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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 value of gamma differs for each instance across a series of
119 :     * splits, and is generated using a slightly stripped-down variant
120 :     * of the same algorithm, but operating across calls to split(),
121 : dl 1.2 * not calls to nextSeed(): Each instance carries the state of
122 : dl 1.1 * this generator as nextSplit, and uses mix64(nextSplit) as its
123 :     * own gamma value. Computations of gammas themselves use a fixed
124 :     * constant as the second argument to the addGammaModGeorge
125 : dl 1.12 * function, GAMMA_GAMMA. The value of GAMMA_GAMMA is arbitrary
126 :     * (except must be at least 13), but because it serves as the base
127 :     * of split sequences, should be subject to validation of
128 :     * consequent random number quality metrics.
129 : dl 1.1 *
130 :     * The mix64 bit-mixing function called by nextLong and other
131 :     * methods computes the same value as the "64-bit finalizer"
132 :     * function in Austin Appleby's MurmurHash3 algorithm. See
133 :     * http://code.google.com/p/smhasher/wiki/MurmurHash3 , which
134 :     * comments: "The constants for the finalizers were generated by a
135 :     * simple simulated-annealing algorithm, and both avalanche all
136 :     * bits of 'h' to within 0.25% bias." It also appears to work to
137 :     * use instead any of the variants proposed by David Stafford at
138 :     * http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html
139 :     * but these variants have not yet been tested as thoroughly
140 :     * in the context of the implementation of SplittableRandom.
141 :     *
142 :     * The mix32 function used for nextInt just consists of two of the
143 :     * five lines of mix64; avalanche testing shows that the 64-bit result
144 :     * has its top 32 bits avalanched well, though not the bottom 32 bits.
145 :     * DieHarder tests show that it is adequate for generating one
146 :     * random int from the 64-bit result of nextSeed.
147 :     *
148 :     * Support for the default (no-argument) constructor relies on an
149 :     * AtomicLong (defaultSeedGenerator) to help perform the
150 :     * equivalent of a split of a statically constructed
151 :     * SplittableRandom. Unlike other cases, this split must be
152 :     * performed in a thread-safe manner. We use
153 :     * AtomicLong.compareAndSet as the (typically) most efficient
154 : dl 1.12 * mechanism. To bootstrap, we start off using a SecureRandom
155 :     * initial default seed, and update using a fixed
156 :     * DEFAULT_SEED_GAMMA. The default constructor uses GAMMA_GAMMA,
157 :     * not 0, for its splitSeed argument (addGammaModGeorge(0,
158 :     * GAMMA_GAMMA) == GAMMA_GAMMA) to reflect that each is split from
159 :     * this root generator, even though the root is not explicitly
160 :     * represented as a SplittableRandom.
161 : dl 1.1 */
162 :    
163 :     /**
164 : dl 1.12 * The value for producing new gamma values. Must be greater or
165 :     * equal to 13. Otherwise, the value is arbitrary subject to
166 :     * validation of the resulting statistical quality of splits.
167 : dl 1.1 */
168 :     private static final long GAMMA_GAMMA = 0xF2281E2DBA6606F3L;
169 :    
170 :     /**
171 : dl 1.12 * The seed update value for default constructors. Must be
172 :     * greater or equal to 13. Otherwise, the value is arbitrary.
173 : dl 1.1 */
174 :     private static final long DEFAULT_SEED_GAMMA = 0xBD24B73A95FB84D9L;
175 :    
176 :     /**
177 : dl 1.11 * The value 13 with 64bit sign bit set. Used in the signed
178 :     * comparison in addGammaModGeorge.
179 :     */
180 :     private static final long BOTTOM13 = 0x800000000000000DL;
181 :    
182 :     /**
183 : dl 1.5 * The least non-zero value returned by nextDouble(). This value
184 : dl 1.7 * is scaled by a random value of 53 bits to produce a result.
185 : dl 1.5 */
186 :     private static final double DOUBLE_UNIT = 1.0 / (1L << 53);
187 :    
188 :     /**
189 : dl 1.1 * The next seed for default constructors.
190 :     */
191 :     private static final AtomicLong defaultSeedGenerator =
192 : dl 1.12 new AtomicLong(getInitialDefaultSeed());
193 : dl 1.1
194 :     /**
195 :     * The seed, updated only via method nextSeed.
196 :     */
197 :     private long seed;
198 :    
199 :     /**
200 :     * The constant value added to seed (mod George) on each update.
201 :     */
202 :     private final long gamma;
203 :    
204 :     /**
205 :     * The next seed to use for splits. Propagated using
206 :     * addGammaModGeorge across instances.
207 :     */
208 :     private final long nextSplit;
209 :    
210 :     /**
211 :     * Adds the given gamma value, g, to the given seed value s, mod
212 :     * George (2^64+13). We regard s and g as unsigned values
213 :     * (ranging from 0 to 2^64-1). We add g to s either once or twice
214 :     * (mod George) as necessary to produce an (unsigned) result less
215 :     * than 2^64. We require that g must be at least 13. This
216 :     * guarantees that if (s+g) mod George >= 2^64 then (s+g+g) mod
217 :     * George < 2^64; thus we need only a conditional, not a loop,
218 :     * to be sure of getting a representable value.
