[FFmpeg-devel] [PATCH v2_2 6/6] lavc/vvc_mc R-V V sad

[Rémi Denis-Courmont]

Le mardi 17 décembre 2024, 11:50:26 EET flow gg a écrit :
> > Don't clobber v8 here.
> > Use vsub.vv here to avoid the sequential dependency.
> 
> Thanks, I will update later
> 
> > Are you sure this does not require tail-undisturbed mode? I think you're
> > setting tail-agnostic mode up.
> 
> I’m not sure if I understood correctly.
> My understanding is that tail-undisturbed is used because the largest lmul
> is applied, so it is necessary to prevent the tail values from being
> incorrectly accumulated.
> However, in this case, vset uses the smallest lmul, so this issue will not
> occur.

That makes zero sense. The logical multiplier does not accommodate larger 
vector lengths than 256 bits as things stand, and in the extreme, you can 
always have vector lengths to large that even the smallest valid multiplier is 
"too" large.

-- 
Rémi