| From: | Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com> |
|---|---|
| To: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
| Cc: | Peter Smith <smithpb2250(at)gmail(dot)com>, Peter Eisentraut <peter(at)eisentraut(dot)org>, pgsql-hackers(at)lists(dot)postgresql(dot)org |
| Subject: | Re: define pg_structiszero(addr, s, r) |
| Date: | 2024-10-29 14:03:02 |
| Message-ID: | ZyDrFgYfRwRXWSmh@ip-10-97-1-34.eu-west-3.compute.internal |
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| Lists: | pgsql-hackers |
Hi,
On Tue, Oct 29, 2024 at 11:39:03AM +0200, Heikki Linnakangas wrote:
> On 29/10/2024 09:54, Bertrand Drouvot wrote:
> > > https://godbolt.org/z/x9hPWjheq.
> >
> > Yeah, I also think that's fine. Peter Smith did some testing in [1] comparing
> > memcmp and simple loop checking (thanks Peter for the testing!):
> >
> > "
> > Iterate 1000000 times...
> > check zeros using loop -- elapsed=0.041196s
> > check zeros using memcmp -- elapsed=0.016407s
> > "
> >
> > So, in this test, the loop is 0.024789s longer means 0.024789s/1000000=24 Nanosecond
> > slower per comparison (If my math is correct).
>
> I believe that test program is bogus. Look at the assembly code; the
> compiler optimized away the loops.
Oh right. It looks like that moving the "scanf" within each loop "helps" and
that both give pretty comparable results.
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
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