Package it.unimi.dsi.util

Class XorShift1024StarPhiRandomGenerator

java.lang.Object
org.apache.commons.math3.random.AbstractRandomGenerator
it.unimi.dsi.util.XorShift1024StarPhiRandomGenerator
All Implemented Interfaces:
Serializable, RandomGenerator
public class XorShift1024StarPhiRandomGenerator extends AbstractRandomGenerator implements Serializable
A fast, high-quality pseudorandom number generator that combines a long-period instance of George Marsaglia's Xorshift generators (described in “Xorshift RNGs”, Journal of Statistical Software, 8:1−6, 2003) with a multiplication. More information can be found at our PRNG page.

By using the supplied jump() method it is possible to generate non-overlapping long sequences for parallel 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.

See Also:

  • Constructor Details

    • XorShift1024StarPhiRandomGenerator

      public XorShift1024StarPhiRandomGenerator()
      Creates a new generator seeded using Util.randomSeed().

    • XorShift1024StarPhiRandomGenerator

      public XorShift1024StarPhiRandomGenerator(long seed)
      Creates a new generator using a given seed.
      Parameters:
      seed - a seed for the generator.

  • Method Details

    • 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.

      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()
      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

      public void jump()
      The jump function for this generator. It is equivalent to 2512 calls to nextLong(); it can be used to generate 2512 non-overlapping subsequences for parallel computations.

    • split

      public XorShift1024StarPhiRandomGenerator 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 the generator.

    • setState

      public void setState(long[] state, int p)
      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 16 longs; at least one must be nonzero.
      p - the internal index.