259 lines
11 KiB
Java
259 lines
11 KiB
Java
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/*
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* Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package jdk.random;
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import java.util.concurrent.atomic.AtomicLong;
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import java.util.random.RandomGenerator;
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import jdk.internal.util.random.RandomSupport;
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import jdk.internal.util.random.RandomSupport.AbstractSplittableWithBrineGenerator;
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import jdk.internal.util.random.RandomSupport.RandomGeneratorProperties;
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/**
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* A "splittable" pseudorandom number generator (PRNG) whose period
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* is roughly 2<sup>96</sup>. Class {@link L32X64MixRandom} implements
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* interfaces {@link RandomGenerator} and {@link SplittableGenerator},
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* and therefore supports methods for producing pseudorandomly chosen
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* values of type {@code int}, {@code long}, {@code float}, {@code double},
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* and {@code boolean} (and for producing streams of pseudorandomly chosen
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* numbers of type {@code int}, {@code long}, and {@code double}),
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* as well as methods for creating new split-off {@link L32X64MixRandom}
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* objects or streams of such objects.
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*
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* <p>The {@link L32X64MixRandom} algorithm is a specific member of
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* the LXM family of algorithms for pseudorandom number generators;
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* for more information, see the documentation for package
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* {@link jdk.random}. Each instance of {@link L32X64MixRandom}
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* has 96 bits of state plus one 32-bit instance-specific parameter.
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*
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* <p>If two instances of {@link L32X64MixRandom} are created with
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* the same seed within the same program execution, and the same
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* sequence of method calls is made for each, they will generate and
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* return identical sequences of values.
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*
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* <p>As with {@link java.util.SplittableRandom}, instances of
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* {@link L32X64MixRandom} are <em>not</em> thread-safe. They are
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* designed to be split, not shared, across threads (see the {@link #split}
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* method). For example, a {@link java.util.concurrent.ForkJoinTask}
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* fork/join-style computation using random numbers might include a
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* construction of the form
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* {@code new Subtask(someL32X64MixRandom.split()).fork()}.
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*
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* <p>This class provides additional methods for generating random
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* streams, that employ the above techniques when used in
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* {@code stream.parallel()} mode.
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*
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* <p>Instances of {@link L32X64MixRandom} are not cryptographically
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* secure. Consider instead using {@link java.security.SecureRandom}
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* in security-sensitive applications. Additionally,
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* default-constructed instances do not use a cryptographically random
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* seed unless the {@linkplain System#getProperty system property}
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* {@code java.util.secureRandomSeed} is set to {@code true}.
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*
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* @since 17
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*
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*/
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@RandomGeneratorProperties(
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name = "L32X64MixRandom",
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group = "LXM",
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i = 64, j = 1, k = 32,
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equidistribution = 1
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)
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public final class L32X64MixRandom extends AbstractSplittableWithBrineGenerator {
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/*
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* Implementation Overview.
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*
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* The split operation uses the current generator to choose four new 32-bit
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* int values that are then used to initialize the parameter `a` and the
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* state variables `s`, `x0`, and `x1` for a newly constructed generator.
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*
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* With high probability, no two generators so chosen will have the same
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* `a` parameter, and testing has indicated that the values generated by
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* two instances of {@link L32X64MixRandom} will be (approximately)
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* independent if the two instances have different values for `a`.
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*
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* The default (no-argument) constructor, in essence, uses
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* "defaultGen" to generate four new 32-bit values for the same
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* purpose. Multiple generators created in this way will certainly
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* differ in their `a` parameters. The defaultGen state must be accessed
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* in a thread-safe manner, so we use an AtomicLong to represent
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* this state. To bootstrap the defaultGen, we start off using a
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* seed based on current time unless the
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* java.util.secureRandomSeed property is set. This serves as a
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* slimmed-down (and insecure) variant of SecureRandom that also
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* avoids stalls that may occur when using /dev/random.
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*
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* File organization: First static fields, then instance
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* fields, then constructors, then instance methods.
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*/
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/* ---------------- static fields ---------------- */
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/**
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* The seed generator for default constructors.
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*/
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private static final AtomicLong defaultGen = new AtomicLong(RandomSupport.initialSeed());
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/*
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* Multiplier used in the LCG portion of the algorithm.
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* Chosen based on research by Sebastiano Vigna and Guy Steele (2019).
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* The spectral scores for dimensions 2 through 8 for the multiplier 0xadb4a92d
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* are [0.975884, 0.936244, 0.755793, 0.877642, 0.751300, 0.789333, 0.728869].
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*/
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private static final int M = 0xadb4a92d;
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/* ---------------- instance fields ---------------- */
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/**
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* The parameter that is used as an additive constant for the LCG.
