Package it.unimi.dsi.util

Class XoRoShiRo128PlusPlusRandomGenerator

java.lang.Object
org.apache.commons.math3.random.AbstractRandomGenerator
it.unimi.dsi.util.XoRoShiRo128PlusPlusRandomGenerator
All Implemented Interfaces:
Serializable, RandomGenerator
public class XoRoShiRo128PlusPlusRandomGenerator extends AbstractRandomGenerator implements Serializable
A fast, all-purpose, rock-solid, small-state pseudorandom number generator. It has excellent speed, but its state space (128 bits) that is large enough for mild parallelism only; it passes all tests we are aware of. In Java, it is slightly faster than a XoRoShiRo128StarStarRandomGenerator. More information can be found at our PRNG page.

Note that starting with Java 17 you can find this generator in java.util.random.

If you need to generate just floating-point numbers, XoRoShiRo128PlusRandomGenerator is slightly faster. If you can use more space, you might try XoShiRo256PlusPlusRandomGenerator.

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:

  • Constructor Details

    • XoRoShiRo128PlusPlusRandomGenerator

      protected XoRoShiRo128PlusPlusRandomGenerator(long s0, long s1)

    • XoRoShiRo128PlusPlusRandomGenerator

      public XoRoShiRo128PlusPlusRandomGenerator()
      Creates a new generator seeded using Util.randomSeed().

    • XoRoShiRo128PlusPlusRandomGenerator

      public XoRoShiRo128PlusPlusRandomGenerator(long seed)
      Creates a new generator using a given seed.
      Parameters:
      seed - a seed for the generator.

  • Method Details

    • copy

      public XoRoShiRo128PlusPlusRandomGenerator 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()
      Specified by:
      nextLong in interface RandomGenerator
      Overrides:
      nextLong in class AbstractRandomGenerator

    • nextInt

      public int nextInt()
      Specified by:
      nextInt in interface RandomGenerator
      Overrides:
      nextInt in class AbstractRandomGenerator

    • nextInt

      public int nextInt(int n)
      Specified by:
      nextInt in interface RandomGenerator
      Overrides:
      nextInt in class AbstractRandomGenerator

    • 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()
      Specified by:
      nextDouble in interface RandomGenerator
      Specified by:
      nextDouble in class AbstractRandomGenerator

    • 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.
      Since:
      2.4.1

    • nextFloat

      public float nextFloat()
      Specified by:
      nextFloat in interface RandomGenerator
      Overrides:
      nextFloat in class AbstractRandomGenerator

    • nextBoolean

      public boolean nextBoolean()
      Specified by:
      nextBoolean in interface RandomGenerator
      Overrides:
      nextBoolean in class AbstractRandomGenerator

    • nextBytes

      public void nextBytes(byte[] bytes)
      Specified by:
      nextBytes in interface RandomGenerator
      Overrides:
      nextBytes in class AbstractRandomGenerator

    • jump

      protected XoRoShiRo128PlusPlusRandomGenerator jump(long[] jump)

    • jump

      public XoRoShiRo128PlusPlusRandomGenerator jump()
      The jump function for this generator. It is equivalent to 264 calls to nextLong(); it can be used to generate 264 non-overlapping subsequences for parallel computations.
      Returns:
      this generator.
      See Also:

    • longJump

      public XoRoShiRo128PlusPlusRandomGenerator longJump()
      The long-jump function for this generator. It is equivalent to 296 calls to nextLong(); it can be used to generate 232 starting points, from each of which jump() will generate 232 non-overlapping subsequences for parallel distributed computations.
      Returns:
      this generator.
      See Also:

    • split

      public XoRoShiRo128PlusPlusRandomGenerator 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.

      Specified by:
      setSeed in interface RandomGenerator
      Specified by:
      setSeed in class AbstractRandomGenerator
      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)