AbstractWell.java
/*
* 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.rng.core.source32;
import java.util.Arrays;
import org.apache.commons.rng.core.util.NumberFactory;
/**
* 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>
*
* @since 1.0
*/
public abstract class AbstractWell extends IntProvider {
/** Block size. */
private static final int BLOCK_SIZE = 32;
/** Current index in the bytes pool. */
protected int index;
/** Bytes pool. */
protected final int[] v;
/**
* Creates an instance with the given {@code seed}.
*
* @param k Number of bits in the pool (not necessarily a multiple of 32).
* @param seed Initial seed.
*/
protected AbstractWell(final int k,
final int[] seed) {
final int r = calculateBlockCount(k);
v = new int[r];
index = 0;
// Initialize the pool content.
setSeedInternal(seed);
}
/** {@inheritDoc} */
@Override
protected byte[] getStateInternal() {
final int[] s = Arrays.copyOf(v, v.length + 1);
s[v.length] = index;
return composeStateInternal(NumberFactory.makeByteArray(s),
super.getStateInternal());
}
/** {@inheritDoc} */
@Override
protected void setStateInternal(byte[] s) {
final byte[][] c = splitStateInternal(s, (v.length + 1) * 4);
final int[] tmp = NumberFactory.makeIntArray(c[0]);
System.arraycopy(tmp, 0, v, 0, v.length);
index = tmp[v.length];
super.setStateInternal(c[1]);
}
/**
* Initializes the generator with the given {@code seed}.
*
* @param seed Seed. Cannot be null.
*/
private void setSeedInternal(final int[] seed) {
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 current = v[i - seed.length];
v[i] = (int) ((1812433253L * (current ^ (current >> 30)) + i) & 0xffffffffL);
}
}
index = 0;
}
/**
* Calculate the number of 32-bits blocks.
*
* @param k Number of bits in the pool (not necessarily a multiple of 32).
* @return the number of 32-bits blocks.
*/
private static int calculateBlockCount(final int k) {
// 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.
return (k + BLOCK_SIZE - 1) / BLOCK_SIZE;
}
/**
* Inner class used to store the indirection index table which is fixed for a given
* type of WELL class of pseudo-random number generator.
*/
protected static final class IndexTable {
/** Index indirection table giving for each index its predecessor taking table size into account. */
private final int[] iRm1;
/** Index indirection table giving for each index its second predecessor taking table size into account. */
private final int[] iRm2;
/** Index indirection table giving for each index the value index + m1 taking table size into account. */
private final int[] i1;
/** Index indirection table giving for each index the value index + m2 taking table size into account. */
private final int[] i2;
/** Index indirection table giving for each index the value index + m3 taking table size into account. */
private final int[] i3;
/** Creates a new pre-calculated indirection index table.
* @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
*/
public IndexTable(final int k, final int m1, final int m2, final int m3) {
final int r = calculateBlockCount(k);
// 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;
}
}
/**
* Returns the predecessor of the given index modulo the table size.
* @param index the index to look at
* @return (index - 1) % table size
*/
public int getIndexPred(final int index) {
return iRm1[index];
}
/**
* Returns the second predecessor of the given index modulo the table size.
* @param index the index to look at
* @return (index - 2) % table size
*/
public int getIndexPred2(final int index) {
return iRm2[index];
}
/**
* Returns index + M1 modulo the table size.
* @param index the index to look at
* @return (index + M1) % table size
*/
public int getIndexM1(final int index) {
return i1[index];
}
/**
* Returns index + M2 modulo the table size.
* @param index the index to look at
* @return (index + M2) % table size
*/
public int getIndexM2(final int index) {
return i2[index];
}
/**
* Returns index + M3 modulo the table size.
* @param index the index to look at
* @return (index + M3) % table size
*/
public int getIndexM3(final int index) {
return i3[index];
}
}
}