--- jsr166/src/main/java/util/SplittableRandom.java	2013/07/12 11:26:34	1.7
+++ jsr166/src/main/java/util/SplittableRandom.java	2013/08/13 17:13:57	1.16
@@ -25,6 +25,7 @@
 
 package java.util;
 
+import java.net.InetAddress;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.Spliterator;
 import java.util.function.IntConsumer;
@@ -41,7 +42,9 @@ import java.util.stream.DoubleStream;
  * generate subtasks. Class 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>
+ * {@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.
@@ -49,7 +52,9 @@ import java.util.stream.DoubleStream;
  * 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.  </li>
+ * 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
@@ -79,103 +84,80 @@ import java.util.stream.DoubleStream;
 public class SplittableRandom {
 
     /*
-     * 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.
-     *
-     * Credits: Primary algorithm and code by Guy Steele.  Stream
-     * support methods by Doug Lea.  Documentation jointly produced
-     * with additional help from Brian Goetz.
-     */
-
-    /*
      * 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, but improves and extends it in several ways.
-     *
-     * The primary update step (see method nextSeed()) is simply to
-     * add a constant ("gamma") to the current seed, modulo a prime
-     * ("George"). However, the nextLong and nextInt methods do not
-     * return this value, but instead the results of bit-mixing
-     * transformations that produce more uniformly distributed
-     * sequences.
-     *
-     * "George" is the otherwise nameless (because it cannot be
-     * represented) prime number 2^64+13. Using a prime number larger
-     * than can fit in a long ensures that all possible long values
-     * can occur, plus 13 others that just get skipped over when they
-     * are encountered; see method addGammaModGeorge. For this to
-     * work, initial gamma values must be at least 13.
-     *
-     * The value of gamma differs for each instance across a series of
-     * splits, and is generated using a slightly stripped-down variant
-     * of the same algorithm, but operating across calls to split(),
-     * not calls to nextSeed(): Each instance carries the state of
-     * this generator as nextSplit, and uses mix64(nextSplit) as its
-     * own gamma value. Computations of gammas themselves use a fixed
-     * constant as the second argument to the addGammaModGeorge
-     * function, GAMMA_GAMMA, a "genuinely random" number from a
-     * radioactive decay reading (obtained from
-     * http://www.fourmilab.ch/hotbits/) meeting the above range
-     * constraint. Using a fixed constant maintains the invariant that
-     * the value of gamma is the same for every instance that is at
-     * the same split-distance from their common root. (Note: there is
-     * nothing especially magic about obtaining this constant from a
-     * "truly random" physical source rather than just choosing one
-     * arbitrarily; using "hotbits" was merely an aesthetically pleasing
-     * choice.  In either case, good statistical behavior of the
-     * algorithm should be, and was, verified by using the DieHarder
-     * test suite.)
-     *
-     * The mix64 bit-mixing function called by nextLong and other
-     * methods computes the same value as the "64-bit finalizer"
-     * function in Austin Appleby's MurmurHash3 algorithm.  See
+     * 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 bit-mixing function computes the same
+     * value as the "64-bit finalizer" function in Austin Appleby's
+     * MurmurHash3 algorithm.  See
      * http://code.google.com/p/smhasher/wiki/MurmurHash3 , which
      * comments: "The constants for the finalizers were generated by a
      * simple simulated-annealing algorithm, and both avalanche all
-     * bits of 'h' to within 0.25% bias." It also appears to work to
-     * use instead any of the variants proposed by David Stafford at
-     * http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html
-     * but these variants have not yet been tested as thoroughly
-     * in the context of the implementation of SplittableRandom.
-     *
-     * The mix32 function used for nextInt just consists of two of the
-     * five lines of mix64; avalanche testing shows that the 64-bit result
-     * has its top 32 bits avalanched well, though not the bottom 32 bits.
-     * DieHarder tests show that it is adequate for generating one
-     * random int from the 64-bit result of nextSeed.
-     *
-     * Support for the default (no-argument) constructor relies on an
-     * AtomicLong (defaultSeedGenerator) to help perform the
-     * equivalent of a split of a statically constructed
-     * SplittableRandom. Unlike other cases, this split must be
-     * performed in a thread-safe manner. We use
-     * AtomicLong.compareAndSet as the (typically) most efficient
-     * mechanism. To bootstrap, we start off using System.nanotime(),
-     * and update using another "genuinely random" constant
-     * DEFAULT_SEED_GAMMA. The default constructor uses GAMMA_GAMMA,
-     * not 0, for its splitSeed argument (addGammaModGeorge(0,
-     * GAMMA_GAMMA) == GAMMA_GAMMA) to reflect that each is split from
-     * this root generator, even though the root is not explicitly
-     * represented as a SplittableRandom.
+     * bits of 'h' to within 0.25% bias." The mix32 function is
+     * equivalent to (int)(mix64(seed) >>> 32), but faster because it
+     * omits a step that doesn't contribute to result.
+     *
+     * 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 nextGamma) uses the "Mix13" constants
+     * for MurmurHash3 described by David Stafford
+     * (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html)
+     * To avoid potential weaknesses in bit-mixing transformations, we
+     * restrict gammas to odd values with at least 12 and no more than
+     * 52 bits set.  Rather than rejecting candidates with too few or
+     * too many bits set, method nextGamma 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<sup>14</sup>, a very tiny percentage, 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 "seeder" 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 seeder, we start
+     * off using a seed based on current time and host. 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.
      */
 
