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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 |
139 |
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* cases, this split must be performed in a thread-safe manner, so |
140 |
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* we use an AtomicLong to represent the seed rather than use an |
141 |
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* explicit SplittableRandom. To bootstrap the seeder, we start |
142 |
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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 |
159 |
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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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*/ |
161 |
< |
private static final long INITIAL_GAMMA = 0x9e3779b97f4a7c15L; |
161 |
> |
private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L; |
162 |
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|
163 |
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/** |
164 |
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* The least non-zero value returned by nextDouble(). This value |
165 |
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* is scaled by a random value of 53 bits to produce a result. |
166 |
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*/ |
167 |
< |
private static final double DOUBLE_UNIT = 1.0 / (1L << 53); |
167 |
> |
private static final double DOUBLE_UNIT = 0x1.0p-53; // 1.0 / (1L << 53); |
168 |
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169 |
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/** |
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* The seed. Updated only via method nextSeed. |
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} |
186 |
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/** |
188 |
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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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*/ |
190 |
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private static long mix64(long z) { |
191 |
< |
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; |
193 |
> |
return z ^ (z >>> 31); |
194 |
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} |
195 |
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|
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/** |
197 |
< |
* Returns the 32 high bits of mix64(z) as int. |
197 |
> |
* 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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} |
203 |
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|
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/** |
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* Returns the gamma value to use for a new split instance. |
206 |
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*/ |
207 |
< |
private static long nextGamma(long z) { |
208 |
< |
z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L; // Stafford "Mix13" |
209 |
< |
z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL; |
210 |
< |
z = (z ^ (z >>> 31)) | 1L; // force to be odd |
211 |
< |
int n = Long.bitCount(z); // ensure enough 0 and 1 bits |
212 |
< |
return (n < 12 || n > 52) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
207 |
> |
private static long mixGamma(long z) { |
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> |
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants |
209 |
> |
z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; |
210 |
> |
z = (z ^ (z >>> 33)) | 1L; // force to be odd |
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> |
int n = Long.bitCount(z ^ (z >>> 1)); // ensure enough transitions |
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> |
return (n < 24) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
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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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*/ |
225 |
< |
private static final AtomicLong seeder = |
225 |
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new AtomicLong(mix64((((long)hashedHostAddress()) << 32) ^ |
226 |
< |
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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/** |
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* Returns hash of local host IP address, if available; else 0. |
229 |
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*/ |
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private static int hashedHostAddress() { |
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try { |
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return InetAddress.getLocalHost().hashCode(); |
233 |
< |
} catch (Exception ex) { |
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< |
return 0; |
235 |
< |
} |
227 |
> |
private static long initialSeed() { |
228 |
> |
String pp = java.security.AccessController.doPrivileged( |
229 |
> |
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 |
> |
} |
238 |
> |
return (mix64(System.currentTimeMillis()) ^ |
239 |
> |
mix64(System.nanoTime())); |
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} |
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// IllegalArgumentException messages |
363 |
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* @param seed the initial seed |
364 |
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*/ |
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public SplittableRandom(long seed) { |
366 |
< |
this(seed, INITIAL_GAMMA); |
366 |
> |
this(seed, GOLDEN_GAMMA); |
367 |
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} |
368 |
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|
369 |
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/** |
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 |
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} |
380 |
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|
381 |
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/** |
393 |
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* @return the new SplittableRandom instance |
394 |
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*/ |
395 |
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public SplittableRandom split() { |
396 |
< |
long s = nextSeed(); |
393 |
< |
return new SplittableRandom(s, nextGamma(s)); |
396 |
> |
return new SplittableRandom(nextLong(), mixGamma(nextSeed())); |
397 |
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} |
398 |
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|
399 |
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/** |
409 |
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* Returns a pseudorandom {@code int} value between zero (inclusive) |
410 |
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* and the specified bound (exclusive). |
411 |
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* |
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 |
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* @return a pseudorandom {@code int} value between zero |
414 |
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* (inclusive) and the bound (exclusive) |
415 |
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* @throws IllegalArgumentException if {@code bound} is not positive |
461 |
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* Returns a pseudorandom {@code long} value between zero (inclusive) |
462 |
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* and the specified bound (exclusive). |
463 |
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* |
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 |
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* @return a pseudorandom {@code long} value between zero |
466 |
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* (inclusive) and the bound (exclusive) |
467 |
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* @throws IllegalArgumentException if {@code bound} is not positive |
505 |
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* (inclusive) and one (exclusive). |
506 |
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* |
507 |
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* @return a pseudorandom {@code double} value between zero |
508 |
< |
* (inclusive) and one (exclusive) |
508 |
> |
* (inclusive) and one (exclusive) |
509 |
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*/ |
510 |
|
public double nextDouble() { |
511 |
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return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT; |
515 |
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* Returns a pseudorandom {@code double} value between 0.0 |
516 |
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* (inclusive) and the specified bound (exclusive). |
517 |
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* |
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 |
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* @return a pseudorandom {@code double} value between zero |
520 |
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* (inclusive) and the bound (exclusive) |
521 |
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* @throws IllegalArgumentException if {@code bound} is not positive |
533 |
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* origin (inclusive) and bound (exclusive). |
534 |
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* |
535 |
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* @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 |
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* (inclusive) and the bound (exclusive) |
539 |
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* @throws IllegalArgumentException if {@code origin} is greater than |
594 |
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|
595 |
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/** |
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 |
|
*/ |