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1 : dl 1.1 /*
2 :     * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved.
3 :     * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 :     *
5 :     * This code is free software; you can redistribute it and/or modify it
6 :     * under the terms of the GNU General Public License version 2 only, as
7 :     * published by the Free Software Foundation. Oracle designates this
8 :     * particular file as subject to the "Classpath" exception as provided
9 :     * by Oracle in the LICENSE file that accompanied this code.
10 :     *
11 :     * This code is distributed in the hope that it will be useful, but WITHOUT
12 :     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 :     * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 :     * version 2 for more details (a copy is included in the LICENSE file that
15 :     * accompanied this code).
16 :     *
17 :     * You should have received a copy of the GNU General Public License version
18 :     * 2 along with this work; if not, write to the Free Software Foundation,
19 :     * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 :     *
21 :     * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 :     * or visit www.oracle.com if you need additional information or have any
23 :     * questions.
24 :     */
25 :    
26 :     package java.util;
27 :    
28 : dl 1.12 import java.security.SecureRandom;
29 : dl 1.1 import java.util.concurrent.atomic.AtomicLong;
30 :     import java.util.Spliterator;
31 :     import java.util.function.IntConsumer;
32 :     import java.util.function.LongConsumer;
33 :     import java.util.function.DoubleConsumer;
34 :     import java.util.stream.StreamSupport;
35 :     import java.util.stream.IntStream;
36 :     import java.util.stream.LongStream;
37 :     import java.util.stream.DoubleStream;
38 :    
39 :     /**
40 :     * A generator of uniform pseudorandom values applicable for use in
41 :     * (among other contexts) isolated parallel computations that may
42 :     * generate subtasks. Class SplittableRandom supports methods for
43 : jsr166 1.3 * producing pseudorandom numbers of type {@code int}, {@code long},
44 : dl 1.1 * and {@code double} with similar usages as for class
45 : jsr166 1.9 * {@link java.util.Random} but differs in the following ways:
46 :     *
47 :     * <ul>
48 : dl 1.1 *
49 :     * <li>Series of generated values pass the DieHarder suite testing
50 :     * independence and uniformity properties of random number generators.
51 :     * (Most recently validated with <a
52 :     * href="http://www.phy.duke.edu/~rgb/General/dieharder.php"> version
53 :     * 3.31.1</a>.) These tests validate only the methods for certain
54 :     * types and ranges, but similar properties are expected to hold, at
55 : dl 1.11 * least approximately, for others as well. The <em>period</em>
56 :     * (length of any series of generated values before it repeats) is at
57 :     * least 2<sup>64</sup>. </li>
58 : dl 1.1 *
59 :     * <li> Method {@link #split} constructs and returns a new
60 :     * SplittableRandom instance that shares no mutable state with the
61 : dl 1.7 * current instance. However, with very high probability, the
62 :     * values collectively generated by the two objects have the same
63 : dl 1.1 * statistical properties as if the same quantity of values were
64 :     * generated by a single thread using a single {@code
65 :     * SplittableRandom} object. </li>
66 :     *
67 :     * <li>Instances of SplittableRandom are <em>not</em> thread-safe.
68 :     * They are designed to be split, not shared, across threads. For
69 :     * example, a {@link java.util.concurrent.ForkJoinTask
70 :     * fork/join-style} computation using random numbers might include a
71 :     * construction of the form {@code new
72 :     * Subtask(aSplittableRandom.split()).fork()}.
73 :     *
74 :     * <li>This class provides additional methods for generating random
75 :     * streams, that employ the above techniques when used in {@code
76 :     * stream.parallel()} mode.</li>
77 :     *
78 :     * </ul>
79 :     *
80 :     * @author Guy Steele
81 : dl 1.2 * @author Doug Lea
82 : dl 1.1 * @since 1.8
83 :     */
84 :     public class SplittableRandom {
85 :    
86 :     /*
87 :     * File organization: First the non-public methods that constitute
88 :     * the main algorithm, then the main public methods, followed by
89 :     * some custom spliterator classes needed for stream methods.
90 :     *
91 :     * Credits: Primary algorithm and code by Guy Steele. Stream
92 :     * support methods by Doug Lea. Documentation jointly produced
93 :     * with additional help from Brian Goetz.
94 :     */
95 :    
96 :     /*
97 :     * Implementation Overview.
98 :     *
99 :     * This algorithm was inspired by the "DotMix" algorithm by
100 :     * Leiserson, Schardl, and Sukha "Deterministic Parallel
101 :     * Random-Number Generation for Dynamic-Multithreading Platforms",
102 :     * PPoPP 2012, but improves and extends it in several ways.
103 :     *
104 : dl 1.7 * The primary update step (see method nextSeed()) is simply to
105 :     * add a constant ("gamma") to the current seed, modulo a prime
106 :     * ("George"). However, the nextLong and nextInt methods do not
107 :     * return this value, but instead the results of bit-mixing
108 :     * transformations that produce more uniformly distributed
109 :     * sequences.
110 : dl 1.1 *
111 :     * "George" is the otherwise nameless (because it cannot be
112 :     * represented) prime number 2^64+13. Using a prime number larger
113 :     * than can fit in a long ensures that all possible long values
114 :     * can occur, plus 13 others that just get skipped over when they
115 :     * are encountered; see method addGammaModGeorge. For this to
116 :     * work, initial gamma values must be at least 13.
117 :     *
118 :     * The mix64 bit-mixing function called by nextLong and other
119 :     * methods computes the same value as the "64-bit finalizer"
120 :     * function in Austin Appleby's MurmurHash3 algorithm. See
121 :     * http://code.google.com/p/smhasher/wiki/MurmurHash3 , which
122 :     * comments: "The constants for the finalizers were generated by a
123 :     * simple simulated-annealing algorithm, and both avalanche all
124 : dl 1.13 * bits of 'h' to within 0.25% bias."
