SplittableRandom.java 38.5 KB
Newer Older
P
psandoz 已提交
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108
/*
 * Copyright (c) 2013, 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.util.concurrent.atomic.AtomicLong;
import java.util.function.IntConsumer;
import java.util.function.LongConsumer;
import java.util.function.DoubleConsumer;
import java.util.stream.StreamSupport;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
import java.util.stream.DoubleStream;

/**
 * A generator of uniform pseudorandom values 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 at
 * least 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
 */
public final class SplittableRandom {

    /*
     * 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.
P
psandoz 已提交
109 110 111 112 113 114 115
     * 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.
P
psandoz 已提交
116 117 118 119
     *
     * 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,
P
psandoz 已提交
120 121 122 123 124 125 126 127
     * 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
P
psandoz 已提交
128 129 130 131 132 133 134 135 136 137
     * 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
P
psandoz 已提交
138 139 140 141
     * 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
142 143 144 145
     * 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.
P
psandoz 已提交
146 147 148 149 150 151 152 153 154 155 156 157
     *
     * 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.
     */

    /**
P
psandoz 已提交
158 159
     * The golden ratio scaled to 64bits, used as the initial gamma
     * value for (unsplit) SplittableRandoms.
P
psandoz 已提交
160
     */
P
psandoz 已提交
161
    private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L;
P
psandoz 已提交
162 163 164 165 166

    /**
     * The least non-zero value returned by nextDouble(). This value
     * is scaled by a random value of 53 bits to produce a result.
     */
P
psandoz 已提交
167
    private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53);
P
psandoz 已提交
168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187

    /**
     * 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;
    }

    /**
P
psandoz 已提交
188
     * Computes Stafford variant 13 of 64bit mix function.
P
psandoz 已提交
189 190
     */
    private static long mix64(long z) {
P
psandoz 已提交
191 192 193
        z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L;
        z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL;
        return z ^ (z >>> 31);
P
psandoz 已提交
194 195 196
    }

    /**
P
psandoz 已提交
197
     * Returns the 32 high bits of Stafford variant 4 mix64 function as int.
P
psandoz 已提交
198 199
     */
    private static int mix32(long z) {
P
psandoz 已提交
200 201
        z = (z ^ (z >>> 33)) * 0x62a9d9ed799705f5L;
        return (int)(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32);
P
psandoz 已提交
202 203 204 205 206
    }

    /**
     * Returns the gamma value to use for a new split instance.
     */
P
psandoz 已提交
207 208 209 210 211 212
    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;
P
psandoz 已提交
213 214 215 216 217 218 219 220 221 222 223 224
    }

    /**
     * Adds gamma to seed.
     */
    private long nextSeed() {
        return seed += gamma;
    }

    /**
     * The seed generator for default constructors.
     */
P
psandoz 已提交
225
    private static final AtomicLong defaultGen = new AtomicLong(initialSeed());
P
psandoz 已提交
226 227 228 229 230 231 232 233 234 235 236 237

    private static long initialSeed() {
        String pp = java.security.AccessController.doPrivileged(
                new sun.security.action.GetPropertyAction(
                        "java.util.secureRandomSeed"));
        if (pp != null && pp.equalsIgnoreCase("true")) {
            byte[] seedBytes = java.security.SecureRandom.getSeed(8);
            long s = (long)(seedBytes[0]) & 0xffL;
            for (int i = 1; i < 8; ++i)
                s = (s << 8) | ((long)(seedBytes[i]) & 0xffL);
            return s;
        }
238
        return (mix64(System.currentTimeMillis()) ^
P
psandoz 已提交
239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365
                mix64(System.nanoTime()));
    }

    // IllegalArgumentException messages
    static final String BadBound = "bound must be positive";
    static final String BadRange = "bound must be greater than origin";
    static final String BadSize  = "size must be non-negative";

    /*
     * Internal versions of nextX methods used by streams, as well as
     * the public nextX(origin, bound) methods.  These exist mainly to
     * avoid the need for multiple versions of stream spliterators
     * across the different exported forms of streams.
     */

