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 */
017
018package org.apache.commons.rng.core.source64;
019
020import org.apache.commons.rng.JumpableUniformRandomProvider;
021import org.apache.commons.rng.UniformRandomProvider;
022
023/**
024 * A fast all-purpose 64-bit generator.
025 *
026 * <p>This is a member of the Xor-Shift-Rotate family of generators. Memory footprint is 128 bits
027 * and the period is 2<sup>128</sup>-1. Speed is expected to be similar to
028 * {@link XoShiRo256StarStar}.</p>
029 *
030 * @see <a href="http://xoshiro.di.unimi.it/xoroshiro128plusplus.c">Original source code</a>
031 * @see <a href="http://xoshiro.di.unimi.it/">xorshiro / xoroshiro generators</a>
032 * @since 1.3
033 */
034public class XoRoShiRo128PlusPlus extends AbstractXoRoShiRo128 {
035    /** The coefficients for the jump function. */
036    private static final long[] JUMP_COEFFICIENTS = {
037        0x2bd7a6a6e99c2ddcL, 0x0992ccaf6a6fca05L
038    };
039    /** The coefficients for the long jump function. */
040    private static final long[] LONG_JUMP_COEFFICIENTS = {
041        0x360fd5f2cf8d5d99L, 0x9c6e6877736c46e3L
042    };
043
044    /**
045     * Creates a new instance.
046     *
047     * @param seed Initial seed.
048     * If the length is larger than 2, only the first 2 elements will
049     * be used; if smaller, the remaining elements will be automatically
050     * set. A seed containing all zeros will create a non-functional generator.
051     */
052    public XoRoShiRo128PlusPlus(long[] seed) {
053        super(seed);
054    }
055
056    /**
057     * Creates a new instance using a 2 element seed.
058     * A seed containing all zeros will create a non-functional generator.
059     *
060     * @param seed0 Initial seed element 0.
061     * @param seed1 Initial seed element 1.
062     */
063    public XoRoShiRo128PlusPlus(long seed0, long seed1) {
064        super(seed0, seed1);
065    }
066
067    /**
068     * Creates a copy instance.
069     *
070     * @param source Source to copy.
071     */
072    protected XoRoShiRo128PlusPlus(XoRoShiRo128PlusPlus source) {
073        super(source);
074    }
075
076    /** {@inheritDoc} */
077    @Override
078    public long next() {
079        // Override the abstract class to use a different state update step.
080        // Note: This requires different jump coefficients.
081
082        final long s0 = state0;
083        long s1 = state1;
084        final long result = Long.rotateLeft(s0 + s1, 17) + s0;
085
086        s1 ^= s0;
087        state0 = Long.rotateLeft(s0, 49) ^ s1 ^ (s1 << 21); // a, b
088        state1 = Long.rotateLeft(s1, 28); // c
089
090        return result;
091    }
092
093    /** {@inheritDoc} */
094    @Override
095    protected long nextOutput() {
096        throw new UnsupportedOperationException("The PlusPlus algorithm redefines the next() method");
097    }
098
099    /** {@inheritDoc} */
100    @Override
101    public UniformRandomProvider jump() {
102        // Duplicated from the abstract class to change the jump coefficients
103        final UniformRandomProvider copy = copy();
104        performJump(JUMP_COEFFICIENTS);
105        return copy;
106    }
107
108    /** {@inheritDoc} */
109    @Override
110    public JumpableUniformRandomProvider longJump() {
111        // Duplicated from the abstract class to change the jump coefficients
112        final JumpableUniformRandomProvider copy = copy();
113        performJump(LONG_JUMP_COEFFICIENTS);
114        return copy;
115    }
116
117    /** {@inheritDoc} */
118    @Override
119    protected XoRoShiRo128PlusPlus copy() {
120        // This exists to ensure the jump function performed in the super class returns
121        // the correct class type. It should not be public.
122        return new XoRoShiRo128PlusPlus(this);
123    }
124}