--- jsr166/src/main/java/util/SplittableRandom.java	2013/07/10 15:40:19	1.1
+++ jsr166/src/main/java/util/SplittableRandom.java	2013/08/05 13:58:02	1.14
@@ -25,6 +25,7 @@
 
 package java.util;
 
+import java.security.SecureRandom;
 import java.util.concurrent.atomic.AtomicLong;
 import java.util.Spliterator;
 import java.util.function.IntConsumer;
@@ -35,14 +36,15 @@ 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 SplittableRandom supports methods for
- * producing pseudorandom nunmbers of type {@code int}, {@code long},
+ * 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.
@@ -50,12 +52,14 @@ 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
- * current instance. However, with very high probability, the set of
- * values collectively generated by the two objects has the same
+ * 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>
@@ -74,6 +78,7 @@ import java.util.stream.DoubleStream;
  * </ul>
  *
  * @author  Guy Steele
+ * @author  Doug Lea
  * @since   1.8
  */
 public class SplittableRandom {
@@ -96,11 +101,12 @@ public class SplittableRandom {
      * Random-Number Generation for Dynamic-Multithreading Platforms",
      * PPoPP 2012, but improves and extends it in several ways.
      *
-     * The primary update step 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.
+     * 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
@@ -109,43 +115,33 @@ public class SplittableRandom {
      * 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 nextLong(): 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
      * 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.
+     * bits of 'h' to within 0.25% bias."
+     *
+     * The value of gamma differs for each instance across a series of
+     * splits, and is generated using an independent 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. Gammas are treated as 57bit values,
+     * advancing by adding GAMMA_GAMMA mod GAMMA_PRIME, and bit-mixed
+     * with a 57-bit version of mix, using the "Mix13" multiplicative
+     * constants for MurmurHash3 described by David Stafford
+     * (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html).
+     * The value of GAMMA_GAMMA is arbitrary (except must be at least
+     * 13 and less than GAMMA_PRIME), but because it serves as the
+     * base of split sequences, should be subject to validation of
+     * consequent random number quality metrics.
      *
      * 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.
+     * 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
@@ -153,8 +149,8 @@ public class SplittableRandom {
      * 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
+     * mechanism. To bootstrap, we start off using a SecureRandom
+     * initial default seed, and update using a fixed
      * 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
@@ -163,24 +159,42 @@ public class SplittableRandom {
      */
 
     /**
-     * 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.
+     * The prime modulus for gamma values.
+     */
+    private static final long GAMMA_PRIME = (1L << 57) - 13L;
+
+    /**
+     * The value for producing new gamma values. Must be greater or
+     * equal to 13 and less than GAMMA_PRIME. Otherwise, the value is
+     * arbitrary subject to validation of the resulting statistical
+     * quality of splits.
+     */
+    private static final long GAMMA_GAMMA = 0x00aae38294f712aabL;
+
+    /**
+     * The seed update value for default constructors.  Must be
+     * greater or equal to 13. Otherwise, the value is arbitrary
+     * subject to quality checks.
      */
-    private static final long GAMMA_GAMMA = 0xF2281E2DBA6606F3L;
+    private static final long DEFAULT_SEED_GAMMA = 0x9e3779b97f4a7c15L;
 
     /**
-     * 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 value 13 with 64bit sign bit set. Used in the signed
+     * comparison in addGammaModGeorge.
      */
-    private static final long DEFAULT_SEED_GAMMA = 0xBD24B73A95FB84D9L;
+    private static final long BOTTOM13 = 0x800000000000000DL;
+
+    /**
+     * The least non-zero value returned by nextDouble(). This value
+     * is scaled by a random value of 53 bits to produce a result.
+     */
+    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());
+        new AtomicLong(getInitialDefaultSeed());
 
     /**
      * The seed, updated only via method nextSeed.
@@ -199,23 +213,6 @@ public class SplittableRandom {
     private final long nextSplit;
 
     /**
-     * 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.
-     */
-    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;
-    }
-
-    /**
      * 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
@@ -225,23 +222,16 @@ public class SplittableRandom {
      * 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
+     * Because Java comparison operators are signed, we implement this
+     * by conceptually offsetting seed values downwards by 2^63, so
+     * 0..13 is represented as Long.MIN_VALUE..BOTTOM13.
+     *
+     * @param s a seed value, viewed as a signed long
      * @param g a gamma value, 13 <= g (as unsigned)
      */
     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);
-    }
-
-    /**
-     * Updates in-place and returns seed.
-     * See above for explanation.
-     */
-    private long nextSeed() {
-        return seed = addGammaModGeorge(seed, gamma);
+        return (p >= s) ? p : ((p >= BOTTOM13) ? p  : p + g) - 13L;
     }
 
