--- jsr166/src/main/java/util/SplittableRandom.java 2013/07/10 15:40:19 1.1
+++ jsr166/src/main/java/util/SplittableRandom.java 2013/07/12 11:26:34 1.7
@@ -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:
*
@@ -54,8 +53,8 @@ import java.util.stream.DoubleStream;
*
* - 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.
@@ -74,6 +73,7 @@ import java.util.stream.DoubleStream;
*
*
* @author Guy Steele
+ * @author Doug Lea
* @since 1.8
*/
public class SplittableRandom {
@@ -96,11 +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
@@ -112,7 +113,7 @@ public class SplittableRandom {
* 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
+ * 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
@@ -177,6 +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 =
@@ -199,23 +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
@@ -237,14 +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.
*/
@@ -268,7 +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;
@@ -310,27 +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());
}
@@ -354,7 +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;
@@ -375,11 +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;
@@ -388,9 +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
*/
@@ -429,21 +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)
@@ -455,7 +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)
;
}
@@ -470,7 +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) {
@@ -482,21 +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)
@@ -523,7 +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) {
@@ -533,15 +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;
}
/**
@@ -550,12 +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
@@ -563,7 +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
@@ -574,7 +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);
}
@@ -583,13 +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)
@@ -617,7 +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.
*
@@ -625,10 +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,
@@ -653,7 +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}
*/
@@ -667,13 +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)
@@ -701,7 +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.
*
@@ -709,10 +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,
@@ -737,7 +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}
*/
@@ -751,13 +759,14 @@ 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 +779,8 @@ 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 +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.
*
@@ -803,7 +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
@@ -826,7 +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
@@ -836,7 +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
@@ -866,8 +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) {
@@ -921,8 +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) {
@@ -977,8 +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) {