[FFmpeg-devel] [PATCH] lavfi/af_aemphasis: remove unnecessary complex number usage

[Ganesh Ajjanagadde]

On Tue, Dec 22, 2015 at 2:10 PM, Paul B Mahol <onemda at gmail.com> wrote:
> On 12/22/15, Ganesh Ajjanagadde <gajjanagadde at gmail.com> wrote:
>> On Tue, Dec 22, 2015 at 12:46 AM, Paul B Mahol <onemda at gmail.com> wrote:
>>> On 12/22/15, Ganesh Ajjanagadde <gajjanagadde at gmail.com> wrote:
>>>> complex is not available on all platforms. Furthermore, it is trivial to
>>>> rewrite complex number expressions to real arithmetic, and in fact
>>>> sometimes advantageous for performance reasons: by wrapping as a
>>>> complex,
>>>> one forces a particular Cartesian representation that is not necessarily
>>>> optimal for the purpose.
>>>>
>>>> Configure tests are also removed, and aemphasis is now available across
>>>> all platforms.
>>>>
>>>> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>>>> ---
>>>>  configure                  | 26 --------------------------
>>>>  libavfilter/af_aemphasis.c | 13 ++++++-------
>>>>  2 files changed, 6 insertions(+), 33 deletions(-)
>>>>
>>>> diff --git a/configure b/configure
>>>> index 0227540..46021c4 100755
>>>> --- a/configure
>>>> +++ b/configure
>>>> @@ -1070,21 +1070,6 @@ int main(void){ $func(); }
>>>>  EOF
>>>>  }
>>>>
>>>> -check_complexfunc(){
>>>> -    log check_complexfunc "$@"
>>>> -    func=$1
>>>> -    narg=$2
>>>> -    shift 2
>>>> -    test $narg = 2 && args="f, g" || args="f * I"
>>>> -    disable $func
>>>> -    check_ld "cc" "$@" <<EOF && enable $func
>>>> -#include <complex.h>
>>>> -#include <math.h>
>>>> -float foo(complex float f, complex float g) { return $func($args); }
>>>> -int main(void){ return (int) foo; }
>>>> -EOF
>>>> -}
>>>> -
>>>>  check_mathfunc(){
>>>>      log check_mathfunc "$@"
>>>>      func=$1
>>>> @@ -1803,11 +1788,6 @@ INTRINSICS_LIST="
>>>>      intrinsics_neon
>>>>  "
>>>>
>>>> -COMPLEX_FUNCS="
>>>> -    cabs
>>>> -    cexp
>>>> -"
>>>> -
>>>>  MATH_FUNCS="
>>>>      atanf
>>>>      atan2f
>>>> @@ -1944,7 +1924,6 @@ HAVE_LIST="
>>>>      $ARCH_FEATURES
>>>>      $ATOMICS_LIST
>>>>      $BUILTIN_LIST
>>>> -    $COMPLEX_FUNCS
>>>>      $HAVE_LIST_CMDLINE
>>>>      $HAVE_LIST_PUB
>>>>      $HEADERS_LIST
>>>> @@ -2835,7 +2814,6 @@ unix_protocol_deps="sys_un_h"
>>>>  unix_protocol_select="network"
>>>>
>>>>  # filters
>>>> -aemphasis_filter_deps="cabs cexp"
>>>>  amovie_filter_deps="avcodec avformat"
>>>>  aresample_filter_deps="swresample"
>>>>  ass_filter_deps="libass"
>>>> @@ -5379,10 +5357,6 @@ for func in $MATH_FUNCS; do
>>>>      eval check_mathfunc $func \${${func}_args:-1}
>>>>  done
>>>>
>>>> -for func in $COMPLEX_FUNCS; do
>>>> -    eval check_complexfunc $func \${${func}_args:-1}
>>>> -done
>>>> -
>>>>  # these are off by default, so fail if requested and not available
>>>>  enabled avfoundation_indev && { check_header_objcc
>>>> AVFoundation/AVFoundation.h || disable avfoundation_indev; }
>>>>  enabled avfoundation_indev && { check_lib2 CoreGraphics/CoreGraphics.h
>>>> CGGetActiveDisplayList -framework CoreGraphics ||
>>>> diff --git a/libavfilter/af_aemphasis.c b/libavfilter/af_aemphasis.c
>>>> index 2966f77..a5b8e30 100644
>>>> --- a/libavfilter/af_aemphasis.c
>>>> +++ b/libavfilter/af_aemphasis.c
>>>> @@ -18,8 +18,6 @@
>>>>   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
>>>> 02110-1301
>>>> USA
>>>>   */
>>>>
>>>> -#include <complex.h>
>>>> -
>>>>  #include "libavutil/opt.h"
>>>>  #include "avfilter.h"
>>>>  #include "internal.h"
>>>> @@ -189,14 +187,15 @@ static inline void set_lp_rbj(BiquadD2 *bq, double
>>>> fc,
>>>> double q, double sr, doub
>>>>
>>>>  static double freq_gain(BiquadCoeffs *c, double freq, double sr)
>>>>  {
>>>> -    double complex z, w;
>>>> +    double zr, zi;
>>>>
>>>>      freq *= 2.0 * M_PI / sr;
>>>> -    w = 0 + I * freq;
>>>> -    z = 1.0 / cexp(w);
>>>> +    zr = cos(freq);
>>>> +    zi = -sin(freq);
>>>>
>>>> -    return cabs(((double complex)c->a0 + c->a1 * z + c->a2 * z*z) /
>>>> -                ((double complex)1.0 + c->b1 * z + c->b2 * z*z));
>>>> +    /* |(a0 + a1*z + a2*z^2)/(1 + b1*z + b2*z^2)| */
>>>> +    return hypot(c->a0 + c->a1*zr + c->a2*(zr*zr-zi*zi), c->a1*zi +
>>>> 2*c->a2*zr*zi) /
>>>> +           hypot(1 + c->b1*zr + c->b2*(zr*zr-zi*zi), c->b1*zi +
>>>> 2*c->b2*zr*zi);
>>>>  }
>>>>
>>>>  static int config_input(AVFilterLink *inlink)
>>>> --
>>>> 2.6.4
>>>>
>>>> _______________________________________________
>>>> ffmpeg-devel mailing list
>>>> ffmpeg-devel at ffmpeg.org
>>>> http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
>>>>
>>>
>>> ok
>>
>> I assume by this you are ok with the configure change as well.
>> Personally, I think the effort needed for writing the configure hacks
>> is higher than using real arithmetic, and hence I removed it to help
>> ensure it is not added back again.
>>
>> This filter was added during the next version work, so does not need a
>> Changelog update. Thanks, will push later.
>>
>
> Please leave configure check alone, I'm writting some code that uses
> complex again.

and how hard is it to use real numbers? It does not take > 5 min to
come up real number expressions...