Package com.github.tommyettinger.random

Class Lamb32Random

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.Lamb32Random
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class Lamb32Random extends EnhancedRandom
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 except 0.

    • stateB

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

  • 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 EnhancedRandom
      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 long getStateA()

    • setStateA

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

    • getStateB

      public long getStateB()

    • setStateB

      public void setStateB(long 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(long) and setStateB(long), 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

    • 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

    • 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()

    • 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()

    • 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

    • nextInt

      public int nextInt(int bound)
      Description copied from class: EnhancedRandom
      Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract of nextInt is that one int value in the specified range is pseudorandomly generated and returned. All bound possible int values are produced with (approximately) equal probability.
      This method clamps bound to be at least 0; it never returns a negative int.
      It should be mentioned that the technique this uses has some bias, depending on bound, but it typically isn't measurable without specifically looking for it. Using the method this does allows this method to always advance the state by one step, instead of a varying and unpredictable amount with the more typical ways of rejection-sampling random numbers and only using numbers that can produce an int within the bound without bias. See M.E. O'Neill's blog about random numbers for discussion of alternative, unbiased methods.
      Specified by:
      nextInt in interface RandomGenerator
      Overrides:
      nextInt in class EnhancedRandom
      Parameters:
      bound - the upper bound (exclusive). If negative or 0, this always returns 0.
      Returns:
      the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive) from this random number generator's sequence

    • nextSignedInt

      public int nextSignedInt(int outerBound)
      Description copied from class: EnhancedRandom
      Returns a pseudorandom, uniformly distributed int value between an inner bound of 0 (inclusive) and the specified outerBound (exclusive). This is meant for cases where the outer bound may be negative, especially if the bound is unknown or may be user-specified. A negative outer bound is used as the lower bound; a positive outer bound is used as the upper bound. An outer bound of -1, 0, or 1 will always return 0, keeping the bound exclusive (except for outer bound 0). This method is slightly slower than EnhancedRandom.nextInt(int).
      Overrides:
      nextSignedInt in class EnhancedRandom
      Parameters:
      outerBound - the outer exclusive bound; may be any int value, allowing negative
      Returns:
      a pseudorandom int between 0 (inclusive) and outerBound (exclusive)
      See Also:

    • nextUnsignedInt

      public int nextUnsignedInt(int bound)
      Description copied from class: EnhancedRandom
      Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract of nextInt is that one int value in the specified range is pseudorandomly generated and returned. All bound possible int values are produced with (approximately) equal probability.
      This method treats the outer bound as unsigned, so if a negative int is passed as bound, it will be treated as positive and larger than Integer.MAX_VALUE. That means this can produce results that are positive or negative, but when you mask the result and the bound with 0xFFFFFFFFL (to treat them as unsigned), the result will always be between 0L (inclusive) and the masked bound (exclusive).
      This is primarily useful as a building block for other methods in this class.
      Overrides:
      nextUnsignedInt in class EnhancedRandom
      Parameters:
      bound - the upper bound (exclusive); treated as unsigned
      Returns:
      the next pseudorandom, uniformly distributed int value between zero (inclusive) and bound (exclusive), treated as unsigned, from this random number generator's sequence

    • nextBytes

      public void nextBytes(byte[] bytes)
      Description copied from class: EnhancedRandom
      Generates random bytes and places them into a user-supplied byte array. The number of random bytes produced is equal to the length of the byte array.
      Specified by:
      nextBytes in interface RandomGenerator
      Overrides:
      nextBytes in class EnhancedRandom
      Parameters:
      bytes - the byte array to fill with random bytes

    • nextInt

      public int nextInt(int innerBound, int outerBound)
      Description copied from class: EnhancedRandom
      Returns a pseudorandom, uniformly distributed int 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 EnhancedRandom.nextSignedInt(int, int). If outerBound is less than innerBound here, this simply returns innerBound.
      Specified by:
      nextInt in interface RandomGenerator
      Overrides:
      nextInt in class EnhancedRandom
      Parameters:
      innerBound - the inclusive inner bound; may be any int, allowing negative
      outerBound - the exclusive outer bound; must be greater than innerBound (otherwise this returns innerBound)
      Returns:
      a pseudorandom int between innerBound (inclusive) and outerBound (exclusive)
      See Also:

    • nextSignedInt

      public int nextSignedInt(int innerBound, int outerBound)
      Description copied from class: EnhancedRandom
      Returns a pseudorandom, uniformly distributed int 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:
      nextSignedInt in class EnhancedRandom
      Parameters:
      innerBound - the inclusive inner bound; may be any int, allowing negative
      outerBound - the exclusive outer bound; may be any int, allowing negative
      Returns:
      a pseudorandom int between innerBound (inclusive) and outerBound (exclusive)
      See Also:

