Re: [FFmpeg-devel] [PATCH 4/5] lavu/intmath.h: Fix UB in ff_ctz_c() and ff_ctzll_c()

From: "Tomas Härdin" <git@haerdin.se>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH 4/5] lavu/intmath.h: Fix UB in ff_ctz_c() and ff_ctzll_c()
Date: Thu, 30 May 2024 16:03:09 +0200
Message-ID: <7572dd13e369feb7b373330a65270f8f4f842598.camel@haerdin.se> (raw)
In-Reply-To: <75356678-105B-433E-AD49-FF15DE4E6523@remlab.net>

tor 2024-05-30 klockan 16:06 +0300 skrev Rémi Denis-Courmont:
> 
> 
> Le 30 mai 2024 12:50:05 GMT+03:00, "Tomas Härdin" <git@haerdin.se> a
> écrit :
> > tor 2024-05-30 klockan 10:54 +0300 skrev Rémi Denis-Courmont:
> > > Can't we just use the compiler built-ins here? AFAIK, they (GCC,
> > > LLVM) use the same algorithm if the CPU doesn't support native
> > > CTZ.
> > > And they will pick the right instruction if CPU does have CTZ.
> > > 
> > > I get it that maybe it wasn't working so well 20 years ago, but
> > > we've
> > > increased compiler version requirements since then.
> > 
> > I think we still support MSVC, but maybe we shouldn't? It's
> > possible to
> > cross-compile for Windows either way.
> 
> I don't get how that prevents using the GCC and Clang builtins (on
> GCC and Clang).

Does MSVC have builtins for these? Do all compilers we support?

/Tomas
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