Package com.github.tommyettinger.random

Class StrangerRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.StrangerRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class StrangerRandom extends EnhancedRandom
A random number generator that acts as a counterpart to WhiskerRandom by guaranteeing a slightly longer period and potentially being faster in some situations because it uses no multiplication. In practice, TrimRandom accomplishes the same goals and is faster, so this is mostly useful as a hedge in case major issues are found with other generators. Like FourWheelRandom, this has four long states, and is quite fast on desktop platforms (FourWheelRandom is about 25% faster, and WhiskerRandom is about 30% faster, but all three are much faster than the Java 17 java.util.random family of generators). It can be considered stable, like the other EnhancedRandom implementations here. I've tested this more than any other generator I've written; it passes 64TB of PractRand, 5PB of hwd, and an absolutely massive amount of another test, remortality, run on a GPU using CUDA. This last test was run while it was still a work in progress, but this class passed over 300PB after over 500 hours.
The reason this has undergone so much testing is that it is built on top of some of the weakest random number generators out there -- two interleaved 64-bit two-step xorshift generators, and some simple chaotic generators that incorporate the results of those xorshift generators. This avoids multiplication entirely; the operations it uses are two xors, one left shift, one unsigned right shift, one addition, two subtractions, and one bitwise rotation. It has a guaranteed minimum period of (2 to the 65) - 2, and the actual minimum period is almost certainly higher (the guarantee comes purely from its stateA and stateB, which interleave two periods of (2 to the 64) - 1; stateC and stateD extend this period by an unknown amount). The xorshift generators are the absolute weakest generators of their kind -- they use constants of 7 and 9, which are the only two full-period constants for a 64-bit xorshift generator. These only cause an avalanche of 4 bits to change when one bit changes in their input, but this turns out to be more than enough for the chaotic stateC and stateD generators. We ensure that stateA and stateB are sufficiently distant in their shared sequence by using a jump polynomial on stateA to get a stateB that is 0x9E3779B97F4A7C15 steps ahead of stateA (11.4 quintillion steps forward or 7 quintillion steps backward). The complicated calculations for the jump polynomial were done by Spencer Fleming; this was not easy. This generator is meant in particular to optimize well for GPU computations, even though Java doesn't have much ability to do this currently. Some uncommon platforms may also optimize this better than FourWheelRandom.
It is strongly recommended that you seed this with setSeed(long) instead of setState(long, 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. The setSeed() method isn't as fast here as it is in some other generators.
It implements all optional methods in EnhancedRandom except EnhancedRandom.skip(long) and previousLong().
See Also:

  • Field Details

    • stateA

      protected long stateA
      The first state; can be any long except 0

    • stateB

      protected long stateB
      The second state; can be any long except 0, and should be a significant distance from stateA in the xorshift sequence.

    • stateC

      protected long stateC
      The third 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.

    • stateD

      protected long stateD
      The fourth state; can be any long.

  • Constructor Details

    • StrangerRandom

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

    • StrangerRandom

      public StrangerRandom(long seed)
      Creates a new StrangerRandom 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

    • StrangerRandom

      public StrangerRandom(long stateA, long stateB, long stateC, long stateD)
      Creates a new StrangerRandom with the given four states; all long values are permitted. These states will be used verbatim, unless stateA or stateB is 0. If stateA is given 0, it instead uses 0xD3833E804F4C574BL; if stateB is given 0, it instead uses 0x790B300BF9FE738FL.
      Parameters:
      stateA - any long value
      stateB - any long value
      stateC - any long value
      stateD - any long value

  • Method Details

    • jump

      public static long jump(long state)
      Jumps state ahead by 0x9E3779B97F4A7C15 steps of the generator StrangerRandom uses for its stateA and stateB. When used how it is here, it ensures stateB is 11.4 quintillion steps ahead of stateA in their shared sequence, or 7 quintillion behind if you look at it another way. It would typically take years of continuously running this generator at 100GB/s to have stateA become any state that stateB has already been. Users only need this function if setting stateB by-hand; in that case, state should be their stateA.
      Massive credit to Spencer Fleming for writing essentially all of this function over several days.
      Parameters:
      state - the initial state of a 7-9 xorshift generator
      Returns:
      state jumped ahead 0x9E3779B97F4A7C15 times (unsigned)

    • 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 treats it as 3 and sets stateD.
      Overrides:
      setSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to set; generally 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, all with a different first value returned by nextLong() (because stateC is guaranteed to be different for every different seed). This ensures stateB is a sufficient distance from stateA in their shared sequence, and also does some randomizing on the seed before it assigns the result to stateC. This isn't an instantaneously-fast method to call like some versions of setSeed(), but it shouldn't be too slow unless it is called before every generated number (even then, it might be fine).
      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 except 0; this treats 0 as 0xD3833E804F4C574BL

    • getStateB

      public long getStateB()

    • setStateB

      public void setStateB(long stateB)
      Sets the second part of the state.
      Parameters:
      stateB - can be any long except 0; this treats 0 as 0x790B300BF9FE738FL

    • getStateC

      public long getStateC()

    • setStateC

      public void setStateC(long stateC)
      Sets the third part of the state. Note that if you call nextLong() immediately after this, it will return the given stateC as-is, so you may want to call some random generation methods (such as nextLong()) and discard the results after setting the state.
      Parameters:
      stateC - can be any long

    • getStateD

      public long getStateD()

    • setStateD

      public void setStateD(long stateD)
      Sets the fourth part of the state.
      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, unless stateA or stateB are 0. This is the same as calling setStateA(long), setStateB(long), setStateC(long), and setStateD(long) as a group. You may want to call nextLong() a few times after setting the states like this, unless the value for stateC (in particular) is already adequately random; the first call to nextLong(), if it is made immediately after calling this, will return stateC as-is.
      Overrides:
      setState in class EnhancedRandom
      Parameters:
      stateA - the first state; can be any long; can be any long except 0
      stateB - the second state; can be any long; can be any long except 0
      stateC - the third state; this will be returned as-is if the next call is to nextLong()
      stateD - the fourth state; can be any long

    • setState

      public void setState(long stateA, long stateC, long stateD)
      Sets the state with three variables, ensuring that the result has states A and B sufficiently separated from each other, while keeping states C and D as given. Note that this does not take a stateB parameter, and instead obtains it by jumping stateA ahead by about 11.4 quintillion steps using jump(long). If stateA is given as 0, this uses 0xD3833E804F4C574BL instead for stateA and 0x790B300BF9FE738FL for stateB. States C and D can each be any long.
      Overrides:
      setState in class EnhancedRandom
      Parameters:
      stateA - the long value to use for stateA and also used to get stateB; can be any long except 0
      stateC - the long value to use for stateC; this will be returned as-is if the next call is to nextLong()
      stateD - the long value to use for stateD; 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 StrangerRandom 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