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package java.util; |
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import java.security.SecureRandom; |
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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.function.DoubleConsumer; |
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import java.util.function.IntConsumer; |
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import java.util.function.LongConsumer; |
32 |
< |
import java.util.function.DoubleConsumer; |
34 |
< |
import java.util.stream.StreamSupport; |
32 |
> |
import java.util.stream.DoubleStream; |
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import java.util.stream.IntStream; |
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import java.util.stream.LongStream; |
35 |
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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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/** |
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* A generator of uniform pseudorandom values applicable for use in |
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* types and ranges, but similar properties are expected to hold, at |
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* least approximately, for others as well. The <em>period</em> |
54 |
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* (length of any series of generated values before it repeats) is at |
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* least 2<sup>64</sup>. </li> |
55 |
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* least 2<sup>64</sup>. |
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* |
57 |
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* <li> Method {@link #split} constructs and returns a new |
57 |
> |
* <li>Method {@link #split} constructs and returns a new |
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* SplittableRandom instance that shares no mutable state with the |
59 |
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* current instance. However, with very high probability, the |
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* values collectively generated by the two objects have the same |
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* statistical properties as if the same quantity of values were |
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* generated by a single thread using a single {@code |
63 |
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* SplittableRandom} object. </li> |
63 |
> |
* SplittableRandom} object. |
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* |
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* <li>Instances of SplittableRandom are <em>not</em> thread-safe. |
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* They are designed to be split, not shared, across threads. For |
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* |
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* <li>This class provides additional methods for generating random |
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* streams, that employ the above techniques when used in {@code |
74 |
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* stream.parallel()} mode.</li> |
74 |
> |
* stream.parallel()} mode. |
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* |
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* </ul> |
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* |
81 |
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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} |
83 |
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* {@code java.util.secureRandomSeed} is set to {@code true}. |
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|
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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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*/ |
89 |
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public class SplittableRandom { |
89 |
> |
public final class SplittableRandom { |
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|
91 |
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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. |
109 |
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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 |
111 |
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* MurmurHash3 algorithm. See |
