--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/src/java.base/share/classes/java/util/random/Xoshiro256StarStar.java Thu Nov 14 12:50:08 2019 -0400
@@ -0,0 +1,308 @@
+/*
+ * 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 Xoshiro256StarStar} 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 Xoshiro256StarStar} 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.
+ * (Most recently validated with
+ * <a href="http://simul.iro.umontreal.ca/testu01/tu01.html">version 1.2.3 of TestU01</a>
+ * and <a href="http://pracrand.sourceforge.net">version 0.90 of PractRand</a>.
+ * Note that TestU01 BigCrush was used to test not only values produced by the {@code nextLong()}
+ * method but also the result of bit-reversing each value produced by {@code nextLong()}.)
+ * 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.
+ * <p>
+ * The class {@link Xoshiro256StarStar} uses the {@code xoshiro256} algorithm,
+ * version 1.0 (parameters 17, 45), with the "**" scrambler (a mixing function).
+ * Its state consists of four {@code long} fields {@code x0}, {@code x1}, {@code x2},
+ * and {@code x3}, which can take on any values provided that they are not all zero.
+ * The period of this generator is 2<sup>256</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>256</sup>-1,
+ * each nonzero {@code long} value is generated 2<sup>192</sup> times,
+ * but the value 0 is generated only 2<sup>192</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 4-equidistributed.
+ * To be precise: consider the (overlapping) length-4 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>256</sup>-1 such subsequences, and each subsequence,
+ * which consists of 4 64-bit values, can have one of 2<sup>256</sup> values. Of those
+ * 2<sup>256</sup> subsequence values, each one is generated exactly once over the course
+ * of the entire cycle, except that the subsequence (0, 0, 0, 0) never appears.
+ * The values produced by the {@code nextInt()}, {@code nextFloat()}, and {@code nextDouble()}
+ * methods are likewise 4-equidistributed, but note that that the subsequence (0, 0, 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 Xoshiro256StarStar} 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 Xoshiro256StarStar} that traverse
+ * other parts of the state cycle.
+ * <p>
+ * Instances of {@link Xoshiro256StarStar} 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 Xoshiro256StarStar implements LeapableGenerator {
+
+ /*
+ * Implementation Overview.
+ *
+ * This is an implementation of the xoroshiro128** algorithm written
+ * in 2018 by David Blackman and Sebastiano Vigna (vigna@acm.org).
+ * 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*128
+ * steps; this has the same effect as calling nextLong() 2**128
+ * times, but is much faster. Similarly, the leap operation moves
+ * the current generator forward by 2*192 steps; this has the same
+ * effect as calling nextLong() 2**192 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 static fields, then instance
+ * fields, then constructors, then instance methods.
+ */
+
+ /* ---------------- 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**256 - 1.
+ */
+ private static final BigInteger PERIOD =
+ BigInteger.ONE.shiftLeft(256).subtract(BigInteger.ONE);
+
+ /* ---------------- instance fields ---------------- */
+
+ /**
+ * The per-instance state.
+ * At least one of the four fields x0, x1, x2, and x3 must be nonzero.
+ */
+ private long x0, x1, x2, x3;
+
+ /* ---------------- 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
+ * @param x2 third word of the initial state
+ * @param x3 fourth word of the initial state
+ */
+ public Xoshiro256StarStar(long x0, long x1, long x2, long x3) {
+ this.x0 = x0;
+ this.x1 = x1;
+ this.x2 = x2;
+ this.x3 = x3;
+ // If x0, x1, x2, and x3 are all zero, we must choose nonzero values.
+ if ((x0 | x1 | x2 | x3) == 0) {
+ // At least three of the four values generated here will be nonzero.
+ this.x0 = RandomSupport.mixStafford13(x0 += RandomSupport.GOLDEN_RATIO_64);
+ this.x1 = (x0 += RandomSupport.GOLDEN_RATIO_64);
+ this.x2 = (x0 += RandomSupport.GOLDEN_RATIO_64);
+ this.x3 = (x0 += RandomSupport.GOLDEN_RATIO_64);
+ }
+ }
+
+ /**
+ * Creates a new instance of {@link Xoshiro256StarStar} using the
+ * specified {@code long} value as the initial seed. Instances of
+ * {@link Xoshiro256StarStar} created with the same seed in the same
+ * program generate identical sequences of values.
+ *
+ * @param seed the initial seed
+ */
+ public Xoshiro256StarStar(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),
+ RandomSupport.mixStafford13(seed += RandomSupport.GOLDEN_RATIO_64),
+ RandomSupport.mixStafford13(seed + RandomSupport.GOLDEN_RATIO_64));
+ }
+
+ /**
+ * Creates a new instance of {@link Xoshiro256StarStar} 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 Xoshiro256StarStar() {
+ // 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 Xoshiro256StarStar} using the specified array of
+ * initial seed bytes. Instances of {@link Xoshiro256StarStar} created with the same
+ * seed array in the same program execution generate identical sequences of values.
+ *
+ * @param seed the initial seed
+ */
+ public Xoshiro256StarStar(byte[] seed) {
+ // Convert the seed to 4 long values, which are not all zero.
+ long[] data = RandomSupport.convertSeedBytesToLongs(seed, 4, 4);
+ long x0 = data[0], x1 = data[1], x2 = data[2], x3 = data[3];
+ this.x0 = x0;
+ this.x1 = x1;
+ this.x2 = x2;
+ this.x3 = x3;
+ }
+
+ /* ---------------- public methods ---------------- */
+
+ public Xoshiro256StarStar copy() {
+ return new Xoshiro256StarStar(x0, x1, x2, x3);
+ }
+
+ /**
+ * Returns a pseudorandom {@code long} value.
+ *
+ * @return a pseudorandom {@code long} value
+ */
+ public long nextLong() {
+ // Compute the result based on current state information
+ // (this allows the computation to be overlapped with state update).
+ final long result = Long.rotateLeft(x0 * 5, 7) * 9; // "starstar" mixing function
+
+ long q0 = x0, q1 = x1, q2 = x2, q3 = x3;
+ { // xoshiro256 1.0
+ long t = q1 << 17;
+ q2 ^= q0;
+ q3 ^= q1;
+ q1 ^= q2;
+ q0 ^= q3;
+ q2 ^= t;
+ q3 = Long.rotateLeft(q3, 45);
+ }
+ x0 = q0; x1 = q1; x2 = q2; x3 = q3;
+ 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 = {
+ 0x180ec6d33cfd0abaL, 0xd5a61266f0c9392cL, 0xa9582618e03fc9aaL, 0x39abdc4529b1661cL };
+
+ private static final long[] LEAP_TABLE = {
+ 0x76e15d3efefdcbbfL, 0xc5004e441c522fb3L, 0x77710069854ee241L, 0x39109bb02acbe635L };
+
+ /**
+ * This is the jump function for the generator. It is equivalent to 2**128 calls to next(); it
+ * can be used to generate 2**128 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**192 calls to next();
+ * it can be used to generate 2**64 starting points, from each of which jump() will generate
+ * 2**64 non-overlapping subsequences for parallel distributed computations.
+ */
+ public void leap() {
+ jumpAlgorithm(LEAP_TABLE);
+ }
+
+ private void jumpAlgorithm(long[] table) {
+ long s0 = 0, s1 = 0, s2 = 0, s3 = 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;
+ s2 ^= x2;
+ s3 ^= x3;
+ }
+ nextLong();
+ }
+ x0 = s0;
+ x1 = s1;
+ x2 = s2;
+ x3 = s3;
+ }
+ }
+
+}