    /**
     * The form of nextLong used by LongStream Spliterators.  If
     * origin is greater than bound, acts as unbounded form of
     * nextLong, else as bounded form.
     *
     * @param origin the least value, unless greater than bound
     * @param bound the upper bound (exclusive), must not equal origin
     * @return a pseudorandom value
     */
    final long internalNextLong(long origin, long bound) {
        /*
         * Four Cases:
         *
         * 1. If the arguments indicate unbounded form, act as
         * nextLong().
         *
         * 2. If the range is an exact power of two, apply the
         * associated bit mask.
         *
         * 3. If the range is positive, loop to avoid potential bias
         * when the implicit nextLong() bound (2<sup>64</sup>) is not
         * evenly divisible by the range. The loop rejects candidates
         * computed from otherwise over-represented values.  The
         * expected number of iterations under an ideal generator
         * varies from 1 to 2, depending on the bound. The loop itself
         * takes an unlovable form. Because the first candidate is
         * already available, we need a break-in-the-middle
         * construction, which is concisely but cryptically performed
         * within the while-condition of a body-less for loop.
         *
         * 4. Otherwise, the range cannot be represented as a positive
         * long.  The loop repeatedly generates unbounded longs until
         * obtaining a candidate meeting constraints (with an expected
         * number of iterations of less than two).
         */

        long r = mix64(nextSeed());
        if (origin < bound) {
            long n = bound - origin, m = n - 1;
            if ((n & m) == 0L)  // power of two
                r = (r & m) + origin;
            else if (n > 0L) {  // reject over-represented candidates
                for (long u = r >>> 1;            // ensure nonnegative
                     u + m - (r = u % n) < 0L;    // rejection check
                     u = mix64(nextSeed()) >>> 1) // retry
                    ;
                r += origin;
            }
            else {              // range not representable as long
                while (r < origin || r >= bound)
                    r = mix64(nextSeed());
            }
        }
        return r;
    }

    /**
     * The form of nextInt used by IntStream Spliterators.
     * Exactly the same as long version, except for types.
     *
     * @param origin the least value, unless greater than bound
     * @param bound the upper bound (exclusive), must not equal origin
     * @return a pseudorandom value
     */
    final int internalNextInt(int origin, int bound) {
        int r = mix32(nextSeed());
        if (origin < bound) {
            int n = bound - origin, m = n - 1;
            if ((n & m) == 0)
                r = (r & m) + origin;
            else if (n > 0) {
                for (int u = r >>> 1;
                     u + m - (r = u % n) < 0;
                     u = mix32(nextSeed()) >>> 1)
                    ;
                r += origin;
            }
            else {
                while (r < origin || r >= bound)
                    r = mix32(nextSeed());
            }
        }
        return r;
    }

    /**
     * The form of nextDouble used by DoubleStream Spliterators.
     *
     * @param origin the least value, unless greater than bound
     * @param bound the upper bound (exclusive), must not equal origin
     * @return a pseudorandom value
     */
    final double internalNextDouble(double origin, double bound) {
        double r = (nextLong() >>> 11) * DOUBLE_UNIT;
        if (origin < bound) {
            r = r * (bound - origin) + origin;
            if (r >= bound) // correct for rounding
                r = Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
        }
        return r;
    }

    /* ---------------- 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) {
P
psandoz 已提交
366
        this(seed, GOLDEN_GAMMA);
P
psandoz 已提交
367 368 369 370 371 372 373 374
    }

    /**
     * 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.
     */
P
psandoz 已提交
375 376 377 378
    public SplittableRandom() { // emulate defaultGen.split()
        long s = defaultGen.getAndAdd(2 * GOLDEN_GAMMA);
        this.seed = mix64(s);
        this.gamma = mixGamma(s + GOLDEN_GAMMA);
P
psandoz 已提交
379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395
    }

    /**
     * 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() {
P
psandoz 已提交
396
        return new SplittableRandom(nextLong(), mixGamma(nextSeed()));
P
psandoz 已提交
397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851 852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902 903 904 905 906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941 942 943 944 945 946 947 948 949 950 951 952 953 954 955 956 957 958 959 960 961 962 963 964 965 966 967 968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984 985 986 987 988 989 990 991
    }

    /**
     * Returns a pseudorandom {@code int} value.
     *
     * @return a pseudorandom {@code int} value
     */
    public int nextInt() {
        return mix32(nextSeed());
    }

    /**
     * Returns a pseudorandom {@code int} value between zero (inclusive)
     * and the specified bound (exclusive).
     *
     * @param bound the upper bound (exclusive).  Must be positive.
     * @return a pseudorandom {@code int} value between zero
     *         (inclusive) and the bound (exclusive)
     * @throws IllegalArgumentException if {@code bound} is not positive
     */
    public int nextInt(int bound) {
        if (bound <= 0)
            throw new IllegalArgumentException(BadBound);
        // Specialize internalNextInt for origin 0
        int r = mix32(nextSeed());
        int m = bound - 1;
        if ((bound & m) == 0) // power of two
            r &= m;
        else { // reject over-represented candidates
            for (int u = r >>> 1;
                 u + m - (r = u % bound) < 0;
                 u = mix32(nextSeed()) >>> 1)
                ;
        }
        return r;
    }

