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.math3.random;
018
019
020/** This class implements the WELL19937a pseudo-random number generator
021 * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
022
023 * <p>This generator is described in a paper by Fran&ccedil;ois Panneton,
024 * Pierre L'Ecuyer and Makoto Matsumoto <a
025 * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
026 * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
027 * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
028 * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.</p>
029
030 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
031 * @since 2.2
032
033 */
034public class Well19937a extends AbstractWell {
035
036    /** Serializable version identifier. */
037    private static final long serialVersionUID = -7462102162223815419L;
038
039    /** Number of bits in the pool. */
040    private static final int K = 19937;
041
042    /** First parameter of the algorithm. */
043    private static final int M1 = 70;
044
045    /** Second parameter of the algorithm. */
046    private static final int M2 = 179;
047
048    /** Third parameter of the algorithm. */
049    private static final int M3 = 449;
050
051    /** Creates a new random number generator.
052     * <p>The instance is initialized using the current time as the
053     * seed.</p>
054     */
055    public Well19937a() {
056        super(K, M1, M2, M3);
057    }
058
059    /** Creates a new random number generator using a single int seed.
060     * @param seed the initial seed (32 bits integer)
061     */
062    public Well19937a(int seed) {
063        super(K, M1, M2, M3, seed);
064    }
065
066    /** Creates a new random number generator using an int array seed.
067     * @param seed the initial seed (32 bits integers array), if null
068     * the seed of the generator will be related to the current time
069     */
070    public Well19937a(int[] seed) {
071        super(K, M1, M2, M3, seed);
072    }
073
074    /** Creates a new random number generator using a single long seed.
075     * @param seed the initial seed (64 bits integer)
076     */
077    public Well19937a(long seed) {
078        super(K, M1, M2, M3, seed);
079    }
080
081    /** {@inheritDoc} */
082    @Override
083    protected int next(final int bits) {
084
085        final int indexRm1 = iRm1[index];
086        final int indexRm2 = iRm2[index];
087
088        final int v0       = v[index];
089        final int vM1      = v[i1[index]];
090        final int vM2      = v[i2[index]];
091        final int vM3      = v[i3[index]];
092
093        final int z0 = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]);
094        final int z1 = (v0 ^ (v0 << 25))  ^ (vM1 ^ (vM1 >>> 27));
095        final int z2 = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1));
096        final int z3 = z1      ^ z2;
097        final int z4 = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21));
098
099        v[index]     = z3;
100        v[indexRm1]  = z4;
101        v[indexRm2] &= 0x80000000;
102        index        = indexRm1;
103
104        return z4 >>> (32 - bits);
105
106    }
107}