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 WELL19937c 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: Well19937c.java 1416643 2012-12-03 19:37:14Z tn $
032     * @since 2.2
033    
034     */
035    public class Well19937c extends AbstractWell {
036    
037        /** Serializable version identifier. */
038        private static final long serialVersionUID = -7203498180754925124L;
039    
040        /** Number of bits in the pool. */
041        private static final int K = 19937;
042    
043        /** First parameter of the algorithm. */
044        private static final int M1 = 70;
045    
046        /** Second parameter of the algorithm. */
047        private static final int M2 = 179;
048    
049        /** Third parameter of the algorithm. */
050        private static final int M3 = 449;
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 Well19937c() {
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 Well19937c(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 Well19937c(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 Well19937c(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            final int z0 = (0x80000000 & v[indexRm1]) ^ (0x7FFFFFFF & v[indexRm2]);
095            final int z1 = (v0 ^ (v0 << 25))  ^ (vM1 ^ (vM1 >>> 27));
096            final int z2 = (vM2 >>> 9) ^ (vM3 ^ (vM3 >>> 1));
097            final int z3 = z1      ^ z2;
098            int z4 = z0 ^ (z1 ^ (z1 << 9)) ^ (z2 ^ (z2 << 21)) ^ (z3 ^ (z3 >>> 21));
099    
100            v[index]     = z3;
101            v[indexRm1]  = z4;
102            v[indexRm2] &= 0x80000000;
103            index        = indexRm1;
104    
105    
106            // add Matsumoto-Kurita tempering
107            // to get a maximally-equidistributed generator
108            z4 = z4 ^ ((z4 <<  7) & 0xe46e1700);
109            z4 = z4 ^ ((z4 << 15) & 0x9b868000);
110    
111            return z4 >>> (32 - bits);
112    
113        }
114    
115    }