     /**
-     * The "genuinely random" value for producing new gamma values.
-     * The value is arbitrary, subject to the requirement that it be
-     * greater or equal to 13.
-     */
-    private static final long GAMMA_GAMMA = 0xF2281E2DBA6606F3L;
-
-    /**
-     * The "genuinely random" seed update value for default constructors.
-     * The value is arbitrary, subject to the requirement that it be
-     * greater or equal to 13.
+     * The initial gamma value for (unsplit) SplittableRandoms. Must
+     * be odd with at least 12 and no more than 52 bits set. Currently
+     * set to the golden ratio scaled to 64bits.
      */
-    private static final long DEFAULT_SEED_GAMMA = 0xBD24B73A95FB84D9L;
+    private static final long INITIAL_GAMMA = 0x9e3779b97f4a7c15L;
 
     /**
      * The least non-zero value returned by nextDouble(). This value
@@ -184,109 +166,82 @@ public class SplittableRandom {
     private static final double DOUBLE_UNIT = 1.0 / (1L << 53);
 
     /**
-     * The next seed for default constructors.
-     */
-    private static final AtomicLong defaultSeedGenerator =
-        new AtomicLong(System.nanoTime());
-
-    /**
-     * The seed, updated only via method nextSeed.
+     * The seed. Updated only via method nextSeed.
      */
     private long seed;
 
     /**
-     * The constant value added to seed (mod George) on each update.
+     * The step value.
      */
     private final long gamma;
 
     /**
-     * The next seed to use for splits. Propagated using
-     * addGammaModGeorge across instances.
-     */
-    private final long nextSplit;
-
-    /**
-     * Adds the given gamma value, g, to the given seed value s, mod
-     * George (2^64+13). We regard s and g as unsigned values
-     * (ranging from 0 to 2^64-1). We add g to s either once or twice
-     * (mod George) as necessary to produce an (unsigned) result less
-     * than 2^64.  We require that g must be at least 13. This
-     * guarantees that if (s+g) mod George >= 2^64 then (s+g+g) mod
-     * George < 2^64; thus we need only a conditional, not a loop,
-     * to be sure of getting a representable value.
-     *
-     * @param s a seed value
-     * @param g a gamma value, 13 <= g (as unsigned)
+     * Internal constructor used by all others except default constructor.
      */
-    private static long addGammaModGeorge(long s, long g) {
-        long p = s + g;
-        if (Long.compareUnsigned(p, g) >= 0)
-            return p;
-        long q = p - 13L;
-        return (Long.compareUnsigned(p, 13L) >= 0) ? q : (q + g);
+    private SplittableRandom(long seed, long gamma) {
+        this.seed = seed;
+        this.gamma = gamma;
     }
 
