Package com.github.tommyettinger.random

Class TraceRandom

java.lang.Object
java.util.Random
com.github.tommyettinger.random.EnhancedRandom
com.github.tommyettinger.random.TraceRandom
All Implemented Interfaces:
Externalizable, Serializable, RandomGenerator
public class TraceRandom extends EnhancedRandom
Like AceRandom with five 64-bit states but also one unchanging 28-bit stream; does not use multiplication, only add, XOR, and bitwise-rotate operations (this is an ARX generator). Has a state that runs like a counter, guaranteeing a minimum period of 2 to the 64, and each stream should be independent of any other stream after a small number of generations. The expected period is about 2 to the 310 calls to nextLong(), though this is an overly cautious estimate. Even if using the old stand-by advice, that only the square root of the period can be used before a generator starts to have problems, would permit an enormous 2 to the 155 calls before becoming, in some vague way, "bad." That's over 45,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 calls to nextLong(). With over 268 million possible streams, on top of that.
At least one stream passes 64TB with no anomalies. All total streams are virtually impossible to test in a mortal lifespan, but each stream does rate as optimal (score 1, with score 0 impossible, when evaluated by EnhancedRandom.rateGamma(long)). This is usually a tiny amount slower than AceRandom (about 5% lower throughput), but strangely is slightly faster than AceRandom when run on GraalVM 24. This passes Initial Correlation Evaluator tests after 26 generations or more.
After about 30 calls to nextLong(), any two different streams with otherwise identical states should have no correlations to each other. This avoids the issue with SplitMix64 where "gamma" receives problem values, because it only this uses four criteria to evaluate each gamma and rejects most attempts at a gamma until it finds one of relatively-few near-perfect gamma values possible. This does also use quite a lot more state than SplitMix64, and those extra 320 bits of state change in their own complex ways, both related and unrelated to the stream.
This replaces the older, now-removed MaceRandom class. MaceRandom is still present in juniper's test files, so if you need it for compatibility, it can be taken from there. TraceRandom is better in every way and its random number generation algorithm is identical -- only its choices of stream are different. A key difference in their APIs is that TraceRandom has you use getStream() and setStream(long), instead of working with streamIdentifier in MaceRandom. Note that setStream() here can change its input if it isn't considered a "good" gamma, but any stream this uses (and so returns with getStream()) will be a "good" gamma, and so won't need changing. Also note that there are two 6-argument constructors; one takes an int for the stream and is meant to accept any int less than 2 to the 28, while the other takes a long for the stream and simply feeds it to setStream(long) to "fix" it if it needs that (using EnhancedRandom.fixGamma(long, int) with threshold 1).
See Also:

  • Field Details

    • stream

      protected long stream
      The unchanging stream; cannot be set directly, but can be obtained directly with getStream() or get/set indirectly via setStream(long), which only changes the input if it isn't already a usable gamma (as determined by EnhancedRandom.fixGamma(long, int) with threshold 1).

    • stateA

      protected long stateA
      The first state; can be any long.

    • stateB

      protected long stateB
      The second state; can be any long. The first call to nextLong() will return this verbatim, if no other methods have been called.

    • stateC

      protected long stateC
      The third state; can be any long.

    • stateD

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

    • stateE

      protected long stateE
      The fifth state; can be any long.

  • Constructor Details

    • TraceRandom

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

    • TraceRandom

      public TraceRandom(long seed)
      Creates a new TraceRandom 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

    • TraceRandom

      public TraceRandom(int streamIdentifier, long stateA, long stateB, long stateC, long stateD, long stateE)
      Creates a new TraceRandom with the given stream identifier and five states; all long values are permitted for states, and all ints between 0 and 268435455 (or 0xFFFFFFF), inclusive, are permitted for streamIdentifier. The states will be used verbatim, and the stream (getStream()) should be used instead of the given streamIdentifier.
      Parameters:
      streamIdentifier - an up-to-28-bit int (between 0 and 268435455, inclusive); higher bits are ignored
      stateA - any long value
      stateB - any long value
      stateC - any long value
      stateD - any long value
      stateE - any long value

