[FFmpeg-devel] [PATCHv2] avutil/mathematics: speed up av_gcd by using Stein's binary GCD algorithm

Ganesh Ajjanagadde gajjanag at mit.edu
Thu Oct 22 13:04:41 CEST 2015


On Thu, Oct 22, 2015 at 5:49 AM, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:
> Ganesh Ajjanagadde <gajjanagadde <at> gmail.com> writes:
>
>> > This broke fate with -ftrapv
>
>> > The problem seems to be in av_gcd() and not the De-Bruijn version of
>> > ff_ctzll since the gcc builtin is being used.
>>
>> Don't have the time to investigate right now - revert for now unless
>> someone can fix it quickly.
>
> Ping?
>
> Please revert if nobody can fix this.

"Fixing" this at the moment is highly dubious - read the thread. It
does not even occur in a reproducible way, does not trigger on ubsan,
I can't even see it on ftrapv. Show me why it is not a toolchain
issue.

>
> Carl Eugen
>
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