L64X256Mix.java

  1. /*
  2.  * Licensed to the Apache Software Foundation (ASF) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * The ASF licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *      http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */

  18. package org.apache.commons.rng.core.source64;

  20. import java.util.stream.Stream;
  21. import org.apache.commons.rng.JumpableUniformRandomProvider;
  22. import org.apache.commons.rng.SplittableUniformRandomProvider;
  23. import org.apache.commons.rng.UniformRandomProvider;
  24. import org.apache.commons.rng.core.util.NumberFactory;
  25. import org.apache.commons.rng.core.util.RandomStreams;

  27. /**
  28.  * A 64-bit all purpose generator.
  29.  *
  30.  * <p>This is a member of the LXM family of generators: L=Linear congruential generator;
  31.  * X=Xor based generator; and M=Mix. This member uses a 64-bit LCG and 256-bit Xor-based
  32.  * generator. It is named as {@code "L64X256MixRandom"} in the {@code java.util.random}
  33.  * package introduced in JDK 17; the LXM family is described in further detail in:
  34.  *
  35.  * <blockquote>Steele and Vigna (2021) LXM: better splittable pseudorandom number generators
  36.  * (and almost as fast). Proceedings of the ACM on Programming Languages, Volume 5,
  37.  * Article 148, pp 1–31.</blockquote>
  38.  *
  39.  * <p>Memory footprint is 384 bits and the period is 2<sup>64</sup> (2<sup>256</sup> - 1).
  40.  *
  41.  * <p>This generator implements
  42.  * {@link org.apache.commons.rng.LongJumpableUniformRandomProvider LongJumpableUniformRandomProvider}.
  43.  * In addition instances created with a different additive parameter for the LCG are robust
  44.  * against accidental correlation in a multi-threaded setting. The additive parameters must be
  45.  * different in the most significant 63-bits.
  46.  *
  47.  * <p>This generator implements
  48.  * {@link org.apache.commons.rng.SplittableUniformRandomProvider SplittableUniformRandomProvider}.
  49.  * The stream of generators created using the {@code splits} methods support parallelisation
  50.  * and are robust against accidental correlation by using unique values for the additive parameter
  51.  * for each instance in the same stream. The primitive streaming methods support parallelisation
  52.  * but with no assurances of accidental correlation; each thread uses a new instance with a
  53.  * randomly initialised state.
  54.  *
  55.  * @see <a href="https://doi.org/10.1145/3485525">Steele &amp; Vigna (2021) Proc. ACM Programming
  56.  *      Languages 5, 1-31</a>
  57.  * @see <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/random/package-summary.html">
  58.  *      JDK 17 java.util.random javadoc</a>
  59.  * @since 1.5
  60.  */
  61. public class L64X256Mix extends AbstractL64 implements SplittableUniformRandomProvider {
  62.     /** Size of the seed vector. */
  63.     private static final int SEED_SIZE = 6;
  64.     /** Size of the XBG state vector. */
  65.     private static final int XBG_STATE_SIZE = 4;
  66.     /** LCG multiplier. */
  67.     private static final long M = LXMSupport.M64;

  69.     /** State 0 of the XBG. */
  70.     private long x0;
  71.     /** State 1 of the XBG. */
  72.     private long x1;
  73.     /** State 2 of the XBG. */
  74.     private long x2;
  75.     /** State 3 of the XBG. */
  76.     private long x3;

  78.     /**
  79.      * Creates a new instance.
  80.      *
  81.      * @param seed Initial seed.
  82.      * If the length is larger than 6, only the first 6 elements will
  83.      * be used; if smaller, the remaining elements will be automatically
  84.      * set. A seed containing all zeros in the last four elements
  85.      * will create a non-functional XBG sub-generator and a low
  86.      * quality output with a period of 2<sup>64</sup>.
  87.      *
  88.      * <p>The 1st element is used to set the LCG increment; the least significant bit
  89.      * is set to odd to ensure a full period LCG. The 2nd element is used
  90.      * to set the LCG state.</p>
  91.      */
  92.     public L64X256Mix(long[] seed) {
  93.         super(seed = extendSeed(seed, SEED_SIZE));
  94.         x0 = seed[2];
  95.         x1 = seed[3];
  96.         x2 = seed[4];
  97.         x3 = seed[5];
  98.     }

  100.     /**
  101.      * Creates a new instance using a 6 element seed.
  102.      * A seed containing all zeros in the last four elements
  103.      * will create a non-functional XBG sub-generator and a low
  104.      * quality output with a period of 2<sup>64</sup>.
  105.      *
  106.      * <p>The 1st element is used to set the LCG increment; the least significant bit
  107.      * is set to odd to ensure a full period LCG. The 2nd element is used
  108.      * to set the LCG state.</p>
  109.      *
  110.      * @param seed0 Initial seed element 0.
  111.      * @param seed1 Initial seed element 1.
  112.      * @param seed2 Initial seed element 2.
  113.      * @param seed3 Initial seed element 3.
  114.      * @param seed4 Initial seed element 4.
  115.      * @param seed5 Initial seed element 5.
  116.      */
  117.     public L64X256Mix(long seed0, long seed1, long seed2, long seed3,
  118.                       long seed4, long seed5) {
  119.         super(seed0, seed1);
  120.         x0 = seed2;
  121.         x1 = seed3;
  122.         x2 = seed4;
  123.         x3 = seed5;
  124.     }

