Re: vectorized CRC on ARM64

On Thu, Mar 19, 2026 at 12:17 AM Haibo Yan <tristan.yim@gmail.com> wrote:
>
> On Tue, Mar 17, 2026 at 11:52 PM John Naylor <johncnaylorls@gmail.com> wrote:

>> I don't know if that's relevant for current server hardware, so it
>> could be pointless. I'm personally not a fan of inline assembly, but I
>> also didn't yet want to put in the effort to alter generated code. I
>> don't think it would be very hard to do, however.
>
>
> Thanks, that makes sense as an explanation for why the inline asm is there today. But it also sounds like this is more of a temporary implementation choice than a conclusion that intrinsics are unsuitable.

I can see how my words imply that, but after a moment's thought I
still don't want to put in that effort without a good reason. For
starters, what I said above about "not very hard" may be wishful
thinking.

> If so, I wonder whether it would be better to treat an intrinsics-based version as the preferred end state unless benchmarks show a clear regression.

To meet your criterion, we'd not only have to rewrite it correctly,
we'd have to test on multiple vendors of non-Apple hardware and
multiple compiler vendors/versions (at least where the binary output
is different) to prove we haven't caused a regression. I wouldn't
recommend anyone to accept that challenge as stated, since the
risk/reward ratio is just not favorable. Especially considering we're
2 1/2 weeks away from feature freeze.

--
John Naylor
Amazon Web Services