Eliminate use of complex.h from iirfilter.c

Originally committed as revision 19396 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/iirfilter.c

@@ -25,7 +25,6 @@
  */
 
 #include "iirfilter.h"
-#include <complex.h>
 #include <math.h>
 
 /**
@@ -56,7 +55,7 @@ struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type
     int i, j, size;
     FFIIRFilterCoeffs *c;
     double wa;
-    double complex p[MAXORDER + 1];
+    double p[MAXORDER + 1][2];
 
     if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS)
         return NULL;
@@ -74,23 +73,39 @@ struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type
     for(i = 1; i < (order >> 1) + 1; i++)
         c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
 
-    p[0] = 1.0;
+    p[0][0] = 1.0;
+    p[0][1] = 0.0;
     for(i = 1; i <= order; i++)
-        p[i] = 0.0;
+        p[i][0] = p[i][1] = 0.0;
     for(i = 0; i < order; i++){
-        double complex zp;
+        double zp[2];
         double th = (i + (order >> 1) + 0.5) * M_PI / order;
-        zp = cexp(I*th) * wa;
-        zp = (zp + 2.0) / (zp - 2.0);
+        double a_re, a_im, c_re, c_im;
+        zp[0] = cos(th) * wa;
+        zp[1] = sin(th) * wa;
+        a_re = zp[0] + 2.0;
+        c_re = zp[0] - 2.0;
+        a_im =
+        c_im = zp[1];
+        zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im);
+        zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im);
 
         for(j = order; j >= 1; j--)
-            p[j] = zp*p[j] + p[j - 1];
-        p[0] *= zp;
+        {
+            a_re = p[j][0];
+            a_im = p[j][1];
+            p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0];
+            p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1];
         }
-    c->gain = creal(p[order]);
+        a_re    = p[0][0]*zp[0] - p[0][1]*zp[1];
+        p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0];
+        p[0][0] = a_re;
+    }
+    c->gain = p[order][0];
     for(i = 0; i < order; i++){
-        c->gain += creal(p[i]);
-        c->cy[i] = creal(-p[i] / p[order]);
+        c->gain += p[i][0];
+        c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) /
+                   (p[order][0] * p[order][0] + p[order][1] * p[order][1]);
     }
     c->gain /= 1 << order;