Re: pgbench - add pseudo-random permutation function

On Mon, 5 Apr 2021 at 13:07, Fabien COELHO <coelho@cri.ensmp.fr> wrote:
>
> Attached a v28 which I hope fixes the many above issues and stays with
> ints. The randu64 is still some kind of a joke, I artificially reduced the
> cost by calling jrand48 once and extending it to 64 bits, so it could give
> an idea of the cost endured if a 64-bit prng was used.
>
> Now you are the committer, you can do as you please, I'm just stating my
> (mathematical) opinions about using floating point computations for that.
> I think that apart from this point of principle/philosophy the permute
> performance and implementation are reasonable, and better than my initial
> version because it avoids int128 computations and the large prime number
> business.
>

Pushed.

I decided not to go with the "joke" randu64() function, but instead
used getrand() directly. This at least removes any *direct* use of
doubles in permute() (though of course they're still used indirectly),
and means that if getrand() is improved in the future, permute() will
benefit too.

Regards,
Dean