| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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.rng.core.source64; |
| |
| import java.util.stream.Stream; |
| import org.apache.commons.rng.SplittableUniformRandomProvider; |
| import org.apache.commons.rng.UniformRandomProvider; |
| import org.apache.commons.rng.core.util.RandomStreams; |
| |
| /** |
| * A 64-bit all purpose generator. |
| * |
| * <p>This is a member of the LXM family of generators: L=Linear congruential generator; |
| * X=Xor based generator; and M=Mix. This member uses a 64-bit LCG and 128-bit Xor-based |
| * generator. It is named as {@code "L64X128StarStarRandom"} in the {@code java.util.random} |
| * package introduced in JDK 17; the LXM family is described in further detail in: |
| * |
| * <blockquote>Steele and Vigna (2021) LXM: better splittable pseudorandom number generators |
| * (and almost as fast). Proceedings of the ACM on Programming Languages, Volume 5, |
| * Article 148, pp 1–31.</blockquote> |
| * |
| * <p>Memory footprint is 256 bits and the period is 2<sup>64</sup> (2<sup>128</sup> - 1). |
| * |
| * <p>This generator implements |
| * {@link org.apache.commons.rng.LongJumpableUniformRandomProvider LongJumpableUniformRandomProvider}. |
| * In addition instances created with a different additive parameter for the LCG are robust |
| * against accidental correlation in a multi-threaded setting. The additive parameters must be |
| * different in the most significant 63-bits. |
| * |
| * @see <a href="https://doi.org/10.1145/3485525">Steele & Vigna (2021) Proc. ACM Programming |
| * Languages 5, 1-31</a> |
| * @see <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/random/package-summary.html"> |
| * JDK 17 java.util.random javadoc</a> |
| * @since 1.5 |
| */ |
| public class L64X128StarStar extends AbstractL64X128 implements SplittableUniformRandomProvider { |
| /** |
| * Creates a new instance. |
| * |
| * @param seed Initial seed. |
| * If the length is larger than 4, only the first 4 elements will |
| * be used; if smaller, the remaining elements will be automatically |
| * set. A seed containing all zeros in the last two elements |
| * will create a non-functional XBG sub-generator and a low |
| * quality output with a period of 2<sup>64</sup>. |
| * |
| * <p>The 1st element is used to set the LCG increment; the least significant bit |
| * is set to odd to ensure a full period LCG. The 2nd element is used |
| * to set the LCG state.</p> |
| */ |
| public L64X128StarStar(long[] seed) { |
| super(seed); |
| } |
| |
| /** |
| * Creates a new instance using a 4 element seed. |
| * A seed containing all zeros in the last two elements |
| * will create a non-functional XBG sub-generator and a low |
| * quality output with a period of 2<sup>64</sup>. |
| * |
| * <p>The 1st element is used to set the LCG increment; the least significant bit |
| * is set to odd to ensure a full period LCG. The 2nd element is used |
| * to set the LCG state.</p> |
| * |
| * @param seed0 Initial seed element 0. |
| * @param seed1 Initial seed element 1. |
| * @param seed2 Initial seed element 2. |
| * @param seed3 Initial seed element 3. |
| */ |
| public L64X128StarStar(long seed0, long seed1, long seed2, long seed3) { |
| super(seed0, seed1, seed2, seed3); |
| } |
| |
| /** |
| * Creates a copy instance. |
| * |
| * @param source Source to copy. |
| */ |
| protected L64X128StarStar(L64X128StarStar source) { |
| super(source); |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public long next() { |
| // LXM generate. |
| // Old state is used for the output allowing parallel pipelining |
| // on processors that support multiple concurrent instructions. |
| |
| final long s0 = x0; |
| final long s = ls; |
| |
| // Mix |
| final long z = Long.rotateLeft((s + s0) * 5, 7) * 9; |
| |
| // LCG update |
| ls = M * s + la; |
| |
| // XBG update |
| long s1 = x1; |
| |
| s1 ^= s0; |
| x0 = Long.rotateLeft(s0, 24) ^ s1 ^ (s1 << 16); // a, b |
| x1 = Long.rotateLeft(s1, 37); // c |
| |
| return z; |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| protected L64X128StarStar copy() { |
| // This exists to ensure the jump function performed in the super class returns |
| // the correct class type. It should not be public. |
| return new L64X128StarStar(this); |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public SplittableUniformRandomProvider split(UniformRandomProvider source) { |
| return create(source.nextLong(), source); |
| } |
| |
| /** {@inheritDoc} */ |
| @Override |
| public Stream<SplittableUniformRandomProvider> splits(long streamSize, SplittableUniformRandomProvider source) { |
| return RandomStreams.generateWithSeed(streamSize, source, L64X128StarStar::create); |
| } |
| |
| /** |
| * Create a new instance using the given {@code seed} and {@code source} of randomness |
| * to initialise the instance. |
| * |
| * @param seed Seed used to initialise the instance. |
| * @param source Source of randomness used to initialise the instance. |
| * @return A new instance. |
| */ |
| private static SplittableUniformRandomProvider create(long seed, UniformRandomProvider source) { |
| // LCG state. The addition uses the input seed. |
| // The LCG addition parameter is set to odd so left-shift the seed. |
| final long s0 = seed << 1; |
| final long s1 = source.nextLong(); |
| // XBG state must not be all zero |
| long x0 = source.nextLong(); |
| long x1 = source.nextLong(); |
| if ((x0 | x1) == 0) { |
| // SplitMix style seed ensures at least one non-zero value |
| x0 = LXMSupport.lea64(s1); |
| x1 = LXMSupport.lea64(s1 + LXMSupport.GOLDEN_RATIO_64); |
| } |
| return new L64X128StarStar(s0, s1, x0, x1); |
| } |
| } |