Cedric Roux
56c66c09aa
Pre-ci test passed git-svn-id: http://svn.eurecom.fr/openair4G/trunk@4000 818b1a75-f10b-46b9-bf7c-635c3b92a50f
61 lines
1.5 KiB
C
61 lines
1.5 KiB
C
#include <math.h>
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// ******* FFT function **********************************************************
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#define PI 3.14159264359
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#define SWAP(a,b) tempr=(a); (a)=(b); (b)=tempr
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void FFT(float *data, // the vector with the outputs
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// real part in even indexes
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// imaginary part in the odd indexes
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// for power conservation, the output should be normalized by 1/sqrt(nn)
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unsigned long nn, // number of complex samples
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int isign) // isign = 1 -> FFT, -1 -> iFFT
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{
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unsigned long n,mmax,m,j,istep,i;
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float 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){ // The bit-reversal
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if(j > i){
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SWAP(data[j-1],data[i-1]); // Exchanging the two complex number
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SWAP(data[j],data[i]);
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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 = mmax << 1;
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theta = isign*(-2*PI/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-1] - wi*data[j];
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tempi = wr*data[j] + wi*data[j-1];
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data[j-1] = data[i-1] - tempr;
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data[j] = data[i] - tempi;
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data[i-1] += tempr;
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data[i] += 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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