| /* |
| * Copyright 2005 The Apache Software Foundation. |
| * |
| * Licensed 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; |
| |
| /** |
| * 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>nextDouble().</code> |
| * 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 |
| * @version $Revision$ $Date$ |
| */ |
| 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</code> 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</code> should call this |
| * method in the implementation of {@link #setSeed(long)} |
| */ |
| public void clear() { |
| cachedNormalDeviate = Double.NaN; |
| } |
| |
| /** |
| * Sets the seed of the underyling random number generator using a |
| * <code>long</code> 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</code> 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 = randInt >> 8; |
| } |
| bytes[bytesOut++] = (byte) randInt; |
| if (bytesOut == bytes.length) { |
| return; |
| } |
| } |
| } |
| } |
| |
| /** |
| * Returns the next pseudorandom, uniformly distributed <code>int</code> |
| * value from this random number generator's sequence. |
| * All 2<font size="-1"><sup>32</sup></font> possible <tt>int</tt> 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</code> |
| * value from this random number generator's sequence |
| */ |
| public int nextInt() { |
| return (int) (nextDouble() * Integer.MAX_VALUE); |
| } |
| |
| /** |
| * Returns a pseudorandom, uniformly distributed <tt>int</tt> 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 <tt>int</tt> |
| * value between 0 (inclusive) and n (exclusive). |
| * @throws IllegalArgumentException if n is not positive. |
| */ |
| public int nextInt(int n) { |
| if (n <= 0 ) { |
| throw new IllegalArgumentException("upper bound must be positive"); |
| } |
| int result = (int) (nextDouble() * n); |
| return result < n ? result : n - 1; |
| } |
| |
| /** |
| * Returns the next pseudorandom, uniformly distributed <code>long</code> |
| * value from this random number generator's sequence. All |
| * 2<font size="-1"><sup>64</sup></font> possible <tt>long</tt> 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</code> |
| *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</code> 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</code> value from this random number generator's |
| * sequence |
| */ |
| public boolean nextBoolean() { |
| return nextDouble() <= 0.5; |
| } |
| |
| /** |
| * Returns the next pseudorandom, uniformly distributed <code>float</code> |
| * value between <code>0.0</code> and <code>1.0</code> 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</code> |
| * value between <code>0.0</code> and <code>1.0</code> from this |
| * random number generator's sequence |
| */ |
| public float nextFloat() { |
| return (float) nextDouble(); |
| } |
| |
| /** |
| * Returns the next pseudorandom, uniformly distributed |
| * <code>double</code> value between <code>0.0</code> and |
| * <code>1.0</code> 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</code> value between <code>0.0</code> and |
| * <code>1.0</code> from this random number generator's sequence |
| */ |
| public abstract double nextDouble(); |
| |
| /** |
| * Returns the next pseudorandom, Gaussian ("normally") distributed |
| * <code>double</code> value with mean <code>0.0</code> and standard |
| * deviation <code>1.0</code> 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</code> value with mean <code>0.0</code> and |
| * standard deviation <code>1.0</code> 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 = Math.sqrt(-2 * Math.log(s) / s); |
| } |
| cachedNormalDeviate = v2 * s; |
| return v1 * s; |
| } |
| } |
