Package org.apache.commons.rng.core.source32

Class ISAACRandom

java.lang.Object

org.apache.commons.rng.core.BaseProvider

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

org.apache.commons.rng.core.source32.ISAACRandom

All Implemented Interfaces:

RandomIntSource, RestorableUniformRandomProvider, UniformRandomProvider

public class ISAACRandom
extends IntProvider

A fast cryptographic pseudo-random number generator.

ISAAC (Indirection, Shift, Accumulate, Add, and Count) generates 32-bit random numbers. ISAAC has been designed to be cryptographically secure and is inspired by RC4. Cycles are guaranteed to be at least 2⁴⁰ values long, and they are 2⁸²⁹⁵ values long on average. The results are uniformly distributed, unbiased, and unpredictable unless you know the seed.

This code is based (with minor changes and improvements) on the original implementation of the algorithm by Bob Jenkins.

Since:

1.0

See Also:

• ISAAC: a fast cryptographic pseudo-random number generator
• ISAAC (Wikipedia)

Field Summary

Fields

Modifier and Type	Field	Description
private final int[]	arr	Service variable.
private int	count	Count through the results in rsl[].
private static final int	GLD_RATIO	The golden ratio.
private static final int	H_SIZE	Half-size of rsl[] and mem[].
private int	isaacA	Accumulator.
private int	isaacB	The last result.
private int	isaacC	Counter, guarantees cycle is at least 2^40.
private int	isaacI	Service variable.
private int	isaacJ	Service variable.
private int	isaacX	Service variable.
private static final int	MASK	For pseudo-random lookup.
private final int[]	mem	The internal state.
private final int[]	rsl	The results given to the user.
private static final int	SIZE	Size of rsl[] and mem[].
private static final int	SIZE_L	Log of size of rsl[] and mem[].

Constructor Summary

Constructors

Constructor	Description
ISAACRandom(int[] seed)	Creates a new ISAAC random number generator.

Method Summary

Modifier and Type	Method	Description
protected byte[]	getStateInternal()	Creates a snapshot of the RNG state.
private void	initState()	Initialize, or reinitialize, this instance of rand.
private void	isaac()	Generate 256 results.
private void	isaac2()	Intermediate internal loop.
private void	isaac3()	Lowest level internal loop.
int	next()	Return the next random value.
private void	setSeedInternal(int[] seed)	Reseeds the RNG.
private void	setState(int start)	Set the state by copying the internal arrays.
protected void	setStateInternal(byte[] s)	Resets the RNG to the given state.
private void	shuffle()	Shuffle array.

Methods inherited from class org.apache.commons.rng.core.source32.IntProvider

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

Methods inherited from class org.apache.commons.rng.core.BaseProvider

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

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.commons.rng.UniformRandomProvider

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

Field Details

SIZE_L

private static final int SIZE_L

Log of size of rsl[] and mem[].

See Also:

• Constant Field Values

SIZE

private static final int SIZE

Size of rsl[] and mem[].

See Also:

• Constant Field Values

H_SIZE

private static final int H_SIZE

Half-size of rsl[] and mem[].

See Also:

• Constant Field Values

MASK

private static final int MASK

For pseudo-random lookup.

See Also:

• Constant Field Values

GLD_RATIO

private static final int GLD_RATIO

The golden ratio.

See Also:

• Constant Field Values

rsl

private final int[] rsl

The results given to the user.

mem

private final int[] mem

The internal state.

count

private int count

Count through the results in rsl[].

isaacA

private int isaacA

Accumulator.

isaacB

private int isaacB

The last result.

isaacC

private int isaacC

Counter, guarantees cycle is at least 2^40.

arr

private final int[] arr

Service variable.

isaacX

private int isaacX

Service variable.

isaacI

private int isaacI

Service variable.

isaacJ

private int isaacJ

Service variable.

Constructor Details

ISAACRandom

public ISAACRandom(int[] seed)

Creates a new ISAAC random number generator.

Parameters:

seed - Initial seed

Method Details

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[] s)

Resets the RNG to the given state.

Overrides:

setStateInternal in class IntProvider

Parameters:

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

See Also:

• BaseProvider.checkStateSize(byte[],int)

setSeedInternal

private void setSeedInternal(int[] seed)

Reseeds the RNG.

Parameters:

seed - Seed. Cannot be null.

next

public int next()

Return the next random value.

Returns:

the next random value.

isaac

private void isaac()

Generate 256 results.

isaac2

private void isaac2()

Intermediate internal loop.

isaac3

private void isaac3()

Lowest level internal loop.

initState

private void initState()

Initialize, or reinitialize, this instance of rand.

shuffle

private void shuffle()

Shuffle array.

setState

private void setState(int start)

Set the state by copying the internal arrays.

Parameters:

start - First index into mem array.