Working codec2 support

libs/libcodec2/src/four1.c

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+/*---------------------------------------------------------------------------*\
+  
+  FILE........: four1.c
+  AUTHOR......: David Rowe
+  DATE CREATED: 20/2/95
+
+  Numerical Recipies in C FFT function.  I have a nasty licence so please
+  replace me.
+
+\*---------------------------------------------------------------------------*/
+
+#include <math.h>
+
+#define SWAP(a,b) tempr=(a);(a)=(b);(b)=tempr
+
+void four1(data,nn,isign)
+float data[];
+int nn,isign;
+{
+	int n,mmax,m,j,istep,i;
+	double wtemp,wr,wpr,wpi,wi,theta;
+	float tempr,tempi;
+
+	n=nn << 1;
+	j=1;
+	for (i=1;i<n;i+=2) {
+		if (j > i) {
+			SWAP(data[j],data[i]);
+			SWAP(data[j+1],data[i+1]);
+		}
+		m=n >> 1;
+		while (m >= 2 && j > m) {
+			j -= m;
+			m >>= 1;
+		}
+		j += m;
+	}
+	mmax=2;
+	while (n > mmax) {
+		istep=2*mmax;
+		theta=6.28318530717959/(isign*mmax);
+		wtemp=sin(0.5*theta);
+		wpr = -2.0*wtemp*wtemp;
+		wpi=sin(theta);
+		wr=1.0;
+		wi=0.0;
+		for (m=1;m<mmax;m+=2) {
+			for (i=m;i<=n;i+=istep) {
+				j=i+mmax;
+				tempr=wr*data[j]-wi*data[j+1];
+				tempi=wr*data[j+1]+wi*data[j];
+				data[j]=data[i]-tempr;
+				data[j+1]=data[i+1]-tempi;
+				data[i] += tempr;
+				data[i+1] += tempi;
+			}
+			wr=(wtemp=wr)*wpr-wi*wpi+wr;
+			wi=wi*wpr+wtemp*wpi+wi;
+		}
+		mmax=istep;
+	}
+}
+
+#undef SWAP