--- jsr166/src/main/java/util/SplittableRandom.java 2013/08/13 17:13:57 1.16
+++ jsr166/src/main/java/util/SplittableRandom.java 2013/10/07 10:54:27 1.24
@@ -25,9 +25,8 @@
package java.util;
-import java.net.InetAddress;
+import java.net.NetworkInterface;
import java.util.concurrent.atomic.AtomicLong;
-import java.util.Spliterator;
import java.util.function.IntConsumer;
import java.util.function.LongConsumer;
import java.util.function.DoubleConsumer;
@@ -39,7 +38,7 @@ 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
+ * generate subtasks. Class {@code 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:
@@ -77,11 +76,18 @@ import java.util.stream.DoubleStream;
*
*
*
+ *
Instances of {@code SplittableRandom} are not cryptographically
+ * secure. Consider instead using {@link java.security.SecureRandom}
+ * in security-sensitive applications. Additionally,
+ * default-constructed instances do not use a cryptographically random
+ * seed unless the {@linkplain System#getProperty system property}
+ * {@code java.util.secureRandomSeed} is set to {@code true}.
+ *
* @author Guy Steele
* @author Doug Lea
* @since 1.8
*/
-public class SplittableRandom {
+public final class SplittableRandom {
/*
* Implementation Overview.
@@ -101,29 +107,25 @@ public class SplittableRandom {
* Methods nextLong, nextInt, and derivatives do not return the
* sequence (seed) values, but instead a hash-like bit-mix of
* their bits, producing more independently distributed sequences.
- * For nextLong, the mix64 bit-mixing function 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." The mix32 function is
- * equivalent to (int)(mix64(seed) >>> 32), but faster because it
- * omits a step that doesn't contribute to result.
+ * For nextLong, the mix64 function is based on David Stafford's
+ * (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html)
+ * "Mix13" variant of the "64-bit finalizer" function in Austin
+ * Appleby's MurmurHash3 algorithm (see
+ * http://code.google.com/p/smhasher/wiki/MurmurHash3). The mix32
+ * function is based on Stafford's Mix04 mix function, but returns
+ * the upper 32 bits cast as int.
*
* The split operation uses the current generator to form the seed
* and gamma for another SplittableRandom. To conservatively
* avoid potential correlations between seed and value generation,
- * gamma selection (method nextGamma) uses the "Mix13" constants
- * for MurmurHash3 described by David Stafford
- * (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html)
- * To avoid potential weaknesses in bit-mixing transformations, we
- * restrict gammas to odd values with at least 12 and no more than
- * 52 bits set. Rather than rejecting candidates with too few or
- * too many bits set, method nextGamma flips some bits (which has
- * the effect of mapping at most 4 to any given gamma value).
- * This reduces the effective set of 64bit odd gamma values by
- * about 214, a very tiny percentage, and serves as an
+ * gamma selection (method mixGamma) uses different
+ * (Murmurhash3's) mix constants. To avoid potential weaknesses
+ * in bit-mixing transformations, we restrict gammas to odd values
+ * with at least 24 0-1 or 1-0 bit transitions. Rather than
+ * rejecting candidates with too few or too many bits set, method
+ * mixGamma flips some bits (which has the effect of mapping at
+ * most 4 to any given gamma value). This reduces the effective
+ * set of 64bit odd gamma values by about 2%, and serves as an
* automated screening for sequence constant selection that is
* left as an empirical decision in some other hashing and crypto
* algorithms.
@@ -134,13 +136,15 @@ public class SplittableRandom {
* avalanching.
*
* The default (no-argument) constructor, in essence, invokes
- * split() for a common "seeder" SplittableRandom. Unlike other
- * cases, this split must be performed in a thread-safe manner, so
- * we use an AtomicLong to represent the seed rather than use an
- * explicit SplittableRandom. To bootstrap the seeder, we start
- * off using a seed based on current time and host. This serves as
- * a slimmed-down (and insecure) variant of SecureRandom that also
- * avoids stalls that may occur when using /dev/random.
