Package squidpony.squidmath

Class MersenneTwister

java.lang.Object
squidpony.squidmath.MersenneTwister
All Implemented Interfaces:
Serializable, RandomnessSource
public class MersenneTwister
extends Object
implements Serializable, RandomnessSource
Mersenne Twister, 64-bit version as a RandomnessSource.
Similar to the regular 32-bit Mersenne Twister but implemented with 64-bit values (Java long), and with different output. This generator is probably not the best to use because of known statistical problems and low speed, but its period is absurdly high, pow(2, 19937) - 1. LongPeriodRNG has significantly better speed and statistical quality, and also has a large period, pow(2, 1024) - 1. IsaacRNG is slower, but offers impeccable quality, and from its webpage, "Cycles are guaranteed to be at least pow(2, 40) values long, and they are pow(2, 8295) values long on average." IsaacRNG should be your choice if security is a concern, LongPeriodRNG if quality and speed are important, and MersenneTwister should be used if period is the only criterion to judge an RNG on. Keep in mind that extremely long periods are not always a good thing; there are known states for the Mersenne Twister that produce dozens of 0 outputs in a row, which is fundamentally impossible for LightRNG or DiverRNG. It also would take longer to exhaust the period of a 128-bit-state generator (generating 100 gigabytes per second) than the amount of time humans have walked the Earth. This has 19968 bits of state... so if 128 is more than is possible to exhaust, why do you need 19968 bits, again? Consider GoatRNG if you want a high-quality 128-bit generator.
This is mostly a straight port of the C-code (mt19937-64.c), but made more "java-like". This version was originally found at an archived version of a Google Code repo, and it is licensed under the 3-clause BSD license, like the Mersenne Twister.
References:
Version:
1.1 -- 07-Oct-2017
Author:
Nick Galbreath -- nickg [at] modp [dot] com, Tommy Ettinger
See Also:
Serialized Form

  • Constructor Summary

    Constructors 
    Constructor Description
    MersenneTwister()
    Seeds this using two calls to Math.random().
    MersenneTwister​(long seed)
    Seeds this with the given long, which will be used to affect the large state.
    MersenneTwister​(long[] seed)
    Seeds this with the given long array, which will be used to affect the large state, and not used directly.

  • Method Summary

    Modifier and Type Method Description
    MersenneTwister copy()
    Produces a copy of this RandomnessSource that, if next() and/or nextLong() are called on this object and the copy, both will generate the same sequence of random numbers from the point copy() was called.
    boolean equals​(Object o)  
    int hashCode()  
    int next​(int bits)
    Returns up to 32 random bits.
    long nextLong()
    Returns 64 random bits.
    void setSeed​(long seed)
    Initalize the pseudo random number generator with 64 bits.
    void setSeed​(long[] array)
    Initalize the pseudo random number generator with a long array of any size, which should not be null but can be.
    String toString()  

    Methods inherited from class java.lang.Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

  • Constructor Details

    • MersenneTwister

      public MersenneTwister()
      Seeds this using two calls to Math.random().

    • MersenneTwister

      public MersenneTwister​(long seed)
      Seeds this with the given long, which will be used to affect the large state.
      Parameters:
      seed - any long

    • MersenneTwister

      public MersenneTwister​(long[] seed)
      Seeds this with the given long array, which will be used to affect the large state, and not used directly.
      Parameters:
      seed - a long array; generally should be non-null

  • Method Details

    • setSeed

      public void setSeed​(long seed)
      Initalize the pseudo random number generator with 64 bits. Not the same as setState() in StatefulRandomness; this changes the seed quite a bit.
      Parameters:
      seed - any long

    • setSeed

      public void setSeed​(long[] array)
      Initalize the pseudo random number generator with a long array of any size, which should not be null but can be. Not the same as setState() in StatefulRandomness; this changes the seed quite a bit.
      Parameters:
      array - any long array

    • next

      public int next​(int bits)
      Returns up to 32 random bits.
      The implementation splits a 64-bit long into two 32-bit chunks.
      Specified by:
      next in interface RandomnessSource
      Parameters:
      bits - the number of bits to output, between 1 and 32 (both inclusive)
      Returns:
      an int with the specified number of pseudo-random bits

    • nextLong

      public long nextLong()
      Returns 64 random bits.
      Specified by:
      nextLong in interface RandomnessSource
      Returns:
      a pseudo-random long, which can have any 64-bit value, positive or negative

    • copy

      public final MersenneTwister copy()
      Description copied from interface: RandomnessSource
      Produces a copy of this RandomnessSource that, if next() and/or nextLong() are called on this object and the copy, both will generate the same sequence of random numbers from the point copy() was called. This just needs to copy the state so it isn't shared, usually, and produce a new value with the same exact state.
      Specified by:
      copy in interface RandomnessSource
      Returns:
      a copy of this RandomnessSource

    • toString

      public String toString()
      Overrides:
      toString in class Object

    • equals

      public boolean equals​(Object o)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object