     /**
@@ -268,7 +258,48 @@ public class SplittableRandom {
     }
 
     /**
-     * Atomically updates and returns next seed for default constructor
+     * Returns a 57-bit mixed transformation of its argument.  See
+     * above for explanation.
+     */
+    private static long mix57(long z) {
+        z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L;
+        z &= 0x01FFFFFFFFFFFFFFL;
+        z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL;
+        z &= 0x01FFFFFFFFFFFFFFL;
+        z ^= (z >>> 31);
+        return z;
+    }
+
+    /**
+     * 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.
+     */
+    private SplittableRandom(long seed, long splitSeed) {
+        this.seed = seed;
+        long s = splitSeed, g;
+        do { // ensure gamma >= 13, considered as an unsigned integer
+            s += GAMMA_GAMMA;
+            if (s >= GAMMA_PRIME)
+                s -= GAMMA_PRIME;
+            g = mix57(s);
+        } while (g < 13L);
+        this.gamma = g;
+        this.nextSplit = s;
+    }
+
+    /**
+     * Updates in-place and returns seed.
+     * See above for explanation.
+     */
+    private long nextSeed() {
+        return seed = addGammaModGeorge(seed, gamma);
+    }
+
+    /**
+     * Atomically updates and returns next seed for default constructor.
      */
     private static long nextDefaultSeed() {
         long oldSeed, newSeed;
@@ -279,6 +310,17 @@ public class SplittableRandom {
         return mix64(newSeed);
     }
 
+    /**
+     * Returns an initial default seed.
+     */
+    private static long getInitialDefaultSeed() {
+        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;
+    }
+
     /*
      * Internal versions of nextX methods used by streams, as well as
      * the public nextX(origin, bound) methods.  These exist mainly to
@@ -310,27 +352,31 @@ public class SplittableRandom {
          * 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.
+         * 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.  Repeatedly generate unbounded longs until obtaining
-         * a candidate meeting constraints (with an expected number of
-         * iterations of less than two).
+         * 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
+            if ((n & m) == 0L)  // power of two
                 r = (r & m) + origin;
-            else if (n > 0) { // reject over-represented candidates
+            else if (n > 0L) {  // reject over-represented candidates
                 for (long u = r >>> 1;            // ensure nonnegative
-                     u + m - (r = u % n) < 0L;    // reject
+                     u + m - (r = u % n) < 0L;    // rejection check
                      u = mix64(nextSeed()) >>> 1) // retry
                     ;
                 r += origin;
             }
-            else {             // range not representable as long
+            else {              // range not representable as long
                 while (r < origin || r >= bound)
                     r = mix64(nextSeed());
             }
@@ -350,11 +396,11 @@ 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;
-                     u + m - (r = u % n) < 0L;
+                     u + m - (r = u % n) < 0;
                      u = mix32(nextSeed()) >>> 1)
                     ;
                 r += origin;
@@ -375,11 +421,10 @@ public class SplittableRandom {
      * @return a pseudorandom value
      */
     final double internalNextDouble(double origin, double bound) {
-        long bits = (1023L << 52) | (nextLong() >>> 12);
-        double r = Double.longBitsToDouble(bits) - 1.0;
+        double r = (nextLong() >>> 11) * DOUBLE_UNIT;
         if (origin < bound) {
             r = r * (bound - origin) + origin;
-            if (r == bound) // correct for rounding
+            if (r >= bound) // correct for rounding
                 r = Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
         }
         return r;
@@ -388,14 +433,14 @@ public class SplittableRandom {
     /* ---------------- public methods ---------------- */
 
     /**
-     * Creates a new SplittableRandom instance using the given initial
-     * seed. Two SplittableRandom instances created with the same seed
-     * generate identical sequences of values.
+     * 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, 0);
+        this(seed, 0L);
     }
 
     /**
@@ -429,21 +474,21 @@ public class SplittableRandom {
     /**
      * Returns a pseudorandom {@code int} value.
      *
-     * @return a pseudorandom value
+     * @return a pseudorandom {@code int} value
      */
     public int nextInt() {
         return mix32(nextSeed());
     }
 
