Package com.github.tommyettinger.random

Class Xoshiro160RoadroxoRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.Enhanced32Random
com.github.tommyettinger.random.Xoshiro160RoadroxoRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class Xoshiro160RoadroxoRandom extends Enhanced32Random
A random number generator that is optimized for performance on 32-bit machines and with Google Web Toolkit, this uses no multiplication and is similar to the published xoshiro128 algorithm, but has an extra 32-bit state that acts like a counter. Unlike any variations on xoshiro128 with four states, this is actually 1-dimensionally equidistributed - existing generators like xoshiro128++ produce the result 0 less frequently (by a tiny difference, but that is enough to mean it isn't equal). This produces all 32-bit results equally frequently with nextInt(). It is also almost 1-dimensionally equidistributed with nextLong(); of the Math.pow(2, 64) possible results for nextLong(), all but Math.pow(2, 32) results are returned Math.pow(2, 128) times, and the remaining Math.pow(2, 32) results are returned Math.pow(2, 128) - 1 times. Note that the pow() call is pseudocode; real Java code would consider Math.pow(2, 128) and Math.pow(2, 128) - 1 equal. It is important to emphasize that nextLong() is not actually equidistributed, just very close to that, in the same way that xoshiro128++ is not actually equidistributed, just very close to it. This is also very close to 2D-equidistributed for 32-bit outputs, with (2 to the 32) output pairs occurring once less often than the remaining (2 to the 64) minus (2 to the 32) pairs. Each output will occur either (2 to the 128) or ((2 to the 128) minus 1) times.
An unusual property of this generator is that the state changes in exactly the same way and by the same distance regardless of whether nextInt() or nextLong() is called (and the same for the reverse-direction methods previousInt() and previousLong()). The result is calculated differently for 64-bit output than 32-bit output. For nextInt(), stateA, stateB, and stateE are combined by rotating some, adding a pair of states, and XORing the two halves. For nextLong(), all states are combined by forming two 32-bit outputs (using the same or similar 32-bit math as for nextInt()) and combining them into one 64-bit value only at the end.
The actual speed of this is going to vary wildly depending on the platform being benchmarked. On GWT, which is the main place where the performance of a random number generator might actually be a bottleneck in a game, this performs very well. On desktop platforms, it is faster at generating int values than long, which is to be expected for a 32-bit generator, but not as fast as some other generators, like ChopRandom. However, this guarantees a larger minimum period than ChopRandom can possibly provide as a maximum period.
Xoshiro160RoadroxoRandom has a guaranteed period of pow(2, 160) - pow(2, 32). The only disallowed states have each of stateA, stateB, stateC, and stateD equal to 0; stateE is unconstrained. It starts returning fully-decorrrelated results even given very-correlated initial states after about 10 calls to nextInt() or nextLong(). This passes 64TB of PractRand with no anomalies, both for nextInt() and the different algorithm for nextLong().
This implements all optional methods in EnhancedRandom except EnhancedRandom.skip(long). It also implements leap() to allow jumping ahead by the equivalent of at least 2 to the 64 calls to nextInt(). Methods that can use only nextInt(), without needing nextLong() to produce equal-quality results, do so.
Based on this public-domain code by Vigna and Blackman.
See Also:

  • Field Details

    • stateA

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

    • stateB

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

    • stateC

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

    • stateD

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

    • stateE

      protected int stateE
      The fifth state; can be any int.

  • Constructor Details

    • Xoshiro160RoadroxoRandom

      public Xoshiro160RoadroxoRandom()
      Creates a new Xoshiro160RoadroxoRandom with a random state.

    • Xoshiro160RoadroxoRandom

      public Xoshiro160RoadroxoRandom(long seed)
      Creates a new Xoshiro160RoadroxoRandom 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

    • Xoshiro160RoadroxoRandom

      public Xoshiro160RoadroxoRandom(int stateA, int stateB, int stateC, int stateD, int stateE)
      Creates a new Xoshiro160RoadroxoRandom with the given four states; all int values are permitted. These states will be used verbatim, unless the first 4 states are each 0 -- if those are all 0, then stateD is replaced with 1. Note that stateE can have any int value without constraining the other states.
      Parameters:
      stateA - any int value
      stateB - any int value
      stateC - any int value
      stateD - any int value
      stateE - any int 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.

