jdk-sandbox: comparison src/java.base/share/classes/java/util/random/Xoroshiro128StarStar.java

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+/*
+* Copyright (c) 2013, 2019, 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.random;
+import java.math.BigInteger;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.random.RandomGenerator.LeapableGenerator;
+/**
+* A generator of uniform pseudorandom values applicable for use in
+* (among other contexts) isolated parallel computations that may
+* generate subtasks.  Class {@link Xoroshiro128StarStar} implements
+* interfaces {@link RandomGenerator} and {@link LeapableGenerator},
+* and therefore supports methods for producing pseudorandomly chosen
+* numbers of type {@code int}, {@code long}, {@code float}, and {@code double}
+* as well as creating new {@link Xoroshiro128StarStar} objects
+* by "jumping" or "leaping".
+* <p>
+* Series of generated values pass the TestU01 BigCrush and PractRand test suites
+* that measure independence and uniformity properties of random number generators.
+* <p>
+* The class {@link Xoroshiro128StarStar} uses the {@code xoroshiro128} algorithm,
+* version 1.0 (parameters 24, 16, 37), with the "**" scrambler (a mixing function).
+* Its state consists of two {@code long} fields {@code x0} and {@code x1},
+* which can take on any values provided that they are not both zero.
+* The period of this generator is 2<sup>128</sup>-1.
+* <p>
+* The 64-bit values produced by the {@code nextLong()} method are equidistributed.
+* To be precise, over the course of the cycle of length 2<sup>128</sup>-1,
+* each nonzero {@code long} value is generated 2<sup>64</sup> times,
+* but the value 0 is generated only 2<sup>64</sup>-1 times.
+* The values produced by the {@code nextInt()}, {@code nextFloat()}, and {@code nextDouble()}
+* methods are likewise equidistributed.
+* <p>
+* In fact, the 64-bit values produced by the {@code nextLong()} method are 2-equidistributed.
+* To be precise: consider the (overlapping) length-2 subsequences of the cycle of 64-bit
+* values produced by {@code nextLong()} (assuming no other methods are called that would
+* affect the state).  There are 2<sup>128</sup>-1 such subsequences, and each subsequence,
+* which consists of 2 64-bit values, can have one of 2<sup>128</sup> values.  Of those
+* 2<sup>128</sup> subsequence values, each one is generated exactly once over the course
+* of the entire cycle, except that the subsequence (0, 0) never appears.
+* The values produced by the {@code nextInt()}, {@code nextFloat()}, and {@code nextDouble()}
+* methods are likewise 2-equidistributed, but note that that the subsequence (0, 0)
+* can also appear (but occurring somewhat less frequently than all other subsequences),
+* because the values produced by those methods have fewer than 64 randomly chosen bits.
+* <p>
+* Instances {@link Xoroshiro128StarStar} are <em>not</em> thread-safe.
+* They are designed to be used so that each thread as its own instance.
+* The methods {@link #jump} and {@link #leap} and {@link #jumps} and {@link #leaps}
+* can be used to construct new instances of {@link Xoroshiro128StarStar} that traverse
+* other parts of the state cycle.
+* <p>
+* Instances of {@link Xoroshiro128StarStar} 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 14
+*/
+public final class Xoroshiro128StarStar implements LeapableGenerator {
+/*
+* Implementation Overview.
+*
+* This is an implementation of the xoroshiro128** algorithm written
+* in 2016 by David Blackman and Sebastiano Vigna (vigna@acm.org),
+* and updated with improved parameters in 2018.
+* See http://xoshiro.di.unimi.it and these two papers:
+*
+*    Sebastiano Vigna. 2016. An Experimental Exploration of Marsaglia's
+*    xorshift Generators, Scrambled. ACM Transactions on Mathematical
+*    Software 42, 4, Article 30 (June 2016), 23 pages.
+*    https://doi.org/10.1145/2845077
+*
+*    David Blackman and Sebastiano Vigna.  2018.  Scrambled Linear
+*    Pseudorandom Number Generators.  Computing Research Repository (CoRR).
+*    http://arxiv.org/abs/1805.01407
+*
+* The jump operation moves the current generator forward by 2*64
+* steps; this has the same effect as calling nextLong() 2**64
+* times, but is much faster.  Similarly, the leap operation moves
+* the current generator forward by 2*96 steps; this has the same
+* effect as calling nextLong() 2**96 times, but is much faster.
+* The copy method may be used to make a copy of the current
+* generator.  Thus one may repeatedly and cumulatively copy and
+* jump to produce a sequence of generators whose states are well
+* spaced apart along the overall state cycle (indeed, the jumps()
+* and leaps() methods each produce a stream of such generators).
+* The generators can then be parceled out to other threads.
+*
+* File organization: First the non-public methods that constitute the
+* main algorithm, then the public methods.  Note that many methods are
+* defined by classes {@link AbstractJumpableGenerator} and {@link AbstractGenerator}.
+*/
+/* ---------------- static fields ---------------- */
+/**
+* The seed generator for default constructors.
+*/
+private static final AtomicLong DEFAULT_GEN = new AtomicLong(RandomSupport.initialSeed());
+/*
+* The period of this generator, which is 2**128 - 1.
+*/
+private static final BigInteger PERIOD =
+BigInteger.ONE.shiftLeft(128).subtract(BigInteger.ONE);
+/* ---------------- instance fields ---------------- */
+/**
+* The per-instance state.
+* At least one of the two fields x0 and x1 must be nonzero.
