src/main/java/org/apache/commons/math/random/Well44497b.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.math.random;


/** This class implements the WELL44497b pseudo-random number generator
 * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto.

 * <p>This generator is described in a paper by Fran&ccedil;ois Panneton,
 * Pierre L'Ecuyer and Makoto Matsumoto <a
 * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
 * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
 * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
 * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.</p>

 * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
 * @version $Revision: 1003892 $ $Date: 2010-10-02 23:28:56 +0200 (sam. 02 oct. 2010) $
 * @since 2.2

 */
public class Well44497b extends AbstractWell {

    /** Serializable version identifier. */
    private static final long serialVersionUID = 4032007538246675492L;

    /** Number of bits in the pool. */
    private static final int K = 44497;

    /** First parameter of the algorithm. */
    private static final int M1 = 23;

    /** Second parameter of the algorithm. */
    private static final int M2 = 481;

    /** Third parameter of the algorithm. */
    private static final int M3 = 229;

    /** Creates a new random number generator.
     * <p>The instance is initialized using the current time as the
     * seed.</p>
     */
    public Well44497b() {
        super(K, M1, M2, M3);
    }

    /** Creates a new random number generator using a single int seed.
     * @param seed the initial seed (32 bits integer)
     */
    public Well44497b(int seed) {
        super(K, M1, M2, M3, seed);
    }

    /** Creates a new random number generator using an int array seed.
     * @param seed the initial seed (32 bits integers array), if null
     * the seed of the generator will be related to the current time
     */
    public Well44497b(int[] seed) {
        super(K, M1, M2, M3, seed);
    }

    /** Creates a new random number generator using a single long seed.
     * @param seed the initial seed (64 bits integer)
     */
    public Well44497b(long seed) {
        super(K, M1, M2, M3, seed);
    }

    /** {@inheritDoc} */
    @Override
    protected int next(final int bits) {

        // compute raw value given by WELL44497a generator
        // which is NOT maximally-equidistributed
        final int indexRm1 = iRm1[index];
        final int indexRm2 = iRm2[index];

        final int v0       = v[index];
        final int vM1      = v[i1[index]];
        final int vM2      = v[i2[index]];
        final int vM3      = v[i3[index]];

        // the values below include the errata of the original article
        final int z0       = (0xFFFF8000 & v[indexRm1]) ^ (0x00007FFF & v[indexRm2]);
        final int z1       = (v0 ^ (v0 << 24))  ^ (vM1 ^ (vM1 >>> 30));
        final int z2       = (vM2 ^ (vM2 << 10)) ^ (vM3 << 26);
        final int z3       = z1      ^ z2;
        final int z2Prime  = ((z2 << 9) ^ (z2 >>> 23)) & 0xfbffffff;
        final int z2Second = ((z2 & 0x00020000) != 0) ? (z2Prime ^ 0xb729fcec) : z2Prime;
        int z4             = z0 ^ (z1 ^ (z1 >>> 20)) ^ z2Second ^ z3;

        v[index]     = z3;
        v[indexRm1]  = z4;
        v[indexRm2] &= 0xFFFF8000;
        index        = indexRm1;

        // add Matsumoto-Kurita tempering
        // to get a maximally-equidistributed generator
        z4 = z4 ^ ((z4 <<  7) & 0x93dd1400);
        z4 = z4 ^ ((z4 << 15) & 0xfa118000);

        return z4 >>> (32 - bits);

    }

}