L128X256Mix.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.JumpableUniformRandomProvider;
import org.apache.commons.rng.SplittableUniformRandomProvider;
import org.apache.commons.rng.UniformRandomProvider;
import org.apache.commons.rng.core.util.NumberFactory;
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 128-bit LCG and 256-bit Xor-based
* generator. It is named as {@code "L128X256MixRandom"} 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 512 bits and the period is 2<sup>128</sup> (2<sup>256</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 127-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 L128X256Mix extends AbstractL128 implements SplittableUniformRandomProvider {
/** Size of the seed vector. */
private static final int SEED_SIZE = 8;
/** Size of the XBG state vector. */
private static final int XBG_STATE_SIZE = 4;
/** Low half of 128-bit LCG multiplier. */
private static final long ML = LXMSupport.M128L;
/** State 0 of the XBG. */
private long x0;
/** State 1 of the XBG. */
private long x1;
/** State 2 of the XBG. */
private long x2;
/** State 3 of the XBG. */
private long x3;
/**
* Creates a new instance.
*
* @param seed Initial seed.
* If the length is larger than 8, only the first 8 elements will
* be used; if smaller, the remaining elements will be automatically
* set. A seed containing all zeros in the last four elements
* will create a non-functional XBG sub-generator and a low
* quality output with a period of 2<sup>128</sup>.
*
* <p>The 1st and 2nd elements are used to set the LCG increment; the least significant bit
* is set to odd to ensure a full period LCG. The 3rd and 4th elements are used
* to set the LCG state.</p>
*/
public L128X256Mix(long[] seed) {
super(seed = extendSeed(seed, SEED_SIZE));
x0 = seed[4];
x1 = seed[5];
x2 = seed[6];
x3 = seed[7];
}
/**
* Creates a new instance using an 8 element seed.
* A seed containing all zeros in the last four elements
* will create a non-functional XBG sub-generator and a low
* quality output with a period of 2<sup>128</sup>.
*
* <p>The 1st and 2nd elements are used to set the LCG increment; the least significant bit
* is set to odd to ensure a full period LCG. The 3rd and 4th elements are 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.
* @param seed4 Initial seed element 4.
* @param seed5 Initial seed element 5.
* @param seed6 Initial seed element 6.
* @param seed7 Initial seed element 7.
*/
public L128X256Mix(long seed0, long seed1, long seed2, long seed3,
long seed4, long seed5, long seed6, long seed7) {
super(seed0, seed1, seed2, seed3);
x0 = seed4;
x1 = seed5;
x2 = seed6;
x3 = seed7;
}
/**
* Creates a copy instance.
*
* @param source Source to copy.
*/
protected L128X256Mix(L128X256Mix source) {
super(source);
x0 = source.x0;
x1 = source.x1;
x2 = source.x2;
x3 = source.x3;
}
/** {@inheritDoc} */
@Override
protected byte[] getStateInternal() {
return composeStateInternal(NumberFactory.makeByteArray(
new long[] {x0, x1, x2, x3}),
super.getStateInternal());
}
/** {@inheritDoc} */
@Override
protected void setStateInternal(byte[] s) {
final byte[][] c = splitStateInternal(s, XBG_STATE_SIZE * Long.BYTES);
final long[] tmp = NumberFactory.makeLongArray(c[0]);
x0 = tmp[0];
x1 = tmp[1];
x2 = tmp[2];
x3 = tmp[3];
super.setStateInternal(c[1]);
}
/** {@inheritDoc} */
@Override
public long next() {
// LXM generate.
// Old state is used for the output allowing parallel pipelining
// on processors that support multiple concurrent instructions.
long s0 = x0;
final long sh = lsh;
// Mix
final long z = LXMSupport.lea64(sh + s0);
// LCG update
// The LCG is, in effect, "s = m * s + a" where m = ((1LL << 64) + ML)
final long sl = lsl;
final long al = lal;
final long u = ML * sl;
// High half
lsh = ML * sh + LXMSupport.unsignedMultiplyHigh(ML, sl) + sl + lah +
// Carry propagation
LXMSupport.unsignedAddHigh(u, al);
// Low half
lsl = u + al;
// XBG update
long s1 = x1;
long s2 = x2;
long s3 = x3;
final long t = s1 << 17;
s2 ^= s0;
s3 ^= s1;
s1 ^= s2;
s0 ^= s3;
s2 ^= t;
s3 = Long.rotateLeft(s3, 45);
x0 = s0;
x1 = s1;
x2 = s2;
x3 = s3;
return z;
}
/**
* {@inheritDoc}
*
* <p>The jump size is the equivalent of moving the state <em>backwards</em> by
* (2<sup>256</sup> - 1) positions. It can provide up to 2<sup>128</sup>
* non-overlapping subsequences.
*/
@Override
public UniformRandomProvider jump() {
return super.jump();
}
/**
* {@inheritDoc}
*
* <p>The jump size is the equivalent of moving the state <em>backwards</em> by
* 2<sup>64</sup> (2<sup>256</sup> - 1) positions. It can provide up to
* 2<sup>64</sup> non-overlapping subsequences of length 2<sup>64</sup>
* (2<sup>256</sup> - 1); each subsequence can provide up to 2<sup>64</sup>
* non-overlapping subsequences of length (2<sup>256</sup> - 1) using the
* {@link #jump()} method.
*/
@Override
public JumpableUniformRandomProvider longJump() {
return super.longJump();
}
/** {@inheritDoc} */
@Override
AbstractL128 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 L128X256Mix(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, L128X256Mix::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 lower-half uses the input seed.
// The LCG addition parameter is set to odd so left-shift the seed.
final long s0 = source.nextLong();
final long s1 = seed << 1;
final long s2 = source.nextLong();
final long s3 = source.nextLong();
// XBG state must not be all zero
long x0 = source.nextLong();
long x1 = source.nextLong();
long x2 = source.nextLong();
long x3 = source.nextLong();
if ((x0 | x1 | x2 | x3) == 0) {
// SplitMix style seed ensures at least one non-zero value
long z = s3;
x0 = LXMSupport.lea64(z);
x1 = LXMSupport.lea64(z += LXMSupport.GOLDEN_RATIO_64);
x2 = LXMSupport.lea64(z += LXMSupport.GOLDEN_RATIO_64);
x3 = LXMSupport.lea64(z + LXMSupport.GOLDEN_RATIO_64);
}
// The LCG addition parameter is set to odd so left-shift the seed
return new L128X256Mix(s0, s1, s2, s3, x0, x1, x2, x3);
}
}