Package com.github.tommyettinger.random

Class Chill32Random

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.Enhanced32Random
com.github.tommyettinger.random.Chill32Random
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class Chill32Random extends Enhanced32Random
A random number generator that is optimized for performance on 32-bit machines and with Google Web Toolkit, Chill32Random is a 32-bit-native generator that doesn't have any shorter subcycles (because it only has one cycle, of length 2 to the 96). It effectively shares this property with Xoshiro128PlusPlusRandom, except that Xoshiro128PlusPlusRandom doesn't permit the state to be all 0s, while Chill32Random isn't adversely affected by that condition. This generator has three int states and doesn't use any multiplication. It does use the count leading zeros instruction, which is Integer.numberOfLeadingZeros(int) on most platforms, or the JS function Math.clz32() on GWT. This only counts leading zeros for the purposes of its state transition (for stateB and stateC), and using it the way this does is what allows the period to be so high. This is meant to be faster on GWT and TeaVM than the 64-bit-native generators here.
This algorithm passes 64TB of PractRand testing with no anomalies. It was tested as a 64-bit generator (using both 64-bit and 32-bit "folding modes"), because this is designed to be much faster at calling nextLong() on any platform (relative to other 32-bit-native generators) while still using 32-bit math. Essentially, it always generates 64 bits of result, but only uses 32 of them from nextInt() (and doesn't need to produce a long on GWT in nextInt(), which is a slow task).
When the state is given exactly with Chill32Random(int, int, int) or setState(long, long, long), this doesn't have any generations at the start where numerically similar states show correlation. This is different from generators like AceRandom, which take some time to become adequately random, but similar to generators like DistinctRandom and FlowRandom, which hash their state(s) to get a random output from predictable state changes. Some generators never stop showing correlation from similar initial states, such as WhiskerRandom or Xoshiro256StarStarRandom; this doesn't affect how useful they are if you have only one generator or if they are seeded in an adequately-random manner.
A notable quality of the implementation is that nextInt() and nextLong() return the same values for their lowest 32 bits, and nextLong() advances the state by the same amount as nextInt(). This is not a cryptographically-secure generator (at all), even though it uses only operations that should be immune or resistant to timing attacks.
The hash-like construction used to randomize the three counter-like states is loosely based on the Speck cipher (using only 4 rounds), but adds in an extra rotation at each round, and uses very different rotation constants in every round. The input states A and B correspond to plaintext, and stateC to the key.
This implements all optional methods in EnhancedRandom except EnhancedRandom.skip(long).
See Also:

  • Field Details

    • stateA

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

    • stateB

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

    • stateC

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

  • Constructor Details

    • Chill32Random

      public Chill32Random()
      Creates a new Chill32Random with a random state.

    • Chill32Random

      public Chill32Random(long seed)
      Creates a new Chill32Random 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

    • Chill32Random

      public Chill32Random(int stateA, int stateB, int stateC)
      Creates a new Chill32Random with the given three states. All int values are permitted.
      Parameters:
      stateA - any int value
      stateB - any int value
      stateC - 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.

    • getMinimumPeriod

      public BigInteger getMinimumPeriod()
      2 to the 96.
      Overrides:
      getMinimumPeriod in class EnhancedRandom
      Returns:
      2 to the 96

    • 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:

    • getStateCount

      public int getStateCount()
      This generator has 3 int 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. The value for selection should be between 0 and 2, inclusive; if it is any other value this gets state C as if 2 was given.
      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, 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, and 2 refer to states A, B, and C, and if the selection is anything else, this treats it as 2 and sets stateC. This always casts value to an int before using it.
      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) known-good initial generator states can be produced here.
      Specified by:
      setSeed in class EnhancedRandom
      Parameters:
      seed - the initial seed; may be any long

    • 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

    • setState

      public void setState(long stateA, long stateB, long stateC)
      Sets the state completely to the given four state variables, casting each to an int. This is the same as calling setStateA(int), setStateB(int), and setStateC(int) as a group.
      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

    • setState

      public void setState(int stateA, int stateB, int stateC)
      Like the superclass method setState(long, long, long), but takes three int values instead of long. This can avoid creating longs on JS-targeting platforms, which tends to be quite slow.
      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

    • 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()

    • 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

    • 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()

    • 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 Chill32Random 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