Package com.github.tommyettinger.random

Class QoaxsrRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.QoaxsrRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class QoaxsrRandom extends EnhancedRandom
A good generator with 64 bits of state, meant to avoid large "magic numbers." This has a period of 2 to the 64. This changes the state by adding ((state times state) OR 123456789); this is a "QOA" operation and is full-period. It takes the current state and performs some mixing on it at every call to nextLong(). The mixing is a XOR-shift right by 29, then another identical QOA operation on the currently mixed value, then returning that XOR-shifted right by 27.
Useful traits of this generator are that it has exactly one long of state, and that all values are permitted for that state. This generator passes 128TB of PractRand tests for quality, without any anomalies. It also passes Initial Correlation Evaluator and Immediate Initial Correlation Evaluator tests.
This is decently fast, but not as fast as most generators here that can operate using instruction-level parallelism and don't use multiplication. Having such a small state may allow it to run faster on GraalVM.
The constant 123456789 can be changed to any long where the low 3 bits are equal to 5 or equal to 7. The binary representation of 123456789 is 0b111010110111100110100010101L; the last three bits can be 0b101 or 0b111. This initially used 7 as the constant in the same place, but the high bits change more quickly for constants that are larger than just 5 or 7. 123456789 is a 27-bit number, and using a mid-size constant like that makes the low 27 bits of the result, before mixing, more predictable. However, after mixing with a right XOR-shift, the low-order bits improve dramatically. Using other constants might not pass PractRand (or might pass with anomalies). If the low 3 bits aren't 0b101 or 0b111, this won't be a full-period generator.
The name Qoaxsr is an abbreviation of the operations it uses: Quad (squaring state), OR, Add, XOR-Shift, Repeat. The suggested pronunciation is "quack-scissor." The QOA operation is a direct descendant of the XQO operation found in this hash-prospector issue by fp64 and Marc B. Reynolds, among others. It is also related to the formula for the nth triangular number, (n + n * n) / 2, which is a bijection mod n if you can compute it without overflow.
This class is an EnhancedRandom from juniper and is also a JDK Random as a result.
Some other generators in juniper have the "distinct" quality this generator has: DistinctRandom, HornRandom, Mx3Random, WoolRandom, LCG64Random, GoldenQuasiRandom, and VanDerCorputQuasiRandom all will also output every long value exactly once over their period, each of which has the same period as this.
This doesn't randomize the seed when given one with setSeed(long), but the results are decorrelated well even for sequential seeds after one generation.
This implements all methods from EnhancedRandom, except the optional EnhancedRandom.skip(long) method. It implements previousLong() without using skip(). Notably, previousLong() is significantly slower than nextLong(), requiring 64 loop iterations in addition to the work nextLong() performs.
See Also:

  • Field Details

    • state

      public long state
      The only long state variable; can be any long.

  • Constructor Details

    • QoaxsrRandom

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

    • QoaxsrRandom

      public QoaxsrRandom(long state)
      Creates a new QoaxsrRandom with the given state; all long values are permitted.
      Parameters:
      state - 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 64.
      Overrides:
      getMinimumPeriod in class EnhancedRandom
      Returns:
      2 to the 64

    • getStateCount

      public int getStateCount()
      This has one long state.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      1 (one)

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the only state, which can be any long value.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - ignored; this always returns the same, only state
      Returns:
      the only state's exact value

    • setSelectedState

      public void setSelectedState(int selection, long value)
      Sets the only state, which can be given any long value. The selection can be anything and is ignored.
      Overrides:
      setSelectedState in class EnhancedRandom
      Parameters:
      selection - ignored; this always sets the same, only state
      value - the exact value to use for the state; all longs are valid

    • setSeed

      public void setSeed(long seed)
      Sets the only state, which can be given any long value; this seed value will not be altered. Equivalent to setSelectedState(int, long) with any selection and seed passed as the value.
      Specified by:
      setSeed in class EnhancedRandom
      Parameters:
      seed - the exact value to use for the state; all longs are valid

    • getState

      public long getState()
      Gets the current state; it's already public, but I guess this could still be useful. The state can be any long.
      Returns:
      the current state, as a long

    • setState

      public void setState(long state)
      Sets each state variable to the given state. This implementation simply sets the one state variable to state.
      Overrides:
      setState in class EnhancedRandom
      Parameters:
      state - the long value to use for the state variable

    • 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 QoaxsrRandom 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