Class MiddleSquareWeylSequence

java.lang.Object

org.apache.commons.rng.core.BaseProvider

org.apache.commons.rng.core.source32.IntProvider

org.apache.commons.rng.core.source32.MiddleSquareWeylSequence

All Implemented Interfaces:

RandomIntSource, RestorableUniformRandomProvider, UniformRandomProvider

public class MiddleSquareWeylSequence
extends IntProvider

Middle Square Weyl Sequence Random Number Generator.

A fast all-purpose 32-bit generator. Memory footprint is 192 bits and the period is at least 2^64.

Implementation is based on the paper Middle Square Weyl Sequence RNG.

Since:

1.3

See Also:

• Middle Square Method

Field Summary

Fields

Modifier and Type	Field	Description
private static final long[]	DEFAULT_SEED	The default seed.
private long	s	Increment for the Weyl sequence.
private static final int	SEED_SIZE	Size of the seed array.
private long	w	State of the Weyl sequence.
private long	x	State of the generator.

Constructor Summary

Constructors

Constructor	Description
MiddleSquareWeylSequence(long[] seed)	Creates a new instance.

Method Summary

Modifier and Type	Method	Description
protected byte[]	getStateInternal()	Creates a snapshot of the RNG state.
int	next()	Return the next random value.
long	nextLong()	Generates a long value.
private void	setSeedInternal(long[] seed)	Seeds the RNG.
protected void	setStateInternal(byte[] state)	Resets the RNG to the given state.

Methods inherited from class IntProvider

nextBoolean, nextBytes, nextBytes, nextBytesFill, nextDouble, nextInt, resetCachedState

Methods inherited from class BaseProvider

checkIndex, checkStateSize, composeStateInternal, extendSeed, extendSeed, fillState, fillState, restoreState, saveState, splitStateInternal, toString

Methods inherited from class Object

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

Methods inherited from interface UniformRandomProvider

doubles, doubles, doubles, doubles, ints, ints, ints, ints, longs, longs, longs, longs, nextDouble, nextDouble, nextFloat, nextFloat, nextFloat, nextInt, nextInt, nextLong, nextLong

Field Details

SEED_SIZE

private static final int SEED_SIZE

Size of the seed array.

See Also:

• Constant Field Values

DEFAULT_SEED

private static final long[] DEFAULT_SEED

The default seed. This has a high quality Weyl increment (containing many bit state transitions).

x

private long x

State of the generator.

w

private long w

State of the Weyl sequence.

s

private long s

Increment for the Weyl sequence. This must be odd to ensure a full period.

This is not final to support the restore functionality.

Constructor Details

MiddleSquareWeylSequence

public MiddleSquareWeylSequence(long[] seed)

Creates a new instance.

Note: The generator output quality is highly dependent on the initial seed. If the generator is seeded poorly (for example with all zeros) it is possible the generator may output zero for many cycles before the internal state recovers randomness. The seed elements are used to set:

1. The state of the generator
2. The state of the Weyl sequence
3. The increment of the Weyl sequence

The third element is set to odd to ensure a period of at least 2⁶⁴. If the increment is of low complexity then the Weyl sequence does not contribute high quality randomness. It is recommended to use a permutation of 8 hex characters for the upper and lower 32-bits of the increment.

The state of the generator is squared during each cycle. There is a possibility that different seeds can produce the same output, for example 0 and 2³² produce the same square. This can be avoided by using the high complexity Weyl increment for the state seed element.

Parameters:

seed - Initial seed. If the length is larger than 3, only the first 3 elements will be used; if smaller, the remaining elements will be automatically set.

Method Details

setSeedInternal

private void setSeedInternal(long[] seed)

Seeds the RNG.

Parameters:

seed - Seed.

getStateInternal

protected byte[] getStateInternal()

Creates a snapshot of the RNG state.

Overrides:

getStateInternal in class IntProvider

Returns:

the internal state.

setStateInternal

protected void setStateInternal(byte[] state)

Resets the RNG to the given state.

Overrides:

setStateInternal in class IntProvider

Parameters:

state - State (previously obtained by a call to BaseProvider.getStateInternal()).

See Also:

• BaseProvider.checkStateSize(byte[],int)

next

public int next()

Return the next random value.

Returns:

the next random value.

nextLong

public long nextLong()

Generates a long value.

Specified by:

nextLong in interface UniformRandomProvider

Overrides:

nextLong in class IntProvider

Returns:

the next random value.