+ * split() for a common "defaultGen" SplittableRandom. Unlike
+ * other cases, this split must be performed in a thread-safe
+ * manner, so we use an AtomicLong to represent the seed rather
+ * than use an explicit SplittableRandom. To bootstrap the
+ * defaultGen, we start off using a seed based on current time and
+ * network interface address unless the java.util.secureRandomSeed
+ * property is set. This serves as a slimmed-down (and insecure)
+ * variant of SecureRandom that also avoids stalls that may occur
+ * when using /dev/random.
*
* It is a relatively simple matter to apply the basic design here
* to use 128 bit seeds. However, emulating 128bit arithmetic and
@@ -153,17 +157,16 @@ public class SplittableRandom {
*/
/**
- * The initial gamma value for (unsplit) SplittableRandoms. Must
- * be odd with at least 12 and no more than 52 bits set. Currently
- * set to the golden ratio scaled to 64bits.
+ * The golden ratio scaled to 64bits, used as the initial gamma
+ * value for (unsplit) SplittableRandoms.
*/
- private static final long INITIAL_GAMMA = 0x9e3779b97f4a7c15L;
+ private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L;
/**
* 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);
+ private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53);
/**
* The seed. Updated only via method nextSeed.
@@ -184,31 +187,31 @@ public class SplittableRandom {
}
/**
- * Computes MurmurHash3 64bit mix function.
+ * Computes Stafford variant 13 of 64bit mix function.
*/
private static long mix64(long z) {
- z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL;
- z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L;
- return z ^ (z >>> 33);
+ z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L;
+ z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL;
+ return z ^ (z >>> 31);
}
/**
- * Returns the 32 high bits of mix64(z) as int.
+ * Returns the 32 high bits of Stafford variant 4 mix64 function as int.
*/
private static int mix32(long z) {
- z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL;
- return (int)(((z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L) >>> 32);
+ z = (z ^ (z >>> 33)) * 0x62a9d9ed799705f5L;
+ return (int)(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32);
}
/**
* Returns the gamma value to use for a new split instance.
*/
- private static long nextGamma(long z) {
- z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; // Stafford "Mix13"
- z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL;
- z = (z ^ (z >>> 31)) | 1L; // force to be odd
- int n = Long.bitCount(z); // ensure enough 0 and 1 bits
- return (n < 12 || n > 52) ? z ^ 0xaaaaaaaaaaaaaaaaL : z;
+ private static long mixGamma(long z) {
+ z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants
+ z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L;
+ z = (z ^ (z >>> 33)) | 1L; // force to be odd
+ int n = Long.bitCount(z ^ (z >>> 1)); // ensure enough transitions
+ return (n < 24) ? z ^ 0xaaaaaaaaaaaaaaaaL : z;
}
/**
@@ -221,20 +224,48 @@ public class SplittableRandom {
/**
* The seed generator for default constructors.
*/
- private static final AtomicLong seeder =
- new AtomicLong(mix64((((long)hashedHostAddress()) << 32) ^
- System.currentTimeMillis()) ^
- mix64(System.nanoTime()));
+ private static final AtomicLong defaultGen = new AtomicLong(initialSeed());
- /**
- * Returns hash of local host IP address, if available; else 0.
- */
- private static int hashedHostAddress() {
- try {
- return InetAddress.getLocalHost().hashCode();
- } catch (Exception ex) {
- return 0;
- }
+ private static long initialSeed() {
+ String pp = java.security.AccessController.doPrivileged(
+ new sun.security.action.GetPropertyAction(
+ "java.util.secureRandomSeed"));
+ if (pp != null && pp.equalsIgnoreCase("true")) {
+ 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;
+ }
+ long h = 0L;
+ try {
+ Enumeration ifcs =
+ NetworkInterface.getNetworkInterfaces();
+ boolean retry = false; // retry once if getHardwareAddress is null
+ while (ifcs.hasMoreElements()) {
+ NetworkInterface ifc = ifcs.nextElement();
+ if (!ifc.isVirtual()) { // skip fake addresses
+ byte[] bs = ifc.getHardwareAddress();
+ if (bs != null) {
+ int n = bs.length;
+ int m = Math.min(n >>> 1, 4);
+ for (int i = 0; i < m; ++i)
+ h = (h << 16) ^ (bs[i] << 8) ^ bs[n-1-i];
+ if (m < 4)
+ h = (h << 8) ^ bs[n-1-m];
+ h = mix64(h);
+ break;
+ }
+ else if (!retry)
+ retry = true;
+ else
+ break;
+ }
+ }
+ } catch (Exception ignore) {
+ }
+ return (h ^ mix64(System.currentTimeMillis()) ^
+ mix64(System.nanoTime()));
}
// IllegalArgumentException messages
@@ -361,7 +392,7 @@ public class SplittableRandom {
* @param seed the initial seed
*/
public SplittableRandom(long seed) {
- this(seed, INITIAL_GAMMA);
+ this(seed, GOLDEN_GAMMA);
}
/**
@@ -370,8 +401,10 @@ public class SplittableRandom {
* of those of any other instances in the current program; and
* may, and typically does, vary across program invocations.
