it.unimi.dsi.util

Class XorShift1024StarRandom

java.lang.Object

java.util.Random

it.unimi.dsi.util.XorShift1024StarRandom

All Implemented Interfaces:

Serializable

public class XorShift1024StarRandom
extends Random

A fast, top-quality pseudorandom number generator that combines a long-period instance of George Marsaglia's Xorshift generators (described in “Xorshift RNGs”, Journal of Statistical Software, 8:1−6, 2003) with a multiplication.

More details can be found in my paper “An experimental exploration of Marsaglia's xorshift generators, scrambled”, ACM Trans. Math. Softw., 2016, and on the xoroshiro+/xorshift*/xorshift+ generators and the PRNG shootout page.

Note that this is not a cryptographic-strength pseudorandom number generator. Its period is 2¹⁰²⁴ − 1, which is more than enough for any massive parallel application (it is actually possible to define analogously a generator with period 2⁴⁰⁹⁶ − 1, but its interest is eminently academic).

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, XorShift1024StarRandomGenerator, Serialized Form

Constructor Summary

Constructors

Constructor and Description
XorShift1024StarRandom() Creates a new generator seeded using Util.randomSeed().
XorShift1024StarRandom(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.
protected int	next(int bits)
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, int p) Sets the state of this generator.
XorShift1024StarRandom	split() Returns a new instance that shares no mutable state with this instance.

Methods inherited from class java.util.Random

doubles, doubles, doubles, doubles, ints, ints, ints, ints, longs, longs, longs, longs, nextGaussian

Methods inherited from class java.lang.Object

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

Constructor Detail

XorShift1024StarRandom

public XorShift1024StarRandom()

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

XorShift1024StarRandom

public XorShift1024StarRandom(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

next

protected int next(int bits)

Overrides:

next in class Random

nextLong

public long nextLong()

Overrides:

nextLong in class Random

nextInt

public int nextInt()

Overrides:

nextInt in class Random

nextInt

public int nextInt(int n)

Overrides:

nextInt in class Random

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()

Overrides:

nextDouble in class Random

nextFloat

public float nextFloat()

Overrides:

nextFloat in class Random

nextBoolean

public boolean nextBoolean()

Overrides:

nextBoolean in class Random

nextBytes

public void nextBytes(byte[] bytes)

Overrides:

nextBytes in class Random

jump

public void jump()

The the jump function for this generator. It is equivalent to 2⁵¹² calls to nextLong(); it can be used to generate 2⁵¹² non-overlapping subsequences for parallel computations.

split

public XorShift1024StarRandom 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 probability 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 probability of starting from a state with a large fraction of bits set to zero astronomically small.

Overrides:

setSeed in class Random

Parameters:

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

setState

public void setState(long[] state,
                     int p)

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 16 longs; at least one must be nonzero.

p - the internal index.