    /**
     * Returns a pseudorandom {@code int} value between the specified
     * origin (inclusive) and the specified bound (exclusive).
     *
     * @param origin the least value returned
     * @param bound the upper bound (exclusive)
     * @return a pseudorandom {@code int} value between the origin
     *         (inclusive) and the bound (exclusive)
     * @throws IllegalArgumentException if {@code origin} is greater than
     *         or equal to {@code bound}
     */
    public int nextInt(int origin, int bound) {
        if (origin >= bound)
            throw new IllegalArgumentException(BadRange);
        return internalNextInt(origin, bound);
    }

    /**
     * Returns a pseudorandom {@code long} value.
     *
     * @return a pseudorandom {@code long} value
     */
    public long nextLong() {
        return mix64(nextSeed());
    }

    /**
     * Returns a pseudorandom {@code long} value between zero (inclusive)
     * and the specified bound (exclusive).
     *
     * @param bound the upper bound (exclusive).  Must be positive.
     * @return a pseudorandom {@code long} value between zero
     *         (inclusive) and the bound (exclusive)
     * @throws IllegalArgumentException if {@code bound} is not positive
     */
    public long nextLong(long bound) {
        if (bound <= 0)
            throw new IllegalArgumentException(BadBound);
        // Specialize internalNextLong for origin 0
        long r = mix64(nextSeed());
        long m = bound - 1;
        if ((bound & m) == 0L) // power of two
            r &= m;
        else { // reject over-represented candidates
            for (long u = r >>> 1;
                 u + m - (r = u % bound) < 0L;
                 u = mix64(nextSeed()) >>> 1)
                ;
        }
        return r;
    }

    /**
     * Returns a pseudorandom {@code long} value between the specified
     * origin (inclusive) and the specified bound (exclusive).
     *
     * @param origin the least value returned
     * @param bound the upper bound (exclusive)
     * @return a pseudorandom {@code long} value between the origin
     *         (inclusive) and the bound (exclusive)
     * @throws IllegalArgumentException if {@code origin} is greater than
     *         or equal to {@code bound}
     */
    public long nextLong(long origin, long bound) {
        if (origin >= bound)
            throw new IllegalArgumentException(BadRange);
        return internalNextLong(origin, bound);
    }

    /**
     * Returns a pseudorandom {@code double} value between zero
     * (inclusive) and one (exclusive).
     *
     * @return a pseudorandom {@code double} value between zero
     *         (inclusive) and one (exclusive)
     */
    public double nextDouble() {
        return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT;
    }

    /**
     * Returns a pseudorandom {@code double} value between 0.0
     * (inclusive) and the specified bound (exclusive).
     *
     * @param bound the upper bound (exclusive).  Must be positive.
     * @return a pseudorandom {@code double} value between zero
     *         (inclusive) and the bound (exclusive)
     * @throws IllegalArgumentException if {@code bound} is not positive
     */
    public double nextDouble(double bound) {
        if (!(bound > 0.0))
            throw new IllegalArgumentException(BadBound);
        double result = (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT * bound;
        return (result < bound) ?  result : // correct for rounding
            Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
    }

    /**
     * Returns a pseudorandom {@code double} value between the specified
     * origin (inclusive) and bound (exclusive).
     *
     * @param origin the least value returned
     * @param bound the upper bound (exclusive)
     * @return a pseudorandom {@code double} value between the origin
     *         (inclusive) and the bound (exclusive)
     * @throws IllegalArgumentException if {@code origin} is greater than
     *         or equal to {@code bound}
     */
    public double nextDouble(double origin, double bound) {
        if (!(origin < bound))
            throw new IllegalArgumentException(BadRange);
        return internalNextDouble(origin, bound);
    }

    /**
     * Returns a pseudorandom {@code boolean} value.
     *
     * @return a pseudorandom {@code boolean} value
     */
    public boolean nextBoolean() {
        return mix32(nextSeed()) < 0;
    }

    // stream methods, coded in a way intended to better isolate for
    // maintenance purposes the small differences across forms.