     /**
-     * Returns a bit-mixed transformation of its argument.
-     * See above for explanation.
+     * Computes MurmurHash3 64bit mix function.
      */
     private static long mix64(long z) {
-        z ^= (z >>> 33);
-        z *= 0xff51afd7ed558ccdL;
-        z ^= (z >>> 33);
-        z *= 0xc4ceb9fe1a85ec53L;
-        z ^= (z >>> 33);
-        return z;
+        z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL;
+        z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L;
+        return z ^ (z >>> 33);
     }
 
     /**
-     * Returns a bit-mixed int transformation of its argument.
-     * See above for explanation.
+     * Returns the 32 high bits of mix64(z) as int.
      */
     private static int mix32(long z) {
-        z ^= (z >>> 33);
-        z *= 0xc4ceb9fe1a85ec53L;
-        return (int)(z >>> 32);
+        z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL;
+        return (int)(((z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L) >>> 32);
     }
 
     /**
-     * Internal constructor used by all other constructors and by
-     * method split. Establishes the initial seed for this instance,
-     * and uses the given splitSeed to establish gamma, as well as the
-     * nextSplit to use by this instance. The loop to skip ineligible
-     * gammas very rarely iterates, and does so at most 13 times.
+     * Returns the gamma value to use for a new split instance.
      */
-    private SplittableRandom(long seed, long splitSeed) {
-        this.seed = seed;
-        long s = splitSeed, g;
-        do { // ensure gamma >= 13, considered as an unsigned integer
-            s = addGammaModGeorge(s, GAMMA_GAMMA);
-            g = mix64(s);
-        } while (Long.compareUnsigned(g, 13L) < 0);
-        this.gamma = g;
-        this.nextSplit = s;
+    private static long nextGamma(long z) {
+        z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; // Stafford "Mix13"
+        z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL;
+        z = (z ^ (z >>> 31)) | 1L; // force to be odd
+        int n = Long.bitCount(z);  // ensure enough 0 and 1 bits
+        return (n < 12 || n > 52) ? z ^ 0xaaaaaaaaaaaaaaaaL : z;
     }
 
     /**
-     * Updates in-place and returns seed.
-     * See above for explanation.
+     * Adds gamma to seed.
      */
     private long nextSeed() {
-        return seed = addGammaModGeorge(seed, gamma);
+        return seed += gamma;
     }
 
     /**
-     * Atomically updates and returns next seed for default constructor.
+     * The seed generator for default constructors.
+     */
+    private static final AtomicLong seeder =
+        new AtomicLong(mix64((((long)hashedHostAddress()) << 32) ^
+                             System.currentTimeMillis()) ^
+                       mix64(System.nanoTime()));
+
+    /**
+     * Returns hash of local host IP address, if available; else 0.
      */
-    private static long nextDefaultSeed() {
-        long oldSeed, newSeed;
-        do {
-            oldSeed = defaultSeedGenerator.get();
-            newSeed = addGammaModGeorge(oldSeed, DEFAULT_SEED_GAMMA);
-        } while (!defaultSeedGenerator.compareAndSet(oldSeed, newSeed));
-        return mix64(newSeed);
+    private static int hashedHostAddress() {
+	try {
+	    return InetAddress.getLocalHost().hashCode();
+	} catch (Exception ex) {
+	    return 0;
+	}
     }
 
+    // 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
@@ -362,7 +317,7 @@ public class SplittableRandom {
         int r = mix32(nextSeed());
         if (origin < bound) {
             int n = bound - origin, m = n - 1;
-            if ((n & m) == 0L)
+            if ((n & m) == 0)
                 r = (r & m) + origin;
             else if (n > 0) {
                 for (int u = r >>> 1;
@@ -401,12 +356,12 @@ public class SplittableRandom {
     /**
      * Creates a new SplittableRandom instance using the specified
      * initial seed. SplittableRandom instances created with the same
-     * seed generate identical sequences of values.
+     * seed in the same program generate identical sequences of values.
      *
      * @param seed the initial seed
      */
     public SplittableRandom(long seed) {
-        this(seed, 0);
+        this(seed, INITIAL_GAMMA);
     }
 