125 :     *
126 :     * The value of gamma differs for each instance across a series of
127 :     * splits, and is generated using an independent variant of the
128 :     * same algorithm, but operating across calls to split(), not
129 :     * calls to nextSeed(): Each instance carries the state of this
130 :     * generator as nextSplit. Gammas are treated as 57bit values,
131 :     * advancing by adding GAMMA_GAMMA mod GAMMA_PRIME, and bit-mixed
132 : dl 1.14 * with a 57-bit version of mix, using the "Mix13" multiplicative
133 : dl 1.13 * constants for MurmurHash3 described by David Stafford
134 :     * (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html).
135 :     * The value of GAMMA_GAMMA is arbitrary (except must be at least
136 :     * 13 and less than GAMMA_PRIME), but because it serves as the
137 :     * base of split sequences, should be subject to validation of
138 :     * consequent random number quality metrics.
139 : dl 1.1 *
140 :     * The mix32 function used for nextInt just consists of two of the
141 : dl 1.13 * five lines of mix64; avalanche testing shows that the 64-bit
142 :     * result has its top 32 bits avalanched well, though not the
143 :     * bottom 32 bits. DieHarder tests show that it is adequate for
144 :     * generating one random int from the 64-bit result of nextSeed.
145 : dl 1.1 *
146 :     * Support for the default (no-argument) constructor relies on an
147 :     * AtomicLong (defaultSeedGenerator) to help perform the
148 :     * equivalent of a split of a statically constructed
149 :     * SplittableRandom. Unlike other cases, this split must be
150 :     * performed in a thread-safe manner. We use
151 :     * AtomicLong.compareAndSet as the (typically) most efficient
152 : dl 1.12 * mechanism. To bootstrap, we start off using a SecureRandom
153 :     * initial default seed, and update using a fixed
154 :     * DEFAULT_SEED_GAMMA. The default constructor uses GAMMA_GAMMA,
155 :     * not 0, for its splitSeed argument (addGammaModGeorge(0,
156 :     * GAMMA_GAMMA) == GAMMA_GAMMA) to reflect that each is split from
157 :     * this root generator, even though the root is not explicitly
158 :     * represented as a SplittableRandom.
159 : dl 1.1 */
160 :    
161 :     /**
162 : dl 1.13 * The prime modulus for gamma values.
163 :     */
164 :     private static final long GAMMA_PRIME = (1L << 57) - 13L;
165 :    
166 :     /**
167 : dl 1.12 * The value for producing new gamma values. Must be greater or
168 : dl 1.13 * equal to 13 and less than GAMMA_PRIME. Otherwise, the value is
169 :     * arbitrary subject to validation of the resulting statistical
170 :     * quality of splits.
171 : dl 1.1 */
172 : dl 1.13 private static final long GAMMA_GAMMA = 0x00aae38294f712aabL;
173 : dl 1.1
174 :     /**
175 : dl 1.12 * The seed update value for default constructors. Must be
176 : dl 1.13 * greater or equal to 13. Otherwise, the value is arbitrary
177 :     * subject to quality checks.
178 : dl 1.1 */
179 : dl 1.13 private static final long DEFAULT_SEED_GAMMA = 0x9e3779b97f4a7c15L;
180 : dl 1.1
181 :     /**
182 : dl 1.11 * The value 13 with 64bit sign bit set. Used in the signed
183 :     * comparison in addGammaModGeorge.
184 :     */
185 :     private static final long BOTTOM13 = 0x800000000000000DL;
186 :    
187 :     /**
188 : dl 1.5 * The least non-zero value returned by nextDouble(). This value
189 : dl 1.7 * is scaled by a random value of 53 bits to produce a result.
190 : dl 1.5 */
191 :     private static final double DOUBLE_UNIT = 1.0 / (1L << 53);
192 :    
193 :     /**
194 : dl 1.1 * The next seed for default constructors.
195 :     */
196 :     private static final AtomicLong defaultSeedGenerator =
197 : dl 1.12 new AtomicLong(getInitialDefaultSeed());
198 : dl 1.1
199 :     /**
200 :     * The seed, updated only via method nextSeed.
201 :     */
202 :     private long seed;
203 :    
204 :     /**
205 :     * The constant value added to seed (mod George) on each update.
206 :     */
207 :     private final long gamma;
208 :    
209 :     /**
210 :     * The next seed to use for splits. Propagated using
211 :     * addGammaModGeorge across instances.
212 :     */
213 :     private final long nextSplit;
214 :    
215 :     /**
216 :     * Adds the given gamma value, g, to the given seed value s, mod
217 :     * George (2^64+13). We regard s and g as unsigned values
218 :     * (ranging from 0 to 2^64-1). We add g to s either once or twice
219 :     * (mod George) as necessary to produce an (unsigned) result less
220 :     * than 2^64. We require that g must be at least 13. This
221 :     * guarantees that if (s+g) mod George >= 2^64 then (s+g+g) mod
222 :     * George < 2^64; thus we need only a conditional, not a loop,
223 :     * to be sure of getting a representable value.
224 :     *
225 : dl 1.11 * Because Java comparison operators are signed, we implement this
226 :     * by conceptually offsetting seed values downwards by 2^63, so
227 :     * 0..13 is represented as Long.MIN_VALUE..BOTTOM13.
228 :     *
229 :     * @param s a seed value, viewed as a signed long
230 : dl 1.1 * @param g a gamma value, 13 <= g (as unsigned)
231 :     */
232 :     private static long addGammaModGeorge(long s, long g) {
233 :     long p = s + g;
234 : dl 1.11 return (p >= s) ? p : ((p >= BOTTOM13) ? p : p + g) - 13L;
235 : dl 1.1 }
236 :    
237 :     /**
238 :     * Returns a bit-mixed transformation of its argument.
