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package java.util; |
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– |
import java.net.InetAddress; |
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import java.util.concurrent.atomic.AtomicLong; |
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< |
import java.util.Spliterator; |
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> |
import java.util.function.DoubleConsumer; |
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import java.util.function.IntConsumer; |
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import java.util.function.LongConsumer; |
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< |
import java.util.function.DoubleConsumer; |
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< |
import java.util.stream.StreamSupport; |
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> |
import java.util.stream.DoubleStream; |
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import java.util.stream.IntStream; |
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import java.util.stream.LongStream; |
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< |
import java.util.stream.DoubleStream; |
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> |
import java.util.stream.StreamSupport; |
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/** |
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* A generator of uniform pseudorandom values applicable for use in |
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* (among other contexts) isolated parallel computations that may |
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< |
* generate subtasks. Class SplittableRandom supports methods for |
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> |
* generate subtasks. Class {@code SplittableRandom} supports methods for |
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* producing pseudorandom numbers of type {@code int}, {@code long}, |
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* and {@code double} with similar usages as for class |
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* {@link java.util.Random} but differs in the following ways: |
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* |
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* </ul> |
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* |
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* <p>Instances of {@code SplittableRandom} are not cryptographically |
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* secure. Consider instead using {@link java.security.SecureRandom} |
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* in security-sensitive applications. Additionally, |
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* default-constructed instances do not use a cryptographically random |
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* seed unless the {@linkplain System#getProperty system property} |
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* {@code java.util.secureRandomSeed} is set to {@code true}. |
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* |
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* @author Guy Steele |
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* @author Doug Lea |
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* @since 1.8 |
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*/ |
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< |
public class SplittableRandom { |
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> |
public final class SplittableRandom { |
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|
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/* |
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* Implementation Overview. |
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* Methods nextLong, nextInt, and derivatives do not return the |
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* sequence (seed) values, but instead a hash-like bit-mix of |
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* their bits, producing more independently distributed sequences. |
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* For nextLong, the mix64 bit-mixing function computes the same |
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* value as the "64-bit finalizer" function in Austin Appleby's |
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< |
* MurmurHash3 algorithm. See |
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* http://code.google.com/p/smhasher/wiki/MurmurHash3 , which |
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< |
* comments: "The constants for the finalizers were generated by a |
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* simple simulated-annealing algorithm, and both avalanche all |
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< |
* bits of 'h' to within 0.25% bias." The mix32 function is |
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* equivalent to (int)(mix64(seed) >>> 32), but faster because it |
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* omits a step that doesn't contribute to result. |
