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