Package it.unimi.dsi.util

Class XoShiRo256PlusRandomGenerator

java.lang.Object

org.apache.commons.math3.random.AbstractRandomGenerator

it.unimi.dsi.util.XoShiRo256PlusRandomGenerator

All Implemented Interfaces:

Serializable, RandomGenerator

public class XoShiRo256PlusRandomGenerator
extends AbstractRandomGenerator
implements Serializable

A fast, rock-solid pseudorandom number generator for floating-point generation. It has excellent speed, a state space (256 bits) that is large enough for any parallel application, and it is faster than XoShiRo256StarStarRandomGenerator. It passes all tests we are aware of except for the lowest three bits, which might fail linearity tests (and just those), so if low linear complexity is not considered an issue (as it is usually the case) it can be used to generate integer outputs, too. More information can be found at our PRNG page.

If you need a general PRNG, use XoShiRo256StarStarRandomGenerator. If you are tight on space, you might try XoRoShiRo128PlusRandomGenerator.

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.

Warning: before release 2.6.3, the split() method 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 split() is now different, and the result of split() is initialized in a different way.

Note that this is not a secure generator.

Version:

1.0

See Also:

• it.unimi.dsi.util
• RandomGenerator
• XoShiRo256PlusRandom
• Serialized Form

Constructor Summary

Constructors

Modifier	Constructor	Description
	XoShiRo256PlusRandomGenerator()	Creates a new generator seeded using Util.randomSeed().
	XoShiRo256PlusRandomGenerator(long seed)	Creates a new generator using a given seed.
protected	XoShiRo256PlusRandomGenerator(long s0, long s1, long s2, long s3)

Method Summary

Modifier and Type	Method	Description
XoShiRo256PlusRandomGenerator	copy()	Returns a copy of this generator.
XoShiRo256PlusRandomGenerator	jump()	The jump function for this generator.
protected XoShiRo256PlusRandomGenerator	jump(long[] jump)
XoShiRo256PlusRandomGenerator	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.
XoShiRo256PlusRandomGenerator	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 Details

XoShiRo256PlusRandomGenerator

protected XoShiRo256PlusRandomGenerator(long s0,
 long s1,
 long s2,
 long s3)

XoShiRo256PlusRandomGenerator

public XoShiRo256PlusRandomGenerator()

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

XoShiRo256PlusRandomGenerator

public XoShiRo256PlusRandomGenerator(long seed)

Creates a new generator using a given seed.

Parameters:

seed - a seed for the generator.

Method Details

copy

public XoShiRo256PlusRandomGenerator copy()

Returns a copy of this generator. The sequences produced by this generator and by the returned generator will be identical.

This method is particularly useful in conjunction with the jump() (or longJump()) method: by calling repeatedly jump().copy() over a generator it is possible to create several generators producing non-overlapping sequences.

Returns:

a copy of this generator.

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

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()

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

protected XoShiRo256PlusRandomGenerator jump(long[] jump)

jump

public XoShiRo256PlusRandomGenerator 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 XoShiRo256PlusRandomGenerator 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 XoShiRo256PlusRandomGenerator 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.

Warning: before release 2.6.3, this method 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 this instance after a call to this method is now different, and the returned instance is initialized in a different way.

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.

Specified by:

setSeed in interface RandomGenerator

Specified by:

setSeed in class AbstractRandomGenerator

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)