     /**
@@ -415,8 +370,8 @@ public class SplittableRandom {
      * of those of any other instances in the current program; and
      * may, and typically does, vary across program invocations.
      */
-    public SplittableRandom() {
-        this(nextDefaultSeed(), GAMMA_GAMMA);
+    public SplittableRandom() { // emulate seeder.split()
+        this.gamma = nextGamma(this.seed = seeder.addAndGet(INITIAL_GAMMA));
     }
 
     /**
@@ -434,7 +389,8 @@ public class SplittableRandom {
      * @return the new SplittableRandom instance
      */
     public SplittableRandom split() {
-        return new SplittableRandom(nextSeed(), nextSplit);
+        long s = nextSeed();
+        return new SplittableRandom(s, nextGamma(s));
     }
 
     /**
@@ -453,16 +409,16 @@ public class SplittableRandom {
      * @param bound the bound on the random number to be returned.  Must be
      *        positive.
      * @return a pseudorandom {@code int} value between zero
-     *         (inclusive) and the bound (exclusive).
-     * @throws IllegalArgumentException if the bound is less than 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("bound must be positive");
+            throw new IllegalArgumentException(BadBound);
         // Specialize internalNextInt for origin 0
         int r = mix32(nextSeed());
         int m = bound - 1;
-        if ((bound & m) == 0L) // power of two
+        if ((bound & m) == 0) // power of two
             r &= m;
         else { // reject over-represented candidates
             for (int u = r >>> 1;
@@ -480,13 +436,13 @@ public class SplittableRandom {
      * @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).
+     *         (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("bound must be greater than origin");
+            throw new IllegalArgumentException(BadRange);
         return internalNextInt(origin, bound);
     }
 
@@ -506,12 +462,12 @@ public class SplittableRandom {
      * @param bound the bound on the random number to be returned.  Must be
      *        positive.
      * @return a pseudorandom {@code long} value between zero
-     *         (inclusive) and the bound (exclusive).
-     * @throws IllegalArgumentException if {@code bound} is less than 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("bound must be positive");
+            throw new IllegalArgumentException(BadBound);
         // Specialize internalNextLong for origin 0
         long r = mix64(nextSeed());
         long m = bound - 1;
@@ -533,13 +489,13 @@ public class SplittableRandom {
      * @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).
+     *         (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("bound must be greater than origin");
+            throw new IllegalArgumentException(BadRange);
         return internalNextLong(origin, bound);
     }
 
@@ -551,7 +507,7 @@ public class SplittableRandom {
      * (inclusive) and one (exclusive)
      */
     public double nextDouble() {
-        return (nextLong() >>> 11) * DOUBLE_UNIT;
+        return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT;
     }
 
     /**
@@ -561,13 +517,13 @@ public class SplittableRandom {
      * @param bound the bound on the random number to be returned.  Must be
      *        positive.
      * @return a pseudorandom {@code double} value between zero
-     *         (inclusive) and the bound (exclusive).
-     * @throws IllegalArgumentException if {@code bound} is less than 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("bound must be positive");
-        double result = nextDouble() * bound;
+            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);
     }
@@ -579,22 +535,32 @@ public class SplittableRandom {
      * @param origin the least value returned
      * @param bound the upper bound
      * @return a pseudorandom {@code double} value between the origin
-     *         (inclusive) and the bound (exclusive).
+     *         (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("bound must be greater than origin");
+            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.
+     * 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
@@ -603,7 +569,7 @@ public class SplittableRandom {
      */
     public IntStream ints(long streamSize) {
         if (streamSize < 0L)
-            throw new IllegalArgumentException("negative Stream size");
+            throw new IllegalArgumentException(BadSize);
         return StreamSupport.intStream
             (new RandomIntsSpliterator
              (this, 0L, streamSize, Integer.MAX_VALUE, 0),
@@ -612,7 +578,7 @@ public class SplittableRandom {
 
