[FFmpeg-devel] [PATCH] SPARC VIS simple_idct

Michel Lespinasse walken
Sat Aug 25 14:54:44 CEST 2007

On Sat, Aug 25, 2007 at 05:00:04AM -0700, Michel Lespinasse wrote:
> About half of the const vectors had all their elements >= 32768 too so
> these would not even need the mask, actually.

Just looked back - all of the const vectors passed as first argument to
mulu have all their elements >= 32768. So the mask is unnecessary and
you can just implement mulu(a,b) = adds (b, muls (b, a));

The argument order is important here, muls is not commutative because
of the annoying VIS rounding. Using the wrong order loses a lot of
precision, I dont claim to understand why...

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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