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Diffstat (limited to 'src/main/java/org/apache/commons/math3/random/AbstractRandomGenerator.java')
| -rw-r--r-- | src/main/java/org/apache/commons/math3/random/AbstractRandomGenerator.java | 250 |
1 files changed, 250 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math3/random/AbstractRandomGenerator.java b/src/main/java/org/apache/commons/math3/random/AbstractRandomGenerator.java new file mode 100644 index 0000000..ce8ad85 --- /dev/null +++ b/src/main/java/org/apache/commons/math3/random/AbstractRandomGenerator.java @@ -0,0 +1,250 @@ +/* + * 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; + +import org.apache.commons.math3.exception.NotStrictlyPositiveException; +import org.apache.commons.math3.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. + * + * @since 1.1 + */ +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}. Implementations + * 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 underlying 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. + * + * @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}. + * + * @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 >>= 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> + * + * @return the next pseudorandom, uniformly distributed {@code int} value from this random + * number generator's sequence + */ + public int nextInt() { + return (int) ((2d * nextDouble() - 1d) * 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> + * + * @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> + * + * @return the next pseudorandom, uniformly distributed {@code long} value from this random + * number generator's sequence + */ + public long nextLong() { + return (long) ((2d * nextDouble() - 1d) * 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> + * + * @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> + * + * @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. + * + * @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>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)}. + * + * @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; + } +} |