112 |
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* http://code.google.com/p/smhasher/wiki/MurmurHash3 , which |
113 |
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* comments: "The constants for the finalizers were generated by a |
114 |
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* simple simulated-annealing algorithm, and both avalanche all |
115 |
< |
* bits of 'h' to within 0.25% bias." The mix32 function is |
119 |
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* equivalent to (int)(mix64(seed) >>> 32), but faster because it |
120 |
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* omits a step that doesn't contribute to result. |
109 |
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* For nextLong, the mix64 function is based on David Stafford's |
110 |
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* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html) |
111 |
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* "Mix13" variant of the "64-bit finalizer" function in Austin |
112 |
> |
* Appleby's MurmurHash3 algorithm (see |
113 |
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* http://code.google.com/p/smhasher/wiki/MurmurHash3). The mix32 |
114 |
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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, |
120 |
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* gamma selection (method nextGamma) uses the "Mix13" constants |
121 |
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* for MurmurHash3 described by David Stafford |
122 |
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* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html) |
123 |
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* To avoid potential weaknesses in bit-mixing transformations, we |
124 |
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* restrict gammas to odd values with at least 12 and no more than |
125 |
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* 52 bits set. Rather than rejecting candidates with too few or |
126 |
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* too many bits set, method nextGamma flips some bits (which has |
127 |
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* the effect of mapping at most 4 to any given gamma value). |
133 |
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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 |
121 |
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* (Murmurhash3's) mix constants. To avoid potential weaknesses |
122 |
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* in bit-mixing transformations, we restrict gammas to odd values |
123 |
> |
* 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 |
125 |
> |
* mixGamma flips some bits (which has the effect of mapping at |
126 |
> |
* most 4 to any given gamma value). This reduces the effective |
127 |
> |
* 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 |
138 |
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* split() for a common "seeder" SplittableRandom. Unlike other |
139 |
< |
* cases, this split must be performed in a thread-safe manner, so |
140 |
< |
* we use an AtomicLong to represent the seed rather than use an |
141 |
< |
* explicit SplittableRandom. To bootstrap the seeder, we start |
142 |
< |
* off using a seed based on current time and host unless the |
143 |
< |
* SecureRandomSeed property is set. This serves as a |
144 |
< |
* slimmed-down (and insecure) variant of SecureRandom that also |
145 |
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* avoids stalls that may occur when using /dev/random. |
138 |
> |
* split() for a common "defaultGen" SplittableRandom. Unlike |
139 |
> |
* other cases, this split must be performed in a thread-safe |
140 |
> |
* manner, so we use an AtomicLong to represent the seed rather |
141 |
> |
* than use an explicit SplittableRandom. To bootstrap the |
142 |
> |
* defaultGen, we start off using a seed based on current time |
143 |
> |
* unless the java.util.secureRandomSeed property is set. This |
144 |
> |
* serves as a slimmed-down (and insecure) variant of SecureRandom |
145 |
> |
* that also avoids stalls that may occur when using /dev/random. |
146 |
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* |
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* It is a relatively simple matter to apply the basic design here |
