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/*
 * 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); }




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