On Fri, Nov 27, 2015 at 06:32:40AM -0500, Ganesh Ajjanagadde wrote: > On Fri, Nov 27, 2015 at 4:46 AM, Clément Bœsch <u...@pkh.me> wrote: > > On Thu, Nov 26, 2015 at 11:58:10AM -0500, Ganesh Ajjanagadde wrote: > >> Reviewed-by: Ronald S. Bultje <rsbul...@gmail.com> > >> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> > >> --- > >> libavutil/tablegen.h | 33 +++++++++++++++++++++++++++++++++ > >> 1 file changed, 33 insertions(+) > >> create mode 100644 libavutil/tablegen.h > >> > >> diff --git a/libavutil/tablegen.h b/libavutil/tablegen.h > >> new file mode 100644 > >> index 0000000..01c8eea > >> --- /dev/null > >> +++ b/libavutil/tablegen.h > >> @@ -0,0 +1,33 @@ > >> +/* > >> + * This file is part of FFmpeg. > >> + * > >> + * FFmpeg is free software; you can redistribute it and/or > >> + * modify it under the terms of the GNU Lesser General Public > >> + * License as published by the Free Software Foundation; either > >> + * version 2.1 of the License, or (at your option) any later version. > >> + * > >> + * FFmpeg is distributed in the hope that it will be useful, > >> + * but WITHOUT ANY WARRANTY; without even the implied warranty of > >> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > >> + * Lesser General Public License for more details. > >> + * > >> + * You should have received a copy of the GNU Lesser General Public > >> + * License along with FFmpeg; if not, write to the Free Software > >> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA > >> 02110-1301 USA > >> + */ > >> + > >> +/** > >> + * @file > >> + * Compatibility libm for table generation files > >> + */ > >> + > >> +#ifndef AVUTIL_TABLEGEN_H > >> +#define AVUTIL_TABLEGEN_H > >> + > >> +// we lack some functions on all host platforms, and we don't care about > >> +// performance as it's performed at build time > >> +#define cbrt(x) pow(x, 1.0 / 3) > > > >> +#define llrint(x) floor((x) + 0.5) > >> +#define lrint(x) floor((x) + 0.5) > >> + > > > > does it work for x < 0? > > Of course not exactly; I did recognize this. However, there are 2 > reasons for this: > 1. The old tablegen code did exactly a floor(x + 0.5), suggesting that > it did not matter. Thus, this was done for simplicity, anyway these > are imperfect hacks. The hacks can be improved, but felt that belongs > in a separate patch - no matter how they are improved, they remain > hacks (see number 2). > 2. Even if one does the floor if x > 0, ceil if x < 0 trick, it has > issues with corner cases, I recall Michael mentioning something > regarding 0.4999 or something like that. >
it's pretty fine with me to use a simple hack like this, but then i'd argue it's better if the global c namespace is not polluted with openly broken implementations: just name the macro differently (ffrint, simplerint, or whatever) to make sure someone doesn't end up using it in a different context where negative values matter (and where the issue won't get detected quickly) -- Clément B.
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