 } 080}