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* For nextLong, the mix64 function is based on David Stafford's |
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* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html) |
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* "Mix13" variant of the "64-bit finalizer" function in Austin |
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* Appleby's MurmurHash3 algorithm (see |
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* http://code.google.com/p/smhasher/wiki/MurmurHash3). The mix32 |
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* function is based on Stafford's Mix04 mix function, but returns |
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* the upper 32 bits cast as int. |
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* |
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* The split operation uses the current generator to form the seed |
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* and gamma for another SplittableRandom. To conservatively |
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* avoid potential correlations between seed and value generation, |
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* gamma selection (method nextGamma) uses the "Mix13" constants |
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* for MurmurHash3 described by David Stafford |
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* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html) |
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* To avoid potential weaknesses in bit-mixing transformations, we |
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* restrict gammas to odd values with at least 12 and no more than |
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* 52 bits set. Rather than rejecting candidates with too few or |
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< |
* too many bits set, method nextGamma flips some bits (which has |
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< |
* the effect of mapping at most 4 to any given gamma value). |
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* This reduces the effective set of 64bit odd gamma values by |
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* about 2<sup>14</sup>, a very tiny percentage, and serves as an |
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* gamma selection (method mixGamma) uses different |
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* (Murmurhash3's) mix constants. To avoid potential weaknesses |
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* in bit-mixing transformations, we restrict gammas to odd values |
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> |
* with at least 24 0-1 or 1-0 bit transitions. Rather than |
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* rejecting candidates with too few or too many bits set, method |
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> |
* mixGamma flips some bits (which has the effect of mapping at |
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* most 4 to any given gamma value). This reduces the effective |
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* set of 64bit odd gamma values by about 2%, and serves as an |
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* automated screening for sequence constant selection that is |
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* left as an empirical decision in some other hashing and crypto |
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* algorithms. |
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* avalanching. |
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* |
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* The default (no-argument) constructor, in essence, invokes |
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< |
* split() for a common "seeder" SplittableRandom. Unlike other |
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< |
* cases, this split must be performed in a thread-safe manner, so |
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< |
* we use an AtomicLong to represent the seed rather than use an |
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< |
* explicit SplittableRandom. To bootstrap the seeder, we start |
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< |
* off using a seed based on current time and host. This serves as |
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< |
* a slimmed-down (and insecure) variant of SecureRandom that also |
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< |
* avoids stalls that may occur when using /dev/random. |
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> |
* split() for a common "defaultGen" SplittableRandom. Unlike |
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> |
* other cases, this split must be performed in a thread-safe |
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> |
* manner, so we use an AtomicLong to represent the seed rather |
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> |
* than use an explicit SplittableRandom. To bootstrap the |
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> |
* defaultGen, we start off using a seed based on current time |
