Class XoShiRo256StarStarRandom

java.lang.Object
java.util.Random
it.unimi.dsi.util.XoShiRo256StarStarRandom
All Implemented Interfaces:
Serializable

public class XoShiRo256StarStarRandom
extends Random
A fast, all-purpose, rock-solid pseudorandom number generator. It has excellent speed, a state space (256 bits) that is large enough for any parallel application, and it passes all tests we are aware of. In Java, it is slightly slower than a XoShiRo256PlusPlusRandom. More information can be found at our PRNG page.

If you need to generate just floating-point numbers, XoShiRo256PlusRandom is slightly faster. If you are tight on space, you might try XoRoShiRo128StarStarRandom.

By using the supplied jump() method it is possible to generate non-overlapping long sequences for parallel computations; longJump() makes it possible to create several starting points, each providing several non-overlapping sequences, for distributed computations. This class provides also a split() method to support recursive parallel computations, in the spirit of SplittableRandom.

Warning: before release 2.6.3, the split() method would not alter the state of the caller, and it would return instances initialized in the same way if called multiple times. This was a major mistake in the implementation and it has been fixed, but as a consequence the output of the caller after a call to split() is now different, and the result of split() is initialized in a different way.

Note that this is not a secure generator.

Version:
1.0
See Also:
it.unimi.dsi.util, RandomGenerator, XoShiRo256StarStarRandomGenerator, Serialized Form
  • Constructor Details

    • XoShiRo256StarStarRandom

      protected XoShiRo256StarStarRandom​(long s0, long s1, long s2, long s3)
    • XoShiRo256StarStarRandom

      public XoShiRo256StarStarRandom()
      Creates a new generator seeded using Util.randomSeed().
    • XoShiRo256StarStarRandom

      public XoShiRo256StarStarRandom​(long seed)
      Creates a new generator using a given seed.
      Parameters:
      seed - a seed for the generator.
  • Method Details

    • copy

      public XoShiRo256StarStarRandom copy()
      Returns a copy of this generator. The sequences produced by this generator and by the returned generator will be identical.

      This method is particularly useful in conjunction with the jump() (or longJump()) method: by calling repeatedly jump().copy() over a generator it is possible to create several generators producing non-overlapping sequences.

      Returns:
      a copy of this generator.
    • nextLong

      public long nextLong()
      Overrides:
      nextLong in class Random
    • nextInt

      public int nextInt()
      Overrides:
      nextInt in class Random
    • nextInt

      public int nextInt​(int n)
      Overrides:
      nextInt in class Random
    • nextLong

      public long nextLong​(long n)
      Returns a pseudorandom uniformly distributed long value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence. The algorithm used to generate the value guarantees that the result is uniform, provided that the sequence of 64-bit values produced by this generator is.
      Parameters:
      n - the positive bound on the random number to be returned.
      Returns:
      the next pseudorandom long value between 0 (inclusive) and n (exclusive).
    • nextDouble

      public double nextDouble()
      Overrides:
      nextDouble in class Random
    • nextDoubleFast

      public double nextDoubleFast()
      Returns the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence, using a fast multiplication-free method which, however, can provide only 52 significant bits.

      This method is faster than nextDouble(), but it can return only dyadic rationals of the form k / 2−52, instead of the standard k / 2−53. Before version 2.4.1, this was actually the standard implementation of nextDouble(), so you can use this method if you need to reproduce exactly results obtained using previous versions.

      The only difference between the output of this method and that of nextDouble() is an additional least significant bit set in half of the returned values. For most applications, this difference is negligible.

      Returns:
      the next pseudorandom, uniformly distributed double value between 0.0 and 1.0 from this random number generator's sequence, using 52 significant bits only.
    • nextFloat

      public float nextFloat()
      Overrides:
      nextFloat in class Random
    • nextBoolean

      public boolean nextBoolean()
      Overrides:
      nextBoolean in class Random
    • nextBytes

      public void nextBytes​(byte[] bytes)
      Overrides:
      nextBytes in class Random
    • jump

      protected XoShiRo256StarStarRandom jump​(long[] jump)
    • jump

      public XoShiRo256StarStarRandom jump()
      The jump function for this generator. It is equivalent to 2128 calls to nextLong(); it can be used to generate 2128 non-overlapping subsequences for parallel computations.
      Returns:
      this generator.
      See Also:
      copy()
    • longJump

      public XoShiRo256StarStarRandom longJump()
      The long-jump function for this generator. It is equivalent to 2192 calls to nextLong(); it can be used to generate 264 starting points, from each of which jump() will generate 264 non-overlapping subsequences for parallel distributed computations.
      Returns:
      this generator.
      See Also:
      copy()
    • split

      public XoShiRo256StarStarRandom split()
      Returns a new instance that shares no mutable state with this instance. The sequence generated by the new instance depends deterministically from the state of this instance, but the probability that the sequence generated by this instance and by the new instance overlap is negligible.

      Warning: before release 2.6.3, this method would not alter the state of the caller, and it would return instances initialized in the same way if called multiple times. This was a major mistake in the implementation and it has been fixed, but as a consequence the output of this instance after a call to this method is now different, and the returned instance is initialized in a different way.

      Returns:
      the new instance.
    • setSeed

      public void setSeed​(long seed)
      Sets the seed of this generator.

      The argument will be used to seed a SplitMix64RandomGenerator, whose output will in turn be used to seed this generator. This approach makes “warmup” unnecessary, and makes the probability of starting from a state with a large fraction of bits set to zero astronomically small.

      Overrides:
      setSeed in class Random
      Parameters:
      seed - a seed for this generator.
    • setState

      public void setState​(long[] state)
      Sets the state of this generator.

      The internal state of the generator will be reset, and the state array filled with the provided array.

      Parameters:
      state - an array of 2 longs; at least one must be nonzero.
    • main

      public static void main​(String[] arg)