--- jsr166/src/main/java/util/SplittableRandom.java 2013/07/12 11:26:34 1.7
+++ 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;
@@ -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:
+ * {@link java.util.Random} but differs in the following ways:
+ *
+ *
*
* - 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.) 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.
+ * least approximately, for others as well. The period
+ * (length of any series of generated values before it repeats) is at
+ * least 264.
*
* - Method {@link #split} constructs and returns a new
* SplittableRandom instance that shares no mutable state with the
@@ -110,43 +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 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
* 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
@@ -154,8 +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
@@ -164,18 +159,30 @@ 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 = 0xF2281E2DBA6606F3L;
+ private static final long GAMMA_GAMMA = 0x00aae38294f712aabL;
/**
- * 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 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 DEFAULT_SEED_GAMMA = 0xBD24B73A95FB84D9L;
+ private static final long DEFAULT_SEED_GAMMA = 0x9e3779b97f4a7c15L;
+
+ /**
+ * 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
@@ -187,7 +194,7 @@ public class SplittableRandom {
* 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.
@@ -215,15 +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);
+ return (p >= s) ? p : ((p >= BOTTOM13) ? p : p + g) - 13L;
}
/**
@@ -250,6 +258,19 @@ public class SplittableRandom {
}
/**
+ * 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
@@ -260,9 +281,11 @@ public class SplittableRandom {
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);
+ s += GAMMA_GAMMA;
+ if (s >= GAMMA_PRIME)
+ s -= GAMMA_PRIME;
+ g = mix57(s);
+ } while (g < 13L);
this.gamma = g;
this.nextSplit = s;
}
@@ -287,6 +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
@@ -362,7 +396,7 @@ 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 +435,12 @@ 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, 0L);
}
/**
@@ -453,7 +487,7 @@ 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).
+ * (inclusive) and the bound (exclusive)
* @throws IllegalArgumentException if the bound is less than zero
*/
public int nextInt(int bound) {
@@ -462,7 +496,7 @@ 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;
@@ -480,7 +514,7 @@ 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}
*/
@@ -506,7 +540,7 @@ 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).
+ * (inclusive) and the bound (exclusive)
* @throws IllegalArgumentException if {@code bound} is less than zero
*/
public long nextLong(long bound) {
@@ -533,7 +567,7 @@ 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}
*/
@@ -551,7 +585,7 @@ public class SplittableRandom {
* (inclusive) and one (exclusive)
*/
public double nextDouble() {
- return (nextLong() >>> 11) * DOUBLE_UNIT;
+ return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT;
}
/**
@@ -561,13 +595,13 @@ 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).
+ * (inclusive) and the bound (exclusive)
* @throws IllegalArgumentException if {@code bound} is less than zero
*/
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);
}
@@ -579,7 +613,7 @@ 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}
*/
@@ -589,6 +623,15 @@ 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.
@@ -612,7 +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)}.
@@ -635,7 +678,7 @@ 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 streamSize} is
* less than zero, or {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
@@ -662,7 +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}
*/
@@ -718,7 +761,7 @@ 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}
@@ -745,7 +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}
*/
@@ -803,9 +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}
*/
@@ -831,7 +874,7 @@ 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 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}
*/
@@ -852,7 +895,7 @@ 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;
@@ -906,7 +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;
@@ -961,7 +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;
@@ -1013,4 +1056,3 @@ public class SplittableRandom {
}
}
-