| /* |
| * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package jdk.random; |
| |
| import java.util.concurrent.atomic.AtomicLong; |
| import java.util.random.RandomGenerator; |
| import jdk.internal.util.random.RandomSupport; |
| import jdk.internal.util.random.RandomSupport.AbstractSplittableWithBrineGenerator; |
| import jdk.internal.util.random.RandomSupport.RandomGeneratorProperties; |
| |
| /** |
| * A "splittable" pseudorandom number generator (PRNG) whose period |
| * is roughly 2<sup>256</sup>. Class {@link L128X128MixRandom} implements |
| * interfaces {@link RandomGenerator} and {@link SplittableGenerator}, |
| * and therefore supports methods for producing pseudorandomly chosen |
| * values of type {@code int}, {@code long}, {@code float}, {@code double}, |
| * and {@code boolean} (and for producing streams of pseudorandomly chosen |
| * numbers of type {@code int}, {@code long}, and {@code double}), |
| * as well as methods for creating new split-off {@link L128X128MixRandom} |
| * objects or streams of such objects. |
| * |
| * <p>The {@link L128X128MixRandom} algorithm is a specific member of |
| * the LXM family of algorithms for pseudorandom number generators; |
| * for more information, see the documentation for package |
| * {@link jdk.random}. Each instance of {@link L128X128MixRandom} |
| * has 256 bits of state plus one 128-bit instance-specific parameter. |
| * |
| * <p>If two instances of {@link L128X128MixRandom} are created with |
| * the same seed within the same program execution, and the same |
| * sequence of method calls is made for each, they will generate and |
| * return identical sequences of values. |
| * |
| * <p>As with {@link java.util.SplittableRandom}, instances of |
| * {@link L128X128MixRandom} are <em>not</em> thread-safe. They are |
| * designed to be split, not shared, across threads (see the {@link #split} |
| * method). For example, a {@link java.util.concurrent.ForkJoinTask} |
| * fork/join-style computation using random numbers might include a |
| * construction of the form |
| * {@code new Subtask(someL128X128MixRandom.split()).fork()}. |
| * |
| * <p>This class provides additional methods for generating random |
| * streams, that employ the above techniques when used in |
| * {@code stream.parallel()} mode. |
| * |
| * <p>Instances of {@link L128X128MixRandom} are not cryptographically |
| * secure. Consider instead using {@link java.security.SecureRandom} |
| * in security-sensitive applications. Additionally, |
| * default-constructed instances do not use a cryptographically random |
| * seed unless the {@linkplain System#getProperty system property} |
| * {@code java.util.secureRandomSeed} is set to {@code true}. |
| * |
| * @since 17 |
| * |
| */ |
| @RandomGeneratorProperties( |
| name = "L128X128MixRandom", |
| group = "LXM", |
| i = 128, j = 1, k = 128, |
| equidistribution = 1 |
| ) |
| public final class L128X128MixRandom extends AbstractSplittableWithBrineGenerator { |
| |
| /* |
| * Implementation Overview. |
| * |
| * The split operation uses the current generator to choose four new 64-bit |
| * long values that are then used to initialize the parameter `a` and the |
| * state variables `s`, `x0`, and `x1` for a newly constructed generator. |
| * |
| * With extremely high probability, no two generators so chosen |
| * will have the same `a` parameter, and testing has indicated |
| * that the values generated by two instances of {@link L128X128MixRandom} |
| * will be (approximately) independent if have different values for `a`. |
| * |
| * The default (no-argument) constructor, in essence, uses |
| * "defaultGen" to generate four new 64-bit values for the same |
