Package com.github.tommyettinger.random

Class LFSR64QuasiRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.LFSR64QuasiRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class LFSR64QuasiRandom extends EnhancedRandom
A simple 64-bit linear feedback shift register (LFSR) that can be used as a quasi-random number generator. This is not the type of generator that can pass most tests for randomness on its own, but it still can appear at least a little random most of the time. This may be useful to combine with another generator that has a power of two for its minimum period, since the two periods will not overlap for a very long time.
The 64-bit LFSR was found by mlpolygen.
This is largely an excuse to use the hex constant 0xfeedbabedeadbeefL in production, since it is somehow made of real words and is also still a full-period LFSR polynomial. It wasn't too hard to find with mlpolygen, either, even though I needed to look for the reversed bits because this generator uses a left-shift instead of right.
See Also:

  • Field Details

    • state

      protected long state
      The state; can be any long except 0.

  • Constructor Details

    • LFSR64QuasiRandom

      public LFSR64QuasiRandom()
      Creates a new LFSR64QuasiRandom with a random state.

    • LFSR64QuasiRandom

      public LFSR64QuasiRandom(long seed)
      Creates a new LFSR64QuasiRandom with the given seed; all long values are permitted except 0. The seed will be used as-is unless it is 0, in which case 0x9E3779B97F4A7C15L (or -7046029254386353131L) is used instead (which is roughly 2 to the 64 divided by the golden ratio).
      Parameters:
      seed - any long value

  • Method Details

    • getTag

      public String getTag()
      Description copied from class: EnhancedRandom
      Gets the tag used to identify this type of EnhancedRandom, as a String. This tag should be unique, and for uniformity purposes, all tags used in this library are 4 characters long. User-defined tags should have a different length.
      Specified by:
      getTag in class EnhancedRandom
      Returns:
      a unique String identifier for this type of EnhancedRandom; usually 4 chars long.

    • getMinimumPeriod

      public BigInteger getMinimumPeriod()
      (2 to the 64) minus 1.
      Overrides:
      getMinimumPeriod in class EnhancedRandom
      Returns:
      (2 to the 64) minus 1

    • getStateCount

      public int getStateCount()
      This generator has 1 long state, so this returns 1.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      1 (one)

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the state, as-is. The value for selection is ignored.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - ignored
      Returns:
      the value of the state

    • setSelectedState

      public void setSelectedState(int selection, long value)
      Sets the state to value, as-is. If this would cause the state to be 0, it instead sets the state to 0x9E3779B97F4A7C15L.
      Overrides:
      setSelectedState in class EnhancedRandom
      Parameters:
      selection - ignored
      value - the exact value to use for the state, if valid

    • setSeed

      public void setSeed(long seed)
      This is the same as setState(long).
      Specified by:
      setSeed in class EnhancedRandom
      Parameters:
      seed - the initial seed; may be any long

    • getState

      public long getState()

    • setState

      public void setState(long state)
      Sets the state completely to the given four state variables.
      Overrides:
      setState in class EnhancedRandom
      Parameters:
      state - the first state; can be any long

    • nextLong

      public long nextLong()
      Description copied from class: EnhancedRandom
      Returns the next pseudorandom, uniformly distributed long value from this random number generator's sequence. The general contract of nextLong is that one long value is pseudorandomly generated and returned.
      The only methods that need to be implemented by this interface are this and EnhancedRandom.copy(), though other methods can be implemented as appropriate for generators that, for instance, natively produce ints rather than longs.
      Specified by:
      nextLong in interface RandomGenerator
      Specified by:
      nextLong in class EnhancedRandom
      Returns:
      the next pseudorandom, uniformly distributed long value from this random number generator's sequence

    • next

      public int next(int bits)
      Description copied from class: EnhancedRandom
      Generates the next pseudorandom number with a specific maximum size in bits (not a max number). If you want to get a random number in a range, you should usually use EnhancedRandom.nextInt(int) instead. For some specific cases, this method is more efficient and less biased than EnhancedRandom.nextInt(int). For bits values between 1 and 30, this should be similar in effect to nextInt(1 << bits); though it won't typically produce the same values, they will have the correct range. If bits is 31, this can return any non-negative int; note that nextInt(1 << 31) won't behave this way because 1 << 31 is negative. If bits is 32 (or 0), this can return any int.

      The general contract of next is that it returns an int value and if the argument bits is between 1 and 32 (inclusive), then that many low-order bits of the returned value will be (approximately) independently chosen bit values, each of which is (approximately) equally likely to be 0 or 1.

