[flac-dev] Autocorrelation precision insufficient

[Robert Kausch]

Hi Martijn,

Great work!

I concur with David that compression should work the same on all 
platforms. There can be SIMD optimizations for some routines, but they 
should produce the same result as the non-SIMD versions. If outdated 
optimizations cannot be updated, better drop them instead of keeping 
versions that produce different results than the new reference code.

Regarding VSX, you could try to contact Anton Blanchard to ask whether 
he can update the routines. Otherwise, it should be possible to emulate 
VSX with QEMU. You won't be able to verify performance that way, of 
course, but should be able to verify correctness.

Best,
Robert

Am 25.06.2021 um 19:55 schrieb David Willmore:
> Martijn,
>
> Just a lone voice here, but I would opt for the best compression on 
> the most platforms.  As I am one of the people who always run FLAC at 
> the placebo max compression, my vote will always be for best 
> compression over any other resource use.
>
> I also can make ARMv7 hardware available to you or I can do any 
> testing you want on a number of machines.
>
> Thank you for your work!
>
> Cheers,
> David
>
> On Fri, Jun 25, 2021 at 3:48 AM Martijn van Beurden <mvanb1 at gmail.com> 
> wrote:
>
>     Op do 24 jun. 2021 om 09:17 schreef Martijn van Beurden
>     <mvanb1 at gmail.com>:
>     > - Switch to autoc[] as doubles, but remove current SSE and
>     disable VSX
>     > intrinsics for someone to update them later (I don't have any POWER8
>     > or POWER9 hardware to test). This means all platforms will get the
>     > same compression, but some (with only SSE but not SSE2 or with VSX)
>     > will see a large slowdown.
>
>     I see now that besides routines with SSE intrinsics (which I rewrote
>     into SSE2) and with VSX intrinsics (which I don't have hardware for)
>     there is also a open pull request for routines with ARM intrinsics. I
>     am willing and able to rewrite those if this change is accepted and
>     merged. I have access to ARMv8 with 32-bit OS, ARMv8 with 64-bit OS,
>     ARMv6 and I might be able to get hold of ARMv7 hardware.
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