148 |
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* to use 128 bit seeds. However, emulating 128bit arithmetic and |
155 |
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*/ |
156 |
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|
157 |
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/** |
158 |
< |
* The initial gamma value for (unsplit) SplittableRandoms. Must |
159 |
< |
* be odd with at least 12 and no more than 52 bits set. Currently |
167 |
< |
* set to the golden ratio scaled to 64bits. |
158 |
> |
* The golden ratio scaled to 64bits, used as the initial gamma |
159 |
> |
* value for (unsplit) SplittableRandoms. |
160 |
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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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/** |
170 |
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* The seed. Updated only via method nextSeed. |
185 |
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} |
186 |
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|
187 |
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/** |
188 |
< |
* Computes MurmurHash3 64bit mix function. |
188 |
> |
* Computes Stafford variant 13 of 64bit mix function. |
189 |
|
*/ |
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 |
|
} |
195 |
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|
196 |
|
/** |
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 |
|
*/ |
199 |
|
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); |
202 |
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} |
203 |
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|
204 |
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/** |
205 |
|
* Returns the gamma value to use for a new split instance. |
206 |
|
*/ |
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) { |
208 |
> |
z = (z ^ (z >>> 33)) * 0xff51afd7ed558ccdL; // MurmurHash3 mix constants |
209 |
> |
z = (z ^ (z >>> 33)) * 0xc4ceb9fe1a85ec53L; |
210 |
> |
z = (z ^ (z >>> 33)) | 1L; // force to be odd |
211 |
> |
int n = Long.bitCount(z ^ (z >>> 1)); // ensure enough transitions |
212 |
> |
return (n < 24) ? z ^ 0xaaaaaaaaaaaaaaaaL : z; |
213 |
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} |
214 |
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|
215 |
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/** |
219 |
|
return seed += gamma; |
220 |
|
} |
221 |
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|
222 |
+ |
// IllegalArgumentException messages |
223 |
+ |
static final String BAD_BOUND = "bound must be positive"; |
224 |
+ |
static final String BAD_RANGE = "bound must be greater than origin"; |
225 |
+ |
static final String BAD_SIZE = "size must be non-negative"; |
226 |
+ |
|
227 |
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/** |
228 |
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* The seed generator for default constructors. |
229 |
|
*/ |
230 |
< |
private static final AtomicLong seeder = new AtomicLong(initialSeed()); |
231 |
< |
|
232 |
< |
private static long initialSeed() { |
233 |
< |
try { // ignore exceptions in accessing/parsing properties |
234 |
< |
String pp = System.getProperty |
235 |
< |
("java.util.secureRandomSeed"); |
236 |
< |
if (pp != null && pp.equalsIgnoreCase("true")) { |
237 |
< |
byte[] seedBytes = java.security.SecureRandom.getSeed(8); |
238 |
< |
long s = (long)(seedBytes[0]) & 0xffL; |
239 |
< |
for (int i = 1; i < 8; ++i) |
240 |
< |
s = (s << 8) | ((long)(seedBytes[i]) & 0xffL); |
241 |
< |
return s; |
242 |
< |
} |
243 |
< |
} catch (Exception ignore) { |
244 |
< |
} |
245 |
< |
int hh = 0; // hashed host address |
249 |
< |
try { |
250 |
< |
hh = InetAddress.getLocalHost().hashCode(); |
251 |
< |
} catch (Exception ignore) { |
230 |
> |
private static final AtomicLong defaultGen |
231 |
> |
= new AtomicLong(mix64(System.currentTimeMillis()) ^ |
232 |
> |
mix64(System.nanoTime())); |
233 |
> |
|
234 |
> |
// at end of <clinit> to survive static initialization circularity |
235 |
> |
static { |
236 |
> |
if (java.security.AccessController.doPrivileged( |
237 |
> |
new java.security.PrivilegedAction<Boolean>() { |
238 |
> |
public Boolean run() { |
239 |
> |
return Boolean.getBoolean("java.util.secureRandomSeed"); |
240 |
> |
}})) { |
241 |
> |
byte[] seedBytes = java.security.SecureRandom.getSeed(8); |
242 |
> |
long s = (long)seedBytes[0] & 0xffL; |
243 |
> |