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> |
* unless the java.util.secureRandomSeed property is set. This |
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> |
* serves as a slimmed-down (and insecure) variant of SecureRandom |
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> |
* that also avoids stalls that may occur when using /dev/random. |
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* |
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* It is a relatively simple matter to apply the basic design here |
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* to use 128 bit seeds. However, emulating 128bit arithmetic and |
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*/ |
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|
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/** |
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< |
* The initial gamma value for (unsplit) SplittableRandoms. Must |
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< |
* be odd with at least 12 and no more than 52 bits set. Currently |
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< |
* set to the golden ratio scaled to 64bits. |
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> |
* The golden ratio scaled to 64bits, used as the initial gamma |
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> |
* value for (unsplit) SplittableRandoms. |
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*/ |
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< |
private static final long INITIAL_GAMMA = 0x9e3779b97f4a7c15L; |
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> |
private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L; |
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|
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/** |
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* The least non-zero value returned by nextDouble(). This value |
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* is scaled by a random value of 53 bits to produce a result. |
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*/ |
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< |
private static final double DOUBLE_UNIT = 1.0 / (1L << 53); |
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> |
private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53); |
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|
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/** |
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* The seed. Updated only via method nextSeed. |
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} |
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|
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/** |
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< |
* Computes MurmurHash3 64bit mix function. |
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> |
* Computes Stafford variant 13 of 64bit mix function. |
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*/ |
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private static long mix64(long z) { |
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< |
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; |
| 192 |
< |
z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; |
| 193 |
< |
return z ^ (z >>> 33); |
| 191 |
> |
z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; |
| 192 |
> |
z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL; |
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> |
return z ^ (z >>> 31); |
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} |
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|
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/** |
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< |
* Returns the 32 high bits of mix64(z) as int. |
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> |
* Returns the 32 high bits of Stafford variant 4 mix64 function as int. |
| 198 |
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*/ |
| 199 |
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private static int mix32(long z) { |
| 200 |
< |
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; |
| 201 |
< |
return (int)(((z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L) >>> 32); |
| 200 |
> |
z = (z ^ (z >>> 33)) * 0x62a9d9ed799705f5L; |
| 201 |
> |
return (int)(((z ^ (z >>> 28)) * 0xcb24d0a5c88c35b3L) >>> 32); |
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} |
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|
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/** |
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* Returns the gamma value to use for a new split instance. |
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*/ |
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< |
private static long nextGamma(long z) { |
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< |
z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; // Stafford "Mix13" |
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< |
z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL; |
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< |
z = (z ^ (z >>> 31)) | 1L; // force to be odd |
