[FFmpeg-devel] [PATCH 1/5] avfilter/vf_ciescope: Handle black as very dark neutral gray

[Valerii Zapodovnikov]

вс, 6 июн. 2021 г., 18:35 Michael Niedermayer <michael at niedermayer.cc>:

> On Sun, Jun 06, 2021 at 04:50:41PM +0300, Valerii Zapodovnikov wrote:
> > I am sorry, what???
>
> If that is intended as a review comment, please compose
> a english sentance which represents what you are trying to convey.
> That way others know what you mean.
>
> The goal of review is to improve code
>
> Anyway to elaborate on the rather trivial change
> the code before the change has undefined behavior, that is a bug
> in C per definition of what a bug is pretty much.
> the change tried to replace the used value with one thats close
> and not undefined.
> we could skip black pixels or also use x=y=0 but later is
> discontinous on all pathes with non negative color leading to black
> so it felt a bit strange. But probably x=y=0 is a more strictly correct
> choice, so ill change it to that.
>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
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Nice, please change to that. And actually first link in google says
https://stackoverflow.com/questions/42926763/ that it was defined in Annex
F of ISO/IEC 9899 and gcc can do it, while clang cannot. I am not sure how
one catches such NAN exceptions though.

Moreover clang also wants that
https://bugs.llvm.org/show_bug.cgi?id=19535#c13 and
https://bugs.llvm.org/show_bug.cgi?id=17005, the last one even says and I
quote: "The most visible issue caused by this is apparently that using
-fsanitize=undefined on programs that make use of floating point division
by 0.0 (which is perfectly legal udner IEEE floats) will print "runtime
error: division by zero".

(Also see: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=720935)

It's also scary to think that your program might run slightly incorrectly
in corner cases under clang, while it's correct under gcc (at least with
-std=c99, gcc intentionally breaks floating point semantics with
-std=gnu99)."

Another bug in compiler, nothing to worry about IMHO.

>