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 */ 17 18 package org.apache.commons.rng.core.source32; 19 20 import java.util.stream.Stream; 21 import org.apache.commons.rng.JumpableUniformRandomProvider; 22 import org.apache.commons.rng.LongJumpableUniformRandomProvider; 23 import org.apache.commons.rng.SplittableUniformRandomProvider; 24 import org.apache.commons.rng.UniformRandomProvider; 25 import org.apache.commons.rng.core.util.NumberFactory; 26 import org.apache.commons.rng.core.util.RandomStreams; 27 28 /** 29 * A 32-bit all purpose generator. 30 * 31 * <p>This is a member of the LXM family of generators: L=Linear congruential generator; 32 * X=Xor based generator; and M=Mix. This member uses a 32-bit LCG and 64-bit Xor-based 33 * generator. It is named as {@code "L32X64MixRandom"} in the {@code java.util.random} 34 * package introduced in JDK 17; the LXM family is described in further detail in: 35 * 36 * <blockquote>Steele and Vigna (2021) LXM: better splittable pseudorandom number generators 37 * (and almost as fast). Proceedings of the ACM on Programming Languages, Volume 5, 38 * Article 148, pp 1–31.</blockquote> 39 * 40 * <p>Memory footprint is 128 bits and the period is 2<sup>32</sup> (2<sup>64</sup> - 1). 41 * 42 * <p>This generator implements {@link 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 31-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 & 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 final class L32X64Mix extends IntProvider implements LongJumpableUniformRandomProvider, 62 SplittableUniformRandomProvider { 63 // Implementation note: 64 // This does not extend AbstractXoRoShiRo64 as the XBG function is re-implemented 65 // inline to allow parallel pipelining. Inheritance would provide only the XBG state. 66 67 /** LCG multiplier. */ 68 private static final int M = LXMSupport.M32; 69 /** Size of the state vector. */ 70 private static final int SEED_SIZE = 4; 71 72 /** Per-instance LCG additive parameter (must be odd). 73 * Cannot be final to support RestorableUniformRandomProvider. */ 74 private int la; 75 /** State of the LCG generator. */ 76 private int ls; 77 /** State 0 of the XBG generator. */ 78 private int x0; 79 /** State 1 of the XBG generator. */ 80 private int x1; 81 82 /** 83 * Creates a new instance. 84 * 85 * @param seed Initial seed. 86 * If the length is larger than 4, only the first 4 elements will 87 * be used; if smaller, the remaining elements will be automatically 88 * set. A seed containing all zeros in the last two elements 89 * will create a non-functional XBG sub-generator and a low 90 * quality output with a period of 2<sup>32</sup>. 91 * 92 * <p>The 1st element is used to set the LCG increment; the least significant bit 93 * is set to odd to ensure a full period LCG. The 2nd element is used 94 * to set the LCG state.</p> 95 */ 96 public L32X64Mix(int[] seed) { 97 setState(extendSeed(seed, SEED_SIZE)); 98 } 99 100 /** 101 * Creates a new instance using a 4 element seed. 102 * A seed containing all zeros in the last two elements 103 * will create a non-functional XBG sub-generator and a low 104 * quality output with a period of 2<sup>32</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 */ 115 public L32X64Mix(int seed0, int seed1, int seed2, int seed3) { 116 // Additive parameter must be odd 117 la = seed0 | 1; 118 ls = seed1; 119 x0 = seed2; 120 x1 = seed3; 121 } 122 123 /** 124 * Creates a copy instance. 125 * 126 * @param source Source to copy. 127 */ 128 private L32X64Mix(L32X64Mix source) { 129 super(source); 130 la = source.la; 131 ls = source.ls; 132 x0 = source.x0; 133 x1 = source.x1; 134 } 135 136 /** 137 * Copies the state into the generator state. 