lavfi/af_anequalizer: remove cabs, cexp dependencies

Replaces by real arithmetic. Tested the validity of these transformations separately.
Numerical differences are ~1e-15, and should not matter: it is not even
clear which is more precise mathematically.
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>

configure

@@ -2839,7 +2839,6 @@ unix_protocol_select="network"
 
 # filters
 amovie_filter_deps="avcodec avformat"
-anequalizer_filter_deps="cabs cexp"
 aresample_filter_deps="swresample"
 ass_filter_deps="libass"
 asyncts_filter_deps="avresample"

libavfilter/af_anequalizer.c

@@ -19,8 +19,6 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
-#include <complex.h>
-
 #include "libavutil/intreadwrite.h"
 #include "libavutil/avstring.h"
 #include "libavutil/opt.h"
@@ -114,13 +112,17 @@ static void draw_curves(AVFilterContext *ctx, AVFilterLink *inlink, AVFrame *out
             av_parse_color(fg, color, -1, ctx);
 
         for (f = 0; f < s->w; f++) {
-            double complex z;
-            double complex H = 1;
+            double zr, zi, zr2, zi2;
+            double Hr, Hi;
+            double Hmag = 1;
             double w;
             int v, y, x;
 
             w = M_PI * (s->fscale ? pow(s->w - 1, f / s->w) : f) / (s->w - 1);
-            z = 1. / cexp(I * w);
+            zr = cos(w);
+            zr2 = zr * zr;
+            zi = -sin(w);
+            zi2 = zi * zi;
 
             for (n = 0; n < s->nb_filters; n++) {
                 if (s->filters[n].channel != ch ||
@@ -130,12 +132,19 @@ static void draw_curves(AVFilterContext *ctx, AVFilterLink *inlink, AVFrame *out
                 for (i = 0; i < FILTER_ORDER / 2; i++) {
                     FoSection *S = &s->filters[n].section[i];
 
-                    H *= (((((S->b4 * z + S->b3) * z + S->b2) * z + S->b1) * z + S->b0) /
-                          ((((S->a4 * z + S->a3) * z + S->a2) * z + S->a1) * z + S->a0));
+                    /* H *= (((((S->b4 * z + S->b3) * z + S->b2) * z + S->b1) * z + S->b0) /
+                          ((((S->a4 * z + S->a3) * z + S->a2) * z + S->a1) * z + S->a0)); */
+
+                    Hr = S->b4*(1-8*zr2*zi2) + S->b2*(zr2-zi2) + zr*(S->b1+S->b3*(zr2-3*zi2))+ S->b0;
+                    Hi = zi*(S->b3*(3*zr2-zi2) + S->b1 + 2*zr*(2*S->b4*(zr2-zi2) + S->b2));
+                    Hmag *= hypot(Hr, Hi);
+                    Hr = S->a4*(1-8*zr2*zi2) + S->a2*(zr2-zi2) + zr*(S->a1+S->a3*(zr2-3*zi2))+ S->a0;
+                    Hi = zi*(S->a3*(3*zr2-zi2) + S->a1 + 2*zr*(2*S->a4*(zr2-zi2) + S->a2));
+                    Hmag /= hypot(Hr, Hi);
                 }
             }
 
-            v = av_clip((1. + -20 * log10(cabs(H)) / s->mag) * s->h / 2, 0, s->h - 1);
+            v = av_clip((1. + -20 * log10(Hmag) / s->mag) * s->h / 2, 0, s->h - 1);
             x = lrint(f);
             if (prev_v == -1)
                 prev_v = v;