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Comparing jsr166/src/main/java/util/SplittableRandom.java (file contents):
Revision 1.20 by jsr166, Sat Aug 24 06:20:15 2013 UTC vs.
Revision 1.31 by jsr166, Fri Feb 19 03:39:15 2016 UTC

#	Line 25 | Line 25
25
26		package java.util;
27
28	–	import java.security.SecureRandom;
29	–	import java.net.InetAddress;
28		import java.util.concurrent.atomic.AtomicLong;
29	+	import java.util.function.DoubleConsumer;
30		import java.util.function.IntConsumer;
31		import java.util.function.LongConsumer;
32	<	import java.util.function.DoubleConsumer;
34	<	import java.util.stream.StreamSupport;
32	>	import java.util.stream.DoubleStream;
33		import java.util.stream.IntStream;
34		import java.util.stream.LongStream;
35	<	import java.util.stream.DoubleStream;
35	>	import java.util.stream.StreamSupport;
36
37		/**
38		* A generator of uniform pseudorandom values applicable for use in
#	Line 54 | Line 52 | import java.util.stream.DoubleStream;
52		* types and ranges, but similar properties are expected to hold, at
53		* least approximately, for others as well. The <em>period</em>
54		* (length of any series of generated values before it repeats) is at
55	<	* least 2<sup>64</sup>. </li>
55	>	* least 2<sup>64</sup>.
56		*
57	<	* <li> Method {@link #split} constructs and returns a new
57	>	* <li>Method {@link #split} constructs and returns a new
58		* SplittableRandom instance that shares no mutable state with the
59		* current instance. However, with very high probability, the
60		* values collectively generated by the two objects have the same
61		* statistical properties as if the same quantity of values were
62		* generated by a single thread using a single {@code
63	<	* SplittableRandom} object.  </li>
63	>	* SplittableRandom} object.
64		*
65		* <li>Instances of SplittableRandom are <em>not</em> thread-safe.
66		* They are designed to be split, not shared, across threads. For
#	Line 73 | Line 71 | import java.util.stream.DoubleStream;
71		*
72		* <li>This class provides additional methods for generating random
73		* streams, that employ the above techniques when used in {@code
74	<	* stream.parallel()} mode.</li>
74	>	* stream.parallel()} mode.
75		*
76		* </ul>
77		*
#	Line 88 | Line 86 | import java.util.stream.DoubleStream;
86		* @author  Doug Lea
87		* @since   1.8
88		*/
89	<	public class SplittableRandom {
89	>	public final class SplittableRandom {
90
91		/*
92		* Implementation Overview.
#	Line 108 | Line 106 | public class SplittableRandom {
106		* Methods nextLong, nextInt, and derivatives do not return the
107		* sequence (seed) values, but instead a hash-like bit-mix of
108		* their bits, producing more independently distributed sequences.
109	<	* For nextLong, the mix64 bit-mixing function computes the same
110	<	* value as the "64-bit finalizer" function in Austin Appleby's
111	<	* MurmurHash3 algorithm.  See
112	<	* http://code.google.com/p/smhasher/wiki/MurmurHash3 , which
113	<	* comments: "The constants for the finalizers were generated by a
114	<	* simple simulated-annealing algorithm, and both avalanche all
115	<	* bits of 'h' to within 0.25% bias." The mix32 function is
118	<	* equivalent to (int)(mix64(seed) >>> 32), but faster because it
119	<	* omits a step that doesn't contribute to result.
109	>	* For nextLong, the mix64 function is based on David Stafford's
110	>	* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html)
111	>	* "Mix13" variant of the "64-bit finalizer" function in Austin
112	>	* Appleby's MurmurHash3 algorithm (see
113	>	* http://code.google.com/p/smhasher/wiki/MurmurHash3). The mix32
114	>	* function is based on Stafford's Mix04 mix function, but returns
115	>	* the upper 32 bits cast as int.
116		*
117		* The split operation uses the current generator to form the seed
118		* and gamma for another SplittableRandom.  To conservatively
119		* avoid potential correlations between seed and value generation,
120	<	* gamma selection (method nextGamma) uses the "Mix13" constants
121	<	* for MurmurHash3 described by David Stafford
122	<	* (http://zimbry.blogspot.com/2011/09/better-bit-mixing-improving-on.html)
123	<	* To avoid potential weaknesses in bit-mixing transformations, we
124	<	* restrict gammas to odd values with at least 12 and no more than
125	<	* 52 bits set.  Rather than rejecting candidates with too few or
126	<	* too many bits set, method nextGamma flips some bits (which has
127	<	* the effect of mapping at most 4 to any given gamma value).
