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.core.source32;
018
019import org.apache.commons.rng.core.util.NumberFactory;
020
021/**
022 * Implement the Small, Fast, Counting (SFC) 32-bit generator of Chris Doty-Humphrey.
023 * The original source is the PractRand test suite by the same author.
024 *
025 * <p>The state size is 128-bits; the period is a minimum of 2<sup>32</sup> and an
026 * average of approximately 2<sup>127</sup>.</p>
027 *
028 * @see <a href="http://pracrand.sourceforge.net/">PractRand</a>
029 * @since 1.3
030 */
031public class DotyHumphreySmallFastCounting32 extends IntProvider {
032    /** Size of the seed. */
033    private static final int SEED_SIZE = 3;
034
035    /** State a. */
036    private int a;
037    /** State b. */
038    private int b;
039    /** State c. */
040    private int c;
041    /** Counter. */
042    private int counter;
043
044    /**
045     * Creates an instance with the given seed.
046     *
047     * @param seed Initial seed.
048     * If the length is larger than 3, only the first 3 elements will
049     * be used; if smaller, the remaining elements will be automatically set.
050     */
051    public DotyHumphreySmallFastCounting32(int[] seed) {
052        if (seed.length < SEED_SIZE) {
053            final int[] state = new int[SEED_SIZE];
054            fillState(state, seed);
055            setSeedInternal(state);
056        } else {
057            setSeedInternal(seed);
058        }
059    }
060
061    /**
062     * Seeds the RNG.
063     *
064     * @param seed Seed.
065     */
066    private void setSeedInternal(int[] seed) {
067        a = seed[0];
068        b = seed[1];
069        c = seed[2];
070        counter = 1;
071        for (int i = 0; i < 15; i++) {
072            next();
073        }
074    }
075
076    /** {@inheritDoc} */
077    @Override
078    public final int next() {
079        final int tmp = a + b + counter++;
080        a = b ^ (b >>> 9);
081        b = c + (c << 3);
082        c = Integer.rotateLeft(c, 21) + tmp;
083        return tmp;
084    }
085
086    /** {@inheritDoc} */
087    @Override
088    protected byte[] getStateInternal() {
089        return composeStateInternal(NumberFactory.makeByteArray(new int[] {a, b, c, counter}),
090                                    super.getStateInternal());
091    }
092
093    /** {@inheritDoc} */
094    @Override
095    protected void setStateInternal(byte[] s) {
096        final byte[][] parts = splitStateInternal(s, 4 * 4);
097
098        final int[] tmp = NumberFactory.makeIntArray(parts[0]);
099        a = tmp[0];
100        b = tmp[1];
101        c = tmp[2];
102        counter = tmp[3];
103
104        super.setStateInternal(parts[1]);
105    }
106}