[FFmpeg-devel] [PATCH] lavu/libm: add copysign hack

[Hendrik Leppkes]

On Sat, Dec 19, 2015 at 6:54 PM, Ganesh Ajjanagadde
<gajjanagadde at gmail.com> wrote:
> On Sat, Dec 19, 2015 at 8:06 AM, Ganesh Ajjanagadde
> <gajjanagadde at gmail.com> wrote:
>> On Sat, Dec 19, 2015 at 6:26 AM, Ronald S. Bultje <rsbultje at gmail.com> wrote:
>>> Hi,
>>>
>>> On Fri, Dec 18, 2015 at 3:47 PM, Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>>> wrote:
>>>>
>>>> On Fri, Dec 18, 2015 at 12:41 PM, Ronald S. Bultje <rsbultje at gmail.com>
>>>> wrote:
>>>> > Hi,
>>>> >
>>>> > On Fri, Dec 18, 2015 at 2:18 PM, Ganesh Ajjanagadde
>>>> > <gajjanagadde at gmail.com>
>>>> > wrote:
>>>> >>
>>>> >> For systems with broken libms.
>>>> >> Tested with NAN, -NAN, INFINITY, -INFINITY, +/-x for regular double x
>>>> >> and
>>>> >> combinations of these.
>>>> >>
>>>> >> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>>>> >> ---
>>>> >>  configure        | 2 +-
>>>> >>  libavutil/libm.h | 9 +++++++++
>>>> >>  2 files changed, 10 insertions(+), 1 deletion(-)
>>>> >>
>>>> >> diff --git a/configure b/configure
>>>> >> index 123d1df..7917386 100755
>>>> >> --- a/configure
>>>> >> +++ b/configure
>>>> >> @@ -2852,7 +2852,7 @@ cropdetect_filter_deps="gpl"
>>>> >>  delogo_filter_deps="gpl"
>>>> >>  deshake_filter_select="pixelutils"
>>>> >>  drawtext_filter_deps="libfreetype"
>>>> >> -dynaudnorm_filter_deps="copysign erf"
>>>> >> +dynaudnorm_filter_deps="erf"
>>>> >>  ebur128_filter_deps="gpl"
>>>> >>  eq_filter_deps="gpl"
>>>> >>  fftfilt_filter_deps="avcodec"
>>>> >> diff --git a/libavutil/libm.h b/libavutil/libm.h
>>>> >> index 6d8bd68..637de19 100644
>>>> >> --- a/libavutil/libm.h
>>>> >> +++ b/libavutil/libm.h
>>>> >> @@ -62,6 +62,15 @@ static av_always_inline float cbrtf(float x)
>>>> >>  }
>>>> >>  #endif
>>>> >>
>>>> >> +#if !HAVE_COPYSIGN
>>>> >> +static av_always_inline double copysign(double x, double y)
>>>> >> +{
>>>> >> +    uint64_t vx = av_double2int(x);
>>>> >> +    uint64_t vy = av_double2int(y);
>>>> >> +    return av_int2double((vx & 0x7fffffffffffffff) | (vy &
>>>> >> 0x8000000000000000));
>>>> >> +}
>>>> >> +#endif
>>>> >
>>>> >
>>>> > Don't these need type suffixes (e.g. UINT64_C(val)) on some systems?
>>>>
>>>> I believe not, see
>>>> http://en.cppreference.com/w/cpp/language/integer_literal
>>>
>>>
>>> That document confirms that it is indeed legal for a compiler to read the
>>> given literal on a 32bit or windows 64bit system as a 32bit max value, and
>>> your literals don't fit in 32bit.
>>
>> How, the standard clearly says that the literal will be in the type
>> int < unsigned int < long int < unsigned long int < long long int <
>> unsigned long long int, wherever it first fits, and this is also clear
>> from the link I sent.
>>
>> long long is at least 64 bits. I can't speak about broken
>> compilers/environments that lack long long.
>
> This turns out to be the heart of the matter; as usual, Microsoft's
> toolchain is fundamentally broken:
> https://stackoverflow.com/questions/25626022/how-should-a-64-bit-integer-literal-be-represented-in-c.
>

Its behavior would appear to be valid C90 on Windows, since long int
is 32-bit on that platform (which C90 calls for using, not long long)

- Hendrik