SplittableRandom.java

/*
 * 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
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package java.util;

import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.SecureRandom;
import java.util.concurrent.atomic.AtomicLong;
import java.util.function.DoubleConsumer;
import java.util.function.IntConsumer;
import java.util.function.LongConsumer;
import java.util.stream.DoubleStream;
import java.util.stream.IntStream;
import java.util.stream.LongStream;
import java.util.stream.StreamSupport;

/**
 * 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>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>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.
 *
 * </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
 */
/*
 * 伪随机数生成器
 *
 * 非线程安全
 * 适用于少数单线程场景
 *
 * 支持使用内置种子计算的原始种子
 * 支持自定义原始种子
 * 支持使用安全种子（设置运行参数-Djava.util.secureRandomSeed=true）
 */
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.
     * 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.
     */
    
    // IllegalArgumentException messages
    static final String BAD_BOUND = "bound must be positive";
    static final String BAD_RANGE = "bound must be greater than origin";
    static final String BAD_SIZE  = "size must be non-negative";
    
    
    /*▼ 内置种子 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┓ */
    
    /**
     * The seed generator for default constructors.
     */
    // 内置种子，用来生成原始种子
    private static final AtomicLong defaultGen = new AtomicLong(mix64(System.currentTimeMillis()) ^ mix64(System.nanoTime()));
    
    /*▲ 内置种子 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┛ */
    
    
    /*▼ 原始种子 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┓ */
    
    /**
     * The seed. Updated only via method nextSeed.
     */
    // 原始种子，用来生成随机数
    private long seed;
    
    /**
     * The step value.
     */
    // 用于更新原始种子的步长
    private final long gamma;
    
    /*▲ 原始种子 ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓┛ */
    
    
    /**
     * The golden ratio scaled to 64bits, used as the initial gamma value for (unsplit) SplittableRandoms.
     */
    private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L;
    
    /**
     * The least non-zero value returned by nextDouble(). This value
     * is scaled by a random value of 53 bits to produce a result.
     */
    // double值的二进制精度
    private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53);
    
    
    // at end of <clinit> to survive static initialization circularity
    static {
        if(AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
            public Boolean run() {
                return Boolean.getBoolean("java.util.secureRandomSeed");
            }
        })) {
            byte[] seedBytes = SecureRandom.getSeed(8);
            long s = (long) seedBytes[0] & 0xffL;
            for(int i = 1; i<8; ++i) {
                s = (s << 8) | ((long) seedBytes[i] & 0xffL);
            }
            defaultGen.set(s);
        }
    }
    
    
    
    /*▼ 构造方法 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Creates a new SplittableRandom instance that is likely to generate sequences of values
     * that are statistically independent  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(GOLDEN_GAMMA << 1);
        this.seed = mix64(s);
        this.gamma = mixGamma(s + GOLDEN_GAMMA);
    }
    
    /**
     * 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);
    }
    
    /**
     * Internal constructor used by all others except default constructor.
     */
    private SplittableRandom(long seed, long gamma) {
        this.seed = seed;
        this.gamma = gamma;
    }
    
    /*▲ 构造方法 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 种子 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * 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
     */
    // 获取SplittableRandom实例
    public SplittableRandom split() {
        return new SplittableRandom(nextLong(), mixGamma(nextSeed()));
    }
    
    /**
     * Adds gamma to seed.
     */
    // 获取下一个种子
    private long nextSeed() {
        return seed += gamma;
    }
    
    /*▲ 种子 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 生成伪随机数 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Fills a user-supplied byte array with generated pseudorandom bytes.
     *
     * @param bytes the byte array to fill with pseudorandom bytes
     *
     * @throws NullPointerException if bytes is null
     * @since 10
     */
    // 随机填充一个byte数组，有正有负
    public void nextBytes(byte[] bytes) {
        int i = 0;
        int len = bytes.length;
        for(int words = len >> 3; words-->0; ) {
            long rnd = nextLong();
            for(int n = 8; n-->0; rnd >>>= Byte.SIZE)
                bytes[i++] = (byte) rnd;
        }
        if(i<len) {
            for(long rnd = nextLong(); i<len; rnd >>>= Byte.SIZE) {
                bytes[i++] = (byte) rnd;
            }
        }
    }
    
