001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.math3.random;
018
019import java.util.Random;
020import org.apache.commons.math3.exception.NotStrictlyPositiveException;
021
022/**
023 * Utilities for creating {@link RandomGenerator} instances.
024 *
025 * @since 3.3
026 */
027public class RandomGeneratorFactory {
028    /**
029     * Class contains only static methods.
030     */
031    private RandomGeneratorFactory() {}
032
033    /**
034     * Creates a {@link RandomDataGenerator} instance that wraps a
035     * {@link Random} instance.
036     *
037     * @param rng JDK {@link Random} instance that will generate the
038     * the random data.
039     * @return the given RNG, wrapped in a {@link RandomGenerator}.
040     */
041    public static RandomGenerator createRandomGenerator(final Random rng) {
042        return new RandomGenerator() {
043            /** {@inheritDoc} */
044            public void setSeed(int seed) {
045                rng.setSeed((long) seed);
046            }
047
048            /** {@inheritDoc} */
049            public void setSeed(int[] seed) {
050                rng.setSeed(convertToLong(seed));
051            }
052
053            /** {@inheritDoc} */
054            public void setSeed(long seed) {
055                rng.setSeed(seed);
056            }
057
058            /** {@inheritDoc} */
059            public void nextBytes(byte[] bytes) {
060                rng.nextBytes(bytes);
061            }
062
063            /** {@inheritDoc} */
064            public int nextInt() {
065                return rng.nextInt();
066            }
067
068            /** {@inheritDoc} */
069            public int nextInt(int n) {
070                if (n <= 0) {
071                    throw new NotStrictlyPositiveException(n);
072                }
073                return rng.nextInt(n);
074            }
075
076            /** {@inheritDoc} */
077            public long nextLong() {
078                return rng.nextLong();
079            }
080
081            /** {@inheritDoc} */
082            public boolean nextBoolean() {
083                return rng.nextBoolean();
084            }
085
086            /** {@inheritDoc} */
087            public float nextFloat() {
088                return rng.nextFloat();
089            }
090
091            /** {@inheritDoc} */
092            public double nextDouble() {
093                return rng.nextDouble();
094            }
095
096            /** {@inheritDoc} */
097            public double nextGaussian() {
098                return rng.nextGaussian();
099            }
100        };
101    }
102
103    /**
104     * Converts seed from one representation to another.
105     *
106     * @param seed Original seed.
107     * @return the converted seed.
108     */
109    public static long convertToLong(int[] seed) {
110        // The following number is the largest prime that fits
111        // in 32 bits (i.e. 2^32 - 5).
112        final long prime = 4294967291l;
113
114        long combined = 0l;
115        for (int s : seed) {
116            combined = combined * prime + s;
117        }
118
119        return combined;
120    }
121}