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    import java.io.Serializable;
020    
021    
022    /** This abstract class implements the WELL class of pseudo-random number generator
023     * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
024    
025     * <p>This generator is described in a paper by Fran&ccedil;ois Panneton,
026     * Pierre L'Ecuyer and Makoto Matsumoto <a
027     * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved
028     * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM
029     * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
030     * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.</p>
031    
032     * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a>
033     * @version $Id: AbstractWell.java 1416643 2012-12-03 19:37:14Z tn $
034     * @since 2.2
035    
036     */
037    public abstract class AbstractWell extends BitsStreamGenerator implements Serializable {
038    
039        /** Serializable version identifier. */
040        private static final long serialVersionUID = -817701723016583596L;
041    
042        /** Current index in the bytes pool. */
043        protected int index;
044    
045        /** Bytes pool. */
046        protected final int[] v;
047    
048        /** Index indirection table giving for each index its predecessor taking table size into account. */
049        protected final int[] iRm1;
050    
051        /** Index indirection table giving for each index its second predecessor taking table size into account. */
052        protected final int[] iRm2;
053    
054        /** Index indirection table giving for each index the value index + m1 taking table size into account. */
055        protected final int[] i1;
056    
057        /** Index indirection table giving for each index the value index + m2 taking table size into account. */
058        protected final int[] i2;
059    
060        /** Index indirection table giving for each index the value index + m3 taking table size into account. */
061        protected final int[] i3;
062    
063        /** Creates a new random number generator.
064         * <p>The instance is initialized using the current time plus the
065         * system identity hash code of this instance as the seed.</p>
066         * @param k number of bits in the pool (not necessarily a multiple of 32)
067         * @param m1 first parameter of the algorithm
068         * @param m2 second parameter of the algorithm
069         * @param m3 third parameter of the algorithm
070         */
071        protected AbstractWell(final int k, final int m1, final int m2, final int m3) {
072            this(k, m1, m2, m3, null);
073        }
074    
075        /** Creates a new random number generator using a single int seed.
076         * @param k number of bits in the pool (not necessarily a multiple of 32)
077         * @param m1 first parameter of the algorithm
078         * @param m2 second parameter of the algorithm
079         * @param m3 third parameter of the algorithm
080         * @param seed the initial seed (32 bits integer)
081         */
082        protected AbstractWell(final int k, final int m1, final int m2, final int m3, final int seed) {
083            this(k, m1, m2, m3, new int[] { seed });
084        }
085    
086        /** Creates a new random number generator using an int array seed.
087         * @param k number of bits in the pool (not necessarily a multiple of 32)
088         * @param m1 first parameter of the algorithm
089         * @param m2 second parameter of the algorithm
090         * @param m3 third parameter of the algorithm
091         * @param seed the initial seed (32 bits integers array), if null
092         * the seed of the generator will be related to the current time
093         */
094        protected AbstractWell(final int k, final int m1, final int m2, final int m3, final int[] seed) {
095    
096            // the bits pool contains k bits, k = r w - p where r is the number
097            // of w bits blocks, w is the block size (always 32 in the original paper)
098            // and p is the number of unused bits in the last block
099            final int w = 32;
100            final int r = (k + w - 1) / w;
101            this.v      = new int[r];
102            this.index  = 0;
103    
104            // precompute indirection index tables. These tables are used for optimizing access
105            // they allow saving computations like "(j + r - 2) % r" with costly modulo operations
106            iRm1 = new int[r];
107            iRm2 = new int[r];
108            i1   = new int[r];
109            i2   = new int[r];
110            i3   = new int[r];
111            for (int j = 0; j < r; ++j) {
112                iRm1[j] = (j + r - 1) % r;
113                iRm2[j] = (j + r - 2) % r;
114                i1[j]   = (j + m1)    % r;
115                i2[j]   = (j + m2)    % r;
116                i3[j]   = (j + m3)    % r;
117            }
118    
119            // initialize the pool content
120            setSeed(seed);
121    
122        }
123    
124        /** Creates a new random number generator using a single long seed.
125         * @param k number of bits in the pool (not necessarily a multiple of 32)
126         * @param m1 first parameter of the algorithm
127         * @param m2 second parameter of the algorithm
128         * @param m3 third parameter of the algorithm
129         * @param seed the initial seed (64 bits integer)
130         */
131        protected AbstractWell(final int k, final int m1, final int m2, final int m3, final long seed) {
132            this(k, m1, m2, m3, new int[] { (int) (seed >>> 32), (int) (seed & 0xffffffffl) });
133        }
134    
135        /** Reinitialize the generator as if just built with the given int seed.
136         * <p>The state of the generator is exactly the same as a new
137         * generator built with the same seed.</p>
138         * @param seed the initial seed (32 bits integer)
139         */
140        @Override
141        public void setSeed(final int seed) {
142            setSeed(new int[] { seed });
143        }
144    
145        /** Reinitialize the generator as if just built with the given int array seed.
146         * <p>The state of the generator is exactly the same as a new
147         * generator built with the same seed.</p>
148         * @param seed the initial seed (32 bits integers array). If null
149         * the seed of the generator will be the system time plus the system identity
150         * hash code of the instance.
151         */
152        @Override
153        public void setSeed(final int[] seed) {
154            if (seed == null) {
155                setSeed(System.currentTimeMillis() + System.identityHashCode(this));
156                return;
157            }
158    
159            System.arraycopy(seed, 0, v, 0, Math.min(seed.length, v.length));
160    
161            if (seed.length < v.length) {
162                for (int i = seed.length; i < v.length; ++i) {
163                    final long l = v[i - seed.length];
164                    v[i] = (int) ((1812433253l * (l ^ (l >> 30)) + i) & 0xffffffffL);
165                }
166            }
167    
168            index = 0;
169            clear();  // Clear normal deviate cache
170        }
171    
172        /** Reinitialize the generator as if just built with the given long seed.
173         * <p>The state of the generator is exactly the same as a new
174         * generator built with the same seed.</p>
175         * @param seed the initial seed (64 bits integer)
176         */
177        @Override
178        public void setSeed(final long seed) {
179            setSeed(new int[] { (int) (seed >>> 32), (int) (seed & 0xffffffffl) });
180        }
181    
182        /** {@inheritDoc} */
183        @Override
184        protected abstract int next(final int bits);
185    
186    }