    • mainlyGeneratesInt

      public boolean mainlyGeneratesInt()
      This generator is almost as fast at generating long values as it is int values.
      Overrides:
      mainlyGeneratesInt in class Enhanced32Random
      Returns:
      false
      See Also:

    • getMinimumPeriod

      public BigInteger getMinimumPeriod()
      (2 to the 160) - (2 to the 64).
      Overrides:
      getMinimumPeriod in class EnhancedRandom
      Returns:
      (2 to the 160) - (2 to the 64)

    • getStateCount

      public int getStateCount()
      This generator has 5 int states, so this returns 5.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      5 (five)

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the state determined by selection, as-is. The value for selection should be between 0 and 5, inclusive; if it is any other value this gets state E as if 4 was given.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to get; generally 0, 1, 2, 3, or 4
      Returns:
      the value of the selected state, which is an int that will be promoted to long

    • setSelectedState

      public void setSelectedState(int selection, long value)
      Sets one of the states, determined by selection, to the lower 32 bits of value, as-is. Selections 0, 1, 2, 3, and 4 refer to states A, B, C, D, and E and if the selection is anything else, this treats it as 4 and sets stateE. This always casts value to an int before using it. If the first four states would be 0 as a result of this call, it instead sets the fourth part of the state (stateD) to 1.
      Overrides:
      setSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to set; generally 0, 1, 2, 3, or 4
      value - the exact value to use for the selected state, if valid

    • setSeed

      public void setSeed(long seed)
      This initializes all 5 states of the generator to random values based on the given seed. (2 to the 64) possible initial generator states can be produced here. This is not capable of setting the full state to the only invalid value (all zeros).
      Specified by:
      setSeed in class EnhancedRandom
      Parameters:
      seed - the initial seed; may be any long

    • setSeed

      public void setSeed(int seed)
      This initializes all 4 states of the generator to random values based on the given seed. (2 to the 32) possible initial generator states can be produced here.
      Parameters:
      seed - the initial seed; may be any int

    • getStateA

      public int getStateA()

    • setStateA

      public void setStateA(int stateA)
      Sets the first part of the state to the given int.
      Parameters:
      stateA - can be any int

    • getStateB

      public int getStateB()

    • setStateB

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

    • getStateC

      public int getStateC()

    • setStateC

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

    • getStateD

      public int getStateD()

    • setStateD

      public void setStateD(int stateD)
      Sets the fourth part of the state to the given int. If all four states would be 0 as a result of this call, it instead sets the fourth part of the state to 1.
      Parameters:
      stateD - can be any int

    • getStateE

      public int getStateE()

    • setStateE

      public void setStateE(int stateE)
      Sets the fifth part of the state by casting the parameter to an int.
      Parameters:
      stateE - can be any int

    • setState

      public void setState(long stateA, long stateB, long stateC, long stateD, long stateE)
      Sets the state completely to the given five state variables, casting each to an int. This is the same as calling setStateA(int), setStateB(int), setStateC(int), setStateD(int), and setStateE(int) as a group. If the first four states would all be 0 as a result of this call, it instead sets the fourth part of the state to 1.
      Overrides:
      setState in class EnhancedRandom
      Parameters:
      stateA - the first state; can be any long, but will be cast to an int before use
      stateB - the second state; can be any long, but will be cast to an int before use
      stateC - the third state; can be any long, but will be cast to an int before use
      stateD - the fourth state; can be any long, but will be cast to an int before use
      stateE - the fifth state; can be any long, but will be cast to an int before use

    • setState

      public void setState(int stateA, int stateB, int stateC, int stateD, int stateE)
      Like the superclass method setState(long, long, long, long, long), but takes five int values instead of long. This can avoid creating longs on JS-targeting platforms, which tends to be quite slow. If the first four states would all be 0 as a result of this call, it instead sets the fourth part of the state to 1.
      Parameters:
      stateA - the first state; can be any int
      stateB - the second state; can be any int
      stateC - the third state; can be any int
      stateD - the fourth state; can be any int
      stateE - the fifth state; can be any int

    • nextLong

      public long nextLong()
      Description copied from class: Enhanced32Random
      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
      Overrides:
      nextLong in class Enhanced32Random
      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()

    • 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()

    • next

      public int next(int bits)
      Description copied from class: Enhanced32Random
      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 Enhanced32Random.nextInt(int) instead. For some specific cases, this method is more efficient and less biased than Enhanced32Random.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 Enhanced32Random
      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

    • nextInt

      public int nextInt()
      Description copied from class: Enhanced32Random
      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.
      In Enhanced32Random, this throws an UnsupportedOperationException because the concrete subclass must implement this.
      Specified by:
      nextInt in interface RandomGenerator
      Overrides:
      nextInt in class Enhanced32Random
      Returns:
      the next pseudorandom, uniformly distributed int value from this random number generator's sequence