     /**
      * Returns an effectively unlimited stream of pseudorandom {@code int}
-     * values
+     * values from this generator and/or one split from it.
      *
      * @implNote This method is implemented to be equivalent to {@code
      * ints(Long.MAX_VALUE)}.
@@ -627,15 +593,15 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns a stream producing the given {@code streamSize} number of
-     * pseudorandom {@code int} values, each conforming to the given
-     * origin and bound.
+     * Returns a stream producing the given {@code streamSize} number
+     * of pseudorandom {@code int} values, each conforming to the
+     * given origin and bound.
      *
      * @param streamSize the number of values to generate
      * @param randomNumberOrigin the origin of each random value
      * @param randomNumberBound the bound of each random value
      * @return a stream of pseudorandom {@code int} values,
-     *         each with the given origin and bound.
+     *         each with the given origin and bound
      * @throws IllegalArgumentException if {@code streamSize} is
      *         less than zero, or {@code randomNumberOrigin}
      *         is greater than or equal to {@code randomNumberBound}
@@ -643,9 +609,9 @@ public class SplittableRandom {
     public IntStream ints(long streamSize, int randomNumberOrigin,
                           int randomNumberBound) {
         if (streamSize < 0L)
-            throw new IllegalArgumentException("negative Stream size");
+            throw new IllegalArgumentException(BadSize);
         if (randomNumberOrigin >= randomNumberBound)
-            throw new IllegalArgumentException("bound must be greater than origin");
+            throw new IllegalArgumentException(BadRange);
         return StreamSupport.intStream
             (new RandomIntsSpliterator
              (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
@@ -662,13 +628,13 @@ public class SplittableRandom {
      * @param randomNumberOrigin the origin of each random value
      * @param randomNumberBound the bound of each random value
      * @return a stream of pseudorandom {@code int} values,
-     *         each with the given origin and bound.
+     *         each with the given origin and bound
      * @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("bound must be greater than origin");
+            throw new IllegalArgumentException(BadRange);
         return StreamSupport.intStream
             (new RandomIntsSpliterator
              (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
@@ -676,8 +642,9 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns a stream producing the given {@code streamSize} number of
-     * pseudorandom {@code long} values.
+     * 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
@@ -686,7 +653,7 @@ public class SplittableRandom {
      */
     public LongStream longs(long streamSize) {
         if (streamSize < 0L)
-            throw new IllegalArgumentException("negative Stream size");
+            throw new IllegalArgumentException(BadSize);
         return StreamSupport.longStream
             (new RandomLongsSpliterator
              (this, 0L, streamSize, Long.MAX_VALUE, 0L),
@@ -694,8 +661,8 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns an effectively unlimited stream of pseudorandom {@code long}
-     * values.
+     * 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)}.
@@ -718,7 +685,7 @@ public class SplittableRandom {
      * @param randomNumberOrigin the origin of each random value
      * @param randomNumberBound the bound of each random value
      * @return a stream of pseudorandom {@code long} values,
-     *         each with the given origin and bound.
+     *         each with the given origin and bound
      * @throws IllegalArgumentException if {@code streamSize} is
      *         less than zero, or {@code randomNumberOrigin}
      *         is greater than or equal to {@code randomNumberBound}
@@ -726,9 +693,9 @@ public class SplittableRandom {
     public LongStream longs(long streamSize, long randomNumberOrigin,
                             long randomNumberBound) {
         if (streamSize < 0L)
-            throw new IllegalArgumentException("negative Stream size");
+            throw new IllegalArgumentException(BadSize);
         if (randomNumberOrigin >= randomNumberBound)
-            throw new IllegalArgumentException("bound must be greater than origin");
+            throw new IllegalArgumentException(BadRange);
         return StreamSupport.longStream
             (new RandomLongsSpliterator
              (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
@@ -745,13 +712,13 @@ public class SplittableRandom {
      * @param randomNumberOrigin the origin of each random value
      * @param randomNumberBound the bound of each random value
      * @return a stream of pseudorandom {@code long} values,
