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From Alex Herbert <alex.d.herb...@gmail.com>
Subject Re: [Rng] New XoShiRo generators
Date Wed, 06 Mar 2019 21:42:33 GMT


> On 6 Mar 2019, at 21:24, Gilles Sadowski <gilleseran@gmail.com> wrote:
> 
> Hello.
> 
> Le mer. 6 mars 2019 à 21:49, Alex Herbert <alex.d.herbert@gmail.com> a écrit
:
>> 
>> 
>> 
>>> On 6 Mar 2019, at 17:11, Gilles Sadowski <gilleseran@gmail.com> wrote:
>>> 
>>> Do the two variants produce uncorrelated sequences?
>> 
>> I will test this when I branch a new PR for just this code.
> 
> IMHO, it's strange that there would be 2 sources of randomness in a single
> implementation.
> Concretely: If one needs a fast "int" provider, and a fast "long" provider, I'd
> consider the simpler solution of using 2 different providers.

I think this has crossed wires somewhere. I was talking about the variant of the XorShift1024Star
algorithm and whether XorShift1024Star should be deprecated in favour of XorShift1024StarPhi.

The variant of the SplitMix64 algorithm for producing ints was tested in a benchmark that
I am prepared to throw away. The results are in the Jira ticket. The way the SplittableRandom
creates an int is slightly slower than the method used in [RNG] SplitMix64 which divides the
long in half. This ticket can be closed as done and I’ll add a comment that no speed improvement
was found.

I agree that this variant algorithm should have been in a new provider. It would produce a
different output of bytes since the bit shift in the second step is different. But I’m not
going to add this algorithm so it does not matter.

However I will test if XorShift1024Star and XorShift1024StarPhi are correlated just for completeness.

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