Package it.unimi.dsi.util

Class XorShift1024StarPhiRandomGenerator

java.lang.Object

org.apache.commons.math3.random.AbstractRandomGenerator

it.unimi.dsi.util.XorShift1024StarPhiRandomGenerator

All Implemented Interfaces:

java.io.Serializable, org.apache.commons.math3.random.RandomGenerator

public class XorShift1024StarPhiRandomGenerator
extends org.apache.commons.math3.random.AbstractRandomGenerator
implements java.io.Serializable

A fast, high-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 information can be found at our PRNG page.

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 SplittableRandom.

Note that this is not a secure generator.

See Also:

it.unimi.dsi.util, Random, XorShift1024StarPhiRandom, Serialized Form

Constructor Summary

Constructors

Constructor	Description
XorShift1024StarPhiRandomGenerator()	Creates a new generator seeded using Util.randomSeed().
XorShift1024StarPhiRandomGenerator(long seed)	Creates a new generator using a given seed.

Method Summary

Modifier and Type	Method	Description
void	jump()	The jump function for this generator.
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, int p)	Sets the state of this generator.
XorShift1024StarPhiRandomGenerator	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

XorShift1024StarPhiRandomGenerator

public XorShift1024StarPhiRandomGenerator()

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

XorShift1024StarPhiRandomGenerator

public XorShift1024StarPhiRandomGenerator(long seed)

Creates a new generator using a given seed.

Parameters:

seed - a seed for the generator.

Method Detail

nextLong

public long nextLong()

Specified by:

nextLong in interface org.apache.commons.math3.random.RandomGenerator

Overrides:

nextLong in class org.apache.commons.math3.random.AbstractRandomGenerator

nextInt

public int nextInt()

Specified by:

nextInt in interface org.apache.commons.math3.random.RandomGenerator

Overrides:

nextInt in class org.apache.commons.math3.random.AbstractRandomGenerator

nextInt

public int nextInt(int n)

Specified by:

nextInt in interface org.apache.commons.math3.random.RandomGenerator

Overrides:

nextInt in class org.apache.commons.math3.random.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 org.apache.commons.math3.random.RandomGenerator

Specified by:

nextDouble in class org.apache.commons.math3.random.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.

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 org.apache.commons.math3.random.RandomGenerator

Overrides:

nextFloat in class org.apache.commons.math3.random.AbstractRandomGenerator

nextBoolean

public boolean nextBoolean()

Specified by:

nextBoolean in interface org.apache.commons.math3.random.RandomGenerator

Overrides:

nextBoolean in class org.apache.commons.math3.random.AbstractRandomGenerator

nextBytes

public void nextBytes(byte[] bytes)

Specified by:

nextBytes in interface org.apache.commons.math3.random.RandomGenerator

Overrides:

nextBytes in class org.apache.commons.math3.random.AbstractRandomGenerator

jump

public void jump()

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 XorShift1024StarPhiRandomGenerator 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.

Specified by:

setSeed in interface org.apache.commons.math3.random.RandomGenerator

Specified by:

setSeed in class org.apache.commons.math3.random.AbstractRandomGenerator

Parameters:

seed - a seed for the generator.

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.