    • nextLong

      public long nextLong(long bound)
      Description copied from class: EnhancedRandom
      Returns a pseudorandom, uniformly distributed long value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The general contract of nextLong is that one long value in the specified range is pseudorandomly generated and returned. All bound possible long values are produced with (approximately) equal probability, though there is a small amount of bias depending on the bound.
      Note that this advances the state by the same amount as a single call to EnhancedRandom.nextLong(), which allows methods like EnhancedRandom.skip(long) to function correctly, but introduces some bias when bound is very large. This will also advance the state if bound is 0 or negative, so usage with a variable bound will advance the state reliably.
      This method has some bias, particularly on larger bounds. Actually measuring bias with bounds in the trillions or greater is challenging but not impossible, so don't use this for a real-money gambling purpose. The bias isn't especially significant, though.
      Specified by:
      nextLong in interface RandomGenerator
      Overrides:
      nextLong in class EnhancedRandom
      Parameters:
      bound - the upper bound (exclusive). If negative or 0, this always returns 0.
      Returns:
      the next pseudorandom, uniformly distributed long value between zero (inclusive) and bound (exclusive) from this random number generator's sequence
      See Also:

    • nextSignedLong

      public long nextSignedLong(long outer)
      Description copied from class: EnhancedRandom
      Returns a pseudorandom, uniformly distributed long value between an inner bound of 0 (inclusive) and the specified outerBound (exclusive). This is meant for cases where the outer bound may be negative, especially if the bound is unknown or may be user-specified. A negative outer bound is used as the lower bound; a positive outer bound is used as the upper bound. An outer bound of -1, 0, or 1 will always return 0, keeping the bound exclusive (except for outer bound 0).

      Note that this advances the state by the same amount as a single call to EnhancedRandom.nextLong(), which allows methods like EnhancedRandom.skip(long) to function correctly, but introduces some bias when bound is very large. This method should be about as fast as EnhancedRandom.nextLong(long) , unlike the speed difference between EnhancedRandom.nextInt(int) and EnhancedRandom.nextSignedInt(int).

      Overrides:
      nextSignedLong in class EnhancedRandom
      Parameters:
      outer - the outer exclusive bound; may be any long value, allowing negative
      Returns:
      a pseudorandom long between 0 (inclusive) and outerBound (exclusive)
      See Also:

    • nextLong

      public long nextLong(long inner, long outer)
      Description copied from class: EnhancedRandom
      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 EnhancedRandom.nextSignedLong(long, long).
      Specified by:
      nextLong in interface RandomGenerator
      Overrides:
      nextLong in class EnhancedRandom
      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: EnhancedRandom
      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 EnhancedRandom
      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:

    • nextBoolean

      public boolean nextBoolean()
      Description copied from class: EnhancedRandom
      Returns the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence. The general contract of nextBoolean is that one boolean value is pseudorandomly generated and returned. The values true and false are produced with (approximately) equal probability.
      The public implementation simply returns a sign check on EnhancedRandom.nextLong(), returning true if the generated long is negative. This is typically the safest way to implement this method; many types of generators have less statistical quality on their lowest bit, so just returning based on the lowest bit isn't always a good idea.
      Specified by:
      nextBoolean in interface RandomGenerator
      Overrides:
      nextBoolean in class EnhancedRandom
      Returns:
      the next pseudorandom, uniformly distributed boolean value from this random number generator's sequence

    • nextFloat

      public float nextFloat()
      Description copied from class: EnhancedRandom
      Returns the next pseudorandom, uniformly distributed float value between 0.0 (inclusive) and 1.0 (exclusive) from this random number generator's sequence.

      The general contract of nextFloat is that one float value, chosen (approximately) uniformly from the range 0.0f (inclusive) to 1.0f (exclusive), is pseudorandomly generated and returned. All 224 possible float values of the form m x 2-24, where m is a positive integer less than 224, are produced with (approximately) equal probability.

      The public implementation uses the upper 24 bits of EnhancedRandom.nextLong(), with an unsigned right shift and a multiply by a very small float (5.9604645E-8f or 0x1p-24f). It tends to be fast if nextLong() is fast, but alternative implementations could use 24 bits of EnhancedRandom.nextInt() (or just EnhancedRandom.next(int), giving it 24) if that generator doesn't efficiently generate 64-bit longs.

      Specified by:
      nextFloat in interface RandomGenerator
      Overrides:
      nextFloat in class EnhancedRandom
      Returns:
      the next pseudorandom, uniformly distributed float value between 0.0 and 1.0 from this random number generator's sequence

    • nextInclusiveFloat

      public float nextInclusiveFloat()
      Description copied from class: EnhancedRandom
      This is just like EnhancedRandom.nextFloat(), returning a float between 0 and 1, except that it is inclusive on both 0.0 and 1.0. It returns 1.0 rarely, 0.000000000000000005421010862427522% of the time if there is no bias in the generator, but it can happen.
      This method does not return purely-equidistant floats, because there the resolution of possible floats it can generate is higher as it approaches 0.0 . The smallest non-zero float this can return is 2.7105064E-20 (0x1.000006p-65 in hex), and the largest non-one float this can return is 0.99999994f (0x1.fffffep-1 in hex). This uses nearly identical code to EnhancedRandom.nextExclusiveFloat(), but does some really unusual operations on both the bits and the float value to be able to produce 0.0f and 1.0f . This retains the exclusive version's quality of having approximately uniform distributions for every mantissa bit, unlike most ways of generating random floating-point numbers.
      Overrides:
      nextInclusiveFloat in class EnhancedRandom
      Returns:
      a float between 0.0, inclusive, and 1.0, inclusive

    • 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