138 * 139 * @param state the new state 140 */ 141 private void setState(int[] state) { 142 // Additive parameter must be odd 143 la = state[0] | 1; 144 ls = state[1]; 145 x0 = state[2]; 146 x1 = state[3]; 147 } 148 149 /** {@inheritDoc} */ 150 @Override 151 protected byte[] getStateInternal() { 152 return composeStateInternal(NumberFactory.makeByteArray(new int[] {la, ls, x0, x1}), 153 super.getStateInternal()); 154 } 155 156 /** {@inheritDoc} */ 157 @Override 158 protected void setStateInternal(byte[] s) { 159 final byte[][] c = splitStateInternal(s, SEED_SIZE * Integer.BYTES); 160 setState(NumberFactory.makeIntArray(c[0])); 161 super.setStateInternal(c[1]); 162 } 163 164 /** {@inheritDoc} */ 165 @Override 166 public int next() { 167 // LXM generate. 168 // Old state is used for the output allowing parallel pipelining 169 // on processors that support multiple concurrent instructions. 170 171 final int s0 = x0; 172 final int s = ls; 173 174 // Mix 175 final int z = LXMSupport.lea32(s + s0); 176 177 // LCG update 178 ls = M * s + la; 179 180 // XBG update 181 int s1 = x1; 182 183 s1 ^= s0; 184 x0 = Integer.rotateLeft(s0, 26) ^ s1 ^ (s1 << 9); // a, b 185 x1 = Integer.rotateLeft(s1, 13); // c 186 187 return z; 188 } 189 190 /** 191 * Creates a copy of the UniformRandomProvider and then <em>retreats</em> the state of the 192 * current instance. The copy is returned. 193 * 194 * <p>The jump is performed by advancing the state of the LCG sub-generator by 1 cycle. 195 * The XBG state is unchanged. The jump size is the equivalent of moving the state 196 * <em>backwards</em> by (2<sup>64</sup> - 1) positions. It can provide up to 2<sup>32</sup> 197 * non-overlapping subsequences.</p> 198 */ 199 @Override 200 public UniformRandomProvider jump() { 201 final UniformRandomProvider copy = new L32X64Mix(this); 202 // Advance the LCG 1 step 203 ls = M * ls + la; 204 resetCachedState(); 205 return copy; 206 } 207 208 /** 209 * Creates a copy of the UniformRandomProvider and then <em>retreats</em> the state of the 210 * current instance. The copy is returned. 211 * 212 * <p>The jump is performed by advancing the state of the LCG sub-generator by 213 * 2<sup>16</sup> cycles. The XBG state is unchanged. The jump size is the equivalent 214 * of moving the state <em>backwards</em> by 2<sup>16</sup> (2<sup>64</sup> - 1) 215 * positions. It can provide up to 2<sup>16</sup> non-overlapping subsequences of 216 * length 2<sup>16</sup> (2<sup>64</sup> - 1); each subsequence can provide up to 217 * 2<sup>16</sup> non-overlapping subsequences of length (2<sup>64</sup> - 1) using 218 * the {@link #jump()} method.</p> 219 */ 220 @Override 221 public JumpableUniformRandomProvider longJump() { 222 final JumpableUniformRandomProvider copy = new L32X64Mix(this); 223 // Advance the LCG 2^16 steps 224 ls = LXMSupport.M32P * ls + LXMSupport.C32P * la; 225 resetCachedState(); 226 return copy; 227 } 228 229 /** {@inheritDoc} */ 230 @Override 231 public SplittableUniformRandomProvider split(UniformRandomProvider source) { 232 // The upper half of the long seed is discarded so use nextInt 233 return create(source.nextInt(), source); 234 } 235 236 /** {@inheritDoc} */ 237 @Override 238 public Stream<SplittableUniformRandomProvider> splits(long streamSize, SplittableUniformRandomProvider source) { 239 return RandomStreams.generateWithSeed(streamSize, source, L32X64Mix::create); 240 } 241 242 /** 243 * Create a new instance using the given {@code seed} and {@code source} of randomness 244 * to initialise the instance. 245 * 246 * @param seed Seed used to initialise the instance. 247 * @param source Source of randomness used to initialise the instance. 248 * @return A new instance. 249 */ 250 private static SplittableUniformRandomProvider create(long seed, UniformRandomProvider source) { 251 // LCG state. The addition uses the input seed. 252 // The LCG addition parameter is set to odd so left-shift the seed. 253 final int s0 = (int) seed << 1; 254 final int s1 = source.nextInt(); 255 // XBG state must not be all zero 256 int x0 = source.nextInt(); 257 int x1 = source.nextInt(); 258 if ((x0 | x1) == 0) { 259 // SplitMix style seed ensures at least one non-zero value 260 x0 = LXMSupport.lea32(s1); 261 x1 = LXMSupport.lea32(s1 + LXMSupport.GOLDEN_RATIO_32); 262 } 263 return new L32X64Mix(s0, s1, x0, x1); 264 } 265 }