    • TraceRandom

      public TraceRandom(long stream, long stateA, long stateB, long stateC, long stateD, long stateE)
      Creates a new TraceRandom with the given stream identifier and five states; all long values are permitted for states, and while all longs are permitted for stream, if it is an even number or in any way not considered a suitable gamma value by EnhancedRandom.fixGamma(long, int) (with threshold 1), the stream will be changed before it can be used. You can get the actual stream this uses with getStream(). If only odd numbers less than 536870912 are given for the stream, all possible streams will be unique.
      Parameters:
      stream - any odd long, but will be passed to EnhancedRandom.fixGamma(long, int) with threshold 1, so it may change
      stateA - any long value
      stateB - any long value
      stateC - any long value
      stateD - any long value
      stateE - 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 generator has 6 long states, so this returns 6.
      Overrides:
      getStateCount in class EnhancedRandom
      Returns:
      6 (six)

    • getSelectedState

      public long getSelectedState(int selection)
      Gets the state determined by selection, as-is. The value for selection should be between 0 and 5, inclusive; if it is any other value this gets the stream as if 0 was given.
      Overrides:
      getSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to get; generally 0, 1, 2, 3, 4, or 5
      Returns:
      the value of the selected state

    • setSelectedState

      public void setSelectedState(int selection, long value)
      Sets one of the states, determined by selection, to value, as-is. Selections 1, 2, 3, 4, and 5 refer to states A, B, C, D, and E, while selection 0 is the stream. If the selection is anything else, this treats it as 0 and sets the stream. If this would try to set the stream to an even number or any lower-quality value (as determined by EnhancedRandom.fixGamma(long, int) with a threshold of 1), it may change the stream until it has a high-quality gamma.
      Overrides:
      setSelectedState in class EnhancedRandom
      Parameters:
      selection - used to select which state variable to set; generally 0, 1, 2, 3, 4, or 5
      value - the exact value to use for the selected state, if valid

    • setSeed

      public void setSeed(long seed)
      This initializes all 5 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

    • getStream

      public long getStream()

    • setStreamIdentifier

      public void setStreamIdentifier(int streamID)
      Sets the stream using the low-order 28 bits of the given int.
      Parameters:
      streamID - can be any int, but only the lowest-order 28 bits matter

    • setStream

      public void setStream(long stream)
      Sets the stream using the given long, and changing it using EnhancedRandom.fixGamma(long, int) (with threshold 1) if it isn't already considered a good gamma value. The stream should always be an odd number; if an even one is given, 1 will be added to make it odd. If only odd numbers between 1 and 536870912 are given, all streams will be unique; if larger or even numbers are given, there can be duplicates.
      Parameters:
      stream - any odd long; if only odd numbers less than 536870912 are given, all streams will be unique

    • getStateA

      public long getStateA()

    • setStateA

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

    • getStateB

      public long getStateB()

    • setStateB

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

    • getStateC

      public long getStateC()

    • setStateC

      public void setStateC(long stateC)
      Sets the third part of the state.
      Parameters:
      stateC - can be any long

    • getStateD

      public long getStateD()

    • setStateD

      public void setStateD(long stateD)
      Sets the fourth part of the state.
      Parameters:
      stateD - can be any long

    • getStateE

      public long getStateE()

    • setStateE

      public void setStateE(long stateE)
      Sets the fifth part of the state.
      Parameters:
      stateE - can be any long

    • setState

      public void setState(long stream, long stateA, long stateB, long stateC, long stateD, long stateE)
      Sets the state completely to the given six state variables. This is the same as calling setStream(long), setStateA(long), setStateB(long), setStateC(long), setStateD(long), and setStateE(long) as a group.
      Overrides:
      setState in class EnhancedRandom
      Parameters:
      stream - any odd long; if only odd numbers less than 536870912 are given, all streams will be unique
      stateA - the first state; can be any long
      stateB - the second state; can be any long
      stateC - the third state; can be any long
      stateD - the fourth state; can be any long
      stateE - the fifth state; can be any long

    • 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 TraceRandom 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