239 :     * See above for explanation.
240 :     */
241 :     private static long mix64(long z) {
242 :     z ^= (z >>> 33);
243 :     z *= 0xff51afd7ed558ccdL;
244 :     z ^= (z >>> 33);
245 :     z *= 0xc4ceb9fe1a85ec53L;
246 :     z ^= (z >>> 33);
247 :     return z;
248 :     }
249 :    
250 :     /**
251 :     * Returns a bit-mixed int transformation of its argument.
252 :     * See above for explanation.
253 :     */
254 :     private static int mix32(long z) {
255 :     z ^= (z >>> 33);
256 :     z *= 0xc4ceb9fe1a85ec53L;
257 :     return (int)(z >>> 32);
258 :     }
259 :    
260 :     /**
261 : dl 1.13 * Returns a 57-bit mixed transformation of its argument. See
262 :     * above for explanation.
263 :     */
264 :     private static long mix57(long z) {
265 : dl 1.14 z = (z ^ (z >>> 30)) * 0xbf58476d1ce4e5b9L;
266 : dl 1.13 z &= 0x01FFFFFFFFFFFFFFL;
267 : dl 1.14 z = (z ^ (z >>> 27)) * 0x94d049bb133111ebL;
268 : dl 1.13 z &= 0x01FFFFFFFFFFFFFFL;
269 : dl 1.14 z ^= (z >>> 31);
270 : dl 1.13 return z;
271 :     }
272 :    
273 :     /**
274 : dl 1.7 * Internal constructor used by all other constructors and by
275 :     * method split. Establishes the initial seed for this instance,
276 :     * and uses the given splitSeed to establish gamma, as well as the
277 :     * nextSplit to use by this instance. The loop to skip ineligible
278 :     * gammas very rarely iterates, and does so at most 13 times.
279 :     */
280 :     private SplittableRandom(long seed, long splitSeed) {
281 :     this.seed = seed;
282 :     long s = splitSeed, g;
283 :     do { // ensure gamma >= 13, considered as an unsigned integer
284 : dl 1.13 s += GAMMA_GAMMA;
285 :     if (s >= GAMMA_PRIME)
286 :     s -= GAMMA_PRIME;
287 :     g = mix57(s);
288 :     } while (g < 13L);
289 : dl 1.7 this.gamma = g;
290 :     this.nextSplit = s;
291 :     }
292 :    
293 :     /**
294 :     * Updates in-place and returns seed.
295 :     * See above for explanation.
296 :     */
297 :     private long nextSeed() {
298 :     return seed = addGammaModGeorge(seed, gamma);
299 :     }
300 :    
301 :     /**
302 :     * Atomically updates and returns next seed for default constructor.
303 : dl 1.1 */
304 :     private static long nextDefaultSeed() {
305 :     long oldSeed, newSeed;
306 :     do {
307 :     oldSeed = defaultSeedGenerator.get();
308 :     newSeed = addGammaModGeorge(oldSeed, DEFAULT_SEED_GAMMA);
309 :     } while (!defaultSeedGenerator.compareAndSet(oldSeed, newSeed));
310 :     return mix64(newSeed);
311 :     }
312 :    
313 : dl 1.12 /**
314 :     * Returns an initial default seed.
315 :     */
316 :     private static long getInitialDefaultSeed() {
317 :     byte[] seedBytes = java.security.SecureRandom.getSeed(8);
318 :     long s = (long)(seedBytes[0]) & 0xffL;
319 :     for (int i = 1; i < 8; ++i)
320 :     s = (s << 8) | ((long)(seedBytes[i]) & 0xffL);
321 :     return s;
322 :     }
323 :    
324 : dl 1.1 /*
325 :     * Internal versions of nextX methods used by streams, as well as
326 :     * the public nextX(origin, bound) methods. These exist mainly to
327 :     * avoid the need for multiple versions of stream spliterators
328 :     * across the different exported forms of streams.
329 :     */
330 :    
331 :     /**
332 :     * The form of nextLong used by LongStream Spliterators. If
333 :     * origin is greater than bound, acts as unbounded form of
334 :     * nextLong, else as bounded form.
335 :     *
336 :     * @param origin the least value, unless greater than bound
337 :     * @param bound the upper bound (exclusive), must not equal origin
338 :     * @return a pseudorandom value
339 :     */
340 :     final long internalNextLong(long origin, long bound) {
341 :     /*
342 :     * Four Cases:
343 :     *
344 :     * 1. If the arguments indicate unbounded form, act as
345 :     * nextLong().
346 :     *
347 :     * 2. If the range is an exact power of two, apply the
348 :     * associated bit mask.
349 :     *
350 :     * 3. If the range is positive, loop to avoid potential bias
351 :     * when the implicit nextLong() bound (2<sup>64</sup>) is not
352 :     * evenly divisible by the range. The loop rejects candidates
353 :     * computed from otherwise over-represented values. The
354 :     * expected number of iterations under an ideal generator
355 : dl 1.4 * varies from 1 to 2, depending on the bound. The loop itself
356 :     * takes an unlovable form. Because the first candidate is
357 :     * already available, we need a break-in-the-middle
358 :     * construction, which is concisely but cryptically performed
359 :     * within the while-condition of a body-less for loop.
360 : dl 1.1 *
361 :     * 4. Otherwise, the range cannot be represented as a positive
362 : dl 1.4 * long. The loop repeatedly generates unbounded longs until
363 :     * obtaining a candidate meeting constraints (with an expected
364 :     * number of iterations of less than two).
