| /* |
| * Copyright (c) 2013, 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 java.util; |
| |
| import java.math.BigInteger; |
| import java.util.concurrent.atomic.AtomicLong; |
| import java.util.random.RandomGenerator; |
| import java.util.random.RandomGenerator.SplittableGenerator; |
| import java.util.stream.DoubleStream; |
| import java.util.stream.IntStream; |
| import java.util.stream.LongStream; |
| import java.util.stream.Stream; |
| import jdk.internal.util.random.RandomSupport; |
| import jdk.internal.util.random.RandomSupport.AbstractSplittableGenerator; |
| import jdk.internal.util.random.RandomSupport.RandomGeneratorProperties; |
| |
| /** |
| * A generator of uniform pseudorandom values (with period 2<sup>64</sup>) |
| * applicable for use in (among other contexts) isolated parallel |
| * computations that may generate subtasks. Class {@code SplittableRandom} |
| * supports methods for producing pseudorandom numbers of type {@code int}, |
| * {@code long}, and {@code double} with similar usages as for class |
| * {@link java.util.Random} but differs in the following ways: |
| * |
| * <ul> |
| * |
| * <li>Series of generated values pass the DieHarder suite testing |
| * independence and uniformity properties of random number generators. |
| * (Most recently validated with <a |
| * href="http://www.phy.duke.edu/~rgb/General/dieharder.php"> version |
| * 3.31.1</a>.) These tests validate only the methods for certain |
| * types and ranges, but similar properties are expected to hold, at |
| * least approximately, for others as well. The <em>period</em> |
| * (length of any series of generated values before it repeats) is |
| * 2<sup>64</sup>. </li> |
| * |
| * <li> Method {@link #split} constructs and returns a new |
| * SplittableRandom instance that shares no mutable state with the |
| * current instance. However, with very high probability, the |
| * values collectively generated by the two objects have the same |
| * statistical properties as if the same quantity of values were |
| * generated by a single thread using a single {@code |
| * SplittableRandom} object. </li> |
| * |
| * <li>Instances of SplittableRandom are <em>not</em> thread-safe. |
| * They are designed to be split, not shared, across threads. 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(aSplittableRandom.split()).fork()}. |
| * |
| * <li>This class provides additional methods for generating random |
| * streams, that employ the above techniques when used in {@code |
| * stream.parallel()} mode.</li> |
| * |
| * </ul> |
| * |
| * <p>Instances of {@code SplittableRandom} 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}. |
| * |
| * @author Guy Steele |
| * @author Doug Lea |
| * @since 1.8 |
| */ |
| @RandomGeneratorProperties( |
| name = "SplittableRandom", |
| i = 64, j = 0, k = 0, |
| equidistribution = 1 |
| ) |
| public final class SplittableRandom implements RandomGenerator, SplittableGenerator { |
| |
| /* |
| * Implementation Overview. |
| * |
| * This algorithm was inspired by the "DotMix" algorithm by |
| * Leiserson, Schardl, and Sukha "Deterministic Parallel |
| * Random-Number Generation for Dynamic-Multithreading Platforms", |
| * PPoPP 2012, as well as those in "Parallel random numbers: as |
| * easy as 1, 2, 3" by Salmon, Morae, Dror, and Shaw, SC 2011. It |
| * differs mainly in simplifying and cheapening operations. |
| * |
| * The primary update step (method nextSeed()) is to add a |
| * constant ("gamma") to the current (64 bit) seed, forming a |
| * simple sequence. The seed and the gamma values for any two |
| * SplittableRandom instances are highly likely to be different. |
| * |
| * Methods nextLong, nextInt, and derivatives do not return the |
| * sequence (seed) values, but instead a hash-like bit-mix of |
| * their bits, producing more independently distributed sequences. |
| * For nextLong, the mix64 function is based on David Stafford's |
| * (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html) |
| * "Mix13" variant of the "64-bit finalizer" function in Austin |
| * Appleby's MurmurHash3 algorithm (see |
| * http://code.google.com/p/smhasher/wiki/MurmurHash3). The mix32 |
