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With inspiration from other libraries
/*
* 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.math3.random;
import java.io.Serializable;
import org.apache.commons.math3.util.FastMath;
/** This abstract class implements the WELL class of pseudo-random number generator
* from François Panneton, Pierre L'Ecuyer and Makoto Matsumoto.
* This generator is described in a paper by François Panneton,
* Pierre L'Ecuyer and Makoto Matsumoto Improved
* Long-Period Generators Based on Linear Recurrences Modulo 2 ACM
* Transactions on Mathematical Software, 32, 1 (2006). The errata for the paper
* are in wellrng-errata.txt.
* @see WELL Random number generator
* @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.
* The instance is initialized using the current time plus the
* system identity hash code of this instance as the 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
*/
protected AbstractWell(final int k, final int m1, final int m2, final int m3) {
this(k, m1, m2, m3, null);
}
/** 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.
* The state of the generator is exactly the same as a new
* generator built with the same seed.
* @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.
* The state of the generator is exactly the same as a new
* generator built with the same seed.
* @param seed the initial seed (32 bits integers array). If null
* the seed of the generator will be the system time plus the system identity
* hash code of the instance.
*/
@Override
public void setSeed(final int[] seed) {
if (seed == null) {
setSeed(System.currentTimeMillis() + System.identityHashCode(this));
return;
}
System.arraycopy(seed, 0, v, 0, FastMath.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;
clear(); // Clear normal deviate cache
}
/** Reinitialize the generator as if just built with the given long seed.
* The state of the generator is exactly the same as a new
* generator built with the same seed.
* @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);
}