| * purpose. Multiple generators created in this way will certainly |
| * differ in their `a` parameters. The defaultGen state must be accessed |
| * in a thread-safe manner, so we use an AtomicLong to represent |
| * this state. To bootstrap the defaultGen, we start off using a |
| * seed based on current time unless the |
| * java.util.secureRandomSeed property is set. This serves as a |
| * slimmed-down (and insecure) variant of SecureRandom that also |
| * avoids stalls that may occur when using /dev/random. |
| * |
| * File organization: First static fields, then instance |
| * fields, then constructors, then instance methods. |
| */ |
| |
| /* ---------------- static fields ---------------- */ |
| |
| /** |
| * The seed generator for default constructors. |
| */ |
| private static final AtomicLong defaultGen = new AtomicLong(RandomSupport.initialSeed()); |
| |
| /* |
| * Low half of multiplier used in the LCG portion of the algorithm; |
| * the overall multiplier is (2**64 + ML). |
| * Chosen based on research by Sebastiano Vigna and Guy Steele (2019). |
| * The spectral scores for dimensions 2 through 8 for the multiplier 0x1d605bbb58c8abbfdLL |
| * are [0.991889, 0.907938, 0.830964, 0.837980, 0.780378, 0.797464, 0.761493]. |
| */ |
| |
| private static final long ML = 0xd605bbb58c8abbfdL; |
| |
| /* ---------------- instance fields ---------------- */ |
| |
| /** |
| * The parameter that is used as an additive constant for the LCG. |
| * Must be odd (therefore al must be odd). |
| */ |
| private final long ah, al; |
| |
| /** |
| * The per-instance state: sh and sl for the LCG; x0 and x1 for the XBG. |
| * At least one of x0 and x1 must be nonzero. |
| */ |
| private long sh, sl, x0, x1; |
| |
| /* ---------------- constructors ---------------- */ |
| |
| /** |
| * Basic constructor that initializes all fields from parameters. |
| * It then adjusts the field values if necessary to ensure that |
| * all constraints on the values of fields are met. |
| * |
| * @param ah high half of the additive parameter for the LCG |
| * @param al low half of the additive parameter for the LCG |
| * @param sh high half of the initial state for the LCG |
| * @param sl low half of the initial state for the LCG |
| * @param x0 first word of the initial state for the XBG |
| * @param x1 second word of the initial state for the XBG |
| */ |
| public L128X128MixRandom(long ah, long al, long sh, long sl, long x0, long x1) { |
| // Force a to be odd. |
| this.ah = ah; |
| this.al = al | 1; |
| this.sh = sh; |
| this.sl = sl; |
| this.x0 = x0; |
| this.x1 = x1; |
| // If x0 and x1 are both zero, we must choose nonzero values. |
| if ((x0 | x1) == 0) { |
| long v = sh; |
| // At least one of the two values generated here will be nonzero. |
| this.x0 = RandomSupport.mixStafford13(v += RandomSupport.GOLDEN_RATIO_64); |
| this.x1 = RandomSupport.mixStafford13(v + RandomSupport.GOLDEN_RATIO_64); |
| } |
| } |
| |
| /** |
| * Creates a new instance of {@link L128X128MixRandom} using the |
| * specified {@code long} value as the initial seed. Instances of |
| * {@link L128X128MixRandom} created with the same seed in the same |
| * program generate identical sequences of values. |
| * |
| * @param seed the initial seed |
| */ |
| public L128X128MixRandom(long seed) { |
| // Using a value with irregularly spaced 1-bits to xor the seed |
| // argument tends to improve "pedestrian" seeds such as 0 or |
| // other small integers. We may as well use SILVER_RATIO_64. |
| // |
| // The seed is hashed by mixMurmur64 to produce the `a` parameter. |
| // The seed is hashed by mixStafford13 to produce the initial `x0`, |
| // which will then be used to produce the first generated value. |
