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

[Ganesh Ajjanagadde]

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