| From: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
|---|---|
| To: | Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> |
| Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, David Steele <david(at)pgmasters(dot)net>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>, Hironobu SUZUKI <hironobu(at)interdb(dot)jp>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: pgbench - add pseudo-random permutation function |
| Date: | 2021-03-12 21:06:48 |
| Message-ID: | CA+hUKGJJskxpyAev3jcFq-owkTkZLHwC_b71uMFNh+wWuTZzVw@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Mar 8, 2021 at 11:50 PM Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr> wrote:
> > I may have time to become familiar or at least semi-comfortable with all
> > that weird math in it by then.
>
> Yep.
>
> Generating a parametric good-quality low-cost (but not
> cryptographically-secure) pseudo-random permutations on arbitrary sizes
> (not juste power of two sizes) is not a trivial task, I had to be quite
> creative to achieve it, hence the "weird" maths. I had a lot of bad
> not-really-working ideas before the current status of the patch.
>
> The code could be simplified if we assume that PG_INT128_TYPE will be
> available on all relevant architectures, and accept the feature not to be
> available if not.
That doesn't sound like a bad option to me, if it makes this much
simpler. The main modern system without it seems to be MSVC. The
Linux, BSD, Apple, illumos, AIX systems using Clang/GCC with
Intel/AMD/ARM/PowerPC CPUs have it, and the Windows systems using open
source compilers have it.
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