    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.math.random;
    018
    019
    020    /** This class implements the WELL512a 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 $Revision: 1003892 $ $Date: 2010-10-02 23:28:56 +0200 (sam. 02 oct. 2010) $
    032     * @since 2.2
    033
    034     */
    035    public class Well512a extends AbstractWell {
    036
    037        /** Serializable version identifier. */
    038        private static final long serialVersionUID = -6104179812103820574L;
    039
    040        /** Number of bits in the pool. */
    041        private static final int K = 512;
    042
    043        /** First parameter of the algorithm. */
    044        private static final int M1 = 13;
    045
    046        /** Second parameter of the algorithm. */
    047        private static final int M2 = 9;
    048
    049        /** Third parameter of the algorithm. */
    050        private static final int M3 = 5;
    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 Well512a() {
    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 Well512a(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 Well512a(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 Well512a(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
    088            final int vi = v[index];
    089            final int vi1 = v[i1[index]];
    090            final int vi2 = v[i2[index]];
    091            final int z0 = v[indexRm1];
    092
    093            // the values below include the errata of the original article
    094            final int z1 = (vi ^ (vi << 16))   ^ (vi1 ^ (vi1 << 15));
    095            final int z2 = vi2 ^ (vi2 >>> 11);
    096            final int z3 = z1 ^ z2;
    097            final int z4 = (z0 ^ (z0 << 2)) ^ (z1 ^ (z1 << 18)) ^ (z2 << 28) ^ (z3 ^ ((z3 << 5) & 0xda442d24));
    098
    099            v[index] = z3;
    100            v[indexRm1]  = z4;
    101            index    = indexRm1;
    102
    103            return z4 >>> (32 - bits);
    104
    105        }
    106
    107    }