[FFmpeg-devel] [PATCH 1/2] configure+libm.h: add hypot emulation

[Ganesh Ajjanagadde]

On Sat, Nov 14, 2015 at 4:48 PM, Paul B Mahol <onemda at gmail.com> wrote:
> On 11/14/15, Ganesh Ajjanagadde <gajjanagadde at gmail.com> wrote:
>> It is known that the naive sqrt(x*x + y*y) approach for computing the
>> hypotenuse suffers from overflow and accuracy issues, see e.g
>> http://www.johndcook.com/blog/2010/06/02/whats-so-hard-about-finding-a-hypotenuse/.
>> This adds hypot support to FFmpeg, a C99 function.
>>
>> On platforms without hypot, this patch for simplicity does the naive
>> direct computation outlined above. Improvements can be made separately.
>>
>> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>> ---
>>  configure        | 2 ++
>>  libavutil/libm.h | 8 ++++++++
>>  2 files changed, 10 insertions(+)
>>
>> diff --git a/configure b/configure
>> index d518b21..45df724 100755
>> --- a/configure
>> +++ b/configure
>> @@ -1774,6 +1774,7 @@ MATH_FUNCS="
>>      exp2
>>      exp2f
>>      expf
>> +    hypot
>>      isinf
>>      isnan
>>      ldexpf
>> @@ -5309,6 +5310,7 @@ disabled crystalhd || check_lib
>> libcrystalhd/libcrystalhd_if.h DtsCrystalHDVersi
>>
>>  atan2f_args=2
>>  copysign_args=2
>> +hypot_args=2
>>  ldexpf_args=2
>>  powf_args=2
>>
>> diff --git a/libavutil/libm.h b/libavutil/libm.h
>> index 6c17b28..ab5df1b 100644
>> --- a/libavutil/libm.h
>> +++ b/libavutil/libm.h
>> @@ -82,6 +82,14 @@ static av_always_inline float cbrtf(float x)
>>  #define exp2f(x) ((float)exp2(x))
>>  #endif /* HAVE_EXP2F */
>>
>> +#if !HAVE_HYPOT
>> +#undef hypot
>> +static av_always_inline av_const double hypot(double x, double y)
>> +{
>> +    return sqrt(x*x + y*y);
>> +}
>> +#endif /* HAVE_HYPOT */
>> +
>>  #if !HAVE_ISINF
>>  static av_always_inline av_const int isinf(float x)
>>  {
>> --
>> 2.6.2
>>
>> _______________________________________________
>> ffmpeg-devel mailing list
>> ffmpeg-devel at ffmpeg.org
>> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>>
>
> nonsense. either do the right thing or don't touch the code.

Nonsense is technically incorrect: this patch is a Pareto improvement:
on C99, it is a strict improvement, on others it is identical. Please
refrain from such hysterical claims.

I assumed incremental improvements are ok. Will resubmit with a more
elaborate fallback.