add numerical recipes library

lib/nr/k_and_r/recipes/cosft1.c

@@ -0,0 +1,38 @@
+
+#include <math.h>
+#define PI 3.141592653589793
+
+void cosft1(y,n)
+float y[];
+int n;
+{
+	void realft();
+	int j,n2;
+	float sum,y1,y2;
+	double theta,wi=0.0,wpi,wpr,wr=1.0,wtemp;
+
+	theta=PI/n;
+	wtemp=sin(0.5*theta);
+	wpr = -2.0*wtemp*wtemp;
+	wpi=sin(theta);
+	sum=0.5*(y[1]-y[n+1]);
+	y[1]=0.5*(y[1]+y[n+1]);
+	n2=n+2;
+	for (j=2;j<=(n>>1);j++) {
+		wr=(wtemp=wr)*wpr-wi*wpi+wr;
+		wi=wi*wpr+wtemp*wpi+wi;
+		y1=0.5*(y[j]+y[n2-j]);
+		y2=(y[j]-y[n2-j]);
+		y[j]=y1-wi*y2;
+		y[n2-j]=y1+wi*y2;
+		sum += wr*y2;
+	}
+	realft(y,n,1);
+	y[n+1]=y[2];
+	y[2]=sum;
+	for (j=4;j<=n;j+=2) {
+		sum += y[j];
+		y[j]=sum;
+	}
+}
+#undef PI