219 :     *
220 : dl 1.11 * Because Java comparison operators are signed, we implement this
221 :     * by conceptually offsetting seed values downwards by 2^63, so
222 :     * 0..13 is represented as Long.MIN_VALUE..BOTTOM13.
223 :     *
224 :     * @param s a seed value, viewed as a signed long
225 : dl 1.1 * @param g a gamma value, 13 <= g (as unsigned)
226 :     */
227 :     private static long addGammaModGeorge(long s, long g) {
228 :     long p = s + g;
229 : dl 1.11 return (p >= s) ? p : ((p >= BOTTOM13) ? p : p + g) - 13L;
230 : dl 1.1 }
231 :    
232 :     /**
233 :     * Returns a bit-mixed transformation of its argument.
234 :     * See above for explanation.
235 :     */
236 :     private static long mix64(long z) {
237 :     z ^= (z >>> 33);
238 :     z *= 0xff51afd7ed558ccdL;
239 :     z ^= (z >>> 33);
240 :     z *= 0xc4ceb9fe1a85ec53L;
241 :     z ^= (z >>> 33);
242 :     return z;
243 :     }
244 :    
245 :     /**
246 :     * Returns a bit-mixed int transformation of its argument.
247 :     * See above for explanation.
248 :     */
249 :     private static int mix32(long z) {
250 :     z ^= (z >>> 33);
251 :     z *= 0xc4ceb9fe1a85ec53L;
252 :     return (int)(z >>> 32);
253 :     }
254 :    
255 :     /**
256 : dl 1.7 * Internal constructor used by all other constructors and by
257 :     * method split. Establishes the initial seed for this instance,
258 :     * and uses the given splitSeed to establish gamma, as well as the
259 :     * nextSplit to use by this instance. The loop to skip ineligible
260 :     * gammas very rarely iterates, and does so at most 13 times.
261 :     */
262 :     private SplittableRandom(long seed, long splitSeed) {
263 :     this.seed = seed;
264 :     long s = splitSeed, g;
265 :     do { // ensure gamma >= 13, considered as an unsigned integer
266 :     s = addGammaModGeorge(s, GAMMA_GAMMA);
267 :     g = mix64(s);
268 : dl 1.11 } while (g >= 0L && g < 13L);
269 : dl 1.7 this.gamma = g;
270 :     this.nextSplit = s;
271 :     }
272 :    
273 :     /**
274 :     * Updates in-place and returns seed.
275 :     * See above for explanation.
276 :     */
277 :     private long nextSeed() {
278 :     return seed = addGammaModGeorge(seed, gamma);
279 :     }
280 :    
281 :     /**
282 :     * Atomically updates and returns next seed for default constructor.
283 : dl 1.1 */
284 :     private static long nextDefaultSeed() {
285 :     long oldSeed, newSeed;
286 :     do {
287 :     oldSeed = defaultSeedGenerator.get();
288 :     newSeed = addGammaModGeorge(oldSeed, DEFAULT_SEED_GAMMA);
289 :     } while (!defaultSeedGenerator.compareAndSet(oldSeed, newSeed));
290 :     return mix64(newSeed);
291 :     }
292 :    
293 : dl 1.12 /**
294 :     * Returns an initial default seed.
295 :     */
296 :     private static long getInitialDefaultSeed() {
297 :     byte[] seedBytes = java.security.SecureRandom.getSeed(8);
298 :     long s = (long)(seedBytes[0]) & 0xffL;
299 :     for (int i = 1; i < 8; ++i)
300 :     s = (s << 8) | ((long)(seedBytes[i]) & 0xffL);
301 :     return s;
302 :     }
303 :    
304 : dl 1.1 /*
305 :     * Internal versions of nextX methods used by streams, as well as
306 :     * the public nextX(origin, bound) methods. These exist mainly to
307 :     * avoid the need for multiple versions of stream spliterators
308 :     * across the different exported forms of streams.
309 :     */
310 :    
311 :     /**
312 :     * The form of nextLong used by LongStream Spliterators. If
313 :     * origin is greater than bound, acts as unbounded form of
314 :     * nextLong, else as bounded form.
315 :     *
316 :     * @param origin the least value, unless greater than bound
317 :     * @param bound the upper bound (exclusive), must not equal origin
318 :     * @return a pseudorandom value
319 :     */
320 :     final long internalNextLong(long origin, long bound) {
321 :     /*
322 :     * Four Cases:
323 :     *
324 :     * 1. If the arguments indicate unbounded form, act as
325 :     * nextLong().
326 :     *
327 :     * 2. If the range is an exact power of two, apply the
328 :     * associated bit mask.