365 : dl 1.1 */
366 :    
367 :     long r = mix64(nextSeed());
368 :     if (origin < bound) {
369 :     long n = bound - origin, m = n - 1;
370 : dl 1.7 if ((n & m) == 0L) // power of two
371 : dl 1.1 r = (r & m) + origin;
372 : dl 1.7 else if (n > 0L) { // reject over-represented candidates
373 : dl 1.1 for (long u = r >>> 1; // ensure nonnegative
374 : dl 1.7 u + m - (r = u % n) < 0L; // rejection check
375 : dl 1.1 u = mix64(nextSeed()) >>> 1) // retry
376 :     ;
377 :     r += origin;
378 :     }
379 : dl 1.7 else { // range not representable as long
380 : dl 1.1 while (r < origin || r >= bound)
381 :     r = mix64(nextSeed());
382 :     }
383 :     }
384 :     return r;
385 :     }
386 :    
387 :     /**
388 :     * The form of nextInt used by IntStream Spliterators.
389 :     * Exactly the same as long version, except for types.
390 :     *
391 :     * @param origin the least value, unless greater than bound
392 :     * @param bound the upper bound (exclusive), must not equal origin
393 :     * @return a pseudorandom value
394 :     */
395 :     final int internalNextInt(int origin, int bound) {
396 :     int r = mix32(nextSeed());
397 :     if (origin < bound) {
398 :     int n = bound - origin, m = n - 1;
399 : dl 1.13 if ((n & m) == 0)
400 : dl 1.1 r = (r & m) + origin;
401 :     else if (n > 0) {
402 :     for (int u = r >>> 1;
403 : dl 1.7 u + m - (r = u % n) < 0;
404 : dl 1.1 u = mix32(nextSeed()) >>> 1)
405 :     ;
406 :     r += origin;
407 :     }
408 :     else {
409 :     while (r < origin || r >= bound)
410 :     r = mix32(nextSeed());
411 :     }
412 :     }
413 :     return r;
414 :     }
415 :    
416 :     /**
417 :     * The form of nextDouble used by DoubleStream Spliterators.
418 :     *
419 :     * @param origin the least value, unless greater than bound
420 :     * @param bound the upper bound (exclusive), must not equal origin
421 :     * @return a pseudorandom value
422 :     */
423 :     final double internalNextDouble(double origin, double bound) {
424 : dl 1.5 double r = (nextLong() >>> 11) * DOUBLE_UNIT;
425 : dl 1.1 if (origin < bound) {
426 :     r = r * (bound - origin) + origin;
427 : dl 1.7 if (r >= bound) // correct for rounding
428 : dl 1.1 r = Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
429 :     }
430 :     return r;
431 :     }
432 :    
433 :     /* ---------------- public methods ---------------- */
434 :    
435 :     /**
436 : dl 1.7 * Creates a new SplittableRandom instance using the specified
437 :     * initial seed. SplittableRandom instances created with the same
438 : dl 1.11 * seed in the same program generate identical sequences of values.
439 : dl 1.1 *
440 :     * @param seed the initial seed
441 :     */
442 :     public SplittableRandom(long seed) {
443 : dl 1.13 this(seed, 0L);
444 : dl 1.1 }
445 :    
446 :     /**
447 :     * Creates a new SplittableRandom instance that is likely to
448 :     * generate sequences of values that are statistically independent
449 :     * of those of any other instances in the current program; and
450 :     * may, and typically does, vary across program invocations.
451 :     */
452 :     public SplittableRandom() {
453 :     this(nextDefaultSeed(), GAMMA_GAMMA);
454 :     }
455 :    
456 :     /**
457 :     * Constructs and returns a new SplittableRandom instance that
458 :     * shares no mutable state with this instance. However, with very
459 :     * high probability, the set of values collectively generated by
460 :     * the two objects has the same statistical properties as if the
461 :     * same quantity of values were generated by a single thread using
462 :     * a single SplittableRandom object. Either or both of the two
463 :     * objects may be further split using the {@code split()} method,
464 :     * and the same expected statistical properties apply to the
465 :     * entire set of generators constructed by such recursive
466 :     * splitting.
467 :     *
468 :     * @return the new SplittableRandom instance
469 :     */
470 :     public SplittableRandom split() {
471 :     return new SplittableRandom(nextSeed(), nextSplit);
472 :     }
473 :    
474 :     /**
475 :     * Returns a pseudorandom {@code int} value.
476 :     *
477 : dl 1.7 * @return a pseudorandom {@code int} value
478 : dl 1.1 */
479 :     public int nextInt() {
480 :     return mix32(nextSeed());
481 :     }
482 :    
483 :     /**
484 : dl 1.7 * Returns a pseudorandom {@code int} value between zero (inclusive)
485 : dl 1.1 * and the specified bound (exclusive).
486 :     *
487 :     * @param bound the bound on the random number to be returned. Must be
488 :     * positive.
489 : dl 1.7 * @return a pseudorandom {@code int} value between zero
490 : jsr166 1.10 * (inclusive) and the bound (exclusive)
491 : dl 1.7 * @throws IllegalArgumentException if the bound is less than zero
492 : dl 1.1 */
493 :     public int nextInt(int bound) {
494 :     if (bound <= 0)
495 :     throw new IllegalArgumentException("bound must be positive");
496 :     // Specialize internalNextInt for origin 0
497 :     int r = mix32(nextSeed());
498 :     int m = bound - 1;
499 : dl 1.13 if ((bound & m) == 0) // power of two
500 : dl 1.1 r &= m;
501 :     else { // reject over-represented candidates
502 :     for (int u = r >>> 1;
503 : dl 1.7 u + m - (r = u % bound) < 0;
504 : dl 1.1 u = mix32(nextSeed()) >>> 1)
505 :     ;
506 :     }
507 :     return r;
508 :     }
509 :    
510 :     /**
511 :     * Returns a pseudorandom {@code int} value between the specified
512 :     * origin (inclusive) and the specified bound (exclusive).
