SFC64 Small Fast Chaotic PRNG¶

class numpy.random.SFC64(seed=None)¶

BitGenerator for Chris Doty-Humphrey’s Small Fast Chaotic PRNG.

Parameters

seed{None, int, array_like[ints], SeedSequence}, optional: A seed to initialize the BitGenerator. If None, then fresh, unpredictable entropy will be pulled from the OS. If an int or array_like[ints] is passed, then it will be passed to SeedSequence to derive the initial BitGenerator state. One may also pass in a SeedSequence instance.

Notes

SFC64 is a 256-bit implementation of Chris Doty-Humphrey’s Small Fast Chaotic PRNG ([1]). SFC64 has a few different cycles that one might be on, depending on the seed; the expected period will be about

System Message: WARNING/2 (2^{255})

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([2]). SFC64 incorporates a 64-bit counter which means that the absolute minimum cycle length is

System Message: WARNING/2 (2^{64})

and that distinct seeds will not run into each other for at least

System Message: WARNING/2 (2^{64})

iterations.

SFC64 provides a capsule containing function pointers that produce doubles, and unsigned 32 and 64- bit integers. These are not directly consumable in Python and must be consumed by a Generator or similar object that supports low-level access.

State and Seeding

The SFC64 state vector consists of 4 unsigned 64-bit values. The last is a 64-bit counter that increments by 1 each iteration.

The input seed is processed by SeedSequence to generate the first 3 values, then the SFC64 algorithm is iterated a small number of times to mix.

Compatibility Guarantee

SFC64 makes a guarantee that a fixed seed will always produce the same random integer stream.

References

1: “PractRand”
2: “Random Invertible Mapping Statistics”

State¶

state

Get or set the PRNG state

Extending¶

`cffi`	CFFI interface
`ctypes`	ctypes interface

numpy.random.Philox.ctypes numpy.random.SFC64.state

SFC64 Small Fast Chaotic PRNG¶

State¶

Extending¶

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