| * function is based on Stafford's Mix04 mix function, but returns |
| * the upper 32 bits cast as int. |
| * |
| * The split operation uses the current generator to form the seed |
| * and gamma for another SplittableRandom. To conservatively |
| * avoid potential correlations between seed and value generation, |
| * gamma selection (method mixGamma) uses different |
| * (Murmurhash3's) mix constants. To avoid potential weaknesses |
| * in bit-mixing transformations, we restrict gammas to odd values |
| * with at least 24 0-1 or 1-0 bit transitions. Rather than |
| * rejecting candidates with too few or too many bits set, method |
| * mixGamma flips some bits (which has the effect of mapping at |
| * most 4 to any given gamma value). This reduces the effective |
| * set of 64bit odd gamma values by about 2%, and serves as an |
| * automated screening for sequence constant selection that is |
| * left as an empirical decision in some other hashing and crypto |
| * algorithms. |
| * |
| * The resulting generator thus transforms a sequence in which |
| * (typically) many bits change on each step, with an inexpensive |
| * mixer with good (but less than cryptographically secure) |
| * avalanching. |
| * |
| * The default (no-argument) constructor, in essence, invokes |
| * split() for a common "defaultGen" SplittableRandom. Unlike |
| * other cases, this split must be performed in a thread-safe |
| * manner, so we use an AtomicLong to represent the seed rather |
| * than use an explicit SplittableRandom. 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. |
| * |
| * It is a relatively simple matter to apply the basic design here |
| * to use 128 bit seeds. However, emulating 128bit arithmetic and |
| * carrying around twice the state add more overhead than appears |
| * warranted for current usages. |
| * |
| * File organization: First the non-public methods that constitute |
| * the main algorithm, then the main public methods, followed by |
| * some custom spliterator classes needed for stream methods. |
| */ |
| |
| /** |
| * The golden ratio scaled to 64bits, used as the initial gamma |
| * value for (unsplit) SplittableRandoms. |
| */ |
| private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L; |
| |
| /** |
| * The seed. Updated only via method nextSeed. |
| */ |
| private long seed; |
| |
| /** |
| * The step value. |
| */ |
| private final long gamma; |
| |
| /** |
| * Internal constructor used by all others except default constructor. |
| */ |
| private SplittableRandom(long seed, long gamma) { |
| this.seed = seed; |
| this.gamma = gamma; |
| this.proxy = new AbstractSplittableGeneratorProxy(); |
| } |
| |
| /** |
| * Computes Stafford variant 13 of 64bit mix function. |
| * http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html |
| */ |
| private static long mix64(long z) { |
| z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; |
| z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL; |
| return z ^ (z >>> 31); |
| } |
| |
| /** |
| * Returns the 32 high bits of Stafford variant 4 mix64 function as int. |
| * http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html |
| */ |
| private static int mix32(long z) { |
| z = (z ^ (z >>> 33)) * 0x62a9d9ed799705f5L; |
| return (int)(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32); |
| } |
| |
| /** |
| * Returns the gamma value to use for a new split instance. |
| * Uses the 64bit mix function from MurmurHash3. |
| * https://github.com/aappleby/smhasher/wiki/MurmurHash3 |
| */ |
| private static long mixGamma(long z) { |
| z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants |
| z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; |
| z = (z ^ (z >>> 33)) | 1L; // force to be odd |
| int n = Long.bitCount(z ^ (z >>> 1)); // ensure enough transitions |
| return (n < 24) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
| } |
| |
| /** |
| * Proxy class to non-public RandomSupportAbstractSplittableGenerator. |
| */ |
| private class AbstractSplittableGeneratorProxy extends AbstractSplittableGenerator { |
| @Override |
| public int nextInt() { |
| return SplittableRandom.this.nextInt(); |