513 :     *
514 :     * @param origin the least value returned
515 :     * @param bound the upper bound (exclusive)
516 :     * @return a pseudorandom {@code int} value between the origin
517 : jsr166 1.10 * (inclusive) and the bound (exclusive)
518 : dl 1.7 * @throws IllegalArgumentException if {@code origin} is greater than
519 : dl 1.1 * or equal to {@code bound}
520 :     */
521 :     public int nextInt(int origin, int bound) {
522 :     if (origin >= bound)
523 :     throw new IllegalArgumentException("bound must be greater than origin");
524 :     return internalNextInt(origin, bound);
525 :     }
526 :    
527 :     /**
528 :     * Returns a pseudorandom {@code long} value.
529 :     *
530 : dl 1.7 * @return a pseudorandom {@code long} value
531 : dl 1.1 */
532 :     public long nextLong() {
533 :     return mix64(nextSeed());
534 :     }
535 :    
536 :     /**
537 : dl 1.7 * Returns a pseudorandom {@code long} value between zero (inclusive)
538 : dl 1.1 * and the specified bound (exclusive).
539 :     *
540 :     * @param bound the bound on the random number to be returned. Must be
541 :     * positive.
542 : dl 1.7 * @return a pseudorandom {@code long} value between zero
543 : jsr166 1.10 * (inclusive) and the bound (exclusive)
544 : dl 1.7 * @throws IllegalArgumentException if {@code bound} is less than zero
545 : dl 1.1 */
546 :     public long nextLong(long bound) {
547 :     if (bound <= 0)
548 :     throw new IllegalArgumentException("bound must be positive");
549 :     // Specialize internalNextLong for origin 0
550 :     long r = mix64(nextSeed());
551 :     long m = bound - 1;
552 :     if ((bound & m) == 0L) // power of two
553 :     r &= m;
554 :     else { // reject over-represented candidates
555 :     for (long u = r >>> 1;
556 :     u + m - (r = u % bound) < 0L;
557 :     u = mix64(nextSeed()) >>> 1)
558 :     ;
559 :     }
560 :     return r;
561 :     }
562 :    
563 :     /**
564 :     * Returns a pseudorandom {@code long} value between the specified
565 :     * origin (inclusive) and the specified bound (exclusive).
566 :     *
567 :     * @param origin the least value returned
568 :     * @param bound the upper bound (exclusive)
569 :     * @return a pseudorandom {@code long} value between the origin
570 : jsr166 1.10 * (inclusive) and the bound (exclusive)
571 : dl 1.7 * @throws IllegalArgumentException if {@code origin} is greater than
572 : dl 1.1 * or equal to {@code bound}
573 :     */
574 :     public long nextLong(long origin, long bound) {
575 :     if (origin >= bound)
576 :     throw new IllegalArgumentException("bound must be greater than origin");
577 :     return internalNextLong(origin, bound);
578 :     }
579 :    
580 :     /**
581 : dl 1.7 * Returns a pseudorandom {@code double} value between zero
582 :     * (inclusive) and one (exclusive).
583 : dl 1.1 *
584 : dl 1.7 * @return a pseudorandom {@code double} value between zero
585 :     * (inclusive) and one (exclusive)
586 : dl 1.1 */
587 :     public double nextDouble() {
588 : dl 1.11 return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT;
589 : dl 1.1 }
590 :    
591 :     /**
592 :     * Returns a pseudorandom {@code double} value between 0.0
593 :     * (inclusive) and the specified bound (exclusive).
594 :     *
595 :     * @param bound the bound on the random number to be returned. Must be
596 :     * positive.
597 : dl 1.7 * @return a pseudorandom {@code double} value between zero
598 : jsr166 1.10 * (inclusive) and the bound (exclusive)
599 : dl 1.7 * @throws IllegalArgumentException if {@code bound} is less than zero
600 : dl 1.1 */
601 :     public double nextDouble(double bound) {
602 : dl 1.7 if (!(bound > 0.0))
603 : dl 1.1 throw new IllegalArgumentException("bound must be positive");
604 : dl 1.11 double result = (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT * bound;
605 : dl 1.1 return (result < bound) ? result : // correct for rounding
606 :     Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
607 :     }
608 :    
609 :     /**
610 : dl 1.7 * Returns a pseudorandom {@code double} value between the specified
611 : dl 1.1 * origin (inclusive) and bound (exclusive).
612 :     *
613 :     * @param origin the least value returned
614 :     * @param bound the upper bound
615 :     * @return a pseudorandom {@code double} value between the origin
616 : jsr166 1.10 * (inclusive) and the bound (exclusive)
617 : dl 1.1 * @throws IllegalArgumentException if {@code origin} is greater than
618 :     * or equal to {@code bound}
619 :     */
620 :     public double nextDouble(double origin, double bound) {
621 : dl 1.7 if (!(origin < bound))
622 : dl 1.1 throw new IllegalArgumentException("bound must be greater than origin");
623 :     return internalNextDouble(origin, bound);
624 :     }
625 :    
626 : dl 1.11 /**
627 :     * Returns a pseudorandom {@code boolean} value.
628 :     *
629 :     * @return a pseudorandom {@code boolean} value
630 :     */
631 :     public boolean nextBoolean() {
632 :     return mix32(nextSeed()) < 0;
633 :     }
634 :    
635 : dl 1.1 // stream methods, coded in a way intended to better isolate for
636 :     // maintenance purposes the small differences across forms.
637 :    
638 :     /**
639 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
640 : dl 1.1 * pseudorandom {@code int} values.
