Re: [FFmpeg-devel] [PATCH 2/2] swscale/input: Avoid calls to av_pix_fmt_desc_get()

[Michael Niedermayer <michael@niedermayer.cc>]

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On Fri, Sep 09, 2022 at 08:15:22PM +0200, Andreas Rheinhardt wrote:
> Michael Niedermayer:
> > On Thu, Sep 08, 2022 at 11:44:51PM +0200, Andreas Rheinhardt wrote:
> >> Michael Niedermayer:
> >>> On Thu, Sep 08, 2022 at 09:38:51PM +0200, Andreas Rheinhardt wrote:
> >>>> Michael Niedermayer:
> > [...]
> >>> To me if i look at the evolution
> >>> of isBE() / code checking BE-ness it become more messy over time
> >>>
> >>> I think it would be interresting to think about if we can make
> >>> av_pix_fmt_desc_get(compile time constant) work at compile time.
> >>> or if we maybe can return to a simpler implementation
> >>>
> >>
> >> We could put the av_pix_fmt_descriptors array into an internal header
> >> and use something like
> >>
> >> static av_always_inline const AVPixFmtDescriptor
> >> *ff_pix_fmt_descriptor_get(enum AVPixelFormat fmt)
> >> {
> >>     if (av_builtin_constant_p(fmt))
> >>         return &av_pix_fmt_descriptors[fmt];
> >>     return av_pix_fmt_desc_get(fmt);
> >> }
> > 
> > yes thats what i was thinking of too.
> > 
> 
> Seems like Anton is away for a week or so. I am sure he has an opinion
> on the above approach. I think we will wait for him or shall I apply the
> patches as they are given that they do not block any later alternative
> solution?

please dont apply code like "IS_BE(BE_LE)" 
iam sure it makes sense to you today but it requires an additional step
for the reader to understand
simplest is a seperate endianness and isbe variable. on the wrapper
that should be less code too but quite possibly you see a better and
cleaner way


> (There is one thing I already don't like about the alternative solution:
> It relies on av_builtin_constant_p, which not every compiler supports.)

Thats why i didnt suggets to use av_builtin_constant_p() i was hoping you
saw a better way to achieve it.

But this is a problem which occurs more than once in the codebase.
mapping some identifer to some value just depending on the identifer,
something that is compile time constant, yet it calls to a function to
do a lookup

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The bravest are surely those who have the clearest vision
of what is before them, glory and danger alike, and yet
notwithstanding go out to meet it. -- Thucydides

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