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.rng.simple.internal;
018
019import org.apache.commons.rng.core.source64.SplitMix64;
020import org.apache.commons.rng.core.util.NumberFactory;
021
022/**
023 * Uses a {@code long} value to seed a {@link SplitMix64} RNG and
024 * create a {@code int[]} with the requested number of random
025 * values.
026 *
027 * @since 1.0
028 */
029public class Long2IntArray implements Seed2ArrayConverter<Long, int[]> {
030    /** Size of the output array. */
031    private final int size;
032
033    /**
034     * @param size Size of the output array.
035     */
036    public Long2IntArray(int size) {
037        this.size = size;
038    }
039
040    /** {@inheritDoc} */
041    @Override
042    public int[] convert(Long seed) {
043        return convertSeed(seed, size);
044    }
045
046    /**
047     * {@inheritDoc}
048     *
049     * @since 1.3
050     */
051    @Override
052    public int[] convert(Long seed, int outputSize) {
053        return convertSeed(seed, outputSize);
054    }
055
056    /**
057     * Convert the seed.
058     *
059     * @param seed Input seed.
060     * @param size Output array size.
061     * @return the converted seed.
062     */
063    private static int[] convertSeed(Long seed, int size) {
064        final int[] out = new int[size];
065        final SplitMix64 rng = new SplitMix64(seed);
066        // Fill pairs of ints from a long.
067        // The array is filled from the end towards the start.
068        for (int i = size - 1; i > 0; i -= 2) {
069            final long v = rng.nextLong();
070            out[i] = NumberFactory.extractHi(v);
071            out[i - 1] = NumberFactory.extractLo(v);
072        }
073        // An odd size requires a final single int at the start
074        if ((size & 1) == 1) {
075            out[0] = NumberFactory.extractHi(rng.nextLong());
076        }
077        return out;
078    }
079}