Package com.github.tommyettinger.random

Class Taxon32Random

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.Enhanced32Random
com.github.tommyettinger.random.Taxon32Random
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class Taxon32Random extends Enhanced32Random
A random number generator that is optimized for performance on 32-bit machines and with Google Web Toolkit, this uses only the most portable operations (including compatibility with JS), and has a period of exactly 2 to the 64. This passes 64TB of PractRand testing with no anomalies, and also passes juniper's InitialCorrelationEvaluator test. Relatively few generators with this small of a state size have gotten through InitialCorrelationEvaluator and the check ImmediateInitialCorrelationEvaluator (which is not a test for an RNG, but for how hash-like an RNG is), unscathed, so this is a good option to have if you expect to frequently use similar pairs of initial int states. Taxon32Random is somewhat slower than ChopRandom or Choo32Random, but has a longer guaranteed minimum period and a smaller state size. Chop and Choo32 have a rather short minimum period guarantee (2 to the 32 ints), so in the unlikely event that you might encounter a sequence that short, you might prefer Taxon32Random.
This is meant for the somewhat-unusual task of providing a different (short) sequence of random values for any pair of states given to it, with it especially important that numerically-close state pairs produce different sequences. It also was meant to work on GWT without needing super-sourcing; most generators either use long math and so are much slower on GWT, or use int math but need super-sourcing to avoid eventually losing precision. These tasks were required by the pathfinding algorithm library gand, which needed a way to make an arbitrary number of random choices in the same way for any given point (or a pair of points).
This implements all optional methods in EnhancedRandom except EnhancedRandom.skip(long); it does implement previousLong() and previousInt() without using skip().
This uses a mixed left/right xorshift pair, which uses this data found by Pelle Evensen. Various other techniques used in here aren't widely used. Using XOR with an even constant immediately after adding an odd constant produces a full-period sequence, like a counter, but this works on GWT or JS without needing any more bitwise math. I don't think I've seen int aaa = n & (0xAAAAAAAA - n); used before, but it has the useful quality that for all possible values for n, aaa is negative an odd number of times (instead of an even number, which we don't want for period reasons). Rotating aaa left by 1, for all possible values for n, and adding it to a variable will have a longer period than n will alone; because adding (2 to the 32) rotated aaa values is the same as adding an odd number, we would need to repeat that step (2 to the 32) times to cycle, or (2 to the 64) times total.
The name comes from how some of the operations here are difficult to classify.
See Also:

  • Field Details

    • stateA

      protected int stateA
      The first state; can be any int.

    • stateB

      protected int stateB
      The second state; can be any int.

  • Constructor Details

    • Taxon32Random

      public Taxon32Random()
      Creates a new Taxon32Random with a random state.

    • Taxon32Random

      public Taxon32Random(long seed)
      Creates a new Taxon32Random with the given seed; all long values are permitted. The seed will be passed to setSeed(long) to attempt to adequately distribute the seed randomly.
      Parameters:
      seed - any long value

    • Taxon32Random

      public Taxon32Random(int stateA, int stateB)
      Creates a new Taxon32Random with the given two states; all int values are permitted. These states will be used verbatim.
      Parameters:
      stateA - any int value
      stateB - any int 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.

    • mainlyGeneratesInt

      public boolean mainlyGeneratesInt()
      This generator mainly generates int values.
      Overrides:
      mainlyGeneratesInt in class Enhanced32Random
      Returns:
      true
      See Also:

    • getMinimumPeriod

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

    • getStateCount

      public int getStateCount()
      This generator has 2 int states, so this returns 2.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      2 (two)

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the state determined by selection, as-is. The value for selection should be between 0 and 1, inclusive; if it is any other value this gets state B as if 1 was given.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to get; generally 0 or 1
      Returns:
      the value of the selected state, which is an int that will be promoted to long

    • setSelectedState

      public void setSelectedState(int selection, long value)
      Sets one of the states, determined by selection, to the lower 32 bits of value, as-is. Selections 0 and 1 refer to states A and B, and if the selection is anything else, this treats it as 1 and sets stateB. This always casts value to an int before using it.
      Overrides:
      setSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to set; generally 0 or 1
      value - the exact value to use for the selected state, if valid

    • setSeed

      public void setSeed(long seed)
      This initializes both states of the generator to random values based on the given seed. (2 to the 64) possible initial generator states can be produced here, all with a different first value returned by nextLong().
      Specified by:
      setSeed in class EnhancedRandom
      Parameters:
      seed - the initial seed; may be any long

    • getStateA

      public int getStateA()

    • setStateA

      public void setStateA(int stateA)
      Sets the first (dependent counter) part of the state.
      Parameters:
      stateA - can be any int

    • getStateB

      public int getStateB()

    • setStateB

      public void setStateB(int stateB)
      Sets the second (XLCG) part of the state.
      Parameters:
      stateB - can be any int

    • setState

      public void setState(long stateA, long stateB)
      Sets the state completely to the given two state variables. This is the same as calling setStateA(int) and setStateB(int), as a group.
      Overrides:
      setState in class EnhancedRandom
      Parameters:
      stateA - the first state; can be any int
      stateB - the second state; can be any int

    • setState

      public void setState(int stateA, int stateB)
      Like the superclass method setState(long, long), but takes two int values instead of long. This can avoid creating longs on JS-targeting platforms, which tends to be quite slow.
      Parameters:
      stateA - the first state; can be any int
      stateB - the second state; can be any int

    • nextLong

      public long nextLong()
      Description copied from class: Enhanced32Random
      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
      Overrides:
      nextLong in class Enhanced32Random
      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: Enhanced32Random
      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 Enhanced32Random.nextInt(int) instead. For some specific cases, this method is more efficient and less biased than Enhanced32Random.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 Enhanced32Random
      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

    • nextInt

      public int nextInt()
      Description copied from class: Enhanced32Random
      Returns the next pseudorandom, uniformly distributed int value from this random number generator's sequence. The general contract of nextInt is that one int value is pseudorandomly generated and returned. All 232 possible int values are produced with (approximately) equal probability.
      In Enhanced32Random, this throws an UnsupportedOperationException because the concrete subclass must implement this.
      Specified by:
      nextInt in interface RandomGenerator
      Overrides:
      nextInt in class Enhanced32Random
      Returns:
      the next pseudorandom, uniformly distributed int 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()

    • previousInt

      public int previousInt()
      Description copied from class: EnhancedRandom
      Optional; moves the state to its previous value and returns the previous int that would have been produced by EnhancedRandom.nextInt(). This can be equivalent to calling EnhancedRandom.previousLong() and casting to int, but not always; generators that natively generate int results typically move the state once in nextInt() and twice in nextLong(), and should move the state back once here.
      If EnhancedRandom.nextInt() is implemented using a call to EnhancedRandom.nextLong(), the implementation in this class is almost always sufficient and correct. If nextInt() changes state differently from nextLong(), then this should be implemented, if feasible, and EnhancedRandom.previousLong() can be implemented using 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.previousLong() and casts it to int, and if previousLong() and skip() have not been implemented differently, then it will throw an UnsupportedOperationException.
      Overrides:
      previousInt in class EnhancedRandom
      Returns:
      the previous number this would have produced with EnhancedRandom.nextInt()

    • copy

      public Taxon32Random 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