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

[Ganesh Ajjanagadde]

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.