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

Christophe Gisquet christophe.gisquet at gmail.com
Tue Oct 13 13:33:07 CEST 2015


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).

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


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