for (int i = 1; i < 8; ++i) |
244 |
> |
s = (s << 8) | ((long)seedBytes[i] & 0xffL); |
245 |
> |
defaultGen.set(s); |
246 |
|
} |
253 |
– |
return (mix64((((long)hh) << 32) ^ System.currentTimeMillis()) ^ |
254 |
– |
mix64(System.nanoTime())); |
247 |
|
} |
248 |
|
|
257 |
– |
// IllegalArgumentException messages |
258 |
– |
static final String BadBound = "bound must be positive"; |
259 |
– |
static final String BadRange = "bound must be greater than origin"; |
260 |
– |
static final String BadSize = "size must be non-negative"; |
261 |
– |
|
249 |
|
/* |
250 |
|
* Internal versions of nextX methods used by streams, as well as |
251 |
|
* the public nextX(origin, bound) methods. These exist mainly to |
365 |
|
* @param seed the initial seed |
366 |
|
*/ |
367 |
|
public SplittableRandom(long seed) { |
368 |
< |
this(seed, INITIAL_GAMMA); |
368 |
> |
this(seed, GOLDEN_GAMMA); |
369 |
|
} |
370 |
|
|
371 |
|
/** |
374 |
|
* of those of any other instances in the current program; and |
375 |
|
* may, and typically does, vary across program invocations. |
376 |
|
*/ |
377 |
< |
public SplittableRandom() { // emulate seeder.split() |
378 |
< |
this.gamma = nextGamma(this.seed = seeder.addAndGet(INITIAL_GAMMA)); |
377 |
> |
public SplittableRandom() { // emulate defaultGen.split() |
378 |
> |
long s = defaultGen.getAndAdd(GOLDEN_GAMMA << 1); |
379 |
> |
this.seed = mix64(s); |
380 |
> |
this.gamma = mixGamma(s + GOLDEN_GAMMA); |
381 |
|
} |
382 |
|
|
383 |
|
/** |
395 |
|
* @return the new SplittableRandom instance |
396 |
|
*/ |
397 |
|
public SplittableRandom split() { |
398 |
< |
long s = nextSeed(); |
410 |
< |
return new SplittableRandom(s, nextGamma(s)); |
398 |
> |
return new SplittableRandom(nextLong(), mixGamma(nextSeed())); |
399 |
|
} |
400 |
|
|
401 |
|
/** |
418 |
|
*/ |
419 |
|
public int nextInt(int bound) { |
420 |
|
if (bound <= 0) |
421 |
< |
throw new IllegalArgumentException(BadBound); |
421 |
> |
throw new IllegalArgumentException(BAD_BOUND); |
422 |
|
// Specialize internalNextInt for origin 0 |
423 |
|
int r = mix32(nextSeed()); |
424 |
|
int m = bound - 1; |
446 |
|
*/ |
447 |
|
public int nextInt(int origin, int bound) { |
448 |
|
if (origin >= bound) |
449 |
< |
throw new IllegalArgumentException(BadRange); |
449 |
> |
throw new IllegalArgumentException(BAD_RANGE); |
450 |
|
return internalNextInt(origin, bound); |
451 |
|
} |
452 |
|
|
470 |
|
*/ |
471 |
|
public long nextLong(long bound) { |
472 |
|
if (bound <= 0) |
473 |
< |
throw new IllegalArgumentException(BadBound); |
473 |
> |
throw new IllegalArgumentException(BAD_BOUND); |
474 |
|
// Specialize internalNextLong for origin 0 |
475 |
|
long r = mix64(nextSeed()); |
476 |
|
long m = bound - 1; |
498 |
|
*/ |
499 |
|
public long nextLong(long origin, long bound) { |
500 |
|
if (origin >= bound) |
501 |
< |
throw new IllegalArgumentException(BadRange); |
501 |
> |
throw new IllegalArgumentException(BAD_RANGE); |
502 |
|
return internalNextLong(origin, bound); |
503 |
|
} |
504 |
|
|
524 |
|
*/ |
525 |
|
public double nextDouble(double bound) { |
526 |
|
if (!(bound > 0.0)) |
527 |
< |
throw new IllegalArgumentException(BadBound); |
527 |
> |
throw new IllegalArgumentException(BAD_BOUND); |
528 |
|
double result = (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT * bound; |
529 |
|
return (result < bound) ? result : // correct for rounding |
530 |
|
Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1); |
543 |
|
*/ |
544 |
|
public double nextDouble(double origin, double bound) { |
545 |
|
if (!(origin < bound)) |
546 |
< |
throw new IllegalArgumentException(BadRange); |
546 |
> |
throw new IllegalArgumentException(BAD_RANGE); |
547 |
|
return internalNextDouble(origin, bound); |
548 |
|
} |
549 |
|
|
571 |
|
*/ |
572 |
|
public IntStream ints(long streamSize) { |
573 |
|
if (streamSize < 0L) |
574 |
< |
throw new IllegalArgumentException(BadSize); |
574 |
> |
throw new IllegalArgumentException(BAD_SIZE); |
575 |
|
return StreamSupport.intStream |
576 |
|
(new RandomIntsSpliterator |
577 |
|
(this, 0L, streamSize, Integer.MAX_VALUE, 0), |
612 |
|
public IntStream ints(long streamSize, int randomNumberOrigin, |
613 |
|
int randomNumberBound) { |
614 |
|
if (streamSize < 0L) |
615 |
< |
throw new IllegalArgumentException(BadSize); |
615 |
> |
throw new IllegalArgumentException(BAD_SIZE); |
616 |
|
if (randomNumberOrigin >= randomNumberBound) |
617 |
< |
throw new IllegalArgumentException(BadRange); |
617 |
