Package com.github.tommyettinger.random

Class ChopRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.Enhanced32Random
com.github.tommyettinger.random.ChopRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class ChopRandom extends Enhanced32Random
A random number generator that is optimized for performance on 32-bit machines and with Google Web Toolkit, this uses only add, bitwise-rotate, and XOR operations (no multiplication). This generator is nearly identical to TrimRandom in its structure, but uses smaller words (int instead of long), and has better avalanche properties.
The actual speed of this is going to vary wildly depending on the platform being benchmarked. It's hard to find a faster high-quality way to generate long values on GWT (this is, surprisingly, faster than generators like FourWheelRandom or WhiskerRandom on GWT at generating either int or long values, while this is likely half the speed of FourWheelRandom when generating long values on Java 17 HotSpot). ChopRandom has a guaranteed minimum period of 2 to the 32, and is very likely to have a much longer period for almost all initial states.
This generator can be considered stable. It passes 64TB of PractRand testing without anomalies.
The algorithm used here has four states purely to exploit instruction-level parallelism; one state is a counter (this gives the guaranteed minimum period of 2 to the 32), and the others combine the values of the four states across three variables. There's a complex tangle of dependencies across the states, but it is possible to invert the generator given a full 128-bit state; this is vital for its period and quality.
It is strongly recommended that you seed this with setSeed(long) instead of setState(long, long, long, long), because if you give sequential seeds to both setSeed() and setState(), the former will start off random, while the latter will start off repeating the seed sequence. After about 20-40 random numbers generated, any correlation between similarly seeded generators will probably be completely gone, though.
This implements all optional methods in EnhancedRandom except EnhancedRandom.skip(long); it does implement previousLong() and previousInt() without using skip().
This is called ChopRandom because it operates on half the bits as TrimRandom while otherwise being similar.
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. If this has just been set to some value, then the next call to nextInt() will return that value as-is. Later calls will be more random.

    • stateD

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

  • Constructor Details

    • ChopRandom

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

    • ChopRandom

      public ChopRandom(long seed)
      Creates a new ChopRandom 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

    • ChopRandom

      public ChopRandom(int stateA, int stateB, int stateC, int stateD)
      Creates a new ChopRandom with the given four states; all int values are permitted. These states will be used verbatim.
      Parameters:
      stateA - any int value
      stateB - any int value
      stateC - any int value; will be returned exactly on the first call to nextInt()
      stateD - 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 mainly generates int values.
      Overrides:
      mainlyGeneratesInt in class Enhanced32Random
      Returns:
      true
      See Also:

    • getStateCount

      public int getStateCount()
      This generator has 4 int states, so this returns 4.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      4 (four)

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the state determined by selection, as-is. The value for selection should be between 0 and 3, inclusive; if it is any other value this gets state D as if 3 was given.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to get; generally 0, 1, 2, or 3
      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, and 3 refer to states A, B, C, and D, and if the selection is anything else, this treats it as 3 and sets stateD. 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, 2, or 3
      value - the exact value to use for the selected state, if valid

    • setSeed

      public void setSeed(long seed)
      This initializes all 4 states of the generator to random values based on the given seed. (2 to the 64) possible initial generator states can be produced here, all with a different first value returned by nextLong() (because stateC is guaranteed to be different for every different seed).
      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. Note that if you call nextInt() immediately after this, it will return the given stateC (cast to int) as-is, so you may want to call some random generation methods (such as nextInt()) and discard the results after setting the state.
      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.
      Parameters:
      stateD - can be any int

    • setState

      public void setState(long stateA, long stateB, long stateC, long stateD)
      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), setStateC(int), and setStateD(int) as a group. You may want to call nextInt() a few times after setting the states like this, unless the value for stateC (in particular) is already adequately random; the first call to nextInt(), if it is made immediately after calling this, will return stateC as-is.
      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

    • setState

      public void setState(int stateA, int stateB, int stateC, int stateD)
      Like the superclass method setState(long, long, long, long), but takes four 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
      stateD - the fourth 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

    • copy

      public ChopRandom 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