| } |
| |
| @Override |
| public long nextLong() { |
| return SplittableRandom.this.nextLong(); |
| } |
| |
| @Override |
| public java.util.SplittableRandom split(SplittableGenerator source) { |
| return new SplittableRandom(source.nextLong(), mixGamma(source.nextLong())); |
| } |
| } |
| |
| /** |
| * Proxy object to non-public RandomSupportAbstractSplittableGenerator. |
| */ |
| private AbstractSplittableGeneratorProxy proxy; |
| |
| /** |
| * Adds gamma to seed. |
| */ |
| private long nextSeed() { |
| return seed += gamma; |
| } |
| |
| /** |
| * The seed generator for default constructors. |
| */ |
| private static final AtomicLong defaultGen = new AtomicLong(RandomSupport.initialSeed()); |
| |
| /* ---------------- public methods ---------------- */ |
| |
| /** |
| * Creates a new SplittableRandom instance using the specified |
| * initial seed. SplittableRandom instances created with the same |
| * seed in the same program generate identical sequences of values. |
| * |
| * @param seed the initial seed |
| */ |
| public SplittableRandom(long seed) { |
| this(seed, GOLDEN_GAMMA); |
| } |
| |
| /** |
| * Creates a new SplittableRandom instance that is likely to |
| * generate sequences of values that are statistically independent |
| * of those of any other instances in the current program; and |
| * may, and typically does, vary across program invocations. |
| */ |
| public SplittableRandom() { // emulate defaultGen.split() |
| long s = defaultGen.getAndAdd(2 * GOLDEN_GAMMA); |
| this.seed = mix64(s); |
| this.gamma = mixGamma(s + GOLDEN_GAMMA); |
| this.proxy = new AbstractSplittableGeneratorProxy(); |
| } |
| |
| /** |
| * Constructs and returns a new SplittableRandom instance that |
| * shares no mutable state with this instance. However, with very |
| * high probability, the set of values collectively generated by |
| * the two objects has the same statistical properties as if the |
| * same quantity of values were generated by a single thread using |
| * a single SplittableRandom object. Either or both of the two |
| * objects may be further split using the {@code split()} method, |
| * and the same expected statistical properties apply to the |
| * entire set of generators constructed by such recursive |
| * splitting. |
| * |
| * @return the new SplittableRandom instance |
| */ |
| public SplittableRandom split() { |
| return new SplittableRandom(nextLong(), mixGamma(nextSeed())); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| * @since 17 |
| */ |
| public SplittableRandom split(SplittableGenerator source) { |
| return new SplittableRandom(source.nextLong(), mixGamma(source.nextLong())); |
| } |
| |
| @Override |
| public int nextInt() { |
| return mix32(nextSeed()); |
| } |
| |
| @Override |
| public long nextLong() { |
| return mix64(nextSeed()); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| * @since 10 |
| */ |
| @Override |
| public void nextBytes(byte[] bytes) { |
| proxy.nextBytes(bytes); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @implSpec {@inheritDoc} |
| * @since 17 |
| */ |
| @Override |
| public Stream<SplittableGenerator> splits() { |
| return proxy.splits(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @implSpec {@inheritDoc} |
| * @since 17 |
| */ |
| @Override |
| public Stream<SplittableGenerator> splits(long streamSize) { |
| return proxy.splits(streamSize, this); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| * @implSpec {@inheritDoc} |
| * @since 17 |
| */ |
| @Override |
| public Stream<SplittableGenerator> splits(SplittableGenerator source) { |
| return proxy.splits(Long.MAX_VALUE, source); |
| } |
| |
| /** |
| * {@inheritDoc} |
| * @throws NullPointerException {@inheritDoc} |
| * @throws IllegalArgumentException {@inheritDoc} |
| * @implSpec {@inheritDoc} |
| * @since 17 |
| */ |
| @Override |
| public Stream<SplittableGenerator> splits(long streamSize, SplittableGenerator source) { |
| return proxy.splits(streamSize, source); |
| } |
| |
| /** |
| * Returns a stream producing the given {@code streamSize} number |
| * of pseudorandom {@code int} values from this generator and/or |
| * one split from it. |
| * |
