[FFmpeg-devel] [PATCH 00/15] replace pow(10, x) by exp10(x) across FFmpeg

[Ronald S. Bultje]

Hi,

On Thu, Dec 24, 2015 at 11:47 AM, Ganesh Ajjanagadde <gajjanag at mit.edu>
wrote:

> On Thu, Dec 24, 2015 at 8:37 AM, Ronald S. Bultje <rsbultje at gmail.com>
> wrote:
> > Hi,
> >
> > On Wed, Dec 23, 2015 at 7:49 PM, Ganesh Ajjanagadde <gajjanag at mit.edu>
> > wrote:
> >
> >> What I meant was the following (I casually labelled it as ifdef, I
> >> meant some preprocessor stuff):
> >> #if !HAVE_EXP10 || !(defined(_GNU_SOURCE))
> >> ...
> >> #endif
> >>
> >> I have reproduced your issues via a minimal configure line, and the
> >> above idea fixes those. Do you see any issues? Of course, there is the
> >> theoretical one of a libc (more precisely libm) having exp10 without
> >> GNU_SOURCE, but in that case it should just use the fallback.
> >
> >
> > I don't like this as much. In all other instances of any other function
> > whatsoever, we just check if the function exists. We should do the same
> > thing here. If implemented correctly in configure, #if !HAVE_EXP10 should
> > always work. If we can fail to compile when compiling some video filter,
> we
> > can fail alike when testing for the feature in configure.
>
> It is not easy to do via configure, as Michael points out since
> GNU_SOURCE may get enabled from pkg-config and other steps in
> configure. Basically then this will need to be deferred to a stage way
> below in configure, once all cflags have been set to their values.
> This will add IMHO greater complexity to configure than the ugly hack
> above.
>
> Ultimately, it is a question of which one is preferred. If you still
> feel this way, I will delve a bit into configure to see what can be
> done.


exp10 is just one of the many bits where this will come in useful, so I'd
rather have a solution that covers all bases than adding many ||GNU_SOURCE
hacks all across the codebase in random, undefined places.

Ronald