+*/
+private long 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 x0 first word of the initial state
+* @param x1 second word of the initial state
+*/
+public Xoroshiro128StarStar(long x0, long x1) {
+this.x0 = x0;
+this.x1 = x1;
+// If x0 and x1 are both zero, we must choose nonzero values.
+if ((x0 | x1) == 0) {
+this.x0 = RandomSupport.GOLDEN_RATIO_64;
+this.x1 = RandomSupport.SILVER_RATIO_64;
+}
+}
+/**
+* Creates a new instance of {@link Xoroshiro128StarStar} using the
+* specified {@code long} value as the initial seed. Instances of
+* {@link Xoroshiro128StarStar} created with the same seed in the same
+* program generate identical sequences of values.
+*
+* @param seed the initial seed
+*/
+public Xoroshiro128StarStar(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 x values are then filled in as if by a SplitMix PRNG with
+// GOLDEN_RATIO_64 as the gamma value and Stafford13 as the mixer.
+this(RandomSupport.mixStafford13(seed ^= RandomSupport.SILVER_RATIO_64),
+RandomSupport.mixStafford13(seed + RandomSupport.GOLDEN_RATIO_64));
+}
+/**
+* Creates a new instance of {@link Xoroshiro128StarStar} 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 Xoroshiro128StarStar() {
+// Using GOLDEN_RATIO_64 here gives us a good Weyl sequence of values.
+this(DEFAULT_GEN.getAndAdd(RandomSupport.GOLDEN_RATIO_64));
+}
+/**
+* Creates a new instance of {@link Xoroshiro128StarStar} using the specified array of
+* initial seed bytes. Instances of {@link Xoroshiro128StarStar} created with the same
+* seed array in the same program execution generate identical sequences of values.
+*
+* @param seed the initial seed
+*/
+public Xoroshiro128StarStar(byte[] seed) {
+// Convert the seed to 2 long values, which are not both zero.
+long[] data = RandomSupport.convertSeedBytesToLongs(seed, 2, 2);
+long x0 = data[0], x1 = data[1];
+this.x0 = x0;
+this.x1 = x1;
+}
+/* ---------------- public methods ---------------- */
+public Xoroshiro128StarStar copy() { return new Xoroshiro128StarStar(x0, x1); }
+/*
+* To the extent possible under law, the author has dedicated all copyright and related and
+* neighboring rights to this software to the public domain worldwide. This software is
+* distributed without any warranty.
+* <p>
+* See <http://creativecommons.org/publicdomain/zero/1.0/>.
+*/
+/*
+* This is the successor to xorshift128+. It is the fastest full-period generator passing
+* BigCrush without systematic failures, but due to the relatively short period it is acceptable
+* only for applications with a mild amount of parallelism; otherwise, use a xorshift1024*
+* generator.
+* <p>
+* Beside passing BigCrush, this generator passes the PractRand test suite up to (and included)
+* 16TB, with the exception of binary rank tests, which fail due to the lowest bit being an
+* LFSR; all other bits pass all tests. We suggest to use a sign test to extract a random
+* Boolean value.
+* <p>
+* Note that the generator uses a simulated rotate operation, which most C compilers will turn
+* into a single instruction. In Java, you can use Long.rotateLeft(). In languages that do not
+* make low-level rotation instructions accessible xorshift128+ could be faster.
+* <p>
+* The state must be seeded so that it is not everywhere zero. If you have a 64-bit seed, we
+* suggest to seed a splitmix64 generator and use its output to fill s.
+*/
+/**
+* Returns a pseudorandom {@code long} value.
+*
+* @return a pseudorandom {@code long} value
+*/
+public long nextLong() {
+final long s0 = x0;
+long s1 = x1;
+	// Compute the result based on current state information
+	// (this allows the computation to be overlapped with state update).
+final long result = Long.rotateLeft(s0 * 5, 7) * 9;  // "starstar" mixing function
+s1 ^= s0;
+x0 = Long.rotateLeft(s0, 24) ^ s1 ^ (s1 << 16); // a, b
+x1 = Long.rotateLeft(s1, 37); // c
+return result;
+}
+public BigInteger period() {
+return PERIOD;
+}
+public double defaultJumpDistance() {
+return 0x1.0p64;
+}
+public double defaultLeapDistance() {
+return 0x1.0p96;
+}
+private static final long[] JUMP_TABLE = { 0xdf900294d8f554a5L, 0x170865df4b3201fcL };
+private static final long[] LEAP_TABLE = { 0xd2a98b26625eee7bL, 0xdddf9b1090aa7ac1L };
+/**
+* This is the jump function for the generator. It is equivalent to 2**64 calls to nextLong();
+* it can be used to generate 2**64 non-overlapping subsequences for parallel computations.
+*/
+public void jump() {
+jumpAlgorithm(JUMP_TABLE);
+}
+/**
+* This is the long-jump function for the generator. It is equivalent to 2**96 calls to next();
+* it can be used to generate 2**32 starting points, from each of which jump() will generate
+* 2**32 non-overlapping subsequences for parallel distributed computations.
+*/
+public void leap() {
+jumpAlgorithm(LEAP_TABLE);
+}
+private void jumpAlgorithm(long[] table) {
+long s0 = 0, s1 = 0;
+for (int i = 0; i < table.length; i++) {
+for (int b = 0; b < 64; b++) {
+if ((table[i] & (1L << b)) != 0) {
+s0 ^= x0;
+s1 ^= x1;
+}
+nextLong();
+}
+x0 = s0;
+x1 = s1;
+}
+}
+}

branch	JDK-8193209-branch
changeset 59088	da026c172c1e