1 /* 2 * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package jdk.random; 27 28 import java.util.concurrent.atomic.AtomicLong; 29 import java.util.random.RandomGenerator; 30 import jdk.internal.util.random.RandomSupport; 31 import jdk.internal.util.random.RandomSupport.AbstractSplittableWithBrineGenerator; 32 import jdk.internal.util.random.RandomSupport.RandomGeneratorProperties; 33 34 /** 35 * A "splittable" pseudorandom number generator (PRNG) whose period 36 * is roughly 2<sup>320</sup>. Class {@link L64X256MixRandom} implements 37 * interfaces {@link RandomGenerator} and {@link SplittableGenerator}, 38 * and therefore supports methods for producing pseudorandomly chosen 39 * values of type {@code int}, {@code long}, {@code float}, {@code double}, 40 * and {@code boolean} (and for producing streams of pseudorandomly chosen 41 * numbers of type {@code int}, {@code long}, and {@code double}), 42 * as well as methods for creating new split-off {@link L64X256MixRandom} 43 * objects or streams of such objects. 44 * 45 * <p>The {@link L64X256MixRandom} algorithm is a specific member of 46 * the LXM family of algorithms for pseudorandom number generators; 47 * for more information, see the documentation for package 48 * {@link jdk.random}. Each instance of {@link L64X256MixRandom} 49 * has 320 bits of state plus one 64-bit instance-specific parameter. 50 * 51 * <p>If two instances of {@link L64X256MixRandom} are created with 52 * the same seed within the same program execution, and the same 53 * sequence of method calls is made for each, they will generate and 54 * return identical sequences of values. 55 * 56 * <p>As with {@link java.util.SplittableRandom}, instances of 57 * {@link L64X256MixRandom} are <em>not</em> thread-safe. They are 58 * designed to be split, not shared, across threads (see the {@link #split} 59 * method). For example, a {@link java.util.concurrent.ForkJoinTask} 60 * fork/join-style computation using random numbers might include a 61 * construction of the form 62 * {@code new Subtask(someL64X256MixRandom.split()).fork()}. 63 * 64 * <p>This class provides additional methods for generating random 65 * streams, that employ the above techniques when used in 66 * {@code stream.parallel()} mode. 67 * 68 * <p>Instances of {@link L64X256MixRandom} are not cryptographically 69 * secure. Consider instead using {@link java.security.SecureRandom} 70 * in security-sensitive applications. Additionally, 71 * default-constructed instances do not use a cryptographically random 72 * seed unless the {@linkplain System#getProperty system property} 73 * {@code java.util.secureRandomSeed} is set to {@code true}. 74 * 75 * @since 17 76 * 77 */ 78 @RandomGeneratorProperties( 79 name = "L64X256MixRandom", 80 group = "LXM", 81 i = 256, j = 1, k = 64, 82 equidistribution = 4 83 ) 84 public final class L64X256MixRandom extends AbstractSplittableWithBrineGenerator { 85 86 /* 87 * Implementation Overview. 88 * 89 * The split operation uses the current generator to choose six new 64-bit 90 * long values that are then used to initialize the parameter `a` and the 91 * state variables `s`, `x0`, `x1`, `x2`, and `x3` for a newly constructed 92 * generator. 93 * 94 * With extremely high probability, no two generators so chosen 95 * will have the same `a` parameter, and testing has indicated 96 * that the values generated by two instances of {@link L64X256MixRandom} 97 * will be (approximately) independent if have different values for `a`. 98 * 99 * The default (no-argument) constructor, in essence, uses 100 * "defaultGen" to generate six new 64-bit values for the same 101 * purpose. Multiple generators created in this way will certainly 102 * differ in their `a` parameters. The defaultGen state must be accessed 103 * in a thread-safe manner, so we use an AtomicLong to represent 104 * this state. To bootstrap the defaultGen, we start off using a 105 * seed based on current time unless the 106 * java.util.secureRandomSeed property is set. This serves as a 107 * slimmed-down (and insecure) variant of SecureRandom that also 108 * avoids stalls that may occur when using /dev/random. 109 * 110 * File organization: First static fields, then instance 111 * fields, then constructors, then instance methods. 112 */ 113 114 /* ---------------- static fields ---------------- */ 115 116 /** 117 * The seed generator for default constructors. 118 */ 119 private static final AtomicLong defaultGen = new AtomicLong(RandomSupport.initialSeed()); 120 121 /* 122 * Multiplier used in the LCG portion of the algorithm. 123 * Chosen based on research by Sebastiano Vigna and Guy Steele (2019). 124 * The spectral scores for dimensions 2 through 8 for the multiplier 0xd1342543de82ef95 125 * are [0.958602, 0.937479, 0.870757, 0.822326, 0.820405, 0.813065, 0.760215]. 126 */ 127 128 private static final long M = 0xd1342543de82ef95L; 129 130 /* ---------------- instance fields ---------------- */ 131 132 /** 133 * The parameter that is used as an additive constant for the LCG. 134 * Must be odd. 135 */ 136 private final long a; 137 138 /** 139 * The per-instance state: s for the LCG; x0, x1, x2, and x3 for the XBG. 140 * At least one of the four fields x0, x1, x2, and x3 must be nonzero. 