      Note that you can give this values for bits that are outside its expected range of 1 to 32, but the value used, as long as bits is positive, will effectively be bits % 32. As stated before, a value of 0 for bits is the same as a value of 32.

      Overrides:
      next in class EnhancedRandom
      Parameters:
      bits - the amount of random bits to request, from 1 to 32
      Returns:
      the next pseudorandom value from this random number generator's sequence

    • previousLong

      public long previousLong()
      Description copied from class: EnhancedRandom
      Optional; moves the state to its previous value and returns the previous long that would have been produced by EnhancedRandom.nextLong(). This can be equivalent to calling EnhancedRandom.skip(long) with -1L, but not always; many generators can't efficiently skip long distances, but can step back by one value.
      Generators that natively generate int results typically produce long values by generating an int for the high 32 bits and an int for the low 32 bits. When producing the previous long, the order the high and low bits are generated, such as by EnhancedRandom.previousInt(), should be reversed. Generators that natively produce long values usually don't need to implement EnhancedRandom.previousInt(), but those that produce int usually should implement it, and may optionally call previousInt() twice in this method.
      If you know how to implement the reverse of a particular random number generator, it is recommended you do so here, rather than rely on skip(). This isn't always easy, but should always be possible for any decent PRNG (some historical PRNGs, such as the Middle-Square PRNG, cannot be reversed at all). If a generator cannot be reversed because multiple initial states can transition to the same subsequent state, it is known to have statistical problems that are not necessarily present in a generator that matches one initial state to one subsequent state.
      The public implementation calls EnhancedRandom.skip(long) with -1L, and if skip() has not been implemented differently, then it will throw an UnsupportedOperationException.
      Overrides:
      previousLong in class EnhancedRandom
      Returns:
      the previous number this would have produced with EnhancedRandom.nextLong()

    • nextGaussian

      public double nextGaussian()
      Description copied from class: EnhancedRandom
      Returns the next pseudorandom, Gaussian ("normally") distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence.

      The general contract of nextGaussian is that one double value, chosen from (approximately) the usual normal distribution with mean 0.0 and standard deviation 1.0, is pseudorandomly generated and returned.

      This does not use a rough approximation, which is a departure from earlier versions; instead, it uses the Ziggurat method, which produces high-quality variables very quickly. Like earlier versions that used probit() or a bit-counting approximation, this requests exactly one long from the generator's sequence (using EnhancedRandom.nextLong()). This makes it different from code like java.util.Random's nextGaussian() method, which can (rarely) fetch a higher number of random doubles.

      The implementation here was ported from code by Olaf Berstein, based on a paper by Jorgen A. Doornik and some steps from a paper by George Marsaglia. Distributor has more information, for the curious.

      Specified by:
      nextGaussian in interface RandomGenerator
      Overrides:
      nextGaussian in class EnhancedRandom
      Returns:
      the next pseudorandom, Gaussian ("normally") distributed double value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence

    • nextGaussianFloat

      public float nextGaussianFloat()
      Description copied from class: EnhancedRandom
      Returns the next pseudorandom, Gaussian ("normally") distributed float value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence.

      The general contract of nextGaussianFloat is that one float value, chosen from (approximately) the usual normal distribution with mean 0.0 and standard deviation 1.0, is pseudorandomly generated and returned.

      This uses RoughMath.normalRough(long), which actually appears to approximate the normal distribution better than Distributor.normalF(long), though not quite as well as Distributor.normal(long) (which is used by EnhancedRandom.nextGaussian()). Like nextGaussian(), this requests exactly one long from the generator's sequence (using EnhancedRandom.nextLong()). This makes it different from code like java.util.Random's nextGaussian() method, which can (rarely) fetch an arbitrarily higher number of random doubles.

      The implementation here was ported from code by Marc B. Reynolds and modified to only require one call to EnhancedRandom.nextLong().

      Overrides:
      nextGaussianFloat in class EnhancedRandom
      Returns:
      the next pseudorandom, Gaussian ("normally") distributed float value with mean 0.0 and standard deviation 1.0 from this random number generator's sequence

    • copy

      public LFSR64QuasiRandom copy()
      Description copied from class: EnhancedRandom
      Creates a new EnhancedRandom with identical states to this one, so if the same EnhancedRandom methods are called on this object and its copy (in the same order), the same outputs will be produced. This is not guaranteed to copy the inherited state of any parent class, so if you call methods that are only implemented by a superclass (like Random) and not this one, the results may differ.
      Specified by:
      copy in class EnhancedRandom
      Returns:
      a deep copy of this EnhancedRandom.

    • equals

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

    • toString

      public String toString()
      Overrides:
      toString in class Object