  126.     /**
  127.      * Creates a copy instance.
  128.      *
  129.      * @param source Source to copy.
  130.      */
  131.     protected L64X256Mix(L64X256Mix source) {
  132.         super(source);
  133.         x0 = source.x0;
  134.         x1 = source.x1;
  135.         x2 = source.x2;
  136.         x3 = source.x3;
  137.     }

  139.     /** {@inheritDoc} */
  140.     @Override
  141.     protected byte[] getStateInternal() {
  142.         return composeStateInternal(NumberFactory.makeByteArray(
  143.                                         new long[] {x0, x1, x2, x3}),
  144.                                     super.getStateInternal());
  145.     }

  147.     /** {@inheritDoc} */
  148.     @Override
  149.     protected void setStateInternal(byte[] s) {
  150.         final byte[][] c = splitStateInternal(s, XBG_STATE_SIZE * Long.BYTES);
  151.         final long[] tmp = NumberFactory.makeLongArray(c[0]);
  152.         x0 = tmp[0];
  153.         x1 = tmp[1];
  154.         x2 = tmp[2];
  155.         x3 = tmp[3];
  156.         super.setStateInternal(c[1]);
  157.     }

  159.     /** {@inheritDoc} */
  160.     @Override
  161.     public long next() {
  162.         // LXM generate.
  163.         // Old state is used for the output allowing parallel pipelining
  164.         // on processors that support multiple concurrent instructions.

  166.         long s0 = x0;
  167.         final long s = ls;

  169.         // Mix
  170.         final long z = LXMSupport.lea64(s + s0);

  172.         // LCG update
  173.         ls = M * s + la;

  175.         // XBG update
  176.         long s1 = x1;
  177.         long s2 = x2;
  178.         long s3 = x3;

  180.         final long t = s1 << 17;

  182.         s2 ^= s0;
  183.         s3 ^= s1;
  184.         s1 ^= s2;
  185.         s0 ^= s3;

  187.         s2 ^= t;

  189.         s3 = Long.rotateLeft(s3, 45);

  191.         x0 = s0;
  192.         x1 = s1;
  193.         x2 = s2;
  194.         x3 = s3;

  196.         return z;
  197.     }

  199.     /**
  200.      * {@inheritDoc}
  201.      *
  202.      * <p>The jump size is the equivalent of moving the state <em>backwards</em> by
  203.      * (2<sup>256</sup> - 1) positions. It can provide up to 2<sup>64</sup>
  204.      * non-overlapping subsequences.
  205.      */
  206.     @Override
  207.     public UniformRandomProvider jump() {
  208.         return super.jump();
  209.     }

  211.     /**
  212.      * {@inheritDoc}
  213.      *
  214.      * <p>The jump size is the equivalent of moving the state <em>backwards</em> by
  215.      * 2<sup>32</sup> (2<sup>256</sup> - 1) positions. It can provide up to
  216.      * 2<sup>32</sup> non-overlapping subsequences of length 2<sup>32</sup>
  217.      * (2<sup>256</sup> - 1); each subsequence can provide up to 2<sup>32</sup>
  218.      * non-overlapping subsequences of length (2<sup>256</sup> - 1) using the
  219.      * {@link #jump()} method.
  220.      */
  221.     @Override
  222.     public JumpableUniformRandomProvider longJump() {
  223.         return super.longJump();
  224.     }

  226.     /** {@inheritDoc} */
  227.     @Override
  228.     AbstractL64 copy() {
  229.         // This exists to ensure the jump function performed in the super class returns
  230.         // the correct class type. It should not be public.
  231.         return new L64X256Mix(this);
  232.     }

  234.     /** {@inheritDoc} */
  235.     @Override
  236.     public SplittableUniformRandomProvider split(UniformRandomProvider source) {
  237.         return create(source.nextLong(), source);
  238.     }

  240.     /** {@inheritDoc} */
  241.     @Override
  242.     public Stream<SplittableUniformRandomProvider> splits(long streamSize, SplittableUniformRandomProvider source) {
  243.         return RandomStreams.generateWithSeed(streamSize, source, L64X256Mix::create);
  244.     }

  246.     /**
  247.      * Create a new instance using the given {@code seed} and {@code source} of randomness
  248.      * to initialise the instance.
  249.      *
  250.      * @param seed Seed used to initialise the instance.
  251.      * @param source Source of randomness used to initialise the instance.
  252.      * @return A new instance.
  253.      */
  254.     private static SplittableUniformRandomProvider create(long seed, UniformRandomProvider source) {
  255.         // LCG state. The addition uses the input seed.
  256.         // The LCG addition parameter is set to odd so left-shift the seed.
  257.         final long s0 = seed << 1;
  258.         final long s1 = source.nextLong();
  259.         // XBG state must not be all zero
  260.         long x0 = source.nextLong();
  261.         long x1 = source.nextLong();
  262.         long x2 = source.nextLong();
  263.         long x3 = source.nextLong();
  264.         if ((x0 | x1 | x2 | x3) == 0) {
  265.             // SplitMix style seed ensures at least one non-zero value
  266.             long z = s1;
  267.             x0 = LXMSupport.lea64(z);
  268.             x1 = LXMSupport.lea64(z += LXMSupport.GOLDEN_RATIO_64);
  269.             x2 = LXMSupport.lea64(z += LXMSupport.GOLDEN_RATIO_64);
  270.             x3 = LXMSupport.lea64(z + LXMSupport.GOLDEN_RATIO_64);
  271.         }
  272.         return new L64X256Mix(s0, s1, x0, x1, x2, x3);
  273.     }
  274. }
Created with JaCoCo 0.8.12.202403310830Code Coverage Report for Apache Commons RNG 1.6