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

[Anton Khirnov <anton@khirnov.net>]

Quoting Andreas Rheinhardt (2022-09-09 20:15:22)
> 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?
> (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.)

For what my opinion is worth, the patch as is with some extra
explanatory comments for the new IS_BE* macros seems like the best
solution to me. They are indeed slightly confusing at first glance, but
quite obvious if you look at the code for two minutes (less for people
smarter than me). And I think few people will need to understand how
precisely they work anyway.

The other proposals seem significantly more complex and fragile than
this one.

-- 
Anton Khirnov
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