--- jsr166/src/main/java/util/SplittableRandom.java	2013/07/10 23:42:43	1.2
+++ jsr166/src/main/java/util/SplittableRandom.java	2013/07/12 19:45:19	1.8
@@ -35,12 +35,11 @@ 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>
  *
@@ -54,8 +53,8 @@ import java.util.stream.DoubleStream;
  *
  * <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>
@@ -97,11 +96,12 @@ 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
@@ -178,6 +178,12 @@ public class SplittableRandom {
     private static final long DEFAULT_SEED_GAMMA = 0xBD24B73A95FB84D9L;
 
     /**
+     * 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 =
@@ -200,23 +206,6 @@ 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
@@ -238,14 +227,6 @@ public class SplittableRandom {
     }
 
     /**
-     * Updates in-place and returns seed.
-     * See above for explanation.
-     */
-    private long nextSeed() {
-        return seed = addGammaModGeorge(seed, gamma);
-    }
-
-    /**
      * Returns a bit-mixed transformation of its argument.
      * See above for explanation.
      */
@@ -269,7 +250,33 @@ public class SplittableRandom {
     }
 
     /**
-     * Atomically updates and returns next seed for default constructor
+     * 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 = addGammaModGeorge(s, GAMMA_GAMMA);
+            g = mix64(s);
+        } while (Long.compareUnsigned(g, 13L) < 0);
+        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;
@@ -311,27 +318,31 @@ 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());
             }
@@ -355,7 +366,7 @@ public class SplittableRandom {
                 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;
@@ -376,11 +387,10 @@ 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;
@@ -389,9 +399,9 @@ 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 generate identical sequences of values.
      *
      * @param seed the initial seed
      */
@@ -430,21 +440,21 @@ 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}
+     * @return a pseudorandom {@code int} value between zero
      *         (inclusive) and the bound (exclusive).
-     * @exception IllegalArgumentException if the bound is not positive
+     * @throws IllegalArgumentException if the bound is less than zero
      */
     public int nextInt(int bound) {
         if (bound <= 0)
@@ -456,7 +466,7 @@ public class SplittableRandom {
             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)
                 ;
         }
@@ -471,7 +481,7 @@ public class SplittableRandom {
      * @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
+     * @throws IllegalArgumentException if {@code origin} is greater than
      *         or equal to {@code bound}
      */
     public int nextInt(int origin, int bound) {
@@ -483,21 +493,21 @@ 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}
+     * @return a pseudorandom {@code long} value between zero
      *         (inclusive) and the bound (exclusive).
-     * @exception IllegalArgumentException if the bound is not positive
+     * @throws IllegalArgumentException if {@code bound} is less than zero
      */
     public long nextLong(long bound) {
         if (bound <= 0)
@@ -524,7 +534,7 @@ public class SplittableRandom {
      * @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
+     * @throws IllegalArgumentException if {@code origin} is greater than
      *         or equal to {@code bound}
      */
     public long nextLong(long origin, long bound) {
@@ -534,15 +544,14 @@ 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 (nextLong() >>> 11) * DOUBLE_UNIT;
     }
 
     /**
@@ -551,12 +560,12 @@ 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}
+     * @return a pseudorandom {@code double} value between zero
      *         (inclusive) and the bound (exclusive).
-     * @throws IllegalArgumentException if {@code bound} is not positive
+     * @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;
         return (result < bound) ?  result : // correct for rounding
@@ -564,7 +573,7 @@ public class SplittableRandom {
     }
 
     /**
-     * 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
@@ -575,7 +584,7 @@ public class SplittableRandom {
      *         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);
     }
@@ -584,13 +593,13 @@ public class SplittableRandom {
     // 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)
@@ -618,7 +627,7 @@ 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.
      *
@@ -626,10 +635,9 @@ 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,
@@ -654,7 +662,7 @@ 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}
      */
@@ -668,13 +676,13 @@ 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)
@@ -702,7 +710,7 @@ 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.
      *
@@ -710,10 +718,9 @@ 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,
@@ -738,7 +745,7 @@ 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}
      */
@@ -752,14 +759,14 @@ public class SplittableRandom {
     }
 
     /**
-     * Returns a stream with the given {@code streamSize} number of
-     * pseudorandom {@code double} values, each between {@code 0.0}
-     * (inclusive) and {@code 1.0} (exclusive).
+     * 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)
@@ -772,8 +779,8 @@ public class SplittableRandom {
 
     /**
      * Returns an effectively unlimited stream of pseudorandom {@code
-     * double} values, each between {@code 0.0} (inclusive) and {@code
-     * 1.0} (exclusive).
+     * double} values, each between zero (inclusive) and one
+     * (exclusive).
      *
      * @implNote This method is implemented to be equivalent to {@code
      * doubles(Long.MAX_VALUE)}.
@@ -788,7 +795,7 @@ 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.
      *
@@ -806,7 +813,7 @@ 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
@@ -829,7 +836,7 @@ public class SplittableRandom {
      *         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
@@ -839,7 +846,7 @@ 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
@@ -869,8 +876,7 @@ 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) {
@@ -924,8 +930,7 @@ 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) {
@@ -980,8 +985,7 @@ 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) {
@@ -1009,4 +1013,3 @@ public class SplittableRandom {
     }
 
 }
-