[FFmpeg-devel] [PATCH] SPARC VIS simple_idct

Michel Lespinasse walken
Sat Aug 25 14:00:04 CEST 2007

On Sat, Aug 25, 2007 at 01:52:49PM +0200, Balatoni Denes wrote:
> But unfortunatelly I see a problem: you are using unsigned multiplies, which 
> are AFAIK not available on SPARC. This also means that the code might not 
> actually comply with ieee1180, because you are using the sign bit for data, 
> but you can't.

If I remember, the idea was that muls can be implemented easily (looking at
the VIS specs right now, I think its vis_fmul8sux16 + vis_fmul8ulx16).

For mulu you could write mulu(x,y) = muls(x,y) + (x >= 32768) ? y : 0
or when working with vectors, and given that x is a known constant,
mulu(x,y) = muls(x,y) + (y & mask) where the mask would be a constant
with each 16-bit element being either 0 of 65535.
About half of the const vectors had all their elements >= 32768 too so
these would not even need the mask, actually.

I have not looked much at your current code, maybe this trick might
apply there as well ?

Michel "Walken" Lespinasse
"Bill Gates is a monocle and a Persian cat away from being the villain
in a James Bond movie." -- Dennis Miller

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