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