> |
throw new IllegalArgumentException(BAD_RANGE); |
618 |
|
return StreamSupport.intStream |
619 |
|
(new RandomIntsSpliterator |
620 |
|
(this, 0L, streamSize, randomNumberOrigin, randomNumberBound), |
638 |
|
*/ |
639 |
|
public IntStream ints(int randomNumberOrigin, int randomNumberBound) { |
640 |
|
if (randomNumberOrigin >= randomNumberBound) |
641 |
< |
throw new IllegalArgumentException(BadRange); |
641 |
> |
throw new IllegalArgumentException(BAD_RANGE); |
642 |
|
return StreamSupport.intStream |
643 |
|
(new RandomIntsSpliterator |
644 |
|
(this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound), |
657 |
|
*/ |
658 |
|
public LongStream longs(long streamSize) { |
659 |
|
if (streamSize < 0L) |
660 |
< |
throw new IllegalArgumentException(BadSize); |
660 |
> |
throw new IllegalArgumentException(BAD_SIZE); |
661 |
|
return StreamSupport.longStream |
662 |
|
(new RandomLongsSpliterator |
663 |
|
(this, 0L, streamSize, Long.MAX_VALUE, 0L), |
698 |
|
public LongStream longs(long streamSize, long randomNumberOrigin, |
699 |
|
long randomNumberBound) { |
700 |
|
if (streamSize < 0L) |
701 |
< |
throw new IllegalArgumentException(BadSize); |
701 |
> |
throw new IllegalArgumentException(BAD_SIZE); |
702 |
|
if (randomNumberOrigin >= randomNumberBound) |
703 |
< |
throw new IllegalArgumentException(BadRange); |
703 |
> |
throw new IllegalArgumentException(BAD_RANGE); |
704 |
|
return StreamSupport.longStream |
705 |
|
(new RandomLongsSpliterator |
706 |
|
(this, 0L, streamSize, randomNumberOrigin, randomNumberBound), |
724 |
|
*/ |
725 |
|
public LongStream longs(long randomNumberOrigin, long randomNumberBound) { |
726 |
|
if (randomNumberOrigin >= randomNumberBound) |
727 |
< |
throw new IllegalArgumentException(BadRange); |
727 |
> |
throw new IllegalArgumentException(BAD_RANGE); |
728 |
|
return StreamSupport.longStream |
729 |
|
(new RandomLongsSpliterator |
730 |
|
(this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound), |
743 |
|
*/ |
744 |
|
public DoubleStream doubles(long streamSize) { |
745 |
|
if (streamSize < 0L) |
746 |
< |
throw new IllegalArgumentException(BadSize); |
746 |
> |
throw new IllegalArgumentException(BAD_SIZE); |
747 |
|
return StreamSupport.doubleStream |
748 |
|
(new RandomDoublesSpliterator |
749 |
|
(this, 0L, streamSize, Double.MAX_VALUE, 0.0), |
786 |
|
public DoubleStream doubles(long streamSize, double randomNumberOrigin, |
787 |
|
double randomNumberBound) { |
788 |
|
if (streamSize < 0L) |
789 |
< |
throw new IllegalArgumentException(BadSize); |
789 |
> |
throw new IllegalArgumentException(BAD_SIZE); |
790 |
|
if (!(randomNumberOrigin < randomNumberBound)) |
791 |
< |
throw new IllegalArgumentException(BadRange); |
791 |
> |
throw new IllegalArgumentException(BAD_RANGE); |
792 |
|
return StreamSupport.doubleStream |
793 |
|
(new RandomDoublesSpliterator |
794 |
|
(this, 0L, streamSize, randomNumberOrigin, randomNumberBound), |
812 |
|
*/ |
813 |
|
public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) { |
814 |
|
if (!(randomNumberOrigin < randomNumberBound)) |
815 |
< |
throw new IllegalArgumentException(BadRange); |
815 |
> |
throw new IllegalArgumentException(BAD_RANGE); |
816 |
|
return StreamSupport.doubleStream |
817 |
|
(new RandomDoublesSpliterator |
818 |
|
(this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound), |
827 |
|
* approach. The long and double versions of this class are |
828 |
|
* identical except for types. |
829 |
|
*/ |
830 |
< |
static final class RandomIntsSpliterator implements Spliterator.OfInt { |
830 |
> |
private static final class RandomIntsSpliterator |
831 |
> |
implements Spliterator.OfInt { |
832 |
|
final SplittableRandom rng; |
833 |
|
long index; |
834 |
|
final long fence; |
883 |
|
/** |
884 |
|
* Spliterator for long streams. |
885 |
|
*/ |
886 |
< |
static final class RandomLongsSpliterator implements Spliterator.OfLong { |
886 |
> |
private static final class RandomLongsSpliterator |
887 |
> |
implements Spliterator.OfLong { |
888 |
|
final SplittableRandom rng; |
889 |
|
long index; |
890 |
|
final long fence; |
940 |
|
/** |
941 |
|
* Spliterator for double streams. |
942 |
|
*/ |
943 |
< |
static final class RandomDoublesSpliterator implements Spliterator.OfDouble { |
943 |
> |
private static final class RandomDoublesSpliterator |
944 |
> |
implements Spliterator.OfDouble { |
945 |
|
final SplittableRandom rng; |
946 |
|
long index; |
947 |
|
final long fence; |