*/
- public SplittableRandom() { // emulate seeder.split()
- this.gamma = nextGamma(this.seed = seeder.addAndGet(INITIAL_GAMMA));
+ public SplittableRandom() { // emulate defaultGen.split()
+ long s = defaultGen.getAndAdd(2 * GOLDEN_GAMMA);
+ this.seed = mix64(s);
+ this.gamma = mixGamma(s + GOLDEN_GAMMA);
}
/**
@@ -389,8 +422,7 @@ public class SplittableRandom {
* @return the new SplittableRandom instance
*/
public SplittableRandom split() {
- long s = nextSeed();
- return new SplittableRandom(s, nextGamma(s));
+ return new SplittableRandom(nextLong(), mixGamma(nextSeed()));
}
/**
@@ -406,8 +438,7 @@ public class SplittableRandom {
* 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.
+ * @param bound the upper bound (exclusive). Must be positive.
* @return a pseudorandom {@code int} value between zero
* (inclusive) and the bound (exclusive)
* @throws IllegalArgumentException if {@code bound} is not positive
@@ -459,8 +490,7 @@ public class SplittableRandom {
* 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.
+ * @param bound the upper bound (exclusive). Must be positive.
* @return a pseudorandom {@code long} value between zero
* (inclusive) and the bound (exclusive)
* @throws IllegalArgumentException if {@code bound} is not positive
@@ -504,7 +534,7 @@ public class SplittableRandom {
* (inclusive) and one (exclusive).
*
* @return a pseudorandom {@code double} value between zero
- * (inclusive) and one (exclusive)
+ * (inclusive) and one (exclusive)
*/
public double nextDouble() {
return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT;
@@ -514,8 +544,7 @@ public class SplittableRandom {
* Returns a pseudorandom {@code double} value between 0.0
* (inclusive) and the specified bound (exclusive).
*
- * @param bound the bound on the random number to be returned. Must be
- * positive.
+ * @param bound the upper bound (exclusive). Must be positive.
* @return a pseudorandom {@code double} value between zero
* (inclusive) and the bound (exclusive)
* @throws IllegalArgumentException if {@code bound} is not positive
@@ -533,7 +562,7 @@ public class SplittableRandom {
* origin (inclusive) and bound (exclusive).
*
* @param origin the least value returned
- * @param bound the upper bound
+ * @param bound the upper bound (exclusive)
* @return a pseudorandom {@code double} value between the origin
* (inclusive) and the bound (exclusive)
* @throws IllegalArgumentException if {@code origin} is greater than
@@ -594,14 +623,15 @@ public class SplittableRandom {
/**
* Returns a stream producing the given {@code streamSize} number
- * of pseudorandom {@code int} values, each conforming to the
- * given origin and bound.
+ * of pseudorandom {@code int} values from this generator and/or one split
+ * from it; each value conforms to the given origin (inclusive) and bound
+ * (exclusive).
*
* @param streamSize the number of values to generate
- * @param randomNumberOrigin the origin of each random value
- * @param randomNumberBound the bound of each random value
+ * @param randomNumberOrigin the origin (inclusive) of each random value
+ * @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code int} values,
- * each with the given origin and bound
+ * each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero, or {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
@@ -620,15 +650,16 @@ public class SplittableRandom {
/**
* Returns an effectively unlimited stream of pseudorandom {@code
- * int} values, each conforming to the given origin and bound.