-     *         each with the given origin and bound.
+     *         each with the given origin and bound
      * @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("bound must be greater than origin");
+            throw new IllegalArgumentException(BadRange);
         return StreamSupport.longStream
             (new RandomLongsSpliterator
              (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
@@ -770,7 +737,7 @@ public class SplittableRandom {
      */
     public DoubleStream doubles(long streamSize) {
         if (streamSize < 0L)
-            throw new IllegalArgumentException("negative Stream size");
+            throw new IllegalArgumentException(BadSize);
         return StreamSupport.doubleStream
             (new RandomDoublesSpliterator
              (this, 0L, streamSize, Double.MAX_VALUE, 0.0),
@@ -803,18 +770,18 @@ public class SplittableRandom {
      * @param randomNumberOrigin the origin of each random value
      * @param randomNumberBound the bound of each random value
      * @return a stream of pseudorandom {@code double} values,
-     * each with the given origin and bound.
+     * each with the given origin and bound
      * @throws IllegalArgumentException if {@code streamSize} is
-     * less than zero.
+     * 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("negative Stream size");
+            throw new IllegalArgumentException(BadSize);
         if (!(randomNumberOrigin < randomNumberBound))
-            throw new IllegalArgumentException("bound must be greater than origin");
+            throw new IllegalArgumentException(BadRange);
         return StreamSupport.doubleStream
             (new RandomDoublesSpliterator
              (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
@@ -831,13 +798,13 @@ public class SplittableRandom {
      * @param randomNumberOrigin the origin of each random value
      * @param randomNumberBound the bound of each random value
      * @return a stream of pseudorandom {@code double} values,
-     * each with the given origin and bound.
+     * each with the given origin and bound
      * @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("bound must be greater than origin");
+            throw new IllegalArgumentException(BadRange);
         return StreamSupport.doubleStream
             (new RandomDoublesSpliterator
              (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
@@ -852,7 +819,7 @@ public class SplittableRandom {
      * approach. The long and double versions of this class are
      * identical except for types.
      */
-    static class RandomIntsSpliterator implements Spliterator.OfInt {
+    static final class RandomIntsSpliterator implements Spliterator.OfInt {
         final SplittableRandom rng;
         long index;
         final long fence;
@@ -895,9 +862,10 @@ public class SplittableRandom {
             long i = index, f = fence;
             if (i < f) {
                 index = f;
+                SplittableRandom r = rng;
                 int o = origin, b = bound;
                 do {
-                    consumer.accept(rng.internalNextInt(o, b));
+                    consumer.accept(r.internalNextInt(o, b));
                 } while (++i < f);
             }
         }
@@ -906,7 +874,7 @@ public class SplittableRandom {
     /**
      * Spliterator for long streams.
      */
-    static class RandomLongsSpliterator implements Spliterator.OfLong {
+    static final class RandomLongsSpliterator implements Spliterator.OfLong {
         final SplittableRandom rng;
         long index;
         final long fence;
@@ -949,9 +917,10 @@ public class SplittableRandom {
             long i = index, f = fence;
             if (i < f) {
                 index = f;
+                SplittableRandom r = rng;
                 long o = origin, b = bound;
                 do {
-                    consumer.accept(rng.internalNextLong(o, b));
+                    consumer.accept(r.internalNextLong(o, b));
                 } while (++i < f);
             }
         }
@@ -961,7 +930,7 @@ public class SplittableRandom {
     /**
      * Spliterator for double streams.
      */
-    static class RandomDoublesSpliterator implements Spliterator.OfDouble {
+    static final class RandomDoublesSpliterator implements Spliterator.OfDouble {
         final SplittableRandom rng;
         long index;
         final long fence;
@@ -1004,13 +973,13 @@ public class SplittableRandom {
             long i = index, f = fence;
             if (i < f) {
                 index = f;
+                SplittableRandom r = rng;
                 double o = origin, b = bound;
                 do {
-                    consumer.accept(rng.internalNextDouble(o, b));
+                    consumer.accept(r.internalNextDouble(o, b));
                 } while (++i < f);
             }
         }
     }
 
 }
-