it.unimi.dsi.util

Class XorShift128PlusRandom

java.lang.Object

java.util.Random

it.unimi.dsi.util.XorShift128PlusRandom

All Implemented Interfaces:

Serializable

public class XorShift128PlusRandom
extends Random

An unbelievably fast, top-quality 64-bit 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). This is the fastest generator we provide that passes the BigCrush statistical test suite; it is so fast that we can affort a truly uniform nextInt(int) method, instead of relying on the very-slightly-biased-but-fast approximation of XorShift64StarRandom.nextInt(int).

More details about xorshift+ generators can be found in my paper “Further scramblings of Marsaglia's xorshift generators”, 2014. 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.

On an Intel® Core™ i7-4770 CPU @3.40GHz (Haswell), all methods of this class except for nextInt() are faster than those of ThreadLocalRandom (available only from Java 7). See the table in the documentation of XorShift64StarRandom for more details.

This is a top-quality generator: for instance, it performs much better than WELL1024a or MT19937 in the TestU01 BigCrush suite. More details can be found on the xorshift*/xorshift+ generators and the PRNG shootout page.

If you need a longer period, consider using XorShift1024StarRandom or XorShift1024StarRandomGenerator.

See Also:

XorShift128PlusRandomGenerator, Serialized Form

Constructor Summary

Constructors

Constructor and Description
XorShift128PlusRandom() Creates a new generator seeded using Util.randomSeed().
XorShift128PlusRandom(long seed) Creates a new generator using a given seed.

Method Summary

Methods

Modifier and Type	Method and Description
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.

Methods inherited from class java.util.Random

next, nextGaussian

Methods inherited from class java.lang.Object

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

Constructor Detail

XorShift128PlusRandom

public XorShift128PlusRandom()

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

XorShift128PlusRandom

public XorShift128PlusRandom(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()

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

setSeed

public void setSeed(long seed)

Sets the seed of this generator.

The seed will be passed twice through HashCommon.murmurHash3(long). In this way, if the user passes a small value we will avoid the short irregular transient associated with states with a very small number of bits set.

Overrides:

setSeed in class Random

Parameters:

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

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 16 longs; at least one must be nonzero.