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< |
int n = Long.bitCount(z); // ensure enough 0 and 1 bits |
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< |
return (n < 12 || n > 52) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
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> |
private static long mixGamma(long z) { |
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> |
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants |
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> |
z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; |
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> |
z = (z ^ (z >>> 33)) | 1L; // force to be odd |
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> |
int n = Long.bitCount(z ^ (z >>> 1)); // ensure enough transitions |
| 212 |
> |
return (n < 24) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
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} |
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|
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/** |
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/** |
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* The seed generator for default constructors. |
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*/ |
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< |
private static final AtomicLong seeder = |
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< |
new AtomicLong(mix64((((long)hashedHostAddress()) << 32) ^ |
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< |
System.currentTimeMillis()) ^ |
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< |
mix64(System.nanoTime())); |
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> |
private static final AtomicLong defaultGen = new AtomicLong(initialSeed()); |
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|
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< |
/** |
| 228 |
< |
* Returns hash of local host IP address, if available; else 0. |
| 229 |
< |
*/ |
| 230 |
< |
private static int hashedHostAddress() { |
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< |
try { |
| 232 |
< |
return InetAddress.getLocalHost().hashCode(); |
| 233 |
< |
} catch (Exception ex) { |
| 234 |
< |
return 0; |
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> |
private static long initialSeed() { |
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> |
String pp = java.security.AccessController.doPrivileged( |
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> |
new sun.security.action.GetPropertyAction( |
| 230 |
> |
"java.util.secureRandomSeed")); |
| 231 |
> |
if (pp != null && pp.equalsIgnoreCase("true")) { |
| 232 |
> |
byte[] seedBytes = java.security.SecureRandom.getSeed(8); |
| 233 |
> |
long s = (long)(seedBytes[0]) & 0xffL; |
| 234 |
> |
for (int i = 1; i < 8; ++i) |
| 235 |
> |
s = (s << 8) | ((long)(seedBytes[i]) & 0xffL); |
| 236 |
> |
return s; |
| 237 |
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} |
| 238 |
+ |
return (mix64(System.currentTimeMillis()) ^ |
| 239 |
+ |
mix64(System.nanoTime())); |
| 240 |
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} |
| 241 |
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|
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// IllegalArgumentException messages |
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* @param seed the initial seed |
| 364 |
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*/ |
| 365 |
|
public SplittableRandom(long seed) { |
| 366 |
< |
this(seed, INITIAL_GAMMA); |
| 366 |
> |
this(seed, GOLDEN_GAMMA); |
| 367 |
|
} |
| 368 |
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|
| 369 |
|
/** |
| 372 |
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* of those of any other instances in the current program; and |
| 373 |
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* may, and typically does, vary across program invocations. |
| 374 |
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*/ |
| 375 |
< |
public SplittableRandom() { // emulate seeder.split() |
| 376 |
< |
this.gamma = nextGamma(this.seed = seeder.addAndGet(INITIAL_GAMMA)); |
| 375 |
> |
public SplittableRandom() { // emulate defaultGen.split() |
| 376 |
> |
long s = defaultGen.getAndAdd(2 * GOLDEN_GAMMA); |
| 377 |
> |
this.seed = mix64(s); |
| 378 |
> |
this.gamma = mixGamma(s + GOLDEN_GAMMA); |
| 379 |
|
} |
| 380 |
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|
| 381 |
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/** |
| 393 |
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* @return the new SplittableRandom instance |
| 394 |
|
*/ |
| 395 |
|
public SplittableRandom split() { |
| 396 |
< |
long s = nextSeed(); |
| 393 |
< |
return new SplittableRandom(s, nextGamma(s)); |
| 396 |
> |
return new SplittableRandom(nextLong(), mixGamma(nextSeed())); |
| 397 |
|
} |
| 398 |
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|
| 399 |
|
/** |
| 409 |
|
* Returns a pseudorandom {@code int} value between zero (inclusive) |
| 410 |
|
* and the specified bound (exclusive). |
| 411 |
|
* |
| 412 |
< |
* @param bound the bound on the random number to be returned. Must be |
| 410 |
< |
* positive. |
| 412 |
> |