641 :     *
642 :     * @param streamSize the number of values to generate
643 :     * @return a stream of pseudorandom {@code int} values
644 :     * @throws IllegalArgumentException if {@code streamSize} is
645 : dl 1.7 * less than zero
646 : dl 1.1 */
647 :     public IntStream ints(long streamSize) {
648 :     if (streamSize < 0L)
649 :     throw new IllegalArgumentException("negative Stream size");
650 :     return StreamSupport.intStream
651 :     (new RandomIntsSpliterator
652 :     (this, 0L, streamSize, Integer.MAX_VALUE, 0),
653 :     false);
654 :     }
655 :    
656 :     /**
657 :     * Returns an effectively unlimited stream of pseudorandom {@code int}
658 : jsr166 1.10 * values.
659 : dl 1.1 *
660 :     * @implNote This method is implemented to be equivalent to {@code
661 :     * ints(Long.MAX_VALUE)}.
662 :     *
663 :     * @return a stream of pseudorandom {@code int} values
664 :     */
665 :     public IntStream ints() {
666 :     return StreamSupport.intStream
667 :     (new RandomIntsSpliterator
668 :     (this, 0L, Long.MAX_VALUE, Integer.MAX_VALUE, 0),
669 :     false);
670 :     }
671 :    
672 :     /**
673 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
674 : dl 1.1 * pseudorandom {@code int} values, each conforming to the given
675 :     * origin and bound.
676 :     *
677 :     * @param streamSize the number of values to generate
678 :     * @param randomNumberOrigin the origin of each random value
679 :     * @param randomNumberBound the bound of each random value
680 :     * @return a stream of pseudorandom {@code int} values,
681 : jsr166 1.10 * each with the given origin and bound
682 : dl 1.1 * @throws IllegalArgumentException if {@code streamSize} is
683 : dl 1.7 * less than zero, or {@code randomNumberOrigin}
684 : dl 1.1 * is greater than or equal to {@code randomNumberBound}
685 :     */
686 :     public IntStream ints(long streamSize, int randomNumberOrigin,
687 :     int randomNumberBound) {
688 :     if (streamSize < 0L)
689 :     throw new IllegalArgumentException("negative Stream size");
690 :     if (randomNumberOrigin >= randomNumberBound)
691 :     throw new IllegalArgumentException("bound must be greater than origin");
692 :     return StreamSupport.intStream
693 :     (new RandomIntsSpliterator
694 :     (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
695 :     false);
696 :     }
697 :    
698 :     /**
699 :     * Returns an effectively unlimited stream of pseudorandom {@code
700 :     * int} values, each conforming to the given origin and bound.
701 :     *
702 :     * @implNote This method is implemented to be equivalent to {@code
703 :     * ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
704 :     *
705 :     * @param randomNumberOrigin the origin of each random value
706 :     * @param randomNumberBound the bound of each random value
707 :     * @return a stream of pseudorandom {@code int} values,
708 : jsr166 1.10 * each with the given origin and bound
709 : dl 1.1 * @throws IllegalArgumentException if {@code randomNumberOrigin}
710 :     * is greater than or equal to {@code randomNumberBound}
711 :     */
712 :     public IntStream ints(int randomNumberOrigin, int randomNumberBound) {
713 :     if (randomNumberOrigin >= randomNumberBound)
714 :     throw new IllegalArgumentException("bound must be greater than origin");
715 :     return StreamSupport.intStream
716 :     (new RandomIntsSpliterator
717 :     (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
718 :     false);
719 :     }
720 :    
721 :     /**
722 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
723 : dl 1.1 * pseudorandom {@code long} values.
724 :     *
725 :     * @param streamSize the number of values to generate
726 : dl 1.7 * @return a stream of pseudorandom {@code long} values
727 : dl 1.1 * @throws IllegalArgumentException if {@code streamSize} is
728 : dl 1.7 * less than zero
729 : dl 1.1 */
730 :     public LongStream longs(long streamSize) {
731 :     if (streamSize < 0L)
732 :     throw new IllegalArgumentException("negative Stream size");
733 :     return StreamSupport.longStream
734 :     (new RandomLongsSpliterator
735 :     (this, 0L, streamSize, Long.MAX_VALUE, 0L),
736 :     false);
737 :     }
738 :    
739 :     /**
740 :     * Returns an effectively unlimited stream of pseudorandom {@code long}
741 :     * values.
742 :     *
743 :     * @implNote This method is implemented to be equivalent to {@code
744 :     * longs(Long.MAX_VALUE)}.
745 :     *
746 :     * @return a stream of pseudorandom {@code long} values
747 :     */
748 :     public LongStream longs() {
749 :     return StreamSupport.longStream
750 :     (new RandomLongsSpliterator
751 :     (this, 0L, Long.MAX_VALUE, Long.MAX_VALUE, 0L),
752 :     false);
753 :     }
754 :    
755 :     /**
756 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
757 : dl 1.1 * pseudorandom {@code long} values, each conforming to the
758 :     * given origin and bound.
759 :     *
760 :     * @param streamSize the number of values to generate
761 :     * @param randomNumberOrigin the origin of each random value
762 :     * @param randomNumberBound the bound of each random value
763 :     * @return a stream of pseudorandom {@code long} values,
764 : jsr166 1.10 * each with the given origin and bound
765 : dl 1.1 * @throws IllegalArgumentException if {@code streamSize} is
766 : dl 1.7 * less than zero, or {@code randomNumberOrigin}
767 : dl 1.1 * is greater than or equal to {@code randomNumberBound}
768 :     */
769 :     public LongStream longs(long streamSize, long randomNumberOrigin,
770 :     long randomNumberBound) {
771 :     if (streamSize < 0L)
772 :     throw new IllegalArgumentException("negative Stream size");
773 :     if (randomNumberOrigin >= randomNumberBound)
774 :     throw new IllegalArgumentException("bound must be greater than origin");
775 :     return StreamSupport.longStream
776 :     (new RandomLongsSpliterator
777 :     (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
778 :     false);
779 :     }
780 :    
781 :     /**
782 :     * Returns an effectively unlimited stream of pseudorandom {@code
783 :     * long} values, each conforming to the given origin and bound.