329 :     *
330 :     * 3. If the range is positive, loop to avoid potential bias
331 :     * when the implicit nextLong() bound (2<sup>64</sup>) is not
332 :     * evenly divisible by the range. The loop rejects candidates
333 :     * computed from otherwise over-represented values. The
334 :     * expected number of iterations under an ideal generator
335 : dl 1.4 * varies from 1 to 2, depending on the bound. The loop itself
336 :     * takes an unlovable form. Because the first candidate is
337 :     * already available, we need a break-in-the-middle
338 :     * construction, which is concisely but cryptically performed
339 :     * within the while-condition of a body-less for loop.
340 : dl 1.1 *
341 :     * 4. Otherwise, the range cannot be represented as a positive
342 : dl 1.4 * long. The loop repeatedly generates unbounded longs until
343 :     * obtaining a candidate meeting constraints (with an expected
344 :     * number of iterations of less than two).
345 : dl 1.1 */
346 :    
347 :     long r = mix64(nextSeed());
348 :     if (origin < bound) {
349 :     long n = bound - origin, m = n - 1;
350 : dl 1.7 if ((n & m) == 0L) // power of two
351 : dl 1.1 r = (r & m) + origin;
352 : dl 1.7 else if (n > 0L) { // reject over-represented candidates
353 : dl 1.1 for (long u = r >>> 1; // ensure nonnegative
354 : dl 1.7 u + m - (r = u % n) < 0L; // rejection check
355 : dl 1.1 u = mix64(nextSeed()) >>> 1) // retry
356 :     ;
357 :     r += origin;
358 :     }
359 : dl 1.7 else { // range not representable as long
360 : dl 1.1 while (r < origin || r >= bound)
361 :     r = mix64(nextSeed());
362 :     }
363 :     }
364 :     return r;
365 :     }
366 :    
367 :     /**
368 :     * The form of nextInt used by IntStream Spliterators.
369 :     * Exactly the same as long version, except for types.
370 :     *
371 :     * @param origin the least value, unless greater than bound
372 :     * @param bound the upper bound (exclusive), must not equal origin
373 :     * @return a pseudorandom value
374 :     */
375 :     final int internalNextInt(int origin, int bound) {
376 :     int r = mix32(nextSeed());
377 :     if (origin < bound) {
378 :     int n = bound - origin, m = n - 1;
379 :     if ((n & m) == 0L)
380 :     r = (r & m) + origin;
381 :     else if (n > 0) {
382 :     for (int u = r >>> 1;
383 : dl 1.7 u + m - (r = u % n) < 0;
384 : dl 1.1 u = mix32(nextSeed()) >>> 1)
385 :     ;
386 :     r += origin;
387 :     }
388 :     else {
389 :     while (r < origin || r >= bound)
390 :     r = mix32(nextSeed());
391 :     }
392 :     }
393 :     return r;
394 :     }
395 :    
396 :     /**
397 :     * The form of nextDouble used by DoubleStream Spliterators.
398 :     *
399 :     * @param origin the least value, unless greater than bound
400 :     * @param bound the upper bound (exclusive), must not equal origin
401 :     * @return a pseudorandom value
402 :     */
403 :     final double internalNextDouble(double origin, double bound) {
404 : dl 1.5 double r = (nextLong() >>> 11) * DOUBLE_UNIT;
405 : dl 1.1 if (origin < bound) {
406 :     r = r * (bound - origin) + origin;
407 : dl 1.7 if (r >= bound) // correct for rounding
408 : dl 1.1 r = Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
409 :     }
410 :     return r;
411 :     }
412 :    
413 :     /* ---------------- public methods ---------------- */
414 :    
415 :     /**
416 : dl 1.7 * Creates a new SplittableRandom instance using the specified
417 :     * initial seed. SplittableRandom instances created with the same
418 : dl 1.11 * seed in the same program generate identical sequences of values.
419 : dl 1.1 *
420 :     * @param seed the initial seed
421 :     */
422 :     public SplittableRandom(long seed) {
423 :     this(seed, 0);
424 :     }
425 :    
426 :     /**
427 :     * Creates a new SplittableRandom instance that is likely to
428 :     * generate sequences of values that are statistically independent
429 :     * of those of any other instances in the current program; and
430 :     * may, and typically does, vary across program invocations.
431 :     */
432 :     public SplittableRandom() {
433 :     this(nextDefaultSeed(), GAMMA_GAMMA);
434 :     }
435 :    
436 :     /**
437 :     * Constructs and returns a new SplittableRandom instance that
438 :     * shares no mutable state with this instance. However, with very
439 :     * high probability, the set of values collectively generated by
440 :     * the two objects has the same statistical properties as if the
441 :     * same quantity of values were generated by a single thread using
442 :     * a single SplittableRandom object. Either or both of the two
443 :     * objects may be further split using the {@code split()} method,
444 :     * and the same expected statistical properties apply to the
445 :     * entire set of generators constructed by such recursive
446 :     * splitting.