    • nextLong

      public long nextLong(long inner, long outer)
      Description copied from class: Enhanced32Random
      Returns a pseudorandom, uniformly distributed long value between the specified innerBound (inclusive) and the specified outerBound (exclusive). If outerBound is less than or equal to innerBound, this always returns innerBound.
      For any case where outerBound might be valid but less than innerBound, you can use Enhanced32Random.nextSignedLong(long, long).
      Specified by:
      nextLong in interface RandomGenerator
      Overrides:
      nextLong in class Enhanced32Random
      Parameters:
      inner - the inclusive inner bound; may be any long, allowing negative
      outer - the exclusive outer bound; must be greater than innerBound (otherwise this returns innerBound)
      Returns:
      a pseudorandom long between innerBound (inclusive) and outerBound (exclusive)
      See Also:

    • nextSignedLong

      public long nextSignedLong(long inner, long outer)
      Description copied from class: Enhanced32Random
      Returns a pseudorandom, uniformly distributed long value between the specified innerBound (inclusive) and the specified outerBound (exclusive). This is meant for cases where either bound may be negative, especially if the bounds are unknown or may be user-specified.
      Overrides:
      nextSignedLong in class Enhanced32Random
      Parameters:
      inner - the inclusive inner bound; may be any long, allowing negative
      outer - the exclusive outer bound; may be any long, allowing negative
      Returns:
      a pseudorandom long between innerBound (inclusive) and outerBound (exclusive)
      See Also:

    • nextExclusiveDouble

      public double nextExclusiveDouble()
      Description copied from class: Enhanced32Random
      Gets a random double between 0.0 and 1.0, exclusive at both ends; this method is also more uniform than Enhanced32Random.nextDouble() if you use the bit-patterns of the returned doubles. This is a simplified version of this algorithm by Allen Downey. This can return double values between 2.710505431213761E-20 and 0.9999999999999999, or 0x1.0p-65 and 0x1.fffffffffffffp-1 in hex notation. It cannot return 0 or 1. Some cases can prefer Enhanced32Random.nextExclusiveDoubleEquidistant(), which is implemented more traditionally but may have slower performance. This method can also return doubles that are extremely close to 0, but can't return doubles that are as close to 1, due to how floating-point numbers work. However, nextExclusiveDoubleEquidistant() can return only a minimum value that is as distant from 0 as its maximum value is distant from 1.
      To compare, nextDouble() and nextExclusiveDoubleEquidistant() are less likely to produce a "1" bit for their lowest 5 bits of mantissa/significand (the least significant bits numerically, but potentially important for some uses), with the least significant bit produced half as often as the most significant bit in the mantissa. As for this method, it has approximately the same likelihood of producing a "1" bit for any position in the mantissa.
      The implementation may have different performance characteristics than Enhanced32Random.nextDouble(), because this doesn't perform any floating-point multiplication or division, and instead assembles bits obtained by one call to Enhanced32Random.nextLong(). This uses BitConversion.longBitsToDouble(long) and BitConversion.countLeadingZeros(long), both of which typically have optimized intrinsics on HotSpot, and this is branchless and loopless, unlike the original algorithm by Allen Downey. When compared with Enhanced32Random.nextExclusiveDoubleEquidistant(), this method performs better on at least HotSpot JVMs. On GraalVM 17, this is over twice as fast as nextExclusiveDoubleEquidistant().
      Overrides:
      nextExclusiveDouble in class Enhanced32Random
      Returns:
      a random uniform double between 2.710505431213761E-20 and 0.9999999999999999 (both inclusive)

    • copy

      public Xoshiro160RoadroxoRandom 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.

    • leap

      public long leap()
      Jumps extremely far in the generator's sequence, to a state that would normally only be reached by calling nextLong() at least Math.pow(2, 64) times sequentially. "At least" here means a non-zero 32-bit unsigned integer multiple of Math.pow(2, 64), because this only changes states A, B, C, and D -- stateE doesn't change, even though normally calling nextInt() 2 to the 64 times would change stateE by an unpredictable amount. This can be used to create over 18 quintillion distinct substreams of this generator's sequence, each with a period of at least Math.pow(2, 64).
      Returns:
      the result of what nextLong() would return if it was called at the state this jumped to

    • equals

      public boolean equals(Object o)
      Overrides:
      equals in class Object

    • toString

      public String toString()
      Overrides:
      toString in class Object