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 Fran&ccedil;ois 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}