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Diffstat (limited to 'src/main/java/org/apache/commons/math/random/AbstractWell.java')
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diff --git a/src/main/java/org/apache/commons/math/random/AbstractWell.java b/src/main/java/org/apache/commons/math/random/AbstractWell.java new file mode 100644 index 0000000..96e18a2 --- /dev/null +++ b/src/main/java/org/apache/commons/math/random/AbstractWell.java @@ -0,0 +1,186 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ +package org.apache.commons.math.random; + +import java.io.Serializable; + + +/** This abstract class implements the WELL class of pseudo-random number generator + * from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto. + + * <p>This generator is described in a paper by François Panneton, + * Pierre L'Ecuyer and Makoto Matsumoto <a + * href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng.pdf">Improved + * Long-Period Generators Based on Linear Recurrences Modulo 2</a> ACM + * Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper + * are in <a href="http://www.iro.umontreal.ca/~lecuyer/myftp/papers/wellrng-errata.txt">wellrng-errata.txt</a>.</p> + + * @see <a href="http://www.iro.umontreal.ca/~panneton/WELLRNG.html">WELL Random number generator</a> + * @version $Revision: 1003892 $ $Date: 2010-10-02 23:28:56 +0200 (sam. 02 oct. 2010) $ + * @since 2.2 + + */ +public abstract class AbstractWell extends BitsStreamGenerator implements Serializable { + + /** Serializable version identifier. */ + private static final long serialVersionUID = -817701723016583596L; + + /** Current index in the bytes pool. */ + protected int index; + + /** Bytes pool. */ + protected final int[] v; + + /** Index indirection table giving for each index its predecessor taking table size into account. */ + protected final int[] iRm1; + + /** Index indirection table giving for each index its second predecessor taking table size into account. */ + protected final int[] iRm2; + + /** Index indirection table giving for each index the value index + m1 taking table size into account. */ + protected final int[] i1; + + /** Index indirection table giving for each index the value index + m2 taking table size into account. */ + protected final int[] i2; + + /** Index indirection table giving for each index the value index + m3 taking table size into account. */ + protected final int[] i3; + + /** Creates a new random number generator. + * <p>The instance is initialized using the current time as the + * seed.</p> + * @param k number of bits in the pool (not necessarily a multiple of 32) + * @param m1 first parameter of the algorithm + * @param m2 second parameter of the algorithm + * @param m3 third parameter of the algorithm + */ + protected AbstractWell(final int k, final int m1, final int m2, final int m3) { + this(k, m1, m2, m3, System.currentTimeMillis()); + } + + /** Creates a new random number generator using a single int seed. + * @param k number of bits in the pool (not necessarily a multiple of 32) + * @param m1 first parameter of the algorithm + * @param m2 second parameter of the algorithm + * @param m3 third parameter of the algorithm + * @param seed the initial seed (32 bits integer) + */ + protected AbstractWell(final int k, final int m1, final int m2, final int m3, final int seed) { + this(k, m1, m2, m3, new int[] { seed }); + } + + /** Creates a new random number generator using an int array seed. + * @param k number of bits in the pool (not necessarily a multiple of 32) + * @param m1 first parameter of the algorithm + * @param m2 second parameter of the algorithm + * @param m3 third parameter of the algorithm + * @param seed the initial seed (32 bits integers array), if null + * the seed of the generator will be related to the current time + */ + protected AbstractWell(final int k, final int m1, final int m2, final int m3, final int[] seed) { + + // the bits pool contains k bits, k = r w - p where r is the number + // of w bits blocks, w is the block size (always 32 in the original paper) + // and p is the number of unused bits in the last block + final int w = 32; + final int r = (k + w - 1) / w; + this.v = new int[r]; + this.index = 0; + + // precompute indirection index tables. These tables are used for optimizing access + // they allow saving computations like "(j + r - 2) % r" with costly modulo operations + iRm1 = new int[r]; + iRm2 = new int[r]; + i1 = new int[r]; + i2 = new int[r]; + i3 = new int[r]; + for (int j = 0; j < r; ++j) { + iRm1[j] = (j + r - 1) % r; + iRm2[j] = (j + r - 2) % r; + i1[j] = (j + m1) % r; + i2[j] = (j + m2) % r; + i3[j] = (j + m3) % r; + } + + // initialize the pool content + setSeed(seed); + + } + + /** Creates a new random number generator using a single long seed. + * @param k number of bits in the pool (not necessarily a multiple of 32) + * @param m1 first parameter of the algorithm + * @param m2 second parameter of the algorithm + * @param m3 third parameter of the algorithm + * @param seed the initial seed (64 bits integer) + */ + protected AbstractWell(final int k, final int m1, final int m2, final int m3, final long seed) { + this(k, m1, m2, m3, new int[] { (int) (seed >>> 32), (int) (seed & 0xffffffffl) }); + } + + /** Reinitialize the generator as if just built with the given int seed. + * <p>The state of the generator is exactly the same as a new + * generator built with the same seed.</p> + * @param seed the initial seed (32 bits integer) + */ + @Override + public void setSeed(final int seed) { + setSeed(new int[] { seed }); + } + + /** Reinitialize the generator as if just built with the given int array seed. + * <p>The state of the generator is exactly the same as a new + * generator built with the same seed.</p> + * @param seed the initial seed (32 bits integers array), if null + * the seed of the generator will be related to the current time + */ + @Override + public void setSeed(final int[] seed) { + + if (seed == null) { + setSeed(System.currentTimeMillis()); + return; + } + + System.arraycopy(seed, 0, v, 0, Math.min(seed.length, v.length)); + + if (seed.length < v.length) { + for (int i = seed.length; i < v.length; ++i) { + final long l = v[i - seed.length]; + v[i] = (int) ((1812433253l * (l ^ (l >> 30)) + i) & 0xffffffffL); + } + } + + index = 0; + + } + + /** Reinitialize the generator as if just built with the given long seed. + * <p>The state of the generator is exactly the same as a new + * generator built with the same seed.</p> + * @param seed the initial seed (64 bits integer) + */ + @Override + public void setSeed(final long seed) { + setSeed(new int[] { (int) (seed >>> 32), (int) (seed & 0xffffffffl) }); + } + + /** {@inheritDoc} */ + @Override + protected abstract int next(final int bits); + +} |