#include <MATH.H>    
   
void fft(float *x, float *y, int n, int flag)   
{   
    float frac;   
    float a, c, e;   
    int i, j, k, l, m;   
    float s;   
    int n1, n2;   
    float xt, yt;   
       
    frac = (float)(frexp((float) n, &m));    
      
    if (frac == 1.0)    
    {   
    }    
    else    
    {   
    m--;   
    }   
       
    // --------------MAIN FFT LOOPS-----------------------------    
    --y;   
    --x;   
       
    //---------------Function Body -----------------------------    
    n2 = n;   
    for (k = 1; k <= m; ++k) {   
    n1 = n2;   
    n2 /= 2;   
    e = (float)6.283185307179586476925286766559005768394 / n1;   
    if (flag==1){e=-e;} // for ifft    
    a = 0.0;   
    for (j = 1; j <= n2; ++j) {   
        c = (float)(cos(a));   
        s = (float)(sin(a));   
        a = j * e;   
        for (i = j; n1 < 0 ? i >= n : i <= n; i += n1) {   
        l = i + n2;   
        xt = x[i] - x[l];   
        x[i] += x[l];   
        yt = y[i] - y[l];   
        y[i] += y[l];   
        x[l] = c * xt + s * yt;   
        y[l] = c * yt - s * xt;   
        }   
    }   
    }   
       
    //------------DIGIT REVERSE COUNTER-------------------    
       
    j = 1;   
    n1 = n - 1;   
    for (i = 1; i <= n1; ++i) {   
    if (i < j) {   
        xt = x[j]; x[j] = x[i]; x[i] = xt;   
        xt = y[j]; y[j] = y[i]; y[i] = xt;   
    }   
    k = n / 2;   
    while (k<J) pre < ifft---- and fft --- } ="2;" y[j] x[j] { for(j="0;j<=n1;j++)" y++; x++; if(flag="=1)" -------------------------------- ifft for --------------- +="k;" j k -="k;">  
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