447 :     *
448 :     * @return the new SplittableRandom instance
449 :     */
450 :     public SplittableRandom split() {
451 :     return new SplittableRandom(nextSeed(), nextSplit);
452 :     }
453 :    
454 :     /**
455 :     * Returns a pseudorandom {@code int} value.
456 :     *
457 : dl 1.7 * @return a pseudorandom {@code int} value
458 : dl 1.1 */
459 :     public int nextInt() {
460 :     return mix32(nextSeed());
461 :     }
462 :    
463 :     /**
464 : dl 1.7 * Returns a pseudorandom {@code int} value between zero (inclusive)
465 : dl 1.1 * and the specified bound (exclusive).
466 :     *
467 :     * @param bound the bound on the random number to be returned. Must be
468 :     * positive.
469 : dl 1.7 * @return a pseudorandom {@code int} value between zero
470 : jsr166 1.10 * (inclusive) and the bound (exclusive)
471 : dl 1.7 * @throws IllegalArgumentException if the bound is less than zero
472 : dl 1.1 */
473 :     public int nextInt(int bound) {
474 :     if (bound <= 0)
475 :     throw new IllegalArgumentException("bound must be positive");
476 :     // Specialize internalNextInt for origin 0
477 :     int r = mix32(nextSeed());
478 :     int m = bound - 1;
479 :     if ((bound & m) == 0L) // power of two
480 :     r &= m;
481 :     else { // reject over-represented candidates
482 :     for (int u = r >>> 1;
483 : dl 1.7 u + m - (r = u % bound) < 0;
484 : dl 1.1 u = mix32(nextSeed()) >>> 1)
485 :     ;
486 :     }
487 :     return r;
488 :     }
489 :    
490 :     /**
491 :     * Returns a pseudorandom {@code int} value between the specified
492 :     * origin (inclusive) and the specified bound (exclusive).
493 :     *
494 :     * @param origin the least value returned
495 :     * @param bound the upper bound (exclusive)
496 :     * @return a pseudorandom {@code int} value between the origin
497 : jsr166 1.10 * (inclusive) and the bound (exclusive)
498 : dl 1.7 * @throws IllegalArgumentException if {@code origin} is greater than
499 : dl 1.1 * or equal to {@code bound}
500 :     */
501 :     public int nextInt(int origin, int bound) {
502 :     if (origin >= bound)
503 :     throw new IllegalArgumentException("bound must be greater than origin");
504 :     return internalNextInt(origin, bound);
505 :     }
506 :    
507 :     /**
508 :     * Returns a pseudorandom {@code long} value.
509 :     *
510 : dl 1.7 * @return a pseudorandom {@code long} value
511 : dl 1.1 */
512 :     public long nextLong() {
513 :     return mix64(nextSeed());
514 :     }
515 :    
516 :     /**
517 : dl 1.7 * Returns a pseudorandom {@code long} value between zero (inclusive)
518 : dl 1.1 * and the specified bound (exclusive).
519 :     *
520 :     * @param bound the bound on the random number to be returned. Must be
521 :     * positive.
522 : dl 1.7 * @return a pseudorandom {@code long} value between zero
523 : jsr166 1.10 * (inclusive) and the bound (exclusive)
524 : dl 1.7 * @throws IllegalArgumentException if {@code bound} is less than zero
525 : dl 1.1 */
526 :     public long nextLong(long bound) {
527 :     if (bound <= 0)
528 :     throw new IllegalArgumentException("bound must be positive");
529 :     // Specialize internalNextLong for origin 0
530 :     long r = mix64(nextSeed());
531 :     long m = bound - 1;
532 :     if ((bound & m) == 0L) // power of two
533 :     r &= m;
534 :     else { // reject over-represented candidates
535 :     for (long u = r >>> 1;
536 :     u + m - (r = u % bound) < 0L;
537 :     u = mix64(nextSeed()) >>> 1)
538 :     ;
539 :     }
540 :     return r;
541 :     }
542 :    
543 :     /**
544 :     * Returns a pseudorandom {@code long} value between the specified
545 :     * origin (inclusive) and the specified bound (exclusive).
546 :     *
547 :     * @param origin the least value returned
548 :     * @param bound the upper bound (exclusive)
549 :     * @return a pseudorandom {@code long} value between the origin
550 : jsr166 1.10 * (inclusive) and the bound (exclusive)
551 : dl 1.7 * @throws IllegalArgumentException if {@code origin} is greater than
552 : dl 1.1 * or equal to {@code bound}
553 :     */
554 :     public long nextLong(long origin, long bound) {
555 :     if (origin >= bound)
556 :     throw new IllegalArgumentException("bound must be greater than origin");
557 :     return internalNextLong(origin, bound);
558 :     }
559 :    
560 :     /**
561 : dl 1.7 * Returns a pseudorandom {@code double} value between zero
562 :     * (inclusive) and one (exclusive).
