Package com.github.tommyettinger.random

Class FlowRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.FlowRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class FlowRandom extends EnhancedRandom
A hash-on-counters RNG with a period of 2 to the 64 and 2 to the 64 streams. It allows arbitrary skipping within the current stream using skip(long), and you can get the stream as long with getStream(). You can also set the current stream absolutely (with setStream(long)) or relatively (with shiftStream(long)).
Even though a period of 2 to the 64 is just "good enough," it's tens of thousands of times longer than java.util.Random, and equivalent to any individual SplittableRandom. The speed of this generator is unknown, but probably isn't great, especially compared to designs that take advantage of instruction-level parallelism. The streams are meant to avoid correlation, especially when compared to LaserRandom (which has very correlated streams, but the same state size and period).
Has passed 64TB of PractRand without anomalies. ReMort testing is ongoing; over 25 petabytes have passed so far. Any individual stream will return 2 to the 64 long results before repeating, but within a stream, some results will appear multiple times, and other results not at all. If you append all streams to each other to form one sequence of length 2 to the 128, that sequence will be 1-dimensionally equidistributed; that is, each long result will appear as often as any other (2 to the 64 times).
Uses the Moremur unary hash (the same one as DistinctRandom), passing it a combination of the two different Weyl sequences (counters) this has for its state. Using just one sequence is enough to pass a large amount of PractRand, but DistinctRandom would have to change which sequence it uses to have multiple streams. Some sequences are no good, like using an increment of 1; this generator uses a pair of Weyl sequences that are known to work well, and never uses unknown or untested sequences. The relationship between the two sequences is what determines the current stream.
All streams, in time, flow to the sea...
See Also:

  • Field Details

    • stateA

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

    • stateB

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

  • Constructor Details

    • FlowRandom

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

    • FlowRandom

      public FlowRandom(long seed)
      Creates a new FlowRandom 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

    • FlowRandom

      public FlowRandom(long stateA, long stateB)
      Creates a new FlowRandom with the given two states; all long values are permitted for stateA and for stateB. These states are not changed during assignment.
      Parameters:
      stateA - any long value
      stateB - 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.

    • getStateCount

      public int getStateCount()
      This generator has 2 long 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. Selections 0 (or any even number) and 1 (or any odd number) refer to states A and B.
      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

    • setSelectedState

      public void setSelectedState(int selection, long value)
      Sets one of the states, determined by selection, to value, as-is. Selections 0 (or any even number) and 1 (or any odd number) refer to states A and B.
      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 different values; one is seed, the other is ~seed. (2 to the 64) possible initial generator states can be produced here. The initial states don't need to be randomized at all because of the structure of this generator (the hashing stage it does last is meant to make input patterns unrecognizable).
      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.
      Parameters:
      stateA - can be any long

    • getStateB

      public long getStateB()

    • setStateB

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

    • 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(long) and setStateB(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

    • 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

    • 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

    • skip

      public long skip(long advance)
      Description copied from class: EnhancedRandom
      Optional; advances or rolls back the EnhancedRandom' state without actually generating each number. Skips forward or backward a number of steps specified by advance, where a step is equal to one call to EnhancedRandom.nextLong(), and returns the random number produced at that step. Negative numbers can be used to step backward, or 0 can be given to get the most-recently-generated long from EnhancedRandom.nextLong().

      The public implementation throws an UnsupportedOperationException. Many types of random number generator do not have an efficient way of skipping arbitrarily through the state sequence, and those types should not implement this method differently.

      Overrides:
      skip in class EnhancedRandom
      Parameters:
      advance - Number of future generations to skip over; can be negative to backtrack, 0 gets the most-recently-generated number
      Returns:
      the random long generated after skipping forward or backwards by advance numbers

    • getStream

      public long getStream()
      Gets a long that identifies which of the 2 to the 64 possible streams this is on. This takes constant time.
      Returns:
      a long that identifies which stream the main state of the generator is on

    • setStream

      public void setStream(long stream)
      Changes the generator's stream to any of the 2 to the 64 possible streams this can be on. The stream this takes uses the same numbering convention used by getStream() and shiftStream(long). This makes an absolute change to the stream, while shiftStream() is relative.
      This takes constant time.
      Parameters:
      stream - the number of the stream to change to; may be any long

    • shiftStream

      public void shiftStream(long difference)
      Adjusts the generator's stream "up" or "down" to any of the 2 to the 64 possible streams this can be on. The difference this takes will be the difference between the result of getStream() before the shift, and after the shift. This makes a relative change to the stream, while setStream() is absolute.
      This takes constant time.
      Parameters:
      difference - how much to change the stream by; may be any long

    • copy

      public FlowRandom 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