diff options
Diffstat (limited to 'src/main/java/org/apache/commons/math/random/AbstractRandomGenerator.java')
| -rw-r--r-- | src/main/java/org/apache/commons/math/random/AbstractRandomGenerator.java | 272 |
1 files changed, 272 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math/random/AbstractRandomGenerator.java b/src/main/java/org/apache/commons/math/random/AbstractRandomGenerator.java new file mode 100644 index 0000000..afec63e --- /dev/null +++ b/src/main/java/org/apache/commons/math/random/AbstractRandomGenerator.java @@ -0,0 +1,272 @@ +/* + * 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; + +import org.apache.commons.math.exception.NotStrictlyPositiveException; +import org.apache.commons.math.util.FastMath; + +/** + * Abstract class implementing the {@link RandomGenerator} interface. + * Default implementations for all methods other than {@link #nextDouble()} and + * {@link #setSeed(long)} are provided. + * <p> + * All data generation methods are based on {@code code nextDouble()}. + * Concrete implementations <strong>must</strong> override + * this method and <strong>should</strong> provide better / more + * performant implementations of the other methods if the underlying PRNG + * supplies them.</p> + * + * @since 1.1 + * @version $Revision: 990655 $ $Date: 2010-08-29 23:49:40 +0200 (dim. 29 août 2010) $ + */ +public abstract class AbstractRandomGenerator implements RandomGenerator { + + /** + * Cached random normal value. The default implementation for + * {@link #nextGaussian} generates pairs of values and this field caches the + * second value so that the full algorithm is not executed for every + * activation. The value {@code Double.NaN} signals that there is + * no cached value. Use {@link #clear} to clear the cached value. + */ + private double cachedNormalDeviate = Double.NaN; + + /** + * Construct a RandomGenerator. + */ + public AbstractRandomGenerator() { + super(); + + } + + /** + * Clears the cache used by the default implementation of + * {@link #nextGaussian}. Implemementations that do not override the + * default implementation of {@code nextGaussian} should call this + * method in the implementation of {@link #setSeed(long)} + */ + public void clear() { + cachedNormalDeviate = Double.NaN; + } + + /** {@inheritDoc} */ + public void setSeed(int seed) { + setSeed((long) seed); + } + + /** {@inheritDoc} */ + public void setSeed(int[] seed) { + // the following number is the largest prime that fits in 32 bits (it is 2^32 - 5) + final long prime = 4294967291l; + + long combined = 0l; + for (int s : seed) { + combined = combined * prime + s; + } + setSeed(combined); + } + + /** + * Sets the seed of the underyling random number generator using a + * {@code long} seed. Sequences of values generated starting with the + * same seeds should be identical. + * <p> + * Implementations that do not override the default implementation of + * {@code nextGaussian} should include a call to {@link #clear} in the + * implementation of this method.</p> + * + * @param seed the seed value + */ + public abstract void setSeed(long seed); + + /** + * Generates random bytes and places them into a user-supplied + * byte array. The number of random bytes produced is equal to + * the length of the byte array. + * <p> + * The default implementation fills the array with bytes extracted from + * random integers generated using {@link #nextInt}.</p> + * + * @param bytes the non-null byte array in which to put the + * random bytes + */ + public void nextBytes(byte[] bytes) { + int bytesOut = 0; + while (bytesOut < bytes.length) { + int randInt = nextInt(); + for (int i = 0; i < 3; i++) { + if ( i > 0) { + randInt = randInt >> 8; + } + bytes[bytesOut++] = (byte) randInt; + if (bytesOut == bytes.length) { + return; + } + } + } + } + + /** + * Returns the next pseudorandom, uniformly distributed {@code int} + * value from this random number generator's sequence. + * All 2<font size="-1"><sup>32</sup></font> possible {@code int} values + * should be produced with (approximately) equal probability. + * <p> + * The default implementation provided here returns + * <pre> + * <code>(int) (nextDouble() * Integer.MAX_VALUE)</code> + * </pre></p> + * + * @return the next pseudorandom, uniformly distributed {@code int} + * value from this random number generator's sequence + */ + public int nextInt() { + return (int) (nextDouble() * Integer.MAX_VALUE); + } + + /** + * Returns a pseudorandom, uniformly distributed {@code int} value + * between 0 (inclusive) and the specified value (exclusive), drawn from + * this random number generator's sequence. + * <p> + * The default implementation returns + * <pre> + * <code>(int) (nextDouble() * n</code> + * </pre></p> + * + * @param n the bound on the random number to be returned. Must be + * positive. + * @return a pseudorandom, uniformly distributed {@code int} + * value between 0 (inclusive) and n (exclusive). + * @throws NotStrictlyPositiveException if {@code n <= 0}. + */ + public int nextInt(int n) { + if (n <= 0 ) { + throw new NotStrictlyPositiveException(n); + } + int result = (int) (nextDouble() * n); + return result < n ? result : n - 1; + } + + /** + * Returns the next pseudorandom, uniformly distributed {@code long} + * value from this random number generator's sequence. All + * 2<font size="-1"><sup>64</sup></font> possible {@code long} values + * should be produced with (approximately) equal probability. + * <p> + * The default implementation returns + * <pre> + * <code>(long) (nextDouble() * Long.MAX_VALUE)</code> + * </pre></p> + * + * @return the next pseudorandom, uniformly distributed {@code long} + *value from this random number generator's sequence + */ + public long nextLong() { + return (long) (nextDouble() * Long.MAX_VALUE); + } + + /** + * Returns the next pseudorandom, uniformly distributed + * {@code boolean} value from this random number generator's + * sequence. + * <p> + * The default implementation returns + * <pre> + * <code>nextDouble() <= 0.5</code> + * </pre></p> + * + * @return the next pseudorandom, uniformly distributed + * {@code boolean} value from this random number generator's + * sequence + */ + public boolean nextBoolean() { + return nextDouble() <= 0.5; + } + + /** + * Returns the next pseudorandom, uniformly distributed {@code float} + * value between {@code 0.0} and {@code 1.0} from this random + * number generator's sequence. + * <p> + * The default implementation returns + * <pre> + * <code>(float) nextDouble() </code> + * </pre></p> + * + * @return the next pseudorandom, uniformly distributed {@code float} + * value between {@code 0.0} and {@code 1.0} from this + * random number generator's sequence + */ + public float nextFloat() { + return (float) nextDouble(); + } + + /** + * Returns the next pseudorandom, uniformly distributed + * {@code double} value between {@code 0.0} and + * {@code 1.0} from this random number generator's sequence. + * <p> + * This method provides the underlying source of random data used by the + * other methods.</p> + * + * @return the next pseudorandom, uniformly distributed + * {@code double} value between {@code 0.0} and + * {@code 1.0} from this random number generator's sequence + */ + public abstract double nextDouble(); + + /** + * Returns the next pseudorandom, Gaussian ("normally") distributed + * {@code double} value with mean {@code 0.0} and standard + * deviation {@code 1.0} from this random number generator's sequence. + * <p> + * The default implementation uses the <em>Polar Method</em> + * due to G.E.P. Box, M.E. Muller and G. Marsaglia, as described in + * D. Knuth, <u>The Art of Computer Programming</u>, 3.4.1C.</p> + * <p> + * The algorithm generates a pair of independent random values. One of + * these is cached for reuse, so the full algorithm is not executed on each + * activation. Implementations that do not override this method should + * make sure to call {@link #clear} to clear the cached value in the + * implementation of {@link #setSeed(long)}.</p> + * + * @return the next pseudorandom, Gaussian ("normally") distributed + * {@code double} value with mean {@code 0.0} and + * standard deviation {@code 1.0} from this random number + * generator's sequence + */ + public double nextGaussian() { + if (!Double.isNaN(cachedNormalDeviate)) { + double dev = cachedNormalDeviate; + cachedNormalDeviate = Double.NaN; + return dev; + } + double v1 = 0; + double v2 = 0; + double s = 1; + while (s >=1 ) { + v1 = 2 * nextDouble() - 1; + v2 = 2 * nextDouble() - 1; + s = v1 * v1 + v2 * v2; + } + if (s != 0) { + s = FastMath.sqrt(-2 * FastMath.log(s) / s); + } + cachedNormalDeviate = v2 * s; + return v1 * s; + } +} |