563 : dl 1.1 *
564 : dl 1.7 * @return a pseudorandom {@code double} value between zero
565 :     * (inclusive) and one (exclusive)
566 : dl 1.1 */
567 :     public double nextDouble() {
568 : dl 1.11 return (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT;
569 : dl 1.1 }
570 :    
571 :     /**
572 :     * Returns a pseudorandom {@code double} value between 0.0
573 :     * (inclusive) and the specified bound (exclusive).
574 :     *
575 :     * @param bound the bound on the random number to be returned. Must be
576 :     * positive.
577 : dl 1.7 * @return a pseudorandom {@code double} value between zero
578 : jsr166 1.10 * (inclusive) and the bound (exclusive)
579 : dl 1.7 * @throws IllegalArgumentException if {@code bound} is less than zero
580 : dl 1.1 */
581 :     public double nextDouble(double bound) {
582 : dl 1.7 if (!(bound > 0.0))
583 : dl 1.1 throw new IllegalArgumentException("bound must be positive");
584 : dl 1.11 double result = (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT * bound;
585 : dl 1.1 return (result < bound) ? result : // correct for rounding
586 :     Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
587 :     }
588 :    
589 :     /**
590 : dl 1.7 * Returns a pseudorandom {@code double} value between the specified
591 : dl 1.1 * origin (inclusive) and bound (exclusive).
592 :     *
593 :     * @param origin the least value returned
594 :     * @param bound the upper bound
595 :     * @return a pseudorandom {@code double} value between the origin
596 : jsr166 1.10 * (inclusive) and the bound (exclusive)
597 : dl 1.1 * @throws IllegalArgumentException if {@code origin} is greater than
598 :     * or equal to {@code bound}
599 :     */
600 :     public double nextDouble(double origin, double bound) {
601 : dl 1.7 if (!(origin < bound))
602 : dl 1.1 throw new IllegalArgumentException("bound must be greater than origin");
603 :     return internalNextDouble(origin, bound);
604 :     }
605 :    
606 : dl 1.11 /**
607 :     * Returns a pseudorandom {@code boolean} value.
608 :     *
609 :     * @return a pseudorandom {@code boolean} value
610 :     */
611 :     public boolean nextBoolean() {
612 :     return mix32(nextSeed()) < 0;
613 :     }
614 :    
615 : dl 1.1 // stream methods, coded in a way intended to better isolate for
616 :     // maintenance purposes the small differences across forms.
617 :    
618 :     /**
619 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
620 : dl 1.1 * pseudorandom {@code int} values.
621 :     *
622 :     * @param streamSize the number of values to generate
623 :     * @return a stream of pseudorandom {@code int} values
624 :     * @throws IllegalArgumentException if {@code streamSize} is
625 : dl 1.7 * less than zero
626 : dl 1.1 */
627 :     public IntStream ints(long streamSize) {
628 :     if (streamSize < 0L)
629 :     throw new IllegalArgumentException("negative Stream size");
630 :     return StreamSupport.intStream
631 :     (new RandomIntsSpliterator
632 :     (this, 0L, streamSize, Integer.MAX_VALUE, 0),
633 :     false);
634 :     }
635 :    
636 :     /**
637 :     * Returns an effectively unlimited stream of pseudorandom {@code int}
638 : jsr166 1.10 * values.
639 : dl 1.1 *
640 :     * @implNote This method is implemented to be equivalent to {@code
641 :     * ints(Long.MAX_VALUE)}.
642 :     *
643 :     * @return a stream of pseudorandom {@code int} values
644 :     */
645 :     public IntStream ints() {
646 :     return StreamSupport.intStream
647 :     (new RandomIntsSpliterator
648 :     (this, 0L, Long.MAX_VALUE, Integer.MAX_VALUE, 0),
649 :     false);
650 :     }
651 :    
652 :     /**
653 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
654 : dl 1.1 * pseudorandom {@code int} values, each conforming to the given
655 :     * origin and bound.
656 :     *
657 :     * @param streamSize the number of values to generate
658 :     * @param randomNumberOrigin the origin of each random value
659 :     * @param randomNumberBound the bound of each random value
660 :     * @return a stream of pseudorandom {@code int} values,
661 : jsr166 1.10 * each with the given origin and bound
662 : dl 1.1 * @throws IllegalArgumentException if {@code streamSize} is
663 : dl 1.7 * less than zero, or {@code randomNumberOrigin}
664 : dl 1.1 * is greater than or equal to {@code randomNumberBound}
665 :     */
666 :     public IntStream ints(long streamSize, int randomNumberOrigin,
667 :     int randomNumberBound) {
668 :     if (streamSize < 0L)
669 :     throw new IllegalArgumentException("negative Stream size");
670 :     if (randomNumberOrigin >= randomNumberBound)
671 :     throw new IllegalArgumentException("bound must be greater than origin");
672 :     return StreamSupport.intStream
673 :     (new RandomIntsSpliterator
674 :     (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
675 :     false);
676 :     }
677 :    
678 :     /**
679 :     * Returns an effectively unlimited stream of pseudorandom {@code
680 :     * int} values, each conforming to the given origin and bound.