    /**
     * Returns a pseudorandom {@code int} value.
     *
     * @return a pseudorandom {@code int} value
     */
    // 随机生成一个int值，有正有负
    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
     */
    // 随机生成一个[0, bound)之内的int值
    public int nextInt(int bound) {
        if(bound<=0) {
            throw new IllegalArgumentException(BAD_BOUND);
        }
        // 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}
     */
    // 随机生成一个[origin, bound)之内的int值，有正有负
    public int nextInt(int origin, int bound) {
        if(origin >= bound) {
            throw new IllegalArgumentException(BAD_RANGE);
        }
        return internalNextInt(origin, bound);
    }
    
    /**
     * Returns a pseudorandom {@code long} value.
     *
     * @return a pseudorandom {@code long} value
     */
    // 随机生成一个long值，有正有负
    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
     */
    // 随机生成一个[0, bound)之内的long值
    public long nextLong(long bound) {
        if(bound<=0) {
            throw new IllegalArgumentException(BAD_BOUND);
        }
        // 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}
     */
    // 随机生成一个[origin, bound)之内的long值，有正有负
    public long nextLong(long origin, long bound) {
        if(origin >= bound) {
            throw new IllegalArgumentException(BAD_RANGE);
        }
        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)
     */
    // 随机生成一个[0, 1)之内的double值
    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
     */
    // 随机生成一个[0, bound)之内的double值
    public double nextDouble(double bound) {
        if(!(bound>0.0)) {
            throw new IllegalArgumentException(BAD_BOUND);
        }
        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}
     */
    // 随机生成一个[origin, bound)之内的double值，有正有负
    public double nextDouble(double origin, double bound) {
        if(!(origin<bound)) {
            throw new IllegalArgumentException(BAD_RANGE);
        }
        return internalNextDouble(origin, bound);
    }
    
    /**
     * Returns a pseudorandom {@code boolean} value.
     *
     * @return a pseudorandom {@code boolean} value
     */
    // 随机生成一个boolean值
    public boolean nextBoolean() {
        return mix32(nextSeed())<0;
    }
    
