Package com.github.tommyettinger.random

Class TricycleRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.TricycleRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class TricycleRandom extends EnhancedRandom
An unusual RNG that's extremely fast on HotSpot JDK 16 and higher, and still fairly fast on earlier JDKs. It has three long states, which as far as I can tell can be initialized to any values without hitting any known problems for initialization. These states, a, b, and c, are passed around so a is determined by the previous c, b is determined by the previous a, b, and c, and c is determined by the previous b. This updates a with a multiplication, b with two XOR operations, and c with a bitwise-left-rotate by 41 and then an addition with a constant. If you want to alter this generator so results will be harder to reproduce, the simplest way is to change the constant added to c -- it can be any substantially-large odd number, though preferably one with a Long.bitCount(long) of 32.
Other useful traits of this generator are that it almost certainly has a longer period than you need for a game, and that all values are permitted for the states (that we know of). It is possible that some initialization will put the generator in a shorter-period subcycle, but the odds of this being a subcycle that's small enough to run out of period during a game are effectively 0. It's also possible that the generator only has one cycle of length 2 to the 192, though this doesn't seem at all likely. TricycleRandom implements all optional methods in EnhancedRandom except EnhancedRandom.skip(long); it does implement previousLong() without using skip().
This is closely related to Mark Overton's Romu generators, specifically RomuTrio, but this gets a little faster than RomuTrio in some situations by using just one less rotation. Unlike RomuTrio, there isn't a clear problematic state with a period of 1 (which happens when all of its states are 0). This is often slightly slower than RomuTrio, but only by a tiny margin. This generator isn't an ARX generator any more (a previous version was), but its performance isn't much different (like RomuTrio, the one multiplication this uses pipelines very well, so it doesn't slow down the generator).
TricycleRandom passes 64TB of testing with PractRand, which uses a suite of tests to look for a variety of potential problems. It has also passed a whopping 4 petabytes of testing with hwd, can test a much larger amount of data but only runs a single test. The test hwd uses looks for long-range bit-dependencies, where one bit's state earlier in the generated numbers determines the state of a future bit with a higher-than-reasonable likelihood. All the generators here are considered stable.
It is strongly recommended that you seed this with setSeed(long) instead of setState(long, long, long), because if you give sequential seeds to both setSeed() and setState(), the former will start off random, while the latter will start off repeating the seed sequence. After about 20-40 random numbers generated, any correlation between similarly seeded generators will probably be completely gone, though.
See Also:

  • Field Details

    • stateA

      protected long stateA
      The first state; can be any long. If this has just been set to some value, then the next call to nextLong() will return that value as-is. Later calls will be more random.

    • stateB

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

    • stateC

      protected long stateC
      The third state; can be any long.

  • Constructor Details

    • TricycleRandom

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

    • TricycleRandom

      public TricycleRandom(long seed)
      Creates a new TricycleRandom 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

    • TricycleRandom

      public TricycleRandom(long stateA, long stateB, long stateC)
      Creates a new TricycleRandom with the given three states; all long values are permitted. These states will be used verbatim.
      Parameters:
      stateA - any long value
      stateB - any long value
      stateC - 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 3 long states, so this returns 3.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      3 (three)

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the state determined by selection, as-is.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to get; generally 0, 1, or 2
      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, and 2 refer to states A, B, and C, and if the selection is anything else, this treats it as 2 and sets stateC.
      Overrides:
      setSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to set; generally 0, 1, or 2
      value - the exact value to use for the selected state, if valid

    • setSeed

      public void setSeed(long seed)
      This initializes all 3 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() (because stateA is guaranteed to be different for every different seed).
      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. Note that if you call nextLong() immediately after this, it will return the given stateA as-is, so you may want to call some random generation methods (such as nextLong()) and discard the results after setting 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

    • getStateC

      public long getStateC()

    • setStateC

      public void setStateC(long stateC)
      Sets the third part of the state.
      Parameters:
      stateC - can be any long

    • setState

      public void setState(long stateA, long stateB, long stateC)
      Sets the state completely to the given three state variables. This is the same as calling setStateA(long), setStateB(long), and setStateC(long) as a group. You may want to call nextLong() a few times after setting the states like this, unless the value for stateA (in particular) is already adequately random; the first call to nextLong(), if it is made immediately after calling this, will return stateA as-is.
      Overrides:
      setState in class EnhancedRandom
      Parameters:
      stateA - the first state; this will be returned as-is if the next call is to nextLong()
      stateB - the second state; can be any long
      stateC - the third 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

    • copy

      public TricycleRandom 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