681 :     *
682 :     * @implNote This method is implemented to be equivalent to {@code
683 :     * ints(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
684 :     *
685 :     * @param randomNumberOrigin the origin of each random value
686 :     * @param randomNumberBound the bound of each random value
687 :     * @return a stream of pseudorandom {@code int} values,
688 : jsr166 1.10 * each with the given origin and bound
689 : dl 1.1 * @throws IllegalArgumentException if {@code randomNumberOrigin}
690 :     * is greater than or equal to {@code randomNumberBound}
691 :     */
692 :     public IntStream ints(int randomNumberOrigin, int randomNumberBound) {
693 :     if (randomNumberOrigin >= randomNumberBound)
694 :     throw new IllegalArgumentException("bound must be greater than origin");
695 :     return StreamSupport.intStream
696 :     (new RandomIntsSpliterator
697 :     (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
698 :     false);
699 :     }
700 :    
701 :     /**
702 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
703 : dl 1.1 * pseudorandom {@code long} values.
704 :     *
705 :     * @param streamSize the number of values to generate
706 : dl 1.7 * @return a stream of pseudorandom {@code long} values
707 : dl 1.1 * @throws IllegalArgumentException if {@code streamSize} is
708 : dl 1.7 * less than zero
709 : dl 1.1 */
710 :     public LongStream longs(long streamSize) {
711 :     if (streamSize < 0L)
712 :     throw new IllegalArgumentException("negative Stream size");
713 :     return StreamSupport.longStream
714 :     (new RandomLongsSpliterator
715 :     (this, 0L, streamSize, Long.MAX_VALUE, 0L),
716 :     false);
717 :     }
718 :    
719 :     /**
720 :     * Returns an effectively unlimited stream of pseudorandom {@code long}
721 :     * values.
722 :     *
723 :     * @implNote This method is implemented to be equivalent to {@code
724 :     * longs(Long.MAX_VALUE)}.
725 :     *
726 :     * @return a stream of pseudorandom {@code long} values
727 :     */
728 :     public LongStream longs() {
729 :     return StreamSupport.longStream
730 :     (new RandomLongsSpliterator
731 :     (this, 0L, Long.MAX_VALUE, Long.MAX_VALUE, 0L),
732 :     false);
733 :     }
734 :    
735 :     /**
736 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
737 : dl 1.1 * pseudorandom {@code long} values, each conforming to the
738 :     * given origin and bound.
739 :     *
740 :     * @param streamSize the number of values to generate
741 :     * @param randomNumberOrigin the origin of each random value
742 :     * @param randomNumberBound the bound of each random value
743 :     * @return a stream of pseudorandom {@code long} values,
744 : jsr166 1.10 * each with the given origin and bound
745 : dl 1.1 * @throws IllegalArgumentException if {@code streamSize} is
746 : dl 1.7 * less than zero, or {@code randomNumberOrigin}
747 : dl 1.1 * is greater than or equal to {@code randomNumberBound}
748 :     */
749 :     public LongStream longs(long streamSize, long randomNumberOrigin,
750 :     long randomNumberBound) {
751 :     if (streamSize < 0L)
752 :     throw new IllegalArgumentException("negative Stream size");
753 :     if (randomNumberOrigin >= randomNumberBound)
754 :     throw new IllegalArgumentException("bound must be greater than origin");
755 :     return StreamSupport.longStream
756 :     (new RandomLongsSpliterator
757 :     (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
758 :     false);
759 :     }
760 :    
761 :     /**
762 :     * Returns an effectively unlimited stream of pseudorandom {@code
763 :     * long} values, each conforming to the given origin and bound.
764 :     *
765 :     * @implNote This method is implemented to be equivalent to {@code
766 :     * longs(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
767 :     *
768 :     * @param randomNumberOrigin the origin of each random value
769 :     * @param randomNumberBound the bound of each random value
770 :     * @return a stream of pseudorandom {@code long} values,
771 : jsr166 1.10 * each with the given origin and bound
772 : dl 1.1 * @throws IllegalArgumentException if {@code randomNumberOrigin}
773 :     * is greater than or equal to {@code randomNumberBound}
774 :     */
775 :     public LongStream longs(long randomNumberOrigin, long randomNumberBound) {
776 :     if (randomNumberOrigin >= randomNumberBound)
777 :     throw new IllegalArgumentException("bound must be greater than origin");
778 :     return StreamSupport.longStream
779 :     (new RandomLongsSpliterator
780 :     (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
781 :     false);
782 :     }
783 :    
784 :     /**
785 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
786 :     * pseudorandom {@code double} values, each between zero
787 :     * (inclusive) and one (exclusive).
