Package com.github.tommyettinger.random

Class Lamb32Random

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.Enhanced32Random
com.github.tommyettinger.random.Lamb32Random
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class Lamb32Random extends Enhanced32Random
Like HornRandom, but using 32-bit math for its next(int), nextInt(), and previousInt() methods, and meant to be portable to JS. Also like HornRandom, it is meant to fit in a human's memory, avoiding complex constants.
This generator natively generates 32-bit results, and has two 32-bit states. It has the maximum period for a generator with its state size, at (2 to the 64) exactly. All int values are valid for both stateA and stateB.
This passes initial correlation tests (ICE), including immediate initial correlation (IICE). This also passes 64 TB of PractRand with no anomalies.
This uses four "big constants," which each follow a pattern: nine 9's in a row (as a decimal number), nine 7's in a row, nine 5's in a row, and nine 3's in a row. It uses 3 shifts: 12 and -12 (as a rotation), and 23 (as an unsigned right shift at the end). Other than that and the specific operations this uses, there are no "messy" constants to remember, and the bulk of the algorithm is just 4 lines of code for nextInt().
This is built around a 32-bit XLCG (Xor-Linear Congruential Generator) for its stateB, and its stateA updates dependent on stateB's leading zeros. Because adding the leading zeros for every 32-bit value in stateB's cycle produces an odd sum, every time stateB cycles, stateA effectively adds an odd number, making it act like a counter with an odd increment that updates slowly. This is shaken up by stateA multiplying (stateA + countLeadingZeros(stateB)) * 777777777, which it turns out doesn't need to be any kind of multiplier other than odd. (An LCG or XLCG would require the low 3 bits of the multiplier to be a specific pattern.)
This is meant to be portable to JS by using its Math.imul() and Math.clz32() functions. The order in which the arithmetic runs matters; executing imul() last ensures that its output will be a 32-bit integer, and that if either input was outside 32-bit int bounds, it would be corrected before use. Any modifications to the states for producing an output use bitwise math, so they won't exceed int bounds, either, on JS.
See Also:

  • Field Details

    • stateA

      protected int stateA
      The first (dependent counter) state; can be any int.

    • stateB

      protected int stateB
      The second (XLCG) state; can be any int.

  • Constructor Details

    • Lamb32Random

      public Lamb32Random()
      Creates a new Lamb32Random with a random state.

    • Lamb32Random

      public Lamb32Random(long seed)
      Creates a new Lamb32Random 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

    • Lamb32Random

      public Lamb32Random(int stateA, int stateB)
      Creates a new Lamb32Random with the given two states; all int values are permitted.
      Parameters:
      stateA - any int value
      stateB - 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 64).
      Overrides:
      getMinimumPeriod in class EnhancedRandom
      Returns:
      (2 to the 64)

    • getStateCount

      public int getStateCount()
      This generator has 2 int states, so this returns 2.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      2 (two)

    • mainlyGeneratesInt

      public boolean mainlyGeneratesInt()
      Lamb32Random mainly generates int values.
      Overrides:
      mainlyGeneratesInt in class Enhanced32Random
      Returns:
      true
      See Also:

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the state determined by selection, as-is. The value for selection should be 0 or 1; if it is any other value this gets state B as if 1 was given.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to get; generally 0 or 1
      Returns:
      the value of the selected state, treated as long but internally an int

    • setSelectedState

      public void setSelectedState(int selection, long value)
      Sets one of the states, determined by selection, to value, cast to int. Selections 0 refers to state A, and if the selection is anything else, this treats it as 1 and sets stateB.
      Overrides:
      setSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to set; generally 0, 1, 2, or 3
      value - the value to use for the selected state, which will be cast to int

    • setSeed

      public void setSeed(long seed)
      This initializes both states of the generator to random values based on the given seed. (2 to the 64) possible 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 (dependent counter) part of the state.
      Parameters:
      stateA - can be any int

    • getStateB

      public int getStateB()

    • setStateB

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

    • setState

      public void setState(long stateA, long stateB)
      Sets the state completely to the given two state variables. This is the same as calling setStateA(int) and setStateB(int), as a group.
      Overrides:
      setState in class EnhancedRandom
      Parameters:
      stateA - the first state; can be any int
      stateB - the second state; can be any int

    • setState

      public void setState(int stateA, int stateB)
      Like the superclass method setState(long, long), but takes two 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

    • 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

    • 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()

    • 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

    • 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()

    • leap

      public long leap()
      Jumps extremely far in the generator's sequence, such that it requires Math.pow(2, 32) calls to leap() to complete a cycle through the generator's entire sequence. This can be used to create over 4 billion substreams of this generator's sequence, each with a period of Math.pow(2, 32).
      Returns:
      the result of what nextLong() would return if it was called at the state this jumped to

    • copy

      public Lamb32Random 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