| * @param streamSize the number of values to generate |
| * @return a stream of pseudorandom {@code int} values |
| * @throws IllegalArgumentException if {@code streamSize} is |
| * less than zero |
| */ |
| @Override |
| public IntStream ints(long streamSize) { |
| return proxy.ints(streamSize); |
| } |
| |
| /** |
| * Returns an effectively unlimited stream of pseudorandom {@code int} |
| * values from this generator and/or one split from it. |
| * |
| * @implNote This method is implemented to be equivalent to {@code |
| * ints(Long.MAX_VALUE)}. |
| * |
| * @return a stream of pseudorandom {@code int} values |
| */ |
| @Override |
| public IntStream ints() { |
| return proxy.ints(); |
| } |
| |
| /** |
| * Returns a stream producing the given {@code streamSize} number |
| * of pseudorandom {@code int} values from this generator and/or one split |
| * from it; each value conforms to the given origin (inclusive) and bound |
| * (exclusive). |
| * |
| * @param streamSize the number of values to generate |
| * @param randomNumberOrigin the origin (inclusive) of each random value |
| * @param randomNumberBound the bound (exclusive) of each random value |
| * @return a stream of pseudorandom {@code int} values, |
| * each with the given origin (inclusive) and bound (exclusive) |
| * @throws IllegalArgumentException if {@code streamSize} is |
| * less than zero, or {@code randomNumberOrigin} |
| * is greater than or equal to {@code randomNumberBound} |
| */ |
| @Override |
| public IntStream ints(long streamSize, int randomNumberOrigin, int randomNumberBound) { |
| return proxy.ints(streamSize, randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * Returns an effectively unlimited stream of pseudorandom {@code |
| * int} values from this generator and/or one split from it; each value |
| * conforms to the given origin (inclusive) and bound (exclusive). |
| * |
| * @implNote This method is implemented to be equivalent to {@code |
| * ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}. |
| * |
| * @param randomNumberOrigin the origin (inclusive) of each random value |
| * @param randomNumberBound the bound (exclusive) of each random value |
| * @return a stream of pseudorandom {@code int} values, |
| * each with the given origin (inclusive) and bound (exclusive) |
| * @throws IllegalArgumentException if {@code randomNumberOrigin} |
| * is greater than or equal to {@code randomNumberBound} |
| */ |
| @Override |
| public IntStream ints(int randomNumberOrigin, int randomNumberBound) { |
| return proxy.ints(randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * Returns a stream producing the given {@code streamSize} number |
| * of pseudorandom {@code long} values from this generator and/or |
| * one split from it. |
| * |
| * @param streamSize the number of values to generate |
| * @return a stream of pseudorandom {@code long} values |
| * @throws IllegalArgumentException if {@code streamSize} is |
| * less than zero |
| */ |
| @Override |
| public LongStream longs(long streamSize) { |
| return proxy.longs(streamSize); |
| } |
| |
| /** |
| * Returns an effectively unlimited stream of pseudorandom {@code |
| * long} values from this generator and/or one split from it. |
| * |
| * @implNote This method is implemented to be equivalent to {@code |
| * longs(Long.MAX_VALUE)}. |
| * |
| * @return a stream of pseudorandom {@code long} values |
| */ |
| @Override |
| public LongStream longs() { |
| return proxy.longs(); |
| } |
| |
| /** |
| * Returns a stream producing the given {@code streamSize} number of |
| * pseudorandom {@code long} values from this generator and/or one split |
| * from it; each value conforms to the given origin (inclusive) and bound |
| * (exclusive). |
| * |
| * @param streamSize the number of values to generate |
| * @param randomNumberOrigin the origin (inclusive) of each random value |
| * @param randomNumberBound the bound (exclusive) of each random value |
| * @return a stream of pseudorandom {@code long} values, |
| * each with the given origin (inclusive) and bound (exclusive) |
| * @throws IllegalArgumentException if {@code streamSize} is |
| * less than zero, or {@code randomNumberOrigin} |