+ * int} values from this generator and/or one split from it; each value
+ * conforms to the given origin (inclusive) and bound (exclusive).
*
* @implNote This method is implemented to be equivalent to {@code
* ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
*
- * @param randomNumberOrigin the origin of each random value
- * @param randomNumberBound the bound of each random value
+ * @param randomNumberOrigin the origin (inclusive) of each random value
+ * @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code int} values,
- * each with the given origin and bound
+ * each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
*/
@@ -678,14 +709,15 @@ public class SplittableRandom {
/**
* Returns a stream producing the given {@code streamSize} number of
- * pseudorandom {@code long} values, each conforming to the
- * given origin and bound.
+ * pseudorandom {@code long} values from this generator and/or one split
+ * from it; each value conforms to the given origin (inclusive) and bound
+ * (exclusive).
*
* @param streamSize the number of values to generate
- * @param randomNumberOrigin the origin of each random value
- * @param randomNumberBound the bound of each random value
+ * @param randomNumberOrigin the origin (inclusive) of each random value
+ * @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code long} values,
- * each with the given origin and bound
+ * each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code streamSize} is
* less than zero, or {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
@@ -704,15 +736,16 @@ public class SplittableRandom {
/**
* Returns an effectively unlimited stream of pseudorandom {@code
- * long} values, each conforming to the given origin and bound.
+ * long} values from this generator and/or one split from it; each value
+ * conforms to the given origin (inclusive) and bound (exclusive).
*
* @implNote This method is implemented to be equivalent to {@code
* longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
*
- * @param randomNumberOrigin the origin of each random value
- * @param randomNumberBound the bound of each random value
+ * @param randomNumberOrigin the origin (inclusive) of each random value
+ * @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code long} values,
- * each with the given origin and bound
+ * each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
*/
@@ -727,8 +760,8 @@ public class SplittableRandom {
/**
* Returns a stream producing the given {@code streamSize} number of
- * pseudorandom {@code double} values, each between zero
- * (inclusive) and one (exclusive).
+ * pseudorandom {@code double} values from this generator and/or one split
+ * from it; each value is between zero (inclusive) and one (exclusive).
*
* @param streamSize the number of values to generate
* @return a stream of {@code double} values
@@ -746,8 +779,8 @@ public class SplittableRandom {
/**
* Returns an effectively unlimited stream of pseudorandom {@code
- * double} values, each between zero (inclusive) and one
- * (exclusive).
+ * double} values from this generator and/or one split from it; each value
+ * is between zero (inclusive) and one (exclusive).
*
* @implNote This method is implemented to be equivalent to {@code
* doubles(Long.MAX_VALUE)}.
@@ -763,16 +796,17 @@ public class SplittableRandom {
/**
* Returns a stream producing the given {@code streamSize} number of
- * pseudorandom {@code double} values, each conforming to the
- * given origin and bound.
+ * pseudorandom {@code double} values from this generator and/or one split
+ * from it; each value conforms to the given origin (inclusive) and bound
+ * (exclusive).
*
* @param streamSize the number of values to generate
- * @param randomNumberOrigin the origin of each random value
- * @param randomNumberBound the bound of each random value
+ * @param randomNumberOrigin the origin (inclusive) of each random value
+ * @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code double} values,
- * each with the given origin and bound
+ * each with the given origin (inclusive) and bound (exclusive)
* @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}
*/
@@ -790,15 +824,16 @@ public class SplittableRandom {
/**
* Returns an effectively unlimited stream of pseudorandom {@code
- * double} values, each conforming to the given origin and bound.
+ * double} values from this generator and/or one split from it; each value
+ * conforms to the given origin (inclusive) and bound (exclusive).
*
* @implNote This method is implemented to be equivalent to {@code
* doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
*
- * @param randomNumberOrigin the origin of each random value
- * @param randomNumberBound the bound of each random value
+ * @param randomNumberOrigin the origin (inclusive) of each random value
+ * @param randomNumberBound the bound (exclusive) of each random value
* @return a stream of pseudorandom {@code double} values,
- * each with the given origin and bound
+ * each with the given origin (inclusive) and bound (exclusive)
* @throws IllegalArgumentException if {@code randomNumberOrigin}
* is greater than or equal to {@code randomNumberBound}
*/