141 */ 142 private long s, x0, x1, x2, x3; 143 144 /* ---------------- constructors ---------------- */ 145 146 /** 147 * Basic constructor that initializes all fields from parameters. 148 * It then adjusts the field values if necessary to ensure that 149 * all constraints on the values of fields are met. 150 * 151 * @param a additive parameter for the LCG 152 * @param s initial state for the LCG 153 * @param x0 first word of the initial state for the XBG 154 * @param x1 second word of the initial state for the XBG 155 * @param x2 third word of the initial state for the XBG 156 * @param x3 fourth word of the initial state for the XBG 157 */ L64X256MixRandom(long a, long s, long x0, long x1, long x2, long x3)158 public L64X256MixRandom(long a, long s, long x0, long x1, long x2, long x3) { 159 // Force a to be odd. 160 this.a = a | 1; 161 this.s = s; 162 this.x0 = x0; 163 this.x1 = x1; 164 this.x2 = x2; 165 this.x3 = x3; 166 // If x0, x1, x2, and x3 are all zero, we must choose nonzero values. 167 if ((x0 | x1 | x2 | x3) == 0) { 168 long v = s; 169 // At least three of the four values generated here will be nonzero. 170 this.x0 = RandomSupport.mixStafford13(v += RandomSupport.GOLDEN_RATIO_64); 171 this.x1 = RandomSupport.mixStafford13(v += RandomSupport.GOLDEN_RATIO_64); 172 this.x2 = RandomSupport.mixStafford13(v += RandomSupport.GOLDEN_RATIO_64); 173 this.x3 = RandomSupport.mixStafford13(v + RandomSupport.GOLDEN_RATIO_64); 174 } 175 } 176 177 /** 178 * Creates a new instance of {@link L64X256MixRandom} using the 179 * specified {@code long} value as the initial seed. Instances of 180 * {@link L64X256MixRandom} created with the same seed in the same 181 * program generate identical sequences of values. 182 * 183 * @param seed the initial seed 184 */ L64X256MixRandom(long seed)185 public L64X256MixRandom(long seed) { 186 // Using a value with irregularly spaced 1-bits to xor the seed 187 // argument tends to improve "pedestrian" seeds such as 0 or 188 // other small integers. We may as well use SILVER_RATIO_64. 189 // 190 // The seed is hashed by mixMurmur64 to produce the `a` parameter. 191 // The seed is hashed by mixStafford13 to produce the initial `x0`, 192 // which will then be used to produce the first generated value. 193 // The other x values are filled in as if by a SplitMix PRNG with 194 // GOLDEN_RATIO_64 as the gamma value and mixStafford13 as the mixer. 195 this(RandomSupport.mixMurmur64(seed ^= RandomSupport.SILVER_RATIO_64), 196 1, 197 RandomSupport.mixStafford13(seed), 198 RandomSupport.mixStafford13(seed += RandomSupport.GOLDEN_RATIO_64), 199 RandomSupport.mixStafford13(seed += RandomSupport.GOLDEN_RATIO_64), 200 RandomSupport.mixStafford13(seed + RandomSupport.GOLDEN_RATIO_64)); 201 } 202 203 /** 204 * Creates a new instance of {@link L64X256MixRandom} that is likely to 205 * generate sequences of values that are statistically independent 206 * of those of any other instances in the current program execution, 207 * but may, and typically does, vary across program invocations. 208 */ L64X256MixRandom()209 public L64X256MixRandom() { 210 // Using GOLDEN_RATIO_64 here gives us a good Weyl sequence of values. 211 this(defaultGen.getAndAdd(RandomSupport.GOLDEN_RATIO_64)); 212 } 213 214 /** 215 * Creates a new instance of {@link L64X256MixRandom} using the specified array of 216 * initial seed bytes. Instances of {@link L64X256MixRandom} created with the same 217 * seed array in the same program execution generate identical sequences of values. 218 * 219 * @param seed the initial seed 220 */ L64X256MixRandom(byte[] seed)221 public L64X256MixRandom(byte[] seed) { 222 // Convert the seed to 6 long values, of which the last 4 are not all zero. 223 long[] data = RandomSupport.convertSeedBytesToLongs(seed, 6, 4); 224 long a = data[0], s = data[1], x0 = data[2], x1 = data[3], x2 = data[4], x3 = data[5]; 225 // Force a to be odd. 226 this.a = a | 1; 227 this.s = s; 228 this.x0 = x0; 229 this.x1 = x1; 230 this.x2 = x2; 231 this.x3 = x3; 232 } 233 234 /* ---------------- public methods ---------------- */ 235 236 @Override split(SplittableGenerator source, long brine)237 public SplittableGenerator split(SplittableGenerator source, long brine) { 238 // Pick a new instance "at random", but use the brine for `a`. 239 return new L64X256MixRandom(brine << 1, source.nextLong(), 240 source.nextLong(), source.nextLong(), 241 source.nextLong(), source.nextLong()); 242 } 243 244 @Override nextLong()245 public long nextLong() { 246 // Compute the result based on current state information 247 // (this allows the computation to be overlapped with state update). 248 final long result = RandomSupport.mixLea64(s + x0); 249 250 // Update the LCG subgenerator 251 s = M * s + a; 252 253 // Update the XBG subgenerator 254 long q0 = x0, q1 = x1, q2 = x2, q3 = x3; 255 { // xoshiro256 1.0 256 long t = q1 << 17; 257 q2 ^= q0; 258 q3 ^= q1; 259 q1 ^= q2; 260 q0 ^= q3; 261 q2 ^= t; 262 q3 = Long.rotateLeft(q3, 45); 263 } 264 x0 = q0; x1 = q1; x2 = q2; x3 = q3; 265 266 return result; 267 } 268 269 } 270