--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/random/Xoroshiro128StarStar.java Thu Jun 27 18:02:51 2019 -0300
@@ -0,0 +1,294 @@
+/*
+ * 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;
+
+import java.math.BigInteger;
+import java.util.concurrent.atomic.AtomicLong;
+
+/**
+ * A generator of uniform pseudorandom values applicable for use in
+ * (among other contexts) isolated parallel computations that may
+ * generate subtasks. Class {@code Xoroshiro128StarStar} implements
+ * interfaces {@link java.util.Rng} and {@link java.util.LeapableRng},
+ * 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 {@code 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 {@code 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 {@code 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 {@code Xoroshiro128StarStar} that traverse
+ * other parts of the state cycle.
+ *
+ * <p>Instances of {@code 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}.
+ *
+ * @author Guy Steele
+ * @author Doug Lea
+ * @since 1.8
+ */
+public final class Xoroshiro128StarStar implements LeapableRng {
+
+ /*
+ * 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 {@code AbstractJumpableRng} and {@code AbstractRng}.
+ */
+
+ /* ---------------- static fields ---------------- */
+
+ /**
+ * The seed generator for default constructors.
+ */
+ private static final AtomicLong defaultGen = new AtomicLong(RngSupport.initialSeed());
+
+ /*
+ * The period of this generator, which is 2**128 - 1.
+ */
+ private static final BigInteger thePeriod =
+ 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) {
+ // At least one of the two values generated here will be nonzero.
+ this.x0 = RngSupport.mixStafford13(x0 += RngSupport.GOLDEN_RATIO_64);
+ this.x1 = (x0 += RngSupport.GOLDEN_RATIO_64);
+ }
+ }
+
+ /**
+ * Creates a new instance of {@code Xoroshiro128StarStar} using the
+ * specified {@code long} value as the initial seed. Instances of
+ * {@code 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(RngSupport.mixStafford13(seed ^= RngSupport.SILVER_RATIO_64),
+ RngSupport.mixStafford13(seed + RngSupport.GOLDEN_RATIO_64));
+ }
+
+ /**
+ * Creates a new instance of {@code 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(defaultGen.getAndAdd(RngSupport.GOLDEN_RATIO_64));
+ }
+
+ /**
+ * Creates a new instance of {@code Xoroshiro128StarStar} using the specified array of
+ * initial seed bytes. Instances of {@code 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 = RngSupport.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.
+
+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.
+
+ 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.
+
+ 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.
+
+ 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;
+ final long z = s0;
+
+ s1 ^= s0;
+ x0 = Long.rotateLeft(s0, 24) ^ s1 ^ (s1 << 16); // a, b
+ x1 = Long.rotateLeft(s1, 37); // c
+
+ return Long.rotateLeft(z * 5, 7) * 9; // "starstar" mixing function
+ }
+
+ public BigInteger period() { return thePeriod; }
+
+ 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;
+ }
+ }
+}