784 :     *
785 :     * @implNote This method is implemented to be equivalent to {@code
786 :     * longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
787 :     *
788 :     * @param randomNumberOrigin the origin of each random value
789 :     * @param randomNumberBound the bound of each random value
790 :     * @return a stream of pseudorandom {@code long} values,
791 : jsr166 1.10 * each with the given origin and bound
792 : dl 1.1 * @throws IllegalArgumentException if {@code randomNumberOrigin}
793 :     * is greater than or equal to {@code randomNumberBound}
794 :     */
795 :     public LongStream longs(long randomNumberOrigin, long randomNumberBound) {
796 :     if (randomNumberOrigin >= randomNumberBound)
797 :     throw new IllegalArgumentException("bound must be greater than origin");
798 :     return StreamSupport.longStream
799 :     (new RandomLongsSpliterator
800 :     (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
801 :     false);
802 :     }
803 :    
804 :     /**
805 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
806 :     * pseudorandom {@code double} values, each between zero
807 :     * (inclusive) and one (exclusive).
808 : dl 1.1 *
809 :     * @param streamSize the number of values to generate
810 :     * @return a stream of {@code double} values
811 :     * @throws IllegalArgumentException if {@code streamSize} is
812 : dl 1.7 * less than zero
813 : dl 1.1 */
814 :     public DoubleStream doubles(long streamSize) {
815 :     if (streamSize < 0L)
816 :     throw new IllegalArgumentException("negative Stream size");
817 :     return StreamSupport.doubleStream
818 :     (new RandomDoublesSpliterator
819 :     (this, 0L, streamSize, Double.MAX_VALUE, 0.0),
820 :     false);
821 :     }
822 :    
823 :     /**
824 :     * Returns an effectively unlimited stream of pseudorandom {@code
825 : dl 1.7 * double} values, each between zero (inclusive) and one
826 :     * (exclusive).
827 : dl 1.1 *
828 :     * @implNote This method is implemented to be equivalent to {@code
829 :     * doubles(Long.MAX_VALUE)}.
830 :     *
831 :     * @return a stream of pseudorandom {@code double} values
832 :     */
833 :     public DoubleStream doubles() {
834 :     return StreamSupport.doubleStream
835 :     (new RandomDoublesSpliterator
836 :     (this, 0L, Long.MAX_VALUE, Double.MAX_VALUE, 0.0),
837 :     false);
838 :     }
839 :    
840 :     /**
841 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
842 : dl 1.1 * pseudorandom {@code double} values, each conforming to the
843 :     * given origin and bound.
844 :     *
845 :     * @param streamSize the number of values to generate
846 :     * @param randomNumberOrigin the origin of each random value
847 :     * @param randomNumberBound the bound of each random value
848 :     * @return a stream of pseudorandom {@code double} values,
849 : jsr166 1.10 * each with the given origin and bound
850 : dl 1.1 * @throws IllegalArgumentException if {@code streamSize} is
851 : jsr166 1.10 * less than zero
852 : dl 1.1 * @throws IllegalArgumentException if {@code randomNumberOrigin}
853 :     * is greater than or equal to {@code randomNumberBound}
854 :     */
855 :     public DoubleStream doubles(long streamSize, double randomNumberOrigin,
856 :     double randomNumberBound) {
857 :     if (streamSize < 0L)
858 :     throw new IllegalArgumentException("negative Stream size");
859 : dl 1.7 if (!(randomNumberOrigin < randomNumberBound))
860 : dl 1.1 throw new IllegalArgumentException("bound must be greater than origin");
861 :     return StreamSupport.doubleStream
862 :     (new RandomDoublesSpliterator
863 :     (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
864 :     false);
865 :     }
866 :    
867 :     /**
868 :     * Returns an effectively unlimited stream of pseudorandom {@code
869 :     * double} values, each conforming to the given origin and bound.
870 :     *
871 :     * @implNote This method is implemented to be equivalent to {@code
872 :     * doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
873 :     *
874 :     * @param randomNumberOrigin the origin of each random value
875 :     * @param randomNumberBound the bound of each random value
876 :     * @return a stream of pseudorandom {@code double} values,
877 : jsr166 1.10 * each with the given origin and bound
878 : dl 1.1 * @throws IllegalArgumentException if {@code randomNumberOrigin}
879 :     * is greater than or equal to {@code randomNumberBound}
880 :     */
881 :     public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) {
882 : dl 1.7 if (!(randomNumberOrigin < randomNumberBound))
883 : dl 1.1 throw new IllegalArgumentException("bound must be greater than origin");
884 :     return StreamSupport.doubleStream
885 :     (new RandomDoublesSpliterator
886 :     (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
887 :     false);
888 :     }
889 :    
890 :     /**
891 :     * Spliterator for int streams. We multiplex the four int
892 : dl 1.7 * versions into one class by treating a bound less than origin as
893 : dl 1.1 * unbounded, and also by treating "infinite" as equivalent to
894 :     * Long.MAX_VALUE. For splits, it uses the standard divide-by-two
895 :     * approach. The long and double versions of this class are
896 :     * identical except for types.