132	<	* This reduces the effective set of 64bit odd gamma values by
133	<	* about 2<sup>14</sup>, a very tiny percentage, and serves as an
120	>	* gamma selection (method mixGamma) uses different
121	>	* (Murmurhash3's) mix constants.  To avoid potential weaknesses
122	>	* in bit-mixing transformations, we restrict gammas to odd values
123	>	* with at least 24 0-1 or 1-0 bit transitions.  Rather than
124	>	* 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
128		* automated screening for sequence constant selection that is
129		* left as an empirical decision in some other hashing and crypto
130		* algorithms.
#	Line 141 | Line 135 | public class SplittableRandom {
135		* avalanching.
136		*
137		* The default (no-argument) constructor, in essence, invokes
138	<	* 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	<	* java.util.secureRandomSeed property is set. This serves as a
144	<	* slimmed-down (and insecure) variant of SecureRandom that also
145	<	* 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		*
147		* It is a relatively simple matter to apply the basic design here
148		* to use 128 bit seeds. However, emulating 128bit arithmetic and
#	Line 161 | Line 155 | public class SplittableRandom {
155		*/
156
157		/**
158	<	* The initial gamma value for (unsplit) SplittableRandoms. Must
159	<	* be odd with at least 12 and no more than 52 bits set. Currently
166	<	* 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		*/
161	<	private static final long INITIAL_GAMMA = 0x9e3779b97f4a7c15L;
161	>	private static final long GOLDEN_GAMMA = 0x9e3779b97f4a7c15L;
162
163		/**
164		* The least non-zero value returned by nextDouble(). This value
165		* is scaled by a random value of 53 bits to produce a result.
166		*/
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
169		/**
170		* The seed. Updated only via method nextSeed.
#	Line 192 | Line 185 | public class SplittableRandom {
185		}
186
187		/**
188	<	* Computes MurmurHash3 64bit mix function.
188	>	* Computes Stafford variant 13 of 64bit mix function.
189		*/
190		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
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		}
203
204		/**
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		}
214
215		/**
#	Line 229 | Line 222 | public class SplittableRandom {
222		/**
223		* The seed generator for default constructors.
224		*/
225	<	private static final AtomicLong seeder = new AtomicLong(initialSeed());
225	>	private static final AtomicLong defaultGen = new AtomicLong(initialSeed());
226
227		private static long initialSeed() {
228	<	try {  // ignore exceptions in accessing/parsing properties
229	<	String pp = System.getProperty
230	<	("java.util.secureRandomSeed");
231	<	if (pp != null && pp.equalsIgnoreCase("true")) {
232	<	byte[] seedBytes = java.security.SecureRandom.getSeed(8);
233	<	long s = (long)(seedBytes[0]) & 0xffL;
234	<	for (int i = 1; i < 8; ++i)
235	<	s = (s << 8) | ((long)(seedBytes[i]) & 0xffL);
236	<	return s;
237	<	}
245	<	} catch (Exception ignore) {
246	<	}
247	<	int hh = 0; // hashed host address
248	<	try {
249	<	hh = InetAddress.getLocalHost().hashCode();
250	<	} catch (Exception ignore) {
228	>	if (java.security.AccessController.doPrivileged(
229	>	new java.security.PrivilegedAction<Boolean>() {
230	>	public Boolean run() {
231	>	return Boolean.getBoolean("java.util.secureRandomSeed");
232	>	}})) {
233	>	byte[] seedBytes = java.security.SecureRandom.getSeed(8);
234	>	long s = (long)seedBytes[0] & 0xffL;
235	>	for (int i = 1; i < 8; ++i)
236	>	s = (s << 8) | ((long)seedBytes[i] & 0xffL);
237	>	return s;
238		}
239	<	return (mix64((((long)hh) << 32) ^ System.currentTimeMillis()) ^
239	>	return (mix64(System.currentTimeMillis()) ^
240		mix64(System.nanoTime()));
241		}
242
243		// IllegalArgumentException messages
244	<	static final String BadBound = "bound must be positive";
245	<	static final String BadRange = "bound must be greater than origin";
246	<	static final String BadSize  = "size must be non-negative";
244	>	static final String BAD_BOUND = "bound must be positive";
245	>	static final String BAD_RANGE = "bound must be greater than origin";
246	>	static final String BAD_SIZE  = "size must be non-negative";
247
248		/*
249		* Internal versions of nextX methods used by streams, as well as
#	Line 377 | Line 364 | public class SplittableRandom {
364		* @param seed the initial seed
365		*/
366		public SplittableRandom(long seed) {
367	<	this(seed, INITIAL_GAMMA);
367	>	this(seed, GOLDEN_GAMMA);
368		}
369
370		/**
#	Line 386 | Line 373 | public class SplittableRandom {
373		* of those of any other instances in the current program; and
374		* may, and typically does, vary across program invocations.
