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.source64; 19 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; 26 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 128-bit LCG and 128-bit Xor-based 32 * generator. It is named as {@code "L128X128MixRandom"} 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>128</sup> (2<sup>128</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 127-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 class L128X128Mix extends AbstractL128 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 = 2; 66 /** Low half of 128-bit LCG multiplier. */ 67 private static final long ML = LXMSupport.M128L; 68 69 /** State 0 of the XBG. */ 70 private long x0; 71 /** State 1 of the XBG. */ 72 private long x1; 73 74 /** 75 * Creates a new instance. 76 * 77 * @param seed Initial seed. 78 * If the length is larger than 6, only the first 6 elements will 79 * be used; if smaller, the remaining elements will be automatically 80 * set. A seed containing all zeros in the last four elements 81 * will create a non-functional XBG sub-generator and a low 82 * quality output with a period of 2<sup>128</sup>. 83 * 84 * <p>The 1st and 2nd elements are used to set the LCG increment; the least significant bit 85 * is set to odd to ensure a full period LCG. The 3rd and 4th elements are used 86 * to set the LCG state.</p> 87 */ 88 public L128X128Mix(long[] seed) { 89 super(seed = extendSeed(seed, SEED_SIZE)); 90 x0 = seed[4]; 91 x1 = seed[5]; 92 } 93 94 /** 95 * Creates a new instance using a 6 element seed. 96 * A seed containing all zeros in the last four elements 97 * will create a non-functional XBG sub-generator and a low 98 * quality output with a period of 2<sup>128</sup>. 99 * 100 * <p>The 1st and 2nd elements are used to set the LCG increment; the least significant bit 101 * is set to odd to ensure a full period LCG. The 3rd and 4th elements are used 102 * to set the LCG state.</p> 103 * 104 * @param seed0 Initial seed element 0. 105 * @param seed1 Initial seed element 1. 106 * @param seed2 Initial seed element 2. 107 * @param seed3 Initial seed element 3. 108 * @param seed4 Initial seed element 4. 109 * @param seed5 Initial seed element 5. 110 */ 111 public L128X128Mix(long seed0, long seed1, long seed2, long seed3, 112 long seed4, long seed5) { 113 super(seed0, seed1, seed2, seed3); 114 x0 = seed4; 115 x1 = seed5; 116 } 117 118 /** 119 * Creates a copy instance. 120 * 121 * @param source Source to copy. 122 */ 123 protected L128X128Mix(L128X128Mix source) { 124 super(source); 125 x0 = source.x0; 126 x1 = source.x1; 127 } 128 129 /** {@inheritDoc} */ 130 @Override 131 protected byte[] getStateInternal() { 132 return composeStateInternal(NumberFactory.makeByteArray( 133 new long[] {x0, x1}), 134 super.getStateInternal()); 135 } 136 137 /** {@inheritDoc} */ 138 @Override 139 protected void setStateInternal(byte[] s) { 140 final byte[][] c = splitStateInternal(s, XBG_STATE_SIZE * Long.BYTES); 141 final long[] tmp = NumberFactory.makeLongArray(c[0]); 142 x0 = tmp[0]; 143 x1 = tmp[1]; 144 super.setStateInternal(c[1]); 145 } 146 147 /** {@inheritDoc} */ 148 @Override 149 public long next() { 150 // LXM generate. 151 // Old state is used for the output allowing parallel pipelining 152 // on processors that support multiple concurrent instructions. 153 154 final long s0 = x0; 155 final long sh = lsh; 156 157 // Mix 158 final long z = LXMSupport.lea64(sh + s0); 159 160 // LCG update 161 // The LCG is, in effect, "s = m * s + a" where m = ((1LL << 64) + ML) 162 final long sl = lsl; 163 final long al = lal; 164 final long u = ML * sl; 165 // High half 166 lsh = ML * sh + LXMSupport.unsignedMultiplyHigh(ML, sl) + sl + lah + 167 // Carry propagation 168 LXMSupport.unsignedAddHigh(u, al); 169 // Low half 170 lsl = u + al; 171 172 // XBG update 173 long s1 = x1; 174 175 s1 ^= s0; 176 x0 = Long.rotateLeft(s0, 24) ^ s1 ^ (s1 << 16); // a, b 177 x1 = Long.rotateLeft(s1, 37); // c 178 179 return z; 180 } 181 182 /** 183 * {@inheritDoc} 184 * 185 * <p>The jump size is the equivalent of moving the state <em>backwards</em> by 186 * (2<sup>128</sup> - 1) positions. It can provide up to 2<sup>128</sup> 187 * non-overlapping subsequences. 188 */ 189 @Override 190 public UniformRandomProvider jump() { 191 return super.jump(); 192 } 193 194 /** 195 * {@inheritDoc} 196 * 197 * <p>The jump size is the equivalent of moving the state <em>backwards</em> by 198 * 2<sup>64</sup> (2<sup>128</sup> - 1) positions. It can provide up to 199 * 2<sup>64</sup> non-overlapping subsequences of length 2<sup>64</sup> 200 * (2<sup>128</sup> - 1); each subsequence can provide up to 2<sup>64</sup> 201 * non-overlapping subsequences of length (2<sup>128</sup> - 1) using the 202 * {@link #jump()} method. 203 */ 204 @Override 205 public JumpableUniformRandomProvider longJump() { 206 return super.longJump(); 207 } 208 209 /** {@inheritDoc} */ 210 @Override 211 AbstractL128 copy() { 212 // This exists to ensure the jump function performed in the super class returns 213 // the correct class type. It should not be public. 214 return new L128X128Mix(this); 215 } 216 217 /** {@inheritDoc} */ 218 @Override 219 public SplittableUniformRandomProvider split(UniformRandomProvider source) { 220 return create(source.nextLong(), source); 221 } 222 223 /** {@inheritDoc} */ 224 @Override 225 public Stream<SplittableUniformRandomProvider> splits(long streamSize, SplittableUniformRandomProvider source) { 226 return RandomStreams.generateWithSeed(streamSize, source, L128X128Mix::create); 227 } 228 229 /** 230 * Create a new instance using the given {@code seed} and {@code source} of randomness 231 * to initialise the instance. 232 * 233 * @param seed Seed used to initialise the instance. 234 * @param source Source of randomness used to initialise the instance. 235 * @return A new instance. 236 */ 237 private static SplittableUniformRandomProvider create(long seed, UniformRandomProvider source) { 238 // LCG state. The addition lower-half uses the input seed. 239 // The LCG addition parameter is set to odd so left-shift the seed. 240 final long s0 = source.nextLong(); 241 final long s1 = seed << 1; 242 final long s2 = source.nextLong(); 243 final long s3 = source.nextLong(); 244 // XBG state must not be all zero 245 long x0 = source.nextLong(); 246 long x1 = source.nextLong(); 247 if ((x0 | x1) == 0) { 248 // SplitMix style seed ensures at least one non-zero value 249 final long z = s3; 250 x0 = LXMSupport.lea64(z); 251 x1 = LXMSupport.lea64(z + LXMSupport.GOLDEN_RATIO_64); 252 } 253 return new L128X128Mix(s0, s1, s2, s3, x0, x1); 254 } 255 }