[FFmpeg-devel] [PATCHv3 1/3] avutil/tablegen: add tablegen compatibility hacks

[Ganesh Ajjanagadde]

On Fri, Nov 27, 2015 at 4:46 AM, Clément Bœsch <u at pkh.me> wrote:
> On Thu, Nov 26, 2015 at 11:58:10AM -0500, Ganesh Ajjanagadde wrote:
>> Reviewed-by: Ronald S. Bultje <rsbultje at gmail.com>
>> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at 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.

>
> --
> Clément B.
>
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