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 WELL512a 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     * @version $Id: Well512a.java 1416643 2012-12-03 19:37:14Z tn $
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    }