[FFmpeg-devel] [PATCH 5/9] x86: simple_idct10_template: fix overflow in pass

[Michael Niedermayer]

On Tue, Oct 13, 2015 at 01:33:07PM +0200, Christophe Gisquet wrote:
> Hi,
> 
> 2015-10-13 13:10 GMT+02:00 Michael Niedermayer <michael at niedermayer.cc>:
> > hmm, iam a bit concerned that adding the rounder (which effectively is
> > 0.5) causes a overflow, that would if iam not mistaken imlpy that
> > things are very close to overflowing already without it
> 
> It's true, but the immediate cause here is the input coeffs
> overflowing (ie, once the rounder is added, a positive value is seen
> as a negative one to pmaddwd).

have you tried using saturating additions for the rounder ?


> 
> Otherwise, your concern is basically whether 32bits arithmetics is
> enough: then simple_idct may also overflows on x86_32.

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I have often repented speaking, but never of holding my tongue.
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