Package it.unimi.dsi.util

Class XoShiRo256StarStarRandom

java.lang.Object

java.util.Random

it.unimi.dsi.util.XoShiRo256StarStarRandom

All Implemented Interfaces:

Serializable

public class XoShiRo256StarStarRandom
extends Random

A fast, all-purpose, rock-solid pseudorandom number generator. It has excellent speed, a state space (256 bits) that is large enough for any parallel application, and it passes all tests we are aware of. In Java, it is slightly slower than a XoShiRo256PlusPlusRandom. More information can be found at our PRNG page.

If you need to generate just floating-point numbers, XoShiRo256PlusRandom is slightly faster. If you are tight on space, you might try XoRoShiRo128StarStarRandom.

By using the supplied jump() method it is possible to generate non-overlapping long sequences for parallel computations; longJump() makes it possible to create several starting points, each providing several non-overlapping sequences, for distributed computations. This class provides also a split() method to support recursive parallel computations, in the spirit of SplittableRandom.

Note that this is not a secure generator.

Version:

1.0

See Also:

it.unimi.dsi.util, RandomGenerator, XoShiRo256StarStarRandomGenerator, Serialized Form

Constructor Summary

Constructors

Constructor	Description
XoShiRo256StarStarRandom()	Creates a new generator seeded using Util.randomSeed().
XoShiRo256StarStarRandom(long seed)	Creates a new generator using a given seed.

Method Summary

Modifier and Type	Method	Description
XoShiRo256StarStarRandom	jump()	The jump function for this generator.
XoShiRo256StarStarRandom	longJump()	The long-jump function for this generator.
static void	main(String[] arg)
boolean	nextBoolean()
void	nextBytes(byte[] bytes)
double	nextDouble()
double	nextDoubleFast()	Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence, using a fast multiplication-free method which, however, can provide only 52 significant bits.
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.
XoShiRo256StarStarRandom	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, next, nextGaussian

Methods inherited from class java.lang.Object

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

Constructor Detail

XoShiRo256StarStarRandom

public XoShiRo256StarStarRandom()

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

XoShiRo256StarStarRandom

public XoShiRo256StarStarRandom(long seed)

Creates a new generator using a given seed.

Parameters:

seed - a seed for the generator.

Method Detail

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

nextDoubleFast

public double nextDoubleFast()

Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence, using a fast multiplication-free method which, however, can provide only 52 significant bits.

This method is faster than nextDouble(), but it can return only dyadic rationals of the form k / 2⁻⁵², instead of the standard k / 2⁻⁵³. Before version 2.4.1, this was actually the standard implementation of nextDouble(), so you can use this method if you need to reproduce exactly results obtained using previous versions.

The only difference between the output of this method and that of nextDouble() is an additional least significant bit set in half of the returned values. For most applications, this difference is negligible.

Returns:

the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence, using 52 significant bits only.

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 XoShiRo256StarStarRandom jump()

The jump function for this generator. It is equivalent to 2¹²⁸ calls to nextLong(); it can be used to generate 2¹²⁸ non-overlapping subsequences for parallel computations.

Returns:

this generator.

See Also:

#copy()

longJump

public XoShiRo256StarStarRandom longJump()

The long-jump function for this generator. It is equivalent to 2¹⁹² calls to nextLong(); it can be used to generate 2⁶⁴ starting points, from each of which jump() will generate 2⁶⁴ non-overlapping subsequences for parallel distributed computations.

Returns:

this generator.

See Also:

#copy()

split

public XoShiRo256StarStarRandom 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 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)