| * is greater than or equal to {@code randomNumberBound} |
| */ |
| @Override |
| public LongStream longs(long streamSize, long randomNumberOrigin, long randomNumberBound) { |
| return proxy.longs(streamSize, randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * Returns an effectively unlimited stream of pseudorandom {@code |
| * long} values from this generator and/or one split from it; each value |
| * conforms to the given origin (inclusive) and bound (exclusive). |
| * |
| * @implNote This method is implemented to be equivalent to {@code |
| * longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}. |
| * |
| * @param randomNumberOrigin the origin (inclusive) of each random value |
| * @param randomNumberBound the bound (exclusive) of each random value |
| * @return a stream of pseudorandom {@code long} values, |
| * each with the given origin (inclusive) and bound (exclusive) |
| * @throws IllegalArgumentException if {@code randomNumberOrigin} |
| * is greater than or equal to {@code randomNumberBound} |
| */ |
| @Override |
| public LongStream longs(long randomNumberOrigin, long randomNumberBound) { |
| return proxy.longs(randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * Returns a stream producing the given {@code streamSize} number of |
| * pseudorandom {@code double} values from this generator and/or one split |
| * from it; each value is between zero (inclusive) and one (exclusive). |
| * |
| * @param streamSize the number of values to generate |
| * @return a stream of {@code double} values |
| * @throws IllegalArgumentException if {@code streamSize} is |
| * less than zero |
| */ |
| @Override |
| public DoubleStream doubles(long streamSize) { |
| return proxy.doubles(streamSize); |
| } |
| |
| /** |
| * Returns an effectively unlimited stream of pseudorandom {@code |
| * double} values from this generator and/or one split from it; each value |
| * is between zero (inclusive) and one (exclusive). |
| * |
| * @implNote This method is implemented to be equivalent to {@code |
| * doubles(Long.MAX_VALUE)}. |
| * |
| * @return a stream of pseudorandom {@code double} values |
| */ |
| @Override |
| public DoubleStream doubles() { |
| return proxy.doubles(); |
| } |
| |
| /** |
| * Returns a stream producing the given {@code streamSize} number of |
| * pseudorandom {@code double} values from this generator and/or one split |
| * from it; each value conforms to the given origin (inclusive) and bound |
| * (exclusive). |
| * |
| * @param streamSize the number of values to generate |
| * @param randomNumberOrigin the origin (inclusive) of each random value |
| * @param randomNumberBound the bound (exclusive) of each random value |
| * @return a stream of pseudorandom {@code double} values, |
| * each with the given origin (inclusive) and bound (exclusive) |
| * @throws IllegalArgumentException if {@code streamSize} is |
| * less than zero, or {@code randomNumberOrigin} |
| * is greater than or equal to {@code randomNumberBound} |
| */ |
| @Override |
| public DoubleStream doubles(long streamSize, double randomNumberOrigin, double randomNumberBound) { |
| return proxy.doubles(streamSize, randomNumberOrigin, randomNumberBound); |
| } |
| |
| /** |
| * Returns an effectively unlimited stream of pseudorandom {@code |
| * double} values from this generator and/or one split from it; each value |
| * conforms to the given origin (inclusive) and bound (exclusive). |
| * |
| * @implNote This method is implemented to be equivalent to {@code |
| * doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}. |
| * |
| * @param randomNumberOrigin the origin (inclusive) of each random value |
| * @param randomNumberBound the bound (exclusive) of each random value |
| * @return a stream of pseudorandom {@code double} values, |
| * each with the given origin (inclusive) and bound (exclusive) |
| * @throws IllegalArgumentException if {@code randomNumberOrigin} |
| * is greater than or equal to {@code randomNumberBound} |
| */ |
| @Override |
| public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) { |
| return proxy.doubles(randomNumberOrigin, randomNumberBound); |
| } |
| } |
