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Diffstat (limited to 'src/main/java/org/apache/commons/math/random/Well44497b.java')
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1 files changed, 119 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math/random/Well44497b.java b/src/main/java/org/apache/commons/math/random/Well44497b.java new file mode 100644 index 0000000..28b5dbb --- /dev/null +++ b/src/main/java/org/apache/commons/math/random/Well44497b.java @@ -0,0 +1,119 @@ +/* + * 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; + + +/** This class implements the WELL44497b 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 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. + * <p>The instance is initialized using the current time as the + * seed.</p> + */ + 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 ^ ((z4 << 7) & 0x93dd1400); + z4 = z4 ^ ((z4 << 15) & 0xfa118000); + + return z4 >>> (32 - bits); + + } + +} |