    /**
     * 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
     */
    public IntStream ints(long streamSize) {
        if (streamSize < 0L)
            throw new IllegalArgumentException(BadSize);
        return StreamSupport.intStream
            (new RandomIntsSpliterator
             (this, 0L, streamSize, Integer.MAX_VALUE, 0),
             false);
    }

    /**
     * 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
     */
    public IntStream ints() {
        return StreamSupport.intStream
            (new RandomIntsSpliterator
             (this, 0L, Long.MAX_VALUE, Integer.MAX_VALUE, 0),
             false);
    }

    /**
     * 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}
     */
    public IntStream ints(long streamSize, int randomNumberOrigin,
                          int randomNumberBound) {
        if (streamSize < 0L)
            throw new IllegalArgumentException(BadSize);
        if (randomNumberOrigin >= randomNumberBound)
            throw new IllegalArgumentException(BadRange);
        return StreamSupport.intStream
            (new RandomIntsSpliterator
             (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
             false);
    }

    /**
     * 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}
     */
    public IntStream ints(int randomNumberOrigin, int randomNumberBound) {
        if (randomNumberOrigin >= randomNumberBound)
            throw new IllegalArgumentException(BadRange);
        return StreamSupport.intStream
            (new RandomIntsSpliterator
             (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
             false);
    }

    /**
     * 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
     */
    public LongStream longs(long streamSize) {
        if (streamSize < 0L)
            throw new IllegalArgumentException(BadSize);
        return StreamSupport.longStream
            (new RandomLongsSpliterator
             (this, 0L, streamSize, Long.MAX_VALUE, 0L),
             false);
    }

    /**
     * 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
     */
    public LongStream longs() {
        return StreamSupport.longStream
            (new RandomLongsSpliterator
             (this, 0L, Long.MAX_VALUE, Long.MAX_VALUE, 0L),
             false);
    }

    /**
     * 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}
     */
    public LongStream longs(long streamSize, long randomNumberOrigin,
                            long randomNumberBound) {
        if (streamSize < 0L)
            throw new IllegalArgumentException(BadSize);
        if (randomNumberOrigin >= randomNumberBound)
            throw new IllegalArgumentException(BadRange);
        return StreamSupport.longStream
            (new RandomLongsSpliterator
             (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
             false);
    }

    /**
     * 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}
     */
    public LongStream longs(long randomNumberOrigin, long randomNumberBound) {
        if (randomNumberOrigin >= randomNumberBound)
            throw new IllegalArgumentException(BadRange);
        return StreamSupport.longStream
            (new RandomLongsSpliterator
             (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
             false);
    }

    /**
     * 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
     */
    public DoubleStream doubles(long streamSize) {
        if (streamSize < 0L)
            throw new IllegalArgumentException(BadSize);
        return StreamSupport.doubleStream
            (new RandomDoublesSpliterator
             (this, 0L, streamSize, Double.MAX_VALUE, 0.0),
             false);
    }

    /**
     * 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
     */
    public DoubleStream doubles() {
        return StreamSupport.doubleStream
            (new RandomDoublesSpliterator
             (this, 0L, Long.MAX_VALUE, Double.MAX_VALUE, 0.0),
             false);
    }

    /**
     * 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
     * @throws IllegalArgumentException if {@code randomNumberOrigin}
     *         is greater than or equal to {@code randomNumberBound}
     */
    public DoubleStream doubles(long streamSize, double randomNumberOrigin,
                                double randomNumberBound) {
        if (streamSize < 0L)
            throw new IllegalArgumentException(BadSize);
        if (!(randomNumberOrigin < randomNumberBound))
            throw new IllegalArgumentException(BadRange);
        return StreamSupport.doubleStream
            (new RandomDoublesSpliterator
             (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
             false);
    }

    /**
     * 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}
     */
    public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) {
        if (!(randomNumberOrigin < randomNumberBound))
            throw new IllegalArgumentException(BadRange);
        return StreamSupport.doubleStream
            (new RandomDoublesSpliterator
             (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
             false);
    }

