[FFmpeg-devel] [PATCH 1/3] riscv: add CPU flags for the RISC-V Vector extension

[Lynne]

Sep 3, 2022, 21:59 by remi at remlab.net:

> Le lauantaina 3. syyskuuta 2022, 22.20.20 EEST Lynne a écrit :
>
>> Sep 3, 2022, 21:01 by remi at remlab.net:
>> > From: Rémi Denis-Courmont <remi at remlab.net>
>> > 
>> > RVV defines a total of 12 different extensions: V, Zvl32b, Zvl64b,
>> > Zvl128b, Zvl256b, Zvl512b, Zvl1024b, Zve32x, Zve32f, Zve64x, Zve64f and
>> > Zve64d.
>> > 
>> > At this stage, we don't care about the vector length extensions Zvl*,
>> > as most or all optimisations will be running in a loop that is
>> > independent on the data set size.
>>
>> I need to know the maximum length to write an FFT.
>> Could you add flags for it?
>>
>
> I think we should cross that bridge if/when the need actually arises. In most 
> cases, the vector length returned at run-time from VSETVL is good enough.
>

I need to know the length in C, not assembly. Whilst you're at adding
initial support, I think it makes sense to support all code that's targetting
RISC-V, not just the ones it's convenient to. I'll probably write the FFT
as soon as I get access to a real machine.