[FFmpeg-devel] [PATCH] configure+libm.h: add fmin/fmax/fminf/fmaxf emulation

Ganesh Ajjanagadde gajjanag at mit.edu
Sat Oct 31 04:15:41 CET 2015

On Fri, Oct 30, 2015 at 7:29 PM, Michael Niedermayer
<michael at niedermayer.cc> wrote:
> On Fri, Oct 30, 2015 at 06:53:34PM -0400, Ganesh Ajjanagadde wrote:
>> On Fri, Oct 30, 2015 at 6:35 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
>> > From: Michael Niedermayer <michael at niedermayer.cc>
>> >
>> > This should fix the build failure of avf_showcqt.c
>> >
>> > An alternative solution would be to add a check for fmin/fmax to fate-source and
>> > then to replace them by FFMIN/FFMAX, i can do that if preferred?
>> >
>> > Untested due to lack of a affected platform
>> I recall some interest on my end to get fmin, fmax etc for different
>> reasons, and it was remarked that commit
>> 4436a8f44dedc83767b3d9da9beb85d1fae2ca30 may be relevant. The summary
>> seems to be that getting it to work on all platforms is not so simple.
> :/
> ill replace the problematic ones by FFMIN/MAX for now so the build
> failure on the affected msvc platforms is fixed
> tieing a build fix to this complexity would be unwise
>> I am definitely interested in getting it to work in order to replace
>> FFMAX/FFMIN for floating point in especially libavfilter. This will
>> allow better nan signalling at a slight performance cost.
> would that performance cost affect all systems or just ones not
> having fmin/fmax ?
> i think affecting all systems would be bad

A correct fmin and fmax will be slower than FFMIN/FFMAX, simply
because they do NaN handling. How much slower, I have not tested. Also
note that flags may be passed to the compiler to ignore NaN's,
something which can possibly be done locally if desired. However, I
view FFMAX/FFMIN as the cleaner solution if NaN signalling/propagation
is not an issue, so I may not pursue this.

> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
> Many things microsoft did are stupid, but not doing something just because
> microsoft did it is even more stupid. If everything ms did were stupid they
> would be bankrupt already.
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