Date: Tue, 5 Nov 2024 15:03:23 +0000
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: David Rowley <dgrowleyml@gmail.com>
Cc: Ranier Vilela <ranier.vf@gmail.com>,
	Michael Paquier <michael@paquier.xyz>,
	Peter Smith <smithpb2250@gmail.com>,
	Peter Eisentraut <peter@eisentraut.org>,
	Heikki Linnakangas <hlinnaka@iki.fi>,
	pgsql-hackers@lists.postgresql.org
Subject: Re: define pg_structiszero(addr, s, r)
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Hi,

On Tue, Nov 05, 2024 at 05:08:41PM +1300, David Rowley wrote:
> On Tue, 5 Nov 2024 at 06:39, Ranier Vilela <ranier.vf@gmail.com> wrote:
> > I think we can add a small optimization to this last patch [1].
> 
> I think if you want to make it faster, you could partially unroll the
> inner-most loop, like:
> 
> // size_t * 4
> for (; p < aligned_end - (sizeof(size_t) * 3); p += sizeof(size_t) * 4)
> {
>     if (((size_t *) p)[0] != 0 | ((size_t *) p)[1] != 0 | ((size_t *)
> p)[2] != 0 | ((size_t *) p)[3] != 0)
>         return false;
> }

Another option could be to use SIMD instructions to check multiple bytes
is zero in a single operation. Maybe just an idea to keep in mind and experiment
if we feel the need later on.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com