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src.it.unimi.dsi.util.package-info Maven / Gradle / Ivy

/**
 * 
Miscellaneaous utility classes.
 *
 * 
Pseudorandom number generators
 *
 * 
Warning: before release 2.6.3, the {@code split()} method of all generators
 * would not alter the state of the caller, and it would return instances initialized in the same
 * way if called multiple times. This was a major mistake in the implementation and it has been fixed,
 * but as a consequence the output of the caller after a call to {@code split()} is
 * now different, and the result of {@code split()} is initialized in a different way.
 *
 * 
We provide a number of fast, high-quality PRNGs with different features. You can get detailed
 * information about the generators at our PRNG page, together
 * with a reasoned guide to the choice of the generator that's right for you.
 *
 * 
A table summarizing timings is provided below. The timings were measured on an
 * Intel® Core™ i7-8700B CPU @3.20GHz using
 * JMH microbenchmarks. The JMH timings were decreased by 1ns, as
 * using the low-level {@code perfasm} profiler the JMH overhead was estimated at ≈1ns per call.
 *
 * 
 * 
 * 
Timings in nanoseconds for a few generators

 * 
{@link java.util.Random Random}
 * 
{@link java.util.concurrent.ThreadLocalRandom ThreadLocalRandom}
 * 
{@link java.util.SplittableRandom SplittableRandom}
 * 
{@link it.unimi.dsi.util.SplitMix64RandomGenerator SplitMix64}
 * 
{@link it.unimi.dsi.util.XoRoShiRo128PlusPlusRandom xoroshiro128++}
 * 
{@link it.unimi.dsi.util.XoRoShiRo128StarStarRandom xoroshiro128**}
 * 
{@link it.unimi.dsi.util.XoRoShiRo128PlusRandom xoroshiro128+}
 * 
{@link it.unimi.dsi.util.XoShiRo256PlusPlusRandom xoshiro256++}
 * 
{@link it.unimi.dsi.util.XoShiRo256StarStarRandom xoshiro256**}
 * 
{@link it.unimi.dsi.util.XoShiRo256PlusRandom xoshiro256+}
 * 
{@link it.unimi.dsi.util.XorShift1024StarPhiRandom xorshift1024*φ}
 *
 * 
nextLong()                                 
14.419
1.252
1.283
1.241
1.428
1.574
1.295
1.738
1.884
1.653
1.901
 * 
nextInt(100000)                            
6.715
2.045
2.499
2.543
2.336
2.594
1.202
2.607
2.954
2.367
3.119
 * 
nextDouble()                               
14.458
1.876
2.161
2.176
1.918
2.219
1.853
2.304
2.503
2.112
2.755
 * 
 *
 * 
Note that generators that are extremely fast in C, such as xoshiro256+, do not perform particularly well in Java, most likely
 * because of the cost of accessing variables, which rises as the size of the state space grows. Indeed,
 * smaller-state generators are faster. Moreover, generators based on the ++
 * scrambler are slightly faster than those based on the ** scrambler, contrarily to what happens in C.
 *
 * 
For each generator, we provide a version that extends {@link java.util.Random}, overriding (as usual) the {@link java.util.Random#next(int) next(int)} method. Nonetheless,
 * since the generators are all inherently 64-bit also {@link java.util.Random#nextInt() nextInt()}, {@link java.util.Random#nextFloat() nextFloat()},
 * {@link java.util.Random#nextLong() nextLong()}, {@link java.util.Random#nextDouble() nextDouble()}, {@link java.util.Random#nextBoolean() nextBoolean()}
 * and {@link java.util.Random#nextBytes(byte[]) nextBytes(byte[])} have been overridden for speed (preserving, of course, {@link java.util.Random}'s semantics).
 *
 * 
If you do not need an instance of {@link java.util.Random}, or if you need a {@link org.apache.commons.math3.random.RandomGenerator} to use
 * with Commons Math, there is for each generator a corresponding {@link org.apache.commons.math3.random.RandomGenerator RandomGenerator}
 * implementation, which indeed we suggest to use in general if you do not need a generator implementing {@link java.util.Random}.
 */

package it.unimi.dsi.util;