375		*/
376	<	public SplittableRandom() { // emulate seeder.split()
377	<	this.gamma = nextGamma(this.seed = seeder.addAndGet(INITIAL_GAMMA));
376	>	public SplittableRandom() { // emulate defaultGen.split()
377	>	long s = defaultGen.getAndAdd(2 * GOLDEN_GAMMA);
378	>	this.seed = mix64(s);
379	>	this.gamma = mixGamma(s + GOLDEN_GAMMA);
380		}
381
382		/**
#	Line 405 | Line 394 | public class SplittableRandom {
394		* @return the new SplittableRandom instance
395		*/
396		public SplittableRandom split() {
397	<	long s = nextSeed();
409	<	return new SplittableRandom(s, nextGamma(s));
397	>	return new SplittableRandom(nextLong(), mixGamma(nextSeed()));
398		}
399
400		/**
#	Line 429 | Line 417 | public class SplittableRandom {
417		*/
418		public int nextInt(int bound) {
419		if (bound <= 0)
420	<	throw new IllegalArgumentException(BadBound);
420	>	throw new IllegalArgumentException(BAD_BOUND);
421		// Specialize internalNextInt for origin 0
422		int r = mix32(nextSeed());
423		int m = bound - 1;
#	Line 457 | Line 445 | public class SplittableRandom {
445		*/
446		public int nextInt(int origin, int bound) {
447		if (origin >= bound)
448	<	throw new IllegalArgumentException(BadRange);
448	>	throw new IllegalArgumentException(BAD_RANGE);
449		return internalNextInt(origin, bound);
450		}
451
#	Line 481 | Line 469 | public class SplittableRandom {
469		*/
470		public long nextLong(long bound) {
471		if (bound <= 0)
472	<	throw new IllegalArgumentException(BadBound);
472	>	throw new IllegalArgumentException(BAD_BOUND);
473		// Specialize internalNextLong for origin 0
474		long r = mix64(nextSeed());
475		long m = bound - 1;
#	Line 509 | Line 497 | public class SplittableRandom {
497		*/
498		public long nextLong(long origin, long bound) {
499		if (origin >= bound)
500	<	throw new IllegalArgumentException(BadRange);
500	>	throw new IllegalArgumentException(BAD_RANGE);
501		return internalNextLong(origin, bound);
502		}
503
#	Line 535 | Line 523 | public class SplittableRandom {
523		*/
524		public double nextDouble(double bound) {
525		if (!(bound > 0.0))
526	<	throw new IllegalArgumentException(BadBound);
526	>	throw new IllegalArgumentException(BAD_BOUND);
527		double result = (mix64(nextSeed()) >>> 11) * DOUBLE_UNIT * bound;
528		return (result < bound) ?  result : // correct for rounding
529		Double.longBitsToDouble(Double.doubleToLongBits(bound) - 1);
#	Line 554 | Line 542 | public class SplittableRandom {
542		*/
543		public double nextDouble(double origin, double bound) {
544		if (!(origin < bound))
545	<	throw new IllegalArgumentException(BadRange);
545	>	throw new IllegalArgumentException(BAD_RANGE);
546		return internalNextDouble(origin, bound);
547		}
548
#	Line 582 | Line 570 | public class SplittableRandom {
570		*/
571		public IntStream ints(long streamSize) {
572		if (streamSize < 0L)
573	<	throw new IllegalArgumentException(BadSize);
573	>	throw new IllegalArgumentException(BAD_SIZE);
574		return StreamSupport.intStream
575		(new RandomIntsSpliterator
576		(this, 0L, streamSize, Integer.MAX_VALUE, 0),
#	Line 623 | Line 611 | public class SplittableRandom {
611		public IntStream ints(long streamSize, int randomNumberOrigin,
612		int randomNumberBound) {
613		if (streamSize < 0L)
614	<	throw new IllegalArgumentException(BadSize);
614	>	throw new IllegalArgumentException(BAD_SIZE);
615		if (randomNumberOrigin >= randomNumberBound)
616	<	throw new IllegalArgumentException(BadRange);
616	>	throw new IllegalArgumentException(BAD_RANGE);
617		return StreamSupport.intStream
618		(new RandomIntsSpliterator
619		(this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
#	Line 649 | Line 637 | public class SplittableRandom {
637		*/
638		public IntStream ints(int randomNumberOrigin, int randomNumberBound) {
639		if (randomNumberOrigin >= randomNumberBound)
640	<	throw new IllegalArgumentException(BadRange);
640	>	throw new IllegalArgumentException(BAD_RANGE);
641		return StreamSupport.intStream
642		(new RandomIntsSpliterator