* @param bound the upper bound (exclusive). Must be positive. |
| 413 |
|
* @return a pseudorandom {@code int} value between zero |
| 414 |
|
* (inclusive) and the bound (exclusive) |
| 415 |
|
* @throws IllegalArgumentException if {@code bound} is not positive |
| 461 |
|
* Returns a pseudorandom {@code long} value between zero (inclusive) |
| 462 |
|
* and the specified bound (exclusive). |
| 463 |
|
* |
| 464 |
< |
* @param bound the bound on the random number to be returned. Must be |
| 463 |
< |
* positive. |
| 464 |
> |
* @param bound the upper bound (exclusive). Must be positive. |
| 465 |
|
* @return a pseudorandom {@code long} value between zero |
| 466 |
|
* (inclusive) and the bound (exclusive) |
| 467 |
|
* @throws IllegalArgumentException if {@code bound} is not positive |
| 505 |
|
* (inclusive) and one (exclusive). |
| 506 |
|
* |
| 507 |
|
* @return a pseudorandom {@code double} value between zero |
| 508 |
< |
* (inclusive) and one (exclusive) |
| 508 |
> |
* (inclusive) and one (exclusive) |
| 509 |
|
*/ |
| 510 |
|
public double nextDouble() { |
| 511 |
|
return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT; |
| 515 |
|
* Returns a pseudorandom {@code double} value between 0.0 |
| 516 |
|
* (inclusive) and the specified bound (exclusive). |
| 517 |
|
* |
| 518 |
< |
* @param bound the bound on the random number to be returned. Must be |
| 518 |
< |
* positive. |
| 518 |
> |
* @param bound the upper bound (exclusive). Must be positive. |
| 519 |
|
* @return a pseudorandom {@code double} value between zero |
| 520 |
|
* (inclusive) and the bound (exclusive) |
| 521 |
|
* @throws IllegalArgumentException if {@code bound} is not positive |
| 533 |
|
* origin (inclusive) and bound (exclusive). |
| 534 |
|
* |
| 535 |
|
* @param origin the least value returned |
| 536 |
< |
* @param bound the upper bound |
| 536 |
> |
* @param bound the upper bound (exclusive) |
| 537 |
|
* @return a pseudorandom {@code double} value between the origin |
| 538 |
|
* (inclusive) and the bound (exclusive) |
| 539 |
|
* @throws IllegalArgumentException if {@code origin} is greater than |
| 594 |
|
|
| 595 |
|
/** |
| 596 |
|
* Returns a stream producing the given {@code streamSize} number |
| 597 |
< |
* of pseudorandom {@code int} values, each conforming to the |
| 598 |
< |
* given origin and bound. |
| 597 |
> |
* of pseudorandom {@code int} values from this generator and/or one split |
| 598 |
> |
* from it; each value conforms to the given origin (inclusive) and bound |
| 599 |
> |
* (exclusive). |
| 600 |
|
* |
| 601 |
|
* @param streamSize the number of values to generate |
| 602 |
< |
* @param randomNumberOrigin the origin of each random value |
| 603 |
< |
* @param randomNumberBound the bound of each random value |
| 602 |
> |
* @param randomNumberOrigin the origin (inclusive) of each random value |
| 603 |
> |
* @param randomNumberBound the bound (exclusive) of each random value |
| 604 |
|
* @return a stream of pseudorandom {@code int} values, |
| 605 |
< |
* each with the given origin and bound |
| 605 |
> |
* each with the given origin (inclusive) and bound (exclusive) |
| 606 |
|
* @throws IllegalArgumentException if {@code streamSize} is |
| 607 |
|
* less than zero, or {@code randomNumberOrigin} |
| 608 |
|
* is greater than or equal to {@code randomNumberBound} |
| 621 |
|
|
| 622 |
|
/** |
| 623 |
|
* Returns an effectively unlimited stream of pseudorandom {@code |
| 624 |
< |
* int} values, each conforming to the given origin and bound. |
| 624 |
> |
* int} values from this generator and/or one split from it; each value |
| 625 |
> |
* conforms to the given origin (inclusive) and bound (exclusive). |
| 626 |
|
* |
| 627 |
|
* @implNote This method is implemented to be equivalent to {@code |
| 628 |
|
* ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}. |
| 629 |
|
* |
| 630 |
< |
* @param randomNumberOrigin the origin of each random value |
| 631 |
< |
* @param randomNumberBound the bound of each random value |
| 630 |
> |
* @param randomNumberOrigin the origin (inclusive) of each random value |
| 631 |
> |
* @param randomNumberBound the bound (exclusive) of each random value |
| 632 |
|
* @return a stream of pseudorandom {@code int} values, |
| 633 |
< |
* each with the given origin and bound |
| 633 |
> |
* each with the given origin (inclusive) and bound (exclusive) |
| 634 |
|
* @throws IllegalArgumentException if {@code randomNumberOrigin} |
| 635 |
|
* is greater than or equal to {@code randomNumberBound} |
| 636 |
|
*/ |
| 680 |
|
|
| 681 |
|
/** |
| 682 |
|
* Returns a stream producing the given {@code streamSize} number of |
| 683 |
< |
* pseudorandom {@code long} values, each conforming to the |
| 684 |
< |
* given origin and bound. |
| 683 |
> |
* pseudorandom {@code long} values from this generator and/or one split |
| 684 |
> |
* from it; each value conforms to the given origin (inclusive) and bound |
| 685 |
> |
* (exclusive). |
| 686 |
|
* |
| 687 |
|
* @param streamSize the number of values to generate |
| 688 |
< |
* @param randomNumberOrigin the origin of each random value |
| 689 |
< |
* @param randomNumberBound the bound of each random value |
| 688 |
> |
* @param randomNumberOrigin the origin (inclusive) of each random value |
