Class MiddleSquareWeylSequence

All Implemented Interfaces:
RandomIntSource, RestorableUniformRandomProvider, UniformRandomProvider

public class MiddleSquareWeylSequence extends IntProvider
Middle Square Weyl Sequence Random Number Generator.

A fast all-purpose 32-bit generator. Memory footprint is 192 bits and the period is at least 2^64.

Implementation is based on the paper Middle Square Weyl Sequence RNG.

Since:
1.3
See Also:
  • Field Details

    • SEED_SIZE

      private static final int SEED_SIZE
      Size of the seed array.
      See Also:
    • DEFAULT_SEED

      private static final long[] DEFAULT_SEED
      The default seed. This has a high quality Weyl increment (containing many bit state transitions).
    • x

      private long x
      State of the generator.
    • w

      private long w
      State of the Weyl sequence.
    • s

      private long s
      Increment for the Weyl sequence. This must be odd to ensure a full period.

      This is not final to support the restore functionality.

  • Constructor Details

    • MiddleSquareWeylSequence

      public MiddleSquareWeylSequence(long[] seed)
      Creates a new instance.

      Note: The generator output quality is highly dependent on the initial seed. If the generator is seeded poorly (for example with all zeros) it is possible the generator may output zero for many cycles before the internal state recovers randomness. The seed elements are used to set:

      1. The state of the generator
      2. The state of the Weyl sequence
      3. The increment of the Weyl sequence

      The third element is set to odd to ensure a period of at least 264. If the increment is of low complexity then the Weyl sequence does not contribute high quality randomness. It is recommended to use a permutation of 8 hex characters for the upper and lower 32-bits of the increment.

      The state of the generator is squared during each cycle. There is a possibility that different seeds can produce the same output, for example 0 and 232 produce the same square. This can be avoided by using the high complexity Weyl increment for the state seed element.

      Parameters:
      seed - Initial seed. If the length is larger than 3, only the first 3 elements will be used; if smaller, the remaining elements will be automatically set.
  • Method Details