643		(this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
#	Line 668 | Line 656 | public class SplittableRandom {
656		*/
657		public LongStream longs(long streamSize) {
658		if (streamSize < 0L)
659	<	throw new IllegalArgumentException(BadSize);
659	>	throw new IllegalArgumentException(BAD_SIZE);
660		return StreamSupport.longStream
661		(new RandomLongsSpliterator
662		(this, 0L, streamSize, Long.MAX_VALUE, 0L),
#	Line 709 | Line 697 | public class SplittableRandom {
697		public LongStream longs(long streamSize, long randomNumberOrigin,
698		long randomNumberBound) {
699		if (streamSize < 0L)
700	<	throw new IllegalArgumentException(BadSize);
700	>	throw new IllegalArgumentException(BAD_SIZE);
701		if (randomNumberOrigin >= randomNumberBound)
702	<	throw new IllegalArgumentException(BadRange);
702	>	throw new IllegalArgumentException(BAD_RANGE);
703		return StreamSupport.longStream
704		(new RandomLongsSpliterator
705		(this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
#	Line 735 | Line 723 | public class SplittableRandom {
723		*/
724		public LongStream longs(long randomNumberOrigin, long randomNumberBound) {
725		if (randomNumberOrigin >= randomNumberBound)
726	<	throw new IllegalArgumentException(BadRange);
726	>	throw new IllegalArgumentException(BAD_RANGE);
727		return StreamSupport.longStream
728		(new RandomLongsSpliterator
729		(this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
#	Line 754 | Line 742 | public class SplittableRandom {
742		*/
743		public DoubleStream doubles(long streamSize) {
744		if (streamSize < 0L)
745	<	throw new IllegalArgumentException(BadSize);
745	>	throw new IllegalArgumentException(BAD_SIZE);
746		return StreamSupport.doubleStream
747		(new RandomDoublesSpliterator
748		(this, 0L, streamSize, Double.MAX_VALUE, 0.0),
#	Line 797 | Line 785 | public class SplittableRandom {
785		public DoubleStream doubles(long streamSize, double randomNumberOrigin,
786		double randomNumberBound) {
787		if (streamSize < 0L)
788	<	throw new IllegalArgumentException(BadSize);
788	>	throw new IllegalArgumentException(BAD_SIZE);
789		if (!(randomNumberOrigin < randomNumberBound))
790	<	throw new IllegalArgumentException(BadRange);
790	>	throw new IllegalArgumentException(BAD_RANGE);
791		return StreamSupport.doubleStream
792		(new RandomDoublesSpliterator
793		(this, 0L, streamSize, randomNumberOrigin, randomNumberBound),
#	Line 823 | Line 811 | public class SplittableRandom {
811		*/
812		public DoubleStream doubles(double randomNumberOrigin, double randomNumberBound) {
813		if (!(randomNumberOrigin < randomNumberBound))
814	<	throw new IllegalArgumentException(BadRange);
814	>	throw new IllegalArgumentException(BAD_RANGE);
815		return StreamSupport.doubleStream
816		(new RandomDoublesSpliterator
817		(this, 0L, Long.MAX_VALUE, randomNumberOrigin, randomNumberBound),
#	Line 838 | Line 826 | public class SplittableRandom {
826		* approach. The long and double versions of this class are
827		* identical except for types.
828		*/
829	<	static final class RandomIntsSpliterator implements Spliterator.OfInt {
829	>	private static final class RandomIntsSpliterator
830	>	implements Spliterator.OfInt {
831		final SplittableRandom rng;
832		long index;
833		final long fence;
#	Line 893 | Line 882 | public class SplittableRandom {
882		/**
883		* Spliterator for long streams.
884		*/
885	<	static final class RandomLongsSpliterator implements Spliterator.OfLong {
885	>	private static final class RandomLongsSpliterator
886	>	implements Spliterator.OfLong {
887		final SplittableRandom rng;
888		long index;
889		final long fence;
#	Line 949 | Line 939 | public class SplittableRandom {
939		/**
940		* Spliterator for double streams.
941		*/
942	<	static final class RandomDoublesSpliterator implements Spliterator.OfDouble {
942	>	private static final class RandomDoublesSpliterator
943	>	implements Spliterator.OfDouble {
944		final SplittableRandom rng;
945		long index;
946		final long fence;

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