     /**
-     * Returns a pseudorandom {@code int} value between 0 (inclusive)
+     * Returns a pseudorandom {@code int} value between zero (inclusive)
      * and the specified bound (exclusive).
      *
      * @param bound the bound on the random number to be returned.  Must be
      *        positive.
-     * @return a pseudorandom {@code int} value between {@code 0}
-     *         (inclusive) and the bound (exclusive).
-     * @exception IllegalArgumentException if the bound is not positive
+     * @return a pseudorandom {@code int} value between zero
+     *         (inclusive) and the bound (exclusive)
+     * @throws IllegalArgumentException if the bound is less than zero
      */
     public int nextInt(int bound) {
         if (bound <= 0)
@@ -451,11 +496,11 @@ public class SplittableRandom {
         // 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;
-                 u + m - (r = u % bound) < 0L;
+                 u + m - (r = u % bound) < 0;
                  u = mix32(nextSeed()) >>> 1)
                 ;
         }
@@ -469,8 +514,8 @@ 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).
-     * @exception IllegalArgumentException if {@code origin} is greater than
+     *         (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) {
@@ -482,21 +527,21 @@ public class SplittableRandom {
     /**
      * Returns a pseudorandom {@code long} value.
      *
-     * @return a pseudorandom value
+     * @return a pseudorandom {@code long} value
      */
     public long nextLong() {
         return mix64(nextSeed());
     }
 
     /**
-     * Returns a pseudorandom {@code long} value between 0 (inclusive)
+     * Returns a pseudorandom {@code long} value between zero (inclusive)
      * and the specified bound (exclusive).
      *
      * @param bound the bound on the random number to be returned.  Must be
      *        positive.
-     * @return a pseudorandom {@code long} value between {@code 0}
-     *         (inclusive) and the bound (exclusive).
-     * @exception IllegalArgumentException if the bound is not positive
+     * @return a pseudorandom {@code long} value between zero
+     *         (inclusive) and the bound (exclusive)
+     * @throws IllegalArgumentException if {@code bound} is less than zero
      */
     public long nextLong(long bound) {
         if (bound <= 0)
@@ -522,8 +567,8 @@ 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).
-     * @exception IllegalArgumentException if {@code origin} is greater than
+     *         (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) {
@@ -533,15 +578,14 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns a pseudorandom {@code double} value between {@code 0.0}
-     * (inclusive) and {@code 1.0} (exclusive).
+     * Returns a pseudorandom {@code double} value between zero
+     * (inclusive) and one (exclusive).
      *
-     * @return a pseudorandom value between {@code 0.0}
-     * (inclusive) and {@code 1.0} (exclusive)
+     * @return a pseudorandom {@code double} value between zero
+     * (inclusive) and one (exclusive)
      */
     public double nextDouble() {
-        long bits = (1023L << 52) | (nextLong() >>> 12);
-        return Double.longBitsToDouble(bits) - 1.0;
+        return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT;
     }
 
     /**
@@ -550,46 +594,55 @@ public class SplittableRandom {
      *
      * @param bound the bound on the random number to be returned.  Must be
      *        positive.
-     * @return a pseudorandom {@code double} value between {@code 0.0}
-     *         (inclusive) and the bound (exclusive).
-     * @throws IllegalArgumentException if {@code bound} is not positive
+     * @return a pseudorandom {@code double} value between zero
+     *         (inclusive) and the bound (exclusive)
+     * @throws IllegalArgumentException if {@code bound} is less than zero
      */
     public double nextDouble(double bound) {
-        if (bound <= 0.0)
+        if (!(bound > 0.0))
             throw new IllegalArgumentException("bound must be positive");
-        double result = nextDouble() * 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 given
+     * 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
      * @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)
+        if (!(origin < bound))
             throw new IllegalArgumentException("bound must be greater than origin");
         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 with the given {@code streamSize} number of
+     * Returns a stream producing the given {@code streamSize} number of
      * pseudorandom {@code int} values.
      *
      * @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
+     *         less than zero
      */
     public IntStream ints(long streamSize) {
         if (streamSize < 0L)
@@ -602,7 +655,7 @@ public class SplittableRandom {
 