788 : dl 1.1 *
789 :     * @param streamSize the number of values to generate
790 :     * @return a stream of {@code double} values
791 :     * @throws IllegalArgumentException if {@code streamSize} is
792 : dl 1.7 * less than zero
793 : dl 1.1 */
794 :     public DoubleStream doubles(long streamSize) {
795 :     if (streamSize < 0L)
796 :     throw new IllegalArgumentException("negative Stream size");
797 :     return StreamSupport.doubleStream
798 :     (new RandomDoublesSpliterator
799 :     (this, 0L, streamSize, Double.MAX_VALUE, 0.0),
800 :     false);
801 :     }
802 :    
803 :     /**
804 :     * Returns an effectively unlimited stream of pseudorandom {@code
805 : dl 1.7 * double} values, each between zero (inclusive) and one
806 :     * (exclusive).
807 : dl 1.1 *
808 :     * @implNote This method is implemented to be equivalent to {@code
809 :     * doubles(Long.MAX_VALUE)}.
810 :     *
811 :     * @return a stream of pseudorandom {@code double} values
812 :     */
813 :     public DoubleStream doubles() {
814 :     return StreamSupport.doubleStream
815 :     (new RandomDoublesSpliterator
816 :     (this, 0L, Long.MAX_VALUE, Double.MAX_VALUE, 0.0),
817 :     false);
818 :     }
819 :    
820 :     /**
821 : dl 1.7 * Returns a stream producing the given {@code streamSize} number of
822 : dl 1.1 * pseudorandom {@code double} values, each conforming to the
823 :     * given origin and bound.
824 :     *
825 :     * @param streamSize the number of values to generate
826 :     * @param randomNumberOrigin the origin of each random value
827 :     * @param randomNumberBound the bound of each random value
828 :     * @return a stream of pseudorandom {@code double} values,
829 : jsr166 1.10 * each with the given origin and bound
830 : dl 1.1 * @throws IllegalArgumentException if {@code streamSize} is
831 : jsr166 1.10 * less than zero
832 : dl 1.1 * @throws IllegalArgumentException if {@code randomNumberOrigin}
833 :     * is greater than or equal to {@code randomNumberBound}
834 :     */
835 :     public DoubleStream doubles(long streamSize, double randomNumberOrigin,
836 :     double randomNumberBound) {
837 :     if (streamSize < 0L)
838 :     throw new IllegalArgumentException("negative Stream size");
839 : dl 1.7 if (!(randomNumberOrigin < randomNumberBound))
840 : dl 1.1 throw new IllegalArgumentException("bound must be greater than origin");
841 :     return StreamSupport.doubleStream
842 :     (new RandomDoublesSpliterator
843 :     (this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
844 :     false);
845 :     }
846 :    
847 :     /**
848 :     * Returns an effectively unlimited stream of pseudorandom {@code
849 :     * double} values, each conforming to the given origin and bound.
850 :     *
851 :     * @implNote This method is implemented to be equivalent to {@code
852 :     * doubles(Long.MAX_VALUE, randomNumberOrigin, randomNumberBound)}.
853 :     *
854 :     * @param randomNumberOrigin the origin of each random value
855 :     * @param randomNumberBound the bound of each random value
856 :     * @return a stream of pseudorandom {@code double} values,
857 : jsr166 1.10 * each with the given origin and bound
858 : dl 1.1 * @throws IllegalArgumentException if {@code randomNumberOrigin}
859 :     * is greater than or equal to {@code randomNumberBound}
860 :     */
861 :     public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) {
862 : dl 1.7 if (!(randomNumberOrigin < randomNumberBound))
863 : dl 1.1 throw new IllegalArgumentException("bound must be greater than origin");
864 :     return StreamSupport.doubleStream
865 :     (new RandomDoublesSpliterator
866 :     (this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
867 :     false);
868 :     }
869 :    
870 :     /**
871 :     * Spliterator for int streams. We multiplex the four int
872 : dl 1.7 * versions into one class by treating a bound less than origin as
873 : dl 1.1 * unbounded, and also by treating "infinite" as equivalent to
874 :     * Long.MAX_VALUE. For splits, it uses the standard divide-by-two
875 :     * approach. The long and double versions of this class are
876 :     * identical except for types.
877 :     */
878 : dl 1.11 static final class RandomIntsSpliterator implements Spliterator.OfInt {
879 : dl 1.1 final SplittableRandom rng;
880 :     long index;
881 :     final long fence;
882 :     final int origin;
883 :     final int bound;
884 :     RandomIntsSpliterator(SplittableRandom rng, long index, long fence,
885 :     int origin, int bound) {
886 :     this.rng = rng; this.index = index; this.fence = fence;
887 :     this.origin = origin; this.bound = bound;
888 :     }
889 :    
890 :     public RandomIntsSpliterator trySplit() {
891 :     long i = index, m = (i + fence) >>> 1;
892 :     return (m <= i) ? null :
893 :     new RandomIntsSpliterator(rng.split(), i, index = m, origin, bound);
894 :     }
895 :    
896 :     public long estimateSize() {
897 :     return fence - index;
898 :     }
899 :    
900 :     public int characteristics() {
901 :     return (Spliterator.SIZED | Spliterator.SUBSIZED |
902 : dl 1.4 Spliterator.NONNULL | Spliterator.IMMUTABLE);
903 : dl 1.1 }
904 :    
905 :     public boolean tryAdvance(IntConsumer consumer) {
906 :     if (consumer == null) throw new NullPointerException();
907 :     long i = index, f = fence;
908 :     if (i < f) {
909 :     consumer.accept(rng.internalNextInt(origin, bound));
910 :     index = i + 1;
911 :     return true;
912 :     }
913 :     return false;
914 :     }
915 :    
916 :     public void forEachRemaining(IntConsumer consumer) {
917 :     if (consumer == null) throw new NullPointerException();
918 :     long i = index, f = fence;
919 :     if (i < f) {
920 :     index = f;
921 :     int o = origin, b = bound;
922 :     do {
923 :     consumer.accept(rng.internalNextInt(o, b));
924 :     } while (++i < f);
925 :     }
926 :     }
927 :     }
928 :    
929 :     /**
930 :     * Spliterator for long streams.