    /**
     * Spliterator for int streams.  We multiplex the four int
     * versions into one class by treating a bound less than origin as
     * unbounded, and also by treating "infinite" as equivalent to
     * Long.MAX_VALUE. For splits, it uses the standard divide-by-two
     * approach. The long and double versions of this class are
     * identical except for types.
     */
    static final class RandomIntsSpliterator implements Spliterator.OfInt {
        final SplittableRandom rng;
        long index;
        final long fence;
        final int origin;
        final int bound;
        RandomIntsSpliterator(SplittableRandom rng, long index, long fence,
                              int origin, int bound) {
            this.rng = rng; this.index = index; this.fence = fence;
            this.origin = origin; this.bound = bound;
        }

        public RandomIntsSpliterator trySplit() {
            long i = index, m = (i + fence) >>> 1;
            return (m <= i) ? null :
                new RandomIntsSpliterator(rng.split(), i, index = m, origin, bound);
        }

        public long estimateSize() {
            return fence - index;
        }

        public int characteristics() {
            return (Spliterator.SIZED | Spliterator.SUBSIZED |
                    Spliterator.NONNULL | Spliterator.IMMUTABLE);
        }

        public boolean tryAdvance(IntConsumer consumer) {
            if (consumer == null) throw new NullPointerException();
            long i = index, f = fence;
            if (i < f) {
                consumer.accept(rng.internalNextInt(origin, bound));
                index = i + 1;
                return true;
            }
            return false;
        }

        public void forEachRemaining(IntConsumer consumer) {
            if (consumer == null) throw new NullPointerException();
            long i = index, f = fence;
            if (i < f) {
                index = f;
                SplittableRandom r = rng;
                int o = origin, b = bound;
                do {
                    consumer.accept(r.internalNextInt(o, b));
                } while (++i < f);
            }
        }
    }

    /**
     * Spliterator for long streams.
     */
    static final class RandomLongsSpliterator implements Spliterator.OfLong {
        final SplittableRandom rng;
        long index;
        final long fence;
        final long origin;
        final long bound;
        RandomLongsSpliterator(SplittableRandom rng, long index, long fence,
                               long origin, long bound) {
            this.rng = rng; this.index = index; this.fence = fence;
            this.origin = origin; this.bound = bound;
        }

        public RandomLongsSpliterator trySplit() {
            long i = index, m = (i + fence) >>> 1;
            return (m <= i) ? null :
                new RandomLongsSpliterator(rng.split(), i, index = m, origin, bound);
        }

        public long estimateSize() {
            return fence - index;
        }

        public int characteristics() {
            return (Spliterator.SIZED | Spliterator.SUBSIZED |
                    Spliterator.NONNULL | Spliterator.IMMUTABLE);
        }

        public boolean tryAdvance(LongConsumer consumer) {
            if (consumer == null) throw new NullPointerException();
            long i = index, f = fence;
            if (i < f) {
                consumer.accept(rng.internalNextLong(origin, bound));
                index = i + 1;
                return true;
            }
            return false;
        }

        public void forEachRemaining(LongConsumer consumer) {
            if (consumer == null) throw new NullPointerException();
            long i = index, f = fence;
            if (i < f) {
                index = f;
                SplittableRandom r = rng;
                long o = origin, b = bound;
                do {
                    consumer.accept(r.internalNextLong(o, b));
                } while (++i < f);
            }
        }

    }

    /**
     * Spliterator for double streams.
     */
    static final class RandomDoublesSpliterator implements Spliterator.OfDouble {
        final SplittableRandom rng;
        long index;
        final long fence;
        final double origin;
        final double bound;
        RandomDoublesSpliterator(SplittableRandom rng, long index, long fence,
                                 double origin, double bound) {
            this.rng = rng; this.index = index; this.fence = fence;
            this.origin = origin; this.bound = bound;
        }

        public RandomDoublesSpliterator trySplit() {
            long i = index, m = (i + fence) >>> 1;
            return (m <= i) ? null :
                new RandomDoublesSpliterator(rng.split(), i, index = m, origin, bound);
        }

        public long estimateSize() {
            return fence - index;
        }

        public int characteristics() {
            return (Spliterator.SIZED | Spliterator.SUBSIZED |
                    Spliterator.NONNULL | Spliterator.IMMUTABLE);
        }

        public boolean tryAdvance(DoubleConsumer consumer) {
            if (consumer == null) throw new NullPointerException();
            long i = index, f = fence;
            if (i < f) {
                consumer.accept(rng.internalNextDouble(origin, bound));
                index = i + 1;
                return true;
            }
            return false;
        }

        public void forEachRemaining(DoubleConsumer consumer) {
            if (consumer == null) throw new NullPointerException();
            long i = index, f = fence;
            if (i < f) {
                index = f;
                SplittableRandom r = rng;
                double o = origin, b = bound;
                do {
                    consumer.accept(r.internalNextDouble(o, b));
                } while (++i < f);
            }
        }
    }

}