Package com.github.tommyettinger.random

Class Xoshiro512PlusPlusRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.Xoshiro512PlusPlusRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class Xoshiro512PlusPlusRandom extends EnhancedRandom
A random number generator that is fairly fast and guarantees 7-dimensional equidistribution (except for the septet with seven zeroes in a row, every septet of long results is produced exactly 2 to the 64 times over the period). It has a period of (2 to the 512) - 1, which would take millennia to exhaust on current-generation hardware (at least). It can be considered stable, like the other EnhancedRandom implementations here. This passes heavy testing, but isn't a cryptographic generator. The only invalid state is the one with 0 in each state variable, and this won't ever occur in the normal period of that contains all other states. You should generally seed this with setSeed(long), rather than setState(long, long, long, long, long, long, long, long), because if you give similar states to the latter, it tends to produce severely flawed output on at least the low-order bits. This can't happen with setSeed(). The similar-initial-states correlation is shared by most Xoshiro-based and Xoroshiro-based generators, but not Xoshiro256MX3Random because it mixes the output thoroughly. Many other generators also fail tests for that correlation (here called ICE or IICE tests), such as WhiskerRandom.
The main reasons you could prefer this generator to the typically-faster AceRandom are:
  • This generator is 7D-equidistributed, so groups of seven coordinates will always appear equally often.
  • This generator is well-studied and appeared in a peer-reviewed paper.
  • You will never use Java 16, and if you use Java 17, you would rather use the implementation in the JDK there.
  • You need a regular structure to the generated numbers, with guarantees about that structure.

This implements all optional methods in EnhancedRandom except EnhancedRandom.skip(long); it does implement previousLong() without using skip().
Xoshiro512++ was written in 2019 by David Blackman and Sebastiano Vigna. You can consult their paper for technical details: PDF link here.
See Also:

  • Field Details

    • stateA

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

    • stateB

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

    • stateC

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

    • stateD

      protected long stateD
      The fourth state; can be any long, as long as all states are not 0.

    • stateE

      protected long stateE
      The fifth state; can be any long, as long as all states are not 0.

    • stateF

      protected long stateF
      The sixth state; can be any long, as long as all states are not 0.

    • stateG

      protected long stateG
      The seventh state; can be any long, as long as all states are not 0.

    • stateH

      protected long stateH
      The eighth state; can be any long, as long as all states are not 0.

  • Constructor Details

    • Xoshiro512PlusPlusRandom

      public Xoshiro512PlusPlusRandom()
      Creates a new Xoshiro512PlusPlusRandom with a random state.

    • Xoshiro512PlusPlusRandom

      public Xoshiro512PlusPlusRandom(long seed)
      Creates a new Xoshiro512PlusPlusRandom 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

    • Xoshiro512PlusPlusRandom

      public Xoshiro512PlusPlusRandom(long stateA, long stateB, long stateC, long stateD, long stateE, long stateF, long stateG, long stateH)
      Creates a new Xoshiro512PlusPlusRandom with the given eight states; all long values are permitted. These states will be used verbatim, as long as they are not all 0. In that case, stateH is changed.
      Parameters:
      stateA - any long value
      stateB - any long value
      stateC - any long value
      stateD - any long value
      stateE - any long value
      stateF - any long value
      stateG - any long value
      stateH - 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.

    • getMinimumPeriod

      public BigInteger getMinimumPeriod()
      (2 to the 512) - 1.
      Overrides:
      getMinimumPeriod in class EnhancedRandom
      Returns:
      (2 to the 512) - 1

    • getStateCount

      public int getStateCount()
      This generator has 8 long states, so this returns 8.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      8 (eight)

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the state determined by selection, as-is. The value for selection should be between 0 and 7, inclusive; if it is any other value this gets state H as if 7 was given.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to get; generally between 0 and 7, inclusive
      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, 3, 4, 5, 6, and 7 refer to states A, B, C, D, E, F, G, and H, and if the selection is anything else, this treats it as 7 and sets stateH. If this would cause all states to be 0, it instead sets the selected state to 0x9E3779B97F4A7C15L.
      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 stateB 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. This cannot set the state to 0 if all other states are already 0; in that case, it sets this state to 0x9E3779B97F4A7C15L instead.
      Parameters:
      stateA - can be any long

    • getStateB

      public long getStateB()

    • setStateB

      public void setStateB(long stateB)
      Sets the second part of the state. This cannot set the state to 0 if all other states are already 0; in that case, it sets this state to 0x9E3779B97F4A7C15L instead.
      Parameters:
      stateB - can be any long

    • getStateC

      public long getStateC()

    • setStateC

      public void setStateC(long stateC)
      Sets the third part of the state. This cannot set the state to 0 if all other states are already 0; in that case, it sets this state to 0x9E3779B97F4A7C15L instead.
      Parameters:
      stateC - can be any long

    • getStateD

      public long getStateD()

    • setStateD

      public void setStateD(long stateD)
      Sets the fourth part of the state. This cannot set the state to 0 if all other states are already 0; in that case, it sets this state to 0x9E3779B97F4A7C15L instead.
      Parameters:
      stateD - can be any long

    • getStateE

      public long getStateE()

    • setStateE

      public void setStateE(long stateE)
      Sets the fifth part of the state. This cannot set the state to 0 if all other states are already 0; in that case, it sets this state to 0x9E3779B97F4A7C15L instead.
      Parameters:
      stateE - can be any long

    • getStateF

      public long getStateF()

    • setStateF

      public void setStateF(long stateF)
      Sets the sixth part of the state. This cannot set the state to 0 if all other states are already 0; in that case, it sets this state to 0x9E3779B97F4A7C15L instead.
      Parameters:
      stateF - can be any long

    • getStateG

      public long getStateG()

    • setStateG

      public void setStateG(long stateG)
      Sets the seventh part of the state. This cannot set the state to 0 if all other states are already 0; in that case, it sets this state to 0x9E3779B97F4A7C15L instead.
      Parameters:
      stateG - can be any long

    • getStateH

      public long getStateH()

    • setStateH

      public void setStateH(long stateH)
      Sets the eighth part of the state. This cannot set the state to 0 if all other states are already 0; in that case, it sets this state to 0x9E3779B97F4A7C15L instead.
      Parameters:
      stateH - can be any long

    • setState

      public void setState(long stateA, long stateB, long stateC, long stateD, long stateE, long stateF, long stateG, long stateH)
      Sets the state completely to the given eight state variables. This is the same as calling setStateA(long), setStateB(long), setStateC(long), setStateD(long), setStateE(long), setStateF(long), setStateG(long), and setStateH(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 long
      stateE - the fourth state; can be any long
      stateF - the fourth state; can be any long
      stateG - the fourth state; can be any long
      stateH - the fourth 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

    • 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

    • 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()

    • nextInt

      public int nextInt()
      Description copied from class: EnhancedRandom
      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.
      Specified by:
      nextInt in interface RandomGenerator
      Overrides:
      nextInt in class EnhancedRandom
      Returns:
      the next pseudorandom, uniformly distributed int value from this random number generator's sequence

    • 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()

    • leap

      public long leap()
      Jumps extremely far in the generator's sequence, such that it requires Math.pow(2, 128) calls to leap() to complete a cycle through the generator's entire sequence. This can be used to create as many as (2 to the 128) substreams of this generator's sequence, each with a period of Math.pow(2, 384).
      This is called long_jump() in the xoshiro512++ sources.
      Returns:
      the result of what nextLong() would return if it was called at the state this jumped to

    • copy

      public Xoshiro512PlusPlusRandom 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