Re: define pg_structiszero(addr, s, r)

Hi,

On Fri, Nov 01, 2024 at 12:50:10PM +0000, Bertrand Drouvot wrote:
> Hi,
>
> On Fri, Nov 01, 2024 at 09:47:05PM +1300, David Rowley wrote:
> > On Fri, 1 Nov 2024 at 20:49, Michael Paquier <michael(at)paquier(dot)xyz> wrote:
> > I've attached what I thought a more optimal version might look like in
> > case anyone thinks making it better is a good idea.
> >
>
> Thanks for the proposal!
>
> I like the idea, I think that's worth to add a few comments, something like:
>
> 1 ===
>
> + while (((uintptr_t) p & (sizeof(size_t) - 1)) != 0)
>
> Add a comment like "Checks bytes, byte by byte, until the pointer is aligned"?
>
> 2 ===
>
> + for (; p < aligned_end; p += sizeof(size_t))
>
> Add a comment like "Multiple bytes comparison(s) at once"?
>
> 3 ===
>
> + while (p < end)
> + {
>
> Add a comment like "Compare remaining bytes, byte by byte"?
>
> 4 ===
>
> Out of curiosity I did test your proposal and it performs well (see [0]) for
> the PageIsVerifiedExtended() case.

Also,

5 ===

Shouldn't we handle the cases where ptr is NULL and/or len == 0? (should probably
have already been done in the current version of pg_memory_is_all_zeros() though).

Regards,

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