     /**
      * Returns an effectively unlimited stream of pseudorandom {@code int}
-     * values
+     * values.
      *
      * @implNote This method is implemented to be equivalent to {@code
      * ints(Long.MAX_VALUE)}.
@@ -617,7 +670,7 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns a stream with the given {@code streamSize} number of
+     * Returns a stream producing the given {@code streamSize} number of
      * pseudorandom {@code int} values, each conforming to the given
      * origin and bound.
      *
@@ -625,10 +678,9 @@ 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 streamSize} is
-     * less than zero.
-     * @throws IllegalArgumentException if {@code randomNumberOrigin}
+     *         less than zero, or {@code randomNumberOrigin}
      *         is greater than or equal to {@code randomNumberBound}
      */
     public IntStream ints(long streamSize, int randomNumberOrigin,
@@ -653,7 +705,7 @@ 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 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}
      */
@@ -667,13 +719,13 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns a stream with the given {@code streamSize} number of
+     * Returns a stream producing the given {@code streamSize} number of
      * pseudorandom {@code long} values.
      *
      * @param streamSize the number of values to generate
-     * @return a stream of {@code long} values
+     * @return a stream of pseudorandom {@code long} values
      * @throws IllegalArgumentException if {@code streamSize} is
-     * less than zero
+     *         less than zero
      */
     public LongStream longs(long streamSize) {
         if (streamSize < 0L)
@@ -701,7 +753,7 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns a stream with the given {@code streamSize} number of
+     * Returns a stream producing the given {@code streamSize} number of
      * pseudorandom {@code long} values, each conforming to the
      * given origin and bound.
      *
@@ -709,10 +761,9 @@ 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.
-     * @throws IllegalArgumentException if {@code randomNumberOrigin}
+     *         less than zero, or {@code randomNumberOrigin}
      *         is greater than or equal to {@code randomNumberBound}
      */
     public LongStream longs(long streamSize, long randomNumberOrigin,
@@ -737,7 +788,7 @@ 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 randomNumberOrigin}
      *         is greater than or equal to {@code randomNumberBound}
      */
@@ -751,13 +802,14 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns a stream with the given {@code streamSize} number of
-     * pseudorandom {@code double} values.
+     * Returns a stream producing the given {@code streamSize} number of
+     * pseudorandom {@code double} values, each 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
+     *         less than zero
      */
     public DoubleStream doubles(long streamSize) {
         if (streamSize < 0L)
@@ -770,7 +822,8 @@ public class SplittableRandom {
 
     /**
      * Returns an effectively unlimited stream of pseudorandom {@code
-     * double} values.
+     * double} values, each between zero (inclusive) and one
+     * (exclusive).
      *
      * @implNote This method is implemented to be equivalent to {@code
      * doubles(Long.MAX_VALUE)}.
@@ -785,7 +838,7 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns a stream with the given {@code streamSize} number of
+     * Returns a stream producing the given {@code streamSize} number of
      * pseudorandom {@code double} values, each conforming to the
      * given origin and bound.
      *
@@ -793,9 +846,9 @@ 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}
      */
@@ -803,7 +856,7 @@ public class SplittableRandom {
                                 double randomNumberBound) {
         if (streamSize < 0L)
             throw new IllegalArgumentException("negative Stream size");
-        if (randomNumberOrigin >= randomNumberBound)
+        if (!(randomNumberOrigin < randomNumberBound))
             throw new IllegalArgumentException("bound must be greater than origin");
         return StreamSupport.doubleStream
             (new RandomDoublesSpliterator
@@ -821,12 +874,12 @@ 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)
+        if (!(randomNumberOrigin < randomNumberBound))
             throw new IllegalArgumentException("bound must be greater than origin");
         return StreamSupport.doubleStream
             (new RandomDoublesSpliterator
@@ -836,13 +889,13 @@ public class SplittableRandom {
 
     /**
      * Spliterator for int streams.  We multiplex the four int
-     * versions into one class by treating and bound < origin as
+     * 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 class RandomIntsSpliterator implements Spliterator.OfInt {
+    static final class RandomIntsSpliterator implements Spliterator.OfInt {
         final SplittableRandom rng;
         long index;
         final long fence;
@@ -866,8 +919,7 @@ public class SplittableRandom {
 
         public int characteristics() {
             return (Spliterator.SIZED | Spliterator.SUBSIZED |
-                    Spliterator.ORDERED | Spliterator.NONNULL |
-                    Spliterator.IMMUTABLE);
+                    Spliterator.NONNULL | Spliterator.IMMUTABLE);
         }
 
         public boolean tryAdvance(IntConsumer consumer) {
@@ -897,7 +949,7 @@ 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;
@@ -921,8 +973,7 @@ public class SplittableRandom {
 
         public int characteristics() {
             return (Spliterator.SIZED | Spliterator.SUBSIZED |
-                    Spliterator.ORDERED | Spliterator.NONNULL |
-                    Spliterator.IMMUTABLE);
+                    Spliterator.NONNULL | Spliterator.IMMUTABLE);
         }
 
         public boolean tryAdvance(LongConsumer consumer) {
@@ -953,7 +1004,7 @@ 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;
@@ -977,8 +1028,7 @@ public class SplittableRandom {
 
         public int characteristics() {
             return (Spliterator.SIZED | Spliterator.SUBSIZED |
-                    Spliterator.ORDERED | Spliterator.NONNULL |
-                    Spliterator.IMMUTABLE);
+                    Spliterator.NONNULL | Spliterator.IMMUTABLE);
         }
 
         public boolean tryAdvance(DoubleConsumer consumer) {
@@ -1006,4 +1056,3 @@ public class SplittableRandom {
     }
 
 }
-