| 689 |
> |
* @param randomNumberBound the bound (exclusive) of each random value |
| 690 |
|
* @return a stream of pseudorandom {@code long} values, |
| 691 |
< |
* each with the given origin and bound |
| 691 |
> |
* each with the given origin (inclusive) and bound (exclusive) |
| 692 |
|
* @throws IllegalArgumentException if {@code streamSize} is |
| 693 |
|
* less than zero, or {@code randomNumberOrigin} |
| 694 |
|
* is greater than or equal to {@code randomNumberBound} |
| 707 |
|
|
| 708 |
|
/** |
| 709 |
|
* Returns an effectively unlimited stream of pseudorandom {@code |
| 710 |
< |
* long} values, each conforming to the given origin and bound. |
| 710 |
> |
* long} values from this generator and/or one split from it; each value |
| 711 |
> |
* conforms to the given origin (inclusive) and bound (exclusive). |
| 712 |
|
* |
| 713 |
|
* @implNote This method is implemented to be equivalent to {@code |
| 714 |
|
* longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}. |
| 715 |
|
* |
| 716 |
< |
* @param randomNumberOrigin the origin of each random value |
| 717 |
< |
* @param randomNumberBound the bound of each random value |
| 716 |
> |
* @param randomNumberOrigin the origin (inclusive) of each random value |
| 717 |
> |
* @param randomNumberBound the bound (exclusive) of each random value |
| 718 |
|
* @return a stream of pseudorandom {@code long} values, |
| 719 |
< |
* each with the given origin and bound |
| 719 |
> |
* each with the given origin (inclusive) and bound (exclusive) |
| 720 |
|
* @throws IllegalArgumentException if {@code randomNumberOrigin} |
| 721 |
|
* is greater than or equal to {@code randomNumberBound} |
| 722 |
|
*/ |
| 731 |
|
|
| 732 |
|
/** |
| 733 |
|
* Returns a stream producing the given {@code streamSize} number of |
| 734 |
< |
* pseudorandom {@code double} values, each between zero |
| 735 |
< |
* (inclusive) and one (exclusive). |
| 734 |
> |
* pseudorandom {@code double} values from this generator and/or one split |
| 735 |
> |
* from it; each value is between zero (inclusive) and one (exclusive). |
| 736 |
|
* |
| 737 |
|
* @param streamSize the number of values to generate |
| 738 |
|
* @return a stream of {@code double} values |
| 750 |
|
|
| 751 |
|
/** |
| 752 |
|
* Returns an effectively unlimited stream of pseudorandom {@code |
| 753 |
< |
* double} values, each between zero (inclusive) and one |
| 754 |
< |
* (exclusive). |
| 753 |
> |
* double} values from this generator and/or one split from it; each value |
| 754 |
> |
* is between zero (inclusive) and one (exclusive). |
| 755 |
|
* |
| 756 |
|
* @implNote This method is implemented to be equivalent to {@code |
| 757 |
|
* doubles(Long.MAX_VALUE)}. |
| 767 |
|
|
| 768 |
|
/** |
| 769 |
|
* Returns a stream producing the given {@code streamSize} number of |
| 770 |
< |
* pseudorandom {@code double} values, each conforming to the |
| 771 |
< |
* given origin and bound. |
| 770 |
> |
* pseudorandom {@code double} values from this generator and/or one split |
| 771 |
> |
* from it; each value conforms to the given origin (inclusive) and bound |
| 772 |
> |
* (exclusive). |
| 773 |
|
* |
| 774 |
|
* @param streamSize the number of values to generate |
| 775 |
< |
* @param randomNumberOrigin the origin of each random value |
| 776 |
< |
* @param randomNumberBound the bound of each random value |
| 775 |
> |
* @param randomNumberOrigin the origin (inclusive) of each random value |
| 776 |
> |
* @param randomNumberBound the bound (exclusive) of each random value |
| 777 |
|
* @return a stream of pseudorandom {@code double} values, |
| 778 |
< |
* each with the given origin and bound |
| 778 |
> |
* each with the given origin (inclusive) and bound (exclusive) |
| 779 |
|
* @throws IllegalArgumentException if {@code streamSize} is |
| 780 |
< |
* less than zero |
| 780 |
> |
* less than zero |
| 781 |
|
* @throws IllegalArgumentException if {@code randomNumberOrigin} |
| 782 |
|
* is greater than or equal to {@code randomNumberBound} |
| 783 |
|
*/ |
| 795 |
|
|
| 796 |
|
/** |
| 797 |
|
* Returns an effectively unlimited stream of pseudorandom {@code |
| 798 |
< |
* double} values, each conforming to the given origin and bound. |
| 798 |
> |
* double} values from this generator and/or one split from it; each value |
| 799 |
> |
* conforms to the given origin (inclusive) and bound (exclusive). |
| 800 |
|
* |
| 801 |
|
* @implNote This method is implemented to be equivalent to {@code |
| 802 |
|
* doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}. |
| 803 |
|
* |
| 804 |
< |
* @param randomNumberOrigin the origin of each random value |
| 805 |
< |
* @param randomNumberBound the bound of each random value |
| 804 |
> |
* @param randomNumberOrigin the origin (inclusive) of each random value |
| 805 |
> |
* @param randomNumberBound the bound (exclusive) of each random value |
| 806 |
|
* @return a stream of pseudorandom {@code double} values, |
| 807 |
< |
* each with the given origin and bound |
| 807 |
> |
* each with the given origin (inclusive) and bound (exclusive) |
| 808 |
|
* @throws IllegalArgumentException if {@code randomNumberOrigin} |
| 809 |
|
* is greater than or equal to {@code randomNumberBound} |
| 810 |
|
*/ |
