32 lines
671 B
C
32 lines
671 B
C
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void twofft(float data1[], float data2[], float fft1[], float fft2[],
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unsigned long n)
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{
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void four1(float data[], unsigned long nn, int isign);
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unsigned long nn3,nn2,jj,j;
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float rep,rem,aip,aim;
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nn3=1+(nn2=2+n+n);
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for (j=1,jj=2;j<=n;j++,jj+=2) {
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fft1[jj-1]=data1[j];
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fft1[jj]=data2[j];
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}
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four1(fft1,n,1);
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fft2[1]=fft1[2];
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fft1[2]=fft2[2]=0.0;
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for (j=3;j<=n+1;j+=2) {
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rep=0.5*(fft1[j]+fft1[nn2-j]);
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rem=0.5*(fft1[j]-fft1[nn2-j]);
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aip=0.5*(fft1[j+1]+fft1[nn3-j]);
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aim=0.5*(fft1[j+1]-fft1[nn3-j]);
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fft1[j]=rep;
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fft1[j+1]=aim;
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fft1[nn2-j]=rep;
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fft1[nn3-j] = -aim;
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fft2[j]=aip;
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fft2[j+1] = -rem;
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fft2[nn2-j]=aip;
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fft2[nn3-j]=rem;
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}
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}
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