| // Then x1 is filled in as if by a SplitMix PRNG with |
| // GOLDEN_RATIO_64 as the gamma value and mixStafford13 as the mixer. |
| this(RandomSupport.mixMurmur64(seed ^= RandomSupport.SILVER_RATIO_64), |
| RandomSupport.mixMurmur64(seed += RandomSupport.GOLDEN_RATIO_64), |
| 0, |
| 1, |
| RandomSupport.mixStafford13(seed), |
| RandomSupport.mixStafford13(seed + RandomSupport.GOLDEN_RATIO_64)); |
| } |
| |
| /** |
| * Creates a new instance of {@link L128X128MixRandom} that is likely to |
| * generate sequences of values that are statistically independent |
| * of those of any other instances in the current program execution, |
| * but may, and typically does, vary across program invocations. |
| */ |
| public L128X128MixRandom() { |
| // Using GOLDEN_RATIO_64 here gives us a good Weyl sequence of values. |
| this(defaultGen.getAndAdd(RandomSupport.GOLDEN_RATIO_64)); |
| } |
| |
| /** |
| * Creates a new instance of {@link L128X128MixRandom} using the specified array of |
| * initial seed bytes. Instances of {@link L128X128MixRandom} created with the same |
| * seed array in the same program execution generate identical sequences of values. |
| * |
| * @param seed the initial seed |
| */ |
| public L128X128MixRandom(byte[] seed) { |
| // Convert the seed to 6 long values, of which the last 2 are not all zero. |
| long[] data = RandomSupport.convertSeedBytesToLongs(seed, 6, 2); |
| long ah = data[0], al = data[1], sh = data[2], sl = data[3], x0 = data[4], x1 = data[5]; |
| // Force a to be odd. |
| this.ah = ah; |
| this.al = al | 1; |
| this.sh = sh; |
| this.sl = sl; |
| this.x0 = x0; |
| this.x1 = x1; |
| } |
| |
| /* ---------------- public methods ---------------- */ |
| |
| @Override |
| public SplittableGenerator split(SplittableGenerator source, long brine) { |
| // Pick a new instance "at random", but use the brine for (the low half of) `a`. |
| return new L128X128MixRandom(source.nextLong(), brine << 1, |
| source.nextLong(), source.nextLong(), |
| source.nextLong(), source.nextLong()); |
| } |
| |
| @Override |
| public long nextLong() { |
| // Compute the result based on current state information |
| // (this allows the computation to be overlapped with state update). |
| final long result = RandomSupport.mixLea64(sh + x0); |
| |
| // Update the LCG subgenerator |
| // The LCG is, in effect, s = ((1LL << 64) + ML) * s + a, if only we had 128-bit arithmetic. |
| final long u = ML * sl; |
| // Note that Math.multiplyHigh computes the high half of the product of signed values, |
| // but what we need is the high half of the product of unsigned values; for this we use the |
| // formula "unsignedMultiplyHigh(a, b) = multiplyHigh(a, b) + ((a >> 63) & b) + ((b >> 63) & a)"; |
| // in effect, each operand is added to the result iff the sign bit of the other operand is 1. |
| // (See Henry S. Warren, Jr., _Hacker's Delight_ (Second Edition), Addison-Wesley (2013), |
| // Section 8-3, p. 175; or see the First Edition, Addison-Wesley (2003), Section 8-3, p. 133.) |
| // If Math.unsignedMultiplyHigh(long, long) is ever implemented, the following line can become: |
| // sh = (ML * sh) + Math.unsignedMultiplyHigh(ML, sl) + sl + ah; |
| // and this entire comment can be deleted. |
| sh = (ML * sh) + (Math.multiplyHigh(ML, sl) + ((ML >> 63) & sl) + ((sl >> 63) & ML)) + sl + ah; |
| sl = u + al; |
| if (Long.compareUnsigned(sl, u) < 0) ++sh; // Handle the carry propagation from low half to high half. |
| |
| long q0 = x0, q1 = x1; |
| // Update the XBG subgenerator |
| { // xoroshiro128v1_0 |
| q1 ^= q0; |
| q0 = Long.rotateLeft(q0, 24); |
| q0 = q0 ^ q1 ^ (q1 << 16); |
| q1 = Long.rotateLeft(q1, 37); |
| } |
| x0 = q0; x1 = q1; |
| |
| return result; |
| } |
| |
| } |
