it.unimi.dsi.util

Class XorRShR128PlusRandomGenerator

java.lang.Object

org.apache.commons.math3.random.AbstractRandomGenerator

it.unimi.dsi.util.XorRShR128PlusRandomGenerator

All Implemented Interfaces:

RandomGenerator

public class XorRShR128PlusRandomGenerator
extends AbstractRandomGenerator

An unbelievably fast, top-quality pseudorandom number generator that returns the sum of consecutive outputs of a Marsaglia Xorshift generator (described in “Xorshift RNGs”, Journal of Statistical Software, 8:1−6, 2003) with 128 bits of state.

More details can be found in my paper “Further scramblings of Marsaglia's xorshift generators”, 2015, and on the xorshift*/xorshift+ generators and the PRNG shootout page. The basic idea is taken from Mutsuo Saito and Makuto Matsumoto's XSadd generator, which is however based on 32-bit shifts and fails several statistical tests when reversed.

Note that this is not a cryptographic-strength pseudorandom number generator, but its quality is preposterously higher than Random's, and its cycle length is 2¹²⁸ − 1, which is more than enough for any single-thread application.

By using the supplied jump() method it is possible to generate non-overlapping long sequences for parallel computations. This class provides also a split() method to support recursive parallel computations, in the spirit of Java 8's SplittableRandom.

See Also:

it.unimi.dsi.util, Random, XorShift128PlusRandom

Constructor Summary

Constructors

Constructor and Description
XorRShR128PlusRandomGenerator() Creates a new generator seeded using Util.randomSeed().
XorRShR128PlusRandomGenerator(long seed) Creates a new generator using a given seed.

Method Summary

Modifier and Type	Method and Description
void	jump() The the jump function for this generator.
static void	main(String[] arg)
boolean	nextBoolean()
void	nextBytes(byte[] bytes)
double	nextDouble()
float	nextFloat()
int	nextInt()
int	nextInt(int n)
long	nextLong()
long	nextLong(long n) Returns a pseudorandom uniformly distributed long value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.
void	setSeed(long seed) Sets the seed of this generator.
void	setState(long[] state) Sets the state of this generator.
XorRShR128PlusRandomGenerator	split() Returns a new instance that shares no mutable state with this instance.

Methods inherited from class org.apache.commons.math3.random.AbstractRandomGenerator

clear, nextGaussian, setSeed, setSeed

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

XorRShR128PlusRandomGenerator

public XorRShR128PlusRandomGenerator()

Creates a new generator seeded using Util.randomSeed().

XorRShR128PlusRandomGenerator

public XorRShR128PlusRandomGenerator(long seed)

Creates a new generator using a given seed.

Parameters:

seed - a nonzero seed for the generator (if zero, the generator will be seeded with -1).

Method Detail

nextLong

public long nextLong()

Specified by:

nextLong in interface RandomGenerator

Overrides:

nextLong in class AbstractRandomGenerator

nextInt

public int nextInt()

Specified by:

nextInt in interface RandomGenerator

Overrides:

nextInt in class AbstractRandomGenerator

nextInt

public int nextInt(int n)

Specified by:

nextInt in interface RandomGenerator

Overrides:

nextInt in class AbstractRandomGenerator

nextLong

public long nextLong(long n)

Returns a pseudorandom uniformly distributed long value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The algorithm used to generate the value guarantees that the result is uniform, provided that the sequence of 64-bit values produced by this generator is.

Parameters:

n - the positive bound on the random number to be returned.

Returns:

the next pseudorandom long value between 0 (inclusive) and n (exclusive).

nextDouble

public double nextDouble()

Specified by:

nextDouble in interface RandomGenerator

Specified by:

nextDouble in class AbstractRandomGenerator

nextFloat

public float nextFloat()

Specified by:

nextFloat in interface RandomGenerator

Overrides:

nextFloat in class AbstractRandomGenerator

nextBoolean

public boolean nextBoolean()

Specified by:

nextBoolean in interface RandomGenerator

Overrides:

nextBoolean in class AbstractRandomGenerator

nextBytes

public void nextBytes(byte[] bytes)

Specified by:

nextBytes in interface RandomGenerator

Overrides:

nextBytes in class AbstractRandomGenerator

jump

public void jump()

The the jump function for this generator. It is equivalent to 2⁶⁴ calls to nextLong(); it can be used to generate 2⁶⁴ non-overlapping subsequences for parallel computations.

split

public XorRShR128PlusRandomGenerator split()

Returns a new instance that shares no mutable state with this instance. The sequence generated by the new instance depends deterministically from the state of this instance, but the possibility that the sequence generated by this instance and by the new instance overlap is negligible.

Returns:

the new instance.

setSeed

public void setSeed(long seed)

Sets the seed of this generator.

The argument will be used to seed a SplitMix64RandomGenerator, whose output will in turn be used to seed this generator. This approach makes “warmup” unnecessary, and makes the possibility of starting from a state with a large fraction of bits set to zero astronomically small.

Specified by:

setSeed in interface RandomGenerator

Specified by:

setSeed in class AbstractRandomGenerator

Parameters:

seed - a nonzero seed for this generator.

setState

public void setState(long[] state)

Sets the state of this generator.

The internal state of the generator will be reset, and the state array filled with the provided array.

Parameters:

state - an array of 2 longs; at least one must be nonzero.

main

public static void main(String[] arg)