    /*▲ 生成伪随机数 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 流 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Returns an effectively unlimited stream of pseudorandom {@code int}
     * values from this generator and/or one split from it.
     *
     * @return a stream of pseudorandom {@code int} values
     *
     * @implNote This method is implemented to be equivalent to {@code
     * ints(Long.MAX_VALUE)}.
     */
    // 返回的流可以生成Long.MAX_VALUE个随机int值
    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.
     *
     * @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
     */
    // 返回的流可以生成streamSize个随机int值
    public IntStream ints(long streamSize) {
        if(streamSize<0L) {
            throw new IllegalArgumentException(BAD_SIZE);
        }
        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; each value
     * conforms to the given origin (inclusive) and bound (exclusive).
     *
     * @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}
     * @implNote This method is implemented to be equivalent to {@code
     * ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
     */
    // 返回的流可以生成Long.MAX_VALUE个随机int值，取值范围是[randomNumberOrigin, randomNumberBound)
    public IntStream ints(int randomNumberOrigin, int randomNumberBound) {
        if(randomNumberOrigin >= randomNumberBound) {
            throw new IllegalArgumentException(BAD_RANGE);
        }
        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 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}
     */
    // 返回的流可以生成streamSize个随机int值，取值范围是[randomNumberOrigin, randomNumberBound)
    public IntStream ints(long streamSize, int randomNumberOrigin, int randomNumberBound) {
        if(streamSize<0L) {
            throw new IllegalArgumentException(BAD_SIZE);
        }
        if(randomNumberOrigin >= randomNumberBound) {
            throw new IllegalArgumentException(BAD_RANGE);
        }
        return StreamSupport.intStream(new RandomIntsSpliterator(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.
     *
     * @return a stream of pseudorandom {@code long} values
     *
     * @implNote This method is implemented to be equivalent to {@code
     * longs(Long.MAX_VALUE)}.
     */
    // 返回的流可以生成Long.MAX_VALUE个随机long值
    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.
     *
     * @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
     */
    // 返回的流可以生成streamSize个随机long值
    public LongStream longs(long streamSize) {
        if(streamSize<0L) {
            throw new IllegalArgumentException(BAD_SIZE);
        }
        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; each value
     * conforms to the given origin (inclusive) and bound (exclusive).
     *
     * @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}
     * @implNote This method is implemented to be equivalent to {@code
     * longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
     */
    // 返回的流可以生成Long.MAX_VALUE个随机long值，取值范围是[randomNumberOrigin, randomNumberBound)
    public LongStream longs(long randomNumberOrigin, long randomNumberBound) {
        if(randomNumberOrigin >= randomNumberBound) {
            throw new IllegalArgumentException(BAD_RANGE);
        }
        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 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}
     */
    // 返回的流可以生成streamSize个随机long值，取值范围是[randomNumberOrigin, randomNumberBound)
    public LongStream longs(long streamSize, long randomNumberOrigin, long randomNumberBound) {
        if(streamSize<0L) {
            throw new IllegalArgumentException(BAD_SIZE);
        }
        if(randomNumberOrigin >= randomNumberBound) {
            throw new IllegalArgumentException(BAD_RANGE);
        }
        return StreamSupport.longStream(new RandomLongsSpliterator(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
     * is between zero (inclusive) and one (exclusive).
     *
     * @return a stream of pseudorandom {@code double} values
     *
     * @implNote This method is implemented to be equivalent to {@code
     * doubles(Long.MAX_VALUE)}.
     */
    // 返回的流可以生成Long.MAX_VALUE个随机double值，取值范围是[0, 1)
    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 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
     */
    // 返回的流可以生成streamSize个随机double值，取值范围是[0, 1)
    public DoubleStream doubles(long streamSize) {
        if(streamSize<0L) {
            throw new IllegalArgumentException(BAD_SIZE);
        }
        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
     * conforms to the given origin (inclusive) and bound (exclusive).
     *
     * @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}
     * @implNote This method is implemented to be equivalent to {@code
     * doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
     */
    // 返回的流可以生成Long.MAX_VALUE个随机double值，取值范围是[randomNumberOrigin, randomNumberBound)
    public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) {
        if(!(randomNumberOrigin<randomNumberBound)) {
            throw new IllegalArgumentException(BAD_RANGE);
        }
        return StreamSupport.doubleStream(new RandomDoublesSpliterator(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 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}
     */
    // 返回的流可以生成streamSize个随机double值，取值范围是[randomNumberOrigin, randomNumberBound)
    public DoubleStream doubles(long streamSize, double randomNumberOrigin, double randomNumberBound) {
        if(streamSize<0L) {
            throw new IllegalArgumentException(BAD_SIZE);
        }
        if(!(randomNumberOrigin<randomNumberBound)) {
            throw new IllegalArgumentException(BAD_RANGE);
        }
        return StreamSupport.doubleStream(new RandomDoublesSpliterator(this, 0L, streamSize, randomNumberOrigin, randomNumberBound), false);
    }
    
    /*▲ 流 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*
     * 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 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
     */
    // 随机生成一个[origin, bound)之内的int值
    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 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
     */
    // 随机生成一个[origin, bound)之内的long值
    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 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
     */
    // 随机生成一个[origin, bound)之内的double值
    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;
    }
    
    
    /**
     * Returns the 32 high bits of Stafford variant 4 mix64 function as int.
     */
    private static int mix32(long z) {
        z = (z ^ (z >>> 33)) * 0x62a9d9ed799705f5L;
        return (int)(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32);
    }
    
    /**
     * Computes Stafford variant 13 of 64bit mix function.
     */
    private static long mix64(long z) {
        z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L;
        z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL;
        return z ^ (z >>> 31);
    }
    
    /**
     * Returns the gamma value to use for a new split instance.
     */
    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;
    }
    
    
    
    /**
     * 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.
     */
    // 可以随机生成int元素的流
    private static final class RandomIntsSpliterator implements Spliterator.OfInt {
        final SplittableRandom rng;
        
        // 随机数数量：fence-index
        long   index;
        final long   fence;
        // 随机数取值范围：[origin, bound)
        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.
     */
    // 可以随机生成long元素的流
    private static final class RandomLongsSpliterator implements Spliterator.OfLong {
        final SplittableRandom rng;
        
        // 随机数数量：fence-index
        long index;
        final long fence;
        // 随机数取值范围：[origin, bound)
        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.
     */
    // 可以随机生成double元素的流
    private static final class RandomDoublesSpliterator implements Spliterator.OfDouble {
        final SplittableRandom rng;
        
        // 随机数数量：fence-index
        long index;
        final long fence;
        // 随机数取值范围：[origin, bound)
        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);
            }
        }
    }
}