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* Must be odd.
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*/
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private final int a;
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/**
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* The per-instance state: s for the LCG; x0 and x1 for the XBG.
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* At least one of x0 and x1 must be nonzero.
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*/
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private int s, x0, x1;
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/* ---------------- constructors ---------------- */
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/**
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* Basic constructor that initializes all fields from parameters.
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* It then adjusts the field values if necessary to ensure that
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* all constraints on the values of fields are met.
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*
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* @param a additive parameter for the LCG
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* @param s initial state for the LCG
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* @param x0 first word of the initial state for the XBG
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* @param x1 second word of the initial state for the XBG
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*/
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public L32X64MixRandom(int a, int s, int x0, int x1) {
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// Force a to be odd.
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this.a = a | 1;
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this.s = s;
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this.x0 = x0;
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this.x1 = x1;
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// If x0 and x1 are both zero, we must choose nonzero values.
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if ((x0 | x1) == 0) {
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int v = s;
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// At least one of the two values generated here will be nonzero.
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this.x0 = RandomSupport.mixMurmur32(v += RandomSupport.GOLDEN_RATIO_32);
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this.x1 = RandomSupport.mixMurmur32(v + RandomSupport.GOLDEN_RATIO_32);
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}
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}
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/**
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* Creates a new instance of {@link L32X64MixRandom} using the
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* specified {@code long} value as the initial seed. Instances of
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* {@link L32X64MixRandom} created with the same seed in the same
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* program generate identical sequences of values.
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*
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* @param seed the initial seed
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*/
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public L32X64MixRandom(long seed) {
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// Using a value with irregularly spaced 1-bits to xor the seed
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// argument tends to improve "pedestrian" seeds such as 0 or
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// other small integers. We may as well use SILVER_RATIO_64.
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//
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// The high half of the seed is hashed by mixMurmur32 to produce the `a` parameter.
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// The low half of the seed is hashed by mixLea32 to produce the initial `x0`,
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// which will then be used to produce the first generated value.
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// Then x1 is filled in as if by a SplitMix PRNG with
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// GOLDEN_RATIO_32 as the gamma value and mixLea32 as the mixer.
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this(RandomSupport.mixMurmur32((int)((seed ^= RandomSupport.SILVER_RATIO_64) >>> 32)),
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1,
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RandomSupport.mixLea32((int)(seed)),
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RandomSupport.mixLea32((int)(seed) + RandomSupport.GOLDEN_RATIO_32));
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}
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/**
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* Creates a new instance of {@link L32X64MixRandom} that is likely to
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* generate sequences of values that are statistically independent
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* of those of any other instances in the current program execution,
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* but may, and typically does, vary across program invocations.
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*/
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public L32X64MixRandom() {
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// Using GOLDEN_RATIO_64 here gives us a good Weyl sequence of values.
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this(defaultGen.getAndAdd(RandomSupport.GOLDEN_RATIO_64));
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}
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/**
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* Creates a new instance of {@link L32X64MixRandom} using the specified array of
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* initial seed bytes. Instances of {@link L32X64MixRandom} created with the same
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* seed array in the same program execution generate identical sequences of values.
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*
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* @param seed the initial seed
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*/
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public L32X64MixRandom(byte[] seed) {
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// Convert the seed to 4 int values, of which the last 2 are not all zero.
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int[] data = RandomSupport.convertSeedBytesToInts(seed, 4, 2);
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int a = data[0], s = data[1], x0 = data[2], x1 = data[3];
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// Force a to be odd.
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this.a = a | 1;
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this.s = s;
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this.x0 = x0;
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this.x1 = x1;
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}
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/* ---------------- public methods ---------------- */
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@Override
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public SplittableGenerator split(SplittableGenerator source, long brine) {
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// Pick a new instance "at random", but use (the low 31 bits of) the brine for `a`.
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return new L32X64MixRandom((int)brine << 1, source.nextInt(),
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source.nextInt(), source.nextInt());
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}
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@Override
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public int nextInt() {
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// Compute the result based on current state information
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// (this allows the computation to be overlapped with state update).
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final int result = RandomSupport.mixLea32(s + x0);
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// Update the LCG subgenerator
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s = M * s + a;
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// Update the XBG subgenerator
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int q0 = x0, q1 = x1;
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{ // xoroshiro64
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q1 ^= q0;
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q0 = Integer.rotateLeft(q0, 26);
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q0 = q0 ^ q1 ^ (q1 << 9);
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q1 = Integer.rotateLeft(q1, 13);
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}
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x0 = q0; x1 = q1;
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return result;
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}
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@Override
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public long nextLong() {
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return ((long)nextInt() << 32) ^ (long)nextInt();
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}
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}
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