--- jsr166/src/main/java/util/SplittableRandom.java	2013/07/14 08:06:49	1.10
+++ jsr166/src/main/java/util/SplittableRandom.java	2013/07/16 12:32:05	1.11
@@ -51,7 +51,9 @@ 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
@@ -156,13 +158,16 @@ 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
-     * 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.
+     * mechanism. To bootstrap, we start off using a function of the
+     * current System time as seed, 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.  When
+     * establishing the initial seed, we use both
+     * System.currentTimeMillis and System.nanoTime(), to avoid
+     * regularities that may occur if using either alone.
      */
 
     /**
@@ -180,6 +185,12 @@ public class SplittableRandom {
     private static final long DEFAULT_SEED_GAMMA = 0xBD24B73A95FB84D9L;
 
     /**
+     * The value 13 with 64bit sign bit set. Used in the signed
+     * comparison in addGammaModGeorge.
+     */
+    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.
      */
@@ -189,7 +200,8 @@ public class SplittableRandom {
      * The next seed for default constructors.
      */
     private static final AtomicLong defaultSeedGenerator =
-        new AtomicLong(System.nanoTime());
+        new AtomicLong(mix64(System.currentTimeMillis()) ^
+                       mix64(System.nanoTime()));
 
     /**
      * The seed, updated only via method nextSeed.
@@ -217,15 +229,16 @@ 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);
+        return (p >= s) ? p : ((p >= BOTTOM13) ? p  : p + g) - 13L;
     }
 
     /**
@@ -264,7 +277,7 @@ public class SplittableRandom {
         do { // ensure gamma >= 13, considered as an unsigned integer
             s = addGammaModGeorge(s, GAMMA_GAMMA);
             g = mix64(s);
-        } while (Long.compareUnsigned(g, 13L) < 0);
+        } while (g >= 0L && g < 13L);
         this.gamma = g;
         this.nextSplit = s;
     }
@@ -403,7 +416,7 @@ 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
      */
@@ -553,7 +566,7 @@ public class SplittableRandom {
      * (inclusive) and one (exclusive)
      */
     public double nextDouble() {
-        return (nextLong() >>> 11) * DOUBLE_UNIT;
+        return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT;
     }
 
     /**
@@ -569,7 +582,7 @@ public class SplittableRandom {
     public double nextDouble(double bound) {
         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);
     }
@@ -591,6 +604,15 @@ public class SplittableRandom {
         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.
 
@@ -854,7 +876,7 @@ 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;
@@ -908,7 +930,7 @@ 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;
@@ -963,7 +985,7 @@ 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;