931 :     */
932 : dl 1.11 static final class RandomLongsSpliterator implements Spliterator.OfLong {
933 : dl 1.1 final SplittableRandom rng;
934 :     long index;
935 :     final long fence;
936 :     final long origin;
937 :     final long bound;
938 :     RandomLongsSpliterator(SplittableRandom rng, long index, long fence,
939 :     long origin, long bound) {
940 :     this.rng = rng; this.index = index; this.fence = fence;
941 :     this.origin = origin; this.bound = bound;
942 :     }
943 :    
944 :     public RandomLongsSpliterator trySplit() {
945 :     long i = index, m = (i + fence) >>> 1;
946 :     return (m <= i) ? null :
947 :     new RandomLongsSpliterator(rng.split(), i, index = m, origin, bound);
948 :     }
949 :    
950 :     public long estimateSize() {
951 :     return fence - index;
952 :     }
953 :    
954 :     public int characteristics() {
955 :     return (Spliterator.SIZED | Spliterator.SUBSIZED |
956 : dl 1.4 Spliterator.NONNULL | Spliterator.IMMUTABLE);
957 : dl 1.1 }
958 :    
959 :     public boolean tryAdvance(LongConsumer consumer) {
960 :     if (consumer == null) throw new NullPointerException();
961 :     long i = index, f = fence;
962 :     if (i < f) {
963 :     consumer.accept(rng.internalNextLong(origin, bound));
964 :     index = i + 1;
965 :     return true;
966 :     }
967 :     return false;
968 :     }
969 :    
970 :     public void forEachRemaining(LongConsumer consumer) {
971 :     if (consumer == null) throw new NullPointerException();
972 :     long i = index, f = fence;
973 :     if (i < f) {
974 :     index = f;
975 :     long o = origin, b = bound;
976 :     do {
977 :     consumer.accept(rng.internalNextLong(o, b));
978 :     } while (++i < f);
979 :     }
980 :     }
981 :    
982 :     }
983 :    
984 :     /**
985 :     * Spliterator for double streams.
986 :     */
987 : dl 1.11 static final class RandomDoublesSpliterator implements Spliterator.OfDouble {
988 : dl 1.1 final SplittableRandom rng;
989 :     long index;
990 :     final long fence;
991 :     final double origin;
992 :     final double bound;
993 :     RandomDoublesSpliterator(SplittableRandom rng, long index, long fence,
994 :     double origin, double bound) {
995 :     this.rng = rng; this.index = index; this.fence = fence;
996 :     this.origin = origin; this.bound = bound;
997 :     }
998 :    
999 :     public RandomDoublesSpliterator trySplit() {
1000 :     long i = index, m = (i + fence) >>> 1;
1001 :     return (m <= i) ? null :
1002 :     new RandomDoublesSpliterator(rng.split(), i, index = m, origin, bound);
1003 :     }
1004 :    
1005 :     public long estimateSize() {
1006 :     return fence - index;
1007 :     }
1008 :    
1009 :     public int characteristics() {
1010 :     return (Spliterator.SIZED | Spliterator.SUBSIZED |
1011 : dl 1.4 Spliterator.NONNULL | Spliterator.IMMUTABLE);
1012 : dl 1.1 }
1013 :    
1014 :     public boolean tryAdvance(DoubleConsumer consumer) {
1015 :     if (consumer == null) throw new NullPointerException();
1016 :     long i = index, f = fence;
1017 :     if (i < f) {
1018 :     consumer.accept(rng.internalNextDouble(origin, bound));
1019 :     index = i + 1;
1020 :     return true;
1021 :     }
1022 :     return false;
1023 :     }
1024 :    
1025 :     public void forEachRemaining(DoubleConsumer consumer) {
1026 :     if (consumer == null) throw new NullPointerException();
1027 :     long i = index, f = fence;
1028 :     if (i < f) {
1029 :     index = f;
1030 :     double o = origin, b = bound;
1031 :     do {
1032 :     consumer.accept(rng.internalNextDouble(o, b));
1033 :     } while (++i < f);
1034 :     }
1035 :     }
1036 :     }
1037 :    
1038 :     }

Doug Lea
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