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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;
/** This class implements the WELL44497b 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 class Well44497b extends AbstractWell {
/** Serializable version identifier. */
private static final long serialVersionUID = 4032007538246675492L;
/** Number of bits in the pool. */
private static final int K = 44497;
/** First parameter of the algorithm. */
private static final int M1 = 23;
/** Second parameter of the algorithm. */
private static final int M2 = 481;
/** Third parameter of the algorithm. */
private static final int M3 = 229;
/** Creates a new random number generator.
* The instance is initialized using the current time as the
* seed.
*/
public Well44497b() {
super(K, M1, M2, M3);
}
/** Creates a new random number generator using a single int seed.
* @param seed the initial seed (32 bits integer)
*/
public Well44497b(int seed) {
super(K, M1, M2, M3, seed);
}
/** Creates a new random number generator using an int array seed.
* @param seed the initial seed (32 bits integers array), if null
* the seed of the generator will be related to the current time
*/
public Well44497b(int[] seed) {
super(K, M1, M2, M3, seed);
}
/** Creates a new random number generator using a single long seed.
* @param seed the initial seed (64 bits integer)
*/
public Well44497b(long seed) {
super(K, M1, M2, M3, seed);
}
/** {@inheritDoc} */
@Override
protected int next(final int bits) {
// compute raw value given by WELL44497a generator
// which is NOT maximally-equidistributed
final int indexRm1 = iRm1[index];
final int indexRm2 = iRm2[index];
final int v0 = v[index];
final int vM1 = v[i1[index]];
final int vM2 = v[i2[index]];
final int vM3 = v[i3[index]];
// the values below include the errata of the original article
final int z0 = (0xFFFF8000 & v[indexRm1]) ^ (0x00007FFF & v[indexRm2]);
final int z1 = (v0 ^ (v0 << 24)) ^ (vM1 ^ (vM1 >>> 30));
final int z2 = (vM2 ^ (vM2 << 10)) ^ (vM3 << 26);
final int z3 = z1 ^ z2;
final int z2Prime = ((z2 << 9) ^ (z2 >>> 23)) & 0xfbffffff;
final int z2Second = ((z2 & 0x00020000) != 0) ? (z2Prime ^ 0xb729fcec) : z2Prime;
int z4 = z0 ^ (z1 ^ (z1 >>> 20)) ^ z2Second ^ z3;
v[index] = z3;
v[indexRm1] = z4;
v[indexRm2] &= 0xFFFF8000;
index = indexRm1;
// add Matsumoto-Kurita tempering
// to get a maximally-equidistributed generator
z4 ^= (z4 << 7) & 0x93dd1400;
z4 ^= (z4 << 15) & 0xfa118000;
return z4 >>> (32 - bits);
}
}