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 java.util.stream.Stream; 021import org.apache.commons.rng.SplittableUniformRandomProvider; 022import org.apache.commons.rng.UniformRandomProvider; 023import org.apache.commons.rng.core.util.RandomStreams; 024 025/** 026 * A 64-bit all purpose generator. 027 * 028 * <p>This is a member of the LXM family of generators: L=Linear congruential generator; 029 * X=Xor based generator; and M=Mix. This member uses a 64-bit LCG and 128-bit Xor-based 030 * generator. It is named as {@code "L64X128MixRandom"} in the {@code java.util.random} 031 * package introduced in JDK 17; the LXM family is described in further detail in: 032 * 033 * <blockquote>Steele and Vigna (2021) LXM: better splittable pseudorandom number generators 034 * (and almost as fast). Proceedings of the ACM on Programming Languages, Volume 5, 035 * Article 148, pp 1–31.</blockquote> 036 * 037 * <p>Memory footprint is 256 bits and the period is 2<sup>64</sup> (2<sup>128</sup> - 1). 038 * 039 * <p>This generator implements 040 * {@link org.apache.commons.rng.LongJumpableUniformRandomProvider LongJumpableUniformRandomProvider}. 041 * In addition instances created with a different additive parameter for the LCG are robust 042 * against accidental correlation in a multi-threaded setting. The additive parameters must be 043 * different in the most significant 63-bits. 044 * 045 * <p>This generator implements 046 * {@link org.apache.commons.rng.SplittableUniformRandomProvider SplittableUniformRandomProvider}. 047 * The stream of generators created using the {@code splits} methods support parallelisation 048 * and are robust against accidental correlation by using unique values for the additive parameter 049 * for each instance in the same stream. The primitive streaming methods support parallelisation 050 * but with no assurances of accidental correlation; each thread uses a new instance with a 051 * randomly initialised state. 052 * 053 * @see <a href="https://doi.org/10.1145/3485525">Steele & Vigna (2021) Proc. ACM Programming 054 * Languages 5, 1-31</a> 055 * @see <a href="https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/util/random/package-summary.html"> 056 * JDK 17 java.util.random javadoc</a> 057 * @since 1.5 058 */ 059public class L64X128Mix extends AbstractL64X128 implements SplittableUniformRandomProvider { 060 /** 061 * Creates a new instance. 062 * 063 * @param seed Initial seed. 064 * If the length is larger than 4, only the first 4 elements will 065 * be used; if smaller, the remaining elements will be automatically 066 * set. A seed containing all zeros in the last two elements 067 * will create a non-functional XBG sub-generator and a low 068 * quality output with a period of 2<sup>64</sup>. 069 * 070 * <p>The 1st element is used to set the LCG increment; the least significant bit 071 * is set to odd to ensure a full period LCG. The 2nd element is used 072 * to set the LCG state.</p> 073 */ 074 public L64X128Mix(long[] seed) { 075 super(seed); 076 } 077 078 /** 079 * Creates a new instance using a 4 element seed. 080 * A seed containing all zeros in the last two elements 081 * will create a non-functional XBG sub-generator and a low 082 * quality output with a period of 2<sup>64</sup>. 083 * 084 * <p>The 1st element is used to set the LCG increment; the least significant bit 085 * is set to odd to ensure a full period LCG. The 2nd element is used 086 * to set the LCG state.</p> 087 * 088 * @param seed0 Initial seed element 0. 089 * @param seed1 Initial seed element 1. 090 * @param seed2 Initial seed element 2. 091 * @param seed3 Initial seed element 3. 092 */ 093 public L64X128Mix(long seed0, long seed1, long seed2, long seed3) { 094 super(seed0, seed1, seed2, seed3); 095 } 096 097 /** 098 * Creates a copy instance. 099 * 100 * @param source Source to copy. 101 */ 102 protected L64X128Mix(L64X128Mix source) { 103 super(source); 104 } 105 106 /** {@inheritDoc} */ 107 @Override 108 public long next() { 109 // LXM generate. 110 // Old state is used for the output allowing parallel pipelining 111 // on processors that support multiple concurrent instructions. 112 113 final long s0 = x0; 114 final long s = ls; 115 116 // Mix 117 final long z = LXMSupport.lea64(s + s0); 118 119 // LCG update 120 ls = M * s + la; 121 122 // XBG update 123 long s1 = x1; 124 125 s1 ^= s0; 126 x0 = Long.rotateLeft(s0, 24) ^ s1 ^ (s1 << 16); // a, b 127 x1 = Long.rotateLeft(s1, 37); // c 128 129 return z; 130 } 131 132 /** {@inheritDoc} */ 133 @Override 134 protected L64X128Mix copy() { 135 // This exists to ensure the jump function performed in the super class returns 136 // the correct class type. It should not be public. 137 return new L64X128Mix(this); 138 } 139 140 /** {@inheritDoc} */ 141 @Override 142 public SplittableUniformRandomProvider split(UniformRandomProvider source) { 143 return create(source.nextLong(), source); 144 } 145 146 /** {@inheritDoc} */ 147 @Override 148 public Stream<SplittableUniformRandomProvider> splits(long streamSize, SplittableUniformRandomProvider source) { 149 return RandomStreams.generateWithSeed(streamSize, source, L64X128Mix::create); 150 } 151 152 /** 153 * Create a new instance using the given {@code seed} and {@code source} of randomness 154 * to initialise the instance. 155 * 156 * @param seed Seed used to initialise the instance. 157 * @param source Source of randomness used to initialise the instance. 158 * @return A new instance. 159 */ 160 private static SplittableUniformRandomProvider create(long seed, UniformRandomProvider source) { 161 // LCG state. The addition uses the input seed. 162 // The LCG addition parameter is set to odd so left-shift the seed. 163 final long s0 = seed << 1; 164 final long s1 = source.nextLong(); 165 // XBG state must not be all zero 166 long x0 = source.nextLong(); 167 long x1 = source.nextLong(); 168 if ((x0 | x1) == 0) { 169 // SplitMix style seed ensures at least one non-zero value 170 x0 = LXMSupport.lea64(s1); 171 x1 = LXMSupport.lea64(s1 + LXMSupport.GOLDEN_RATIO_64); 172 } 173 return new L64X128Mix(s0, s1, x0, x1); 174 } 175}