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 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 François 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 $Revision: 1003892 $ $Date: 2010-10-02 23:28:56 +0200 (sam. 02 oct. 2010) $
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 as the
065 * 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, System.currentTimeMillis());
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 related to the current time
150 */
151 @Override
152 public void setSeed(final int[] seed) {
153
154 if (seed == null) {
155 setSeed(System.currentTimeMillis());
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
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 }