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];
- }
- }
- }