/** * Miscellaneous 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. * *

* Note that starting with Java 17 xoroshiro128++ and xoshiro256++ are * part of the package java.util.random. * *

* A table summarizing timings is provided below. The timings were measured on a 12th Gen Intel® * Core™ i7-12700KF @3.60GHz using * JMH * microbenchmarks on the * GraalVM virtual machine for Java 19 (release 22.3.0). * * * * * * * * *
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() * 14.522 * 0.699 * 0.536 * 0.518 * 0.817 * 0.937 * 0.732 * 0.911 * 0.852 * 0.760 * 0.776 * *
nextDouble() * 14.513 * 1.813 * 1.609 * 1.608 * 1.607 * 1.609 * 1.608 * 1.607 * 1.610 * 1.608 * 1.609 * *
nextInt(100000) * 7.652 * 1.329 * 1.368 * 1.194 * 1.322 * 1.428 * 1.216 * 1.751 * 1.763 * 1.990 * 1.286 * *
nextInt(230+1) * 16.291 * 10.722 * 9.639 * 1.260 * 1.348 * 1.471 * 1.240 * 1.851 * 1.862 * 1.890 * 1.351 * *
* *

* 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;