    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     */
    017    package org.apache.commons.math3.random;
    018
    019
    020    /** This class implements the WELL44497a pseudo-random number generator
    021     * from Fran&ccedil;ois 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     * @version $Id: Well44497a.java 1416643 2012-12-03 19:37:14Z tn $
    032     * @since 2.2
    033
    034     */
    035    public class Well44497a extends AbstractWell {
    036
    037        /** Serializable version identifier. */
    038        private static final long serialVersionUID = -3859207588353972099L;
    039
    040        /** Number of bits in the pool. */
    041        private static final int K = 44497;
    042
    043        /** First parameter of the algorithm. */
    044        private static final int M1 = 23;
    045
    046        /** Second parameter of the algorithm. */
    047        private static final int M2 = 481;
    048
    049        /** Third parameter of the algorithm. */
    050        private static final int M3 = 229;
    051
    052        /** Creates a new random number generator.
    053         * <p>The instance is initialized using the current time as the
    054         * seed.</p>
    055         */
    056        public Well44497a() {
    057            super(K, M1, M2, M3);
    058        }
    059
    060        /** Creates a new random number generator using a single int seed.
    061         * @param seed the initial seed (32 bits integer)
    062         */
    063        public Well44497a(int seed) {
    064            super(K, M1, M2, M3, seed);
    065        }
    066
    067        /** Creates a new random number generator using an int array seed.
    068         * @param seed the initial seed (32 bits integers array), if null
    069         * the seed of the generator will be related to the current time
    070         */
    071        public Well44497a(int[] seed) {
    072            super(K, M1, M2, M3, seed);
    073        }
    074
    075        /** Creates a new random number generator using a single long seed.
    076         * @param seed the initial seed (64 bits integer)
    077         */
    078        public Well44497a(long seed) {
    079            super(K, M1, M2, M3, seed);
    080        }
    081
    082        /** {@inheritDoc} */
    083        @Override
    084        protected int next(final int bits) {
    085
    086            final int indexRm1 = iRm1[index];
    087            final int indexRm2 = iRm2[index];
    088
    089            final int v0       = v[index];
    090            final int vM1      = v[i1[index]];
    091            final int vM2      = v[i2[index]];
    092            final int vM3      = v[i3[index]];
    093
    094            // the values below include the errata of the original article
    095            final int z0       = (0xFFFF8000 & v[indexRm1]) ^ (0x00007FFF & v[indexRm2]);
    096            final int z1       = (v0 ^ (v0 << 24))  ^ (vM1 ^ (vM1 >>> 30));
    097            final int z2       = (vM2 ^ (vM2 << 10)) ^ (vM3 << 26);
    098            final int z3       = z1      ^ z2;
    099            final int z2Prime  = ((z2 << 9) ^ (z2 >>> 23)) & 0xfbffffff;
    100            final int z2Second = ((z2 & 0x00020000) != 0) ? (z2Prime ^ 0xb729fcec) : z2Prime;
    101            final int z4       = z0 ^ (z1 ^ (z1 >>> 20)) ^ z2Second ^ z3;
    102
    103            v[index]     = z3;
    104            v[indexRm1]  = z4;
    105            v[indexRm2] &= 0xFFFF8000;
    106            index        = indexRm1;
    107
    108            return z4 >>> (32 - bits);
    109
    110        }
    111    }