897 :     */
898 : dl 1.11 static final class RandomIntsSpliterator implements Spliterator.OfInt {
899 : dl 1.1 final SplittableRandom rng;
900 :     long index;
901 :     final long fence;
902 :     final int origin;
903 :     final int bound;
904 :     RandomIntsSpliterator(SplittableRandom rng, long index, long fence,
905 :     int origin, int bound) {
906 :     this.rng = rng; this.index = index; this.fence = fence;
907 :     this.origin = origin; this.bound = bound;
908 :     }
909 :    
910 :     public RandomIntsSpliterator trySplit() {
911 :     long i = index, m = (i + fence) >>> 1;
912 :     return (m <= i) ? null :
913 :     new RandomIntsSpliterator(rng.split(), i, index = m, origin, bound);
914 :     }
915 :    
916 :     public long estimateSize() {
917 :     return fence - index;
918 :     }
919 :    
920 :     public int characteristics() {
921 :     return (Spliterator.SIZED | Spliterator.SUBSIZED |
922 : dl 1.4 Spliterator.NONNULL | Spliterator.IMMUTABLE);
923 : dl 1.1 }
924 :    
925 :     public boolean tryAdvance(IntConsumer consumer) {
926 :     if (consumer == null) throw new NullPointerException();
927 :     long i = index, f = fence;
928 :     if (i < f) {
929 :     consumer.accept(rng.internalNextInt(origin, bound));
930 :     index = i + 1;
931 :     return true;
932 :     }
933 :     return false;
934 :     }
935 :    
936 :     public void forEachRemaining(IntConsumer consumer) {
937 :     if (consumer == null) throw new NullPointerException();
938 :     long i = index, f = fence;
939 :     if (i < f) {
940 :     index = f;
941 :     int o = origin, b = bound;
942 :     do {
943 :     consumer.accept(rng.internalNextInt(o, b));
944 :     } while (++i < f);
945 :     }
946 :     }
947 :     }
948 :    
949 :     /**
950 :     * Spliterator for long streams.
951 :     */
952 : dl 1.11 static final class RandomLongsSpliterator implements Spliterator.OfLong {
953 : dl 1.1 final SplittableRandom rng;
954 :     long index;
955 :     final long fence;
956 :     final long origin;
957 :     final long bound;
958 :     RandomLongsSpliterator(SplittableRandom rng, long index, long fence,
959 :     long origin, long bound) {
960 :     this.rng = rng; this.index = index; this.fence = fence;
961 :     this.origin = origin; this.bound = bound;
962 :     }
963 :    
964 :     public RandomLongsSpliterator trySplit() {
965 :     long i = index, m = (i + fence) >>> 1;
966 :     return (m <= i) ? null :
967 :     new RandomLongsSpliterator(rng.split(), i, index = m, origin, bound);
968 :     }
969 :    
970 :     public long estimateSize() {
971 :     return fence - index;
972 :     }
973 :    
974 :     public int characteristics() {
975 :     return (Spliterator.SIZED | Spliterator.SUBSIZED |
976 : dl 1.4 Spliterator.NONNULL | Spliterator.IMMUTABLE);
977 : dl 1.1 }
978 :    
979 :     public boolean tryAdvance(LongConsumer consumer) {
980 :     if (consumer == null) throw new NullPointerException();
981 :     long i = index, f = fence;
982 :     if (i < f) {
983 :     consumer.accept(rng.internalNextLong(origin, bound));
984 :     index = i + 1;
985 :     return true;
986 :     }
987 :     return false;
988 :     }
989 :    
990 :     public void forEachRemaining(LongConsumer consumer) {
991 :     if (consumer == null) throw new NullPointerException();
992 :     long i = index, f = fence;
993 :     if (i < f) {
994 :     index = f;
995 :     long o = origin, b = bound;
996 :     do {
997 :     consumer.accept(rng.internalNextLong(o, b));
998 :     } while (++i < f);
999 :     }
1000 :     }
1001 :    
1002 :     }
1003 :    
1004 :     /**
1005 :     * Spliterator for double streams.
1006 :     */
1007 : dl 1.11 static final class RandomDoublesSpliterator implements Spliterator.OfDouble {
1008 : dl 1.1 final SplittableRandom rng;
1009 :     long index;
1010 :     final long fence;
1011 :     final double origin;
1012 :     final double bound;
1013 :     RandomDoublesSpliterator(SplittableRandom rng, long index, long fence,
1014 :     double origin, double bound) {
1015 :     this.rng = rng; this.index = index; this.fence = fence;
1016 :     this.origin = origin; this.bound = bound;
1017 :     }
1018 :    
1019 :     public RandomDoublesSpliterator trySplit() {
1020 :     long i = index, m = (i + fence) >>> 1;
1021 :     return (m <= i) ? null :
1022 :     new RandomDoublesSpliterator(rng.split(), i, index = m, origin, bound);
1023 :     }
1024 :    
1025 :     public long estimateSize() {
1026 :     return fence - index;
1027 :     }
1028 :    
1029 :     public int characteristics() {
1030 :     return (Spliterator.SIZED | Spliterator.SUBSIZED |
1031 : dl 1.4 Spliterator.NONNULL | Spliterator.IMMUTABLE);
1032 : dl 1.1 }
1033 :    
1034 :     public boolean tryAdvance(DoubleConsumer consumer) {
1035 :     if (consumer == null) throw new NullPointerException();
1036 :     long i = index, f = fence;
1037 :     if (i < f) {
1038 :     consumer.accept(rng.internalNextDouble(origin, bound));
1039 :     index = i + 1;
1040 :     return true;
1041 :     }
1042 :     return false;
1043 :     }
1044 :    
1045 :     public void forEachRemaining(DoubleConsumer consumer) {
1046 :     if (consumer == null) throw new NullPointerException();
1047 :     long i = index, f = fence;
1048 :     if (i < f) {
1049 :     index = f;
1050 :     double o = origin, b = bound;
1051 :     do {
1052 :     consumer.accept(rng.internalNextDouble(o, b));
1053 :     } while (++i < f);
1054 :     }
1055 :     }
1056 :     }
1057 :    
1058 :     }

Doug Lea
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