Package com.github.tommyettinger.random

Class PouchRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.PouchRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class PouchRandom extends EnhancedRandom
A four-state EnhancedRandom that uses four different operations to generate each number, one operation per state. It has an additive counter (Weyl sequence) that is always an odd number, and has a cycle length on its own of 2 to the 63; this is stateD. The other states are updated A) by multiplying stateC by the odd stateD, B) by bitwise-rotating stateA, and C) by getting the difference between states B and A. Thus, this uses 64-bit addition, subtraction, bitwise-rotation, and multiplication operations. Because multiplication may be pipelined by many processors, there might not be a speed penalty for including a multiply (at least, that's the logic behind RomuTrio).
In addition to the requirement that stateD must be an odd number, if all three of stateA, stateB, and stateC are 0, that combination of states (the invalid triple-zero state) is disallowed. This is a similar constraint to the one RomuTrio has; for both generators, if states A, B, and C are all 0, then only 0 would be produced and the period would be 1.
Because there are some constraints on valid state combinations, setting the state is a tiny bit slower here. Getting the previousLong() is significantly slower than normal because it requires getting the MathTools.modularMultiplicativeInverse(long) of a long, though the slowdown is likely not noticeable. Other than that, this generator is extremely fast when calling nextLong() and anything that uses it. It's almost as fast as AceRandom, which seems to be the fastest generator here, and if it is set in a too-predictable way using setState(long, long, long, long), it still will diffuse to produce random results (AceRandom does this a little more quickly, but WhiskerRandom won't at all). If two states are only different by a very small amount (either numerically or by their bits), then calling nextLong() about 25 times should fully diffuse PouchRandom, or about 18 for AceRandom.
This passes at least 64TB of PractRand testing without anomalies. It also passes 179 PB of ReMort testing without anomalies.
This implements all optional methods in EnhancedRandom except EnhancedRandom.skip(long); it does implement previousLong() without using skip().
The name here comes from the same theme as WhiskerRandom and ScruffRandom (cat anatomy). My cat, Satchmo, has gotten an enormous "primordial pouch" because he's just so fat. He does not seem to mind his condition one bit.
See Also:

  • Field Details

    • stateA

      protected long stateA
      The first state; can be any long, as long as states A, B, and C are not all 0.

    • stateB

      protected long stateB
      The second state; can be any long, as long as states A, B, and C are not all 0.

    • stateC

      protected long stateC
      The third state; can be any long, as long as states A, B, and C are not all 0.

    • stateD

      protected long stateD
      The fourth state; can be any odd-number long.

  • Constructor Details

    • PouchRandom

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

    • PouchRandom

      public PouchRandom(long seed)
      Creates a new PouchRandom 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

    • PouchRandom

      public PouchRandom(long stateA, long stateB, long stateC, long stateD)
      Creates a new PouchRandom with the given four states; all long values are permitted for states A, B, and C, and all odd-number long values are permitted for stateD, with one exception. If stateA, stateB, and stateC are all 0, then that is the "invalid triple-zero state" and it will be avoided by setting stateA to 1. These states will be used verbatim, unless stateD is even (then 1 is added).
      Parameters:
      stateA - any long value (as long as states A, B, and C are not all 0)
      stateB - any long value (as long as states A, B, and C are not all 0)
      stateC - any long value (as long as states A, B, and C are not all 0)
      stateD - any odd 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.

    • getStateCount

      public int getStateCount()
      This generator has 4 long states, so this returns 4.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      4 (four)

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the state determined by selection, as-is. The value for selection should be between 0 and 3, inclusive; if it is any other value this gets state D as if 3 was given.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to get; generally 0, 1, 2, or 3
      Returns:
      the value of the selected state

    • setSelectedState

      public void setSelectedState(int selection, long value)
      Sets one of the states, determined by selection, to value, as-is. Selections 0, 1, 2, and 3 refer to states A, B, C, and D, and if the selection is anything else, this does nothing. If you try to set state A, B, or C to 0 and that would produce the invalid triple-zero state, then this instead sets the state you chose to 1.
      Overrides:
      setSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to set; always 0, 1, 2, or 3
      value - the exact value to use for the selected state, if valid

    • setSeed

      public void setSeed(long seed)
      This initializes all 4 states of the generator to random values based on the given seed. (2 to the 64) possible initial generator states can be produced here.
      Specified by:
      setSeed in class EnhancedRandom
      Parameters:
      seed - the initial seed; may be any long

    • getStateA

      public long getStateA()

    • setStateA

      public void setStateA(long stateA)
      Sets the first part of the state. If this call would result in the invalid triple-zero state, it instead sets the first part of the state to 1.
      Parameters:
      stateA - can be any long

    • getStateB

      public long getStateB()

    • setStateB

      public void setStateB(long stateB)
      Sets the second part of the state. If this call would result in the invalid triple-zero state, it instead sets the second part of the state to 1.
      Parameters:
      stateB - can be any long

    • getStateC

      public long getStateC()

    • setStateC

      public void setStateC(long stateC)
      Sets the third part of the state. If this call would result in the invalid triple-zero state, it instead sets the third part of the state to 1.
      Parameters:
      stateC - can be any long

    • getStateD

      public long getStateD()

    • setStateD

      public void setStateD(long stateD)
      Sets the fourth part of the state. If this call would set the fourth part of the state to an even number, the state is instead set to the odd number one greater than the invalid even number.
      Parameters:
      stateD - can be any long

    • setState

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

    • leap

      public long leap()
      Jumps extremely far in the generator's sequence, such that one call to leap() advances the state as many as Math.pow(2, 48) calls to nextLong(). This can be used to create 32768 substreams of this generator's sequence, each with a period of at least Math.pow(2, 48) but likely much more.
      Returns:
      the result of what nextLong() would return if it was called at the state this jumped to

    • 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()

    • 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

    • copy

      public PouchRandom 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