L64X128Mix.java
/*
* 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 "L64X128MixRandom"} 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.
*
* <p>This generator implements
* {@link org.apache.commons.rng.SplittableUniformRandomProvider SplittableUniformRandomProvider}.
* The stream of generators created using the {@code splits} methods support parallelisation
* and are robust against accidental correlation by using unique values for the additive parameter
* for each instance in the same stream. The primitive streaming methods support parallelisation
* but with no assurances of accidental correlation; each thread uses a new instance with a
* randomly initialised state.
*
* @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 L64X128Mix 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 L64X128Mix(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 L64X128Mix(long seed0, long seed1, long seed2, long seed3) {
super(seed0, seed1, seed2, seed3);
}
/**
* Creates a copy instance.
*
* @param source Source to copy.
*/
protected L64X128Mix(L64X128Mix 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 = LXMSupport.lea64(s + s0);
// 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;
}
/**
* Create a copy.
*
* @return the copy
*/
@Override
protected L64X128Mix 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 L64X128Mix(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, L64X128Mix::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 L64X128Mix(s0, s1, x0, x1);
}
}