fft2f.c

FFT代原碼為C++需要測過才能用

/*
Fast Fourier/Cosine/Sine Transform
    dimension   :one
    data length :power of 2
    decimation  :frequency
    radix       :2
    data        :inplace
    table       :not use
functions
    cdft: Complex Discrete Fourier Transform
    rdft: Real Discrete Fourier Transform
    ddct: Discrete Cosine Transform
    ddst: Discrete Sine Transform
    dfct: Cosine Transform of RDFT (Real Symmetric DFT)
    dfst: Sine Transform of RDFT (Real Anti-symmetric DFT)
function prototypes
    void cdft(int, double, double, double *);
    void rdft(int, double, double, double *);
    void ddct(int, double, double, double *);
    void ddst(int, double, double, double *);
    void dfct(int, double, double, double *);
    void dfst(int, double, double, double *);


-------- Complex DFT (Discrete Fourier Transform) --------
    [definition]
        <case1>
            X[k] = sum_j=0^n-1 x[j]*exp(2*pi*i*j*k/n), 0<=k<n
        <case2>
            X[k] = sum_j=0^n-1 x[j]*exp(-2*pi*i*j*k/n), 0<=k<n
        (notes: sum_j=0^n-1 is a summation from j=0 to n-1)
    [usage]
        <case1>
            cdft(2*n, cos(M_PI/n), sin(M_PI/n), a);
        <case2>
            cdft(2*n, cos(M_PI/n), -sin(M_PI/n), a);
    [parameters]
        2*n          :data length (int)
                      n >= 1, n = power of 2
        a[0...2*n-1] :input/output data (double *)
                      input data
                          a[2*j] = Re(x[j]), a[2*j+1] = Im(x[j]), 0<=j<n
                      output data
                          a[2*k] = Re(X[k]), a[2*k+1] = Im(X[k]), 0<=k<n
    [remark]
        Inverse of 
            cdft(2*n, cos(M_PI/n), -sin(M_PI/n), a);
        is 
            cdft(2*n, cos(M_PI/n), sin(M_PI/n), a);
            for (j = 0; j <= 2 * n - 1; j++) {
                a[j] *= 1.0 / n;
            }
        .


-------- Real DFT / Inverse of Real DFT --------
    [definition]
        <case1> RDFT
            R[k] = sum_j=0^n-1 a[j]*cos(2*pi*j*k/n), 0<=k<=n/2
            I[k] = sum_j=0^n-1 a[j]*sin(2*pi*j*k/n), 0<k<n/2
        <case2> IRDFT (excluding scale)
            a[k] = R[0]/2 + R[n/2]/2 + 
                   sum_j=1^n/2-1 R[j]*cos(2*pi*j*k/n) + 
                   sum_j=1^n/2-1 I[j]*sin(2*pi*j*k/n), 0<=k<n
    [usage]
        <case1>
            rdft(n, cos(M_PI/n), sin(M_PI/n), a);
        <case2>
            rdft(n, cos(M_PI/n), -sin(M_PI/n), a);
    [parameters]
        n            :data length (int)
                      n >= 2, n = power of 2
        a[0...n-1]   :input/output data (double *)
                      <case1>
                          output data
                              a[2*k] = R[k], 0<=k<n/2
                              a[2*k+1] = I[k], 0<k<n/2
                              a[1] = R[n/2]
                      <case2>
                          input data
                              a[2*j] = R[j], 0<=j<n/2
                              a[2*j+1] = I[j], 0<j<n/2
                              a[1] = R[n/2]
    [remark]
        Inverse of 
            rdft(n, cos(M_PI/n), sin(M_PI/n), a);
        is 
            rdft(n, cos(M_PI/n), -sin(M_PI/n), a);
            for (j = 0; j <= n - 1; j++) {
                a[j] *= 2.0 / n;
            }
        .


-------- DCT (Discrete Cosine Transform) / Inverse of DCT --------
    [definition]
        <case1> IDCT (excluding scale)
            C[k] = sum_j=0^n-1 a[j]*cos(pi*j*(k+1/2)/n), 0<=k<n
        <case2> DCT
            C[k] = sum_j=0^n-1 a[j]*cos(pi*(j+1/2)*k/n), 0<=k<n
    [usage]
        <case1>
            ddct(n, cos(M_PI/n/2), sin(M_PI/n/2), a);
        <case2>
            ddct(n, cos(M_PI/n/2), -sin(M_PI/n/2), a);
    [parameters]
        n            :data length (int)
                      n >= 2, n = power of 2
        a[0...n-1]   :input/output data (double *)
                      output data
                          a[k] = C[k], 0<=k<n
    [remark]
        Inverse of 
            ddct(n, cos(M_PI/n/2), -sin(M_PI/n/2), a);
        is 
            a[0] *= 0.5;
            ddct(n, cos(M_PI/n/2), sin(M_PI/n/2), a);
            for (j = 0; j <= n - 1; j++) {
                a[j] *= 2.0 / n;
            }
        .


-------- DST (Discrete Sine Transform) / Inverse of DST --------
    [definition]
        <case1> IDST (excluding scale)
            S[k] = sum_j=1^n A[j]*sin(pi*j*(k+1/2)/n), 0<=k<n
        <case2> DST
            S[k] = sum_j=0^n-1 a[j]*sin(pi*(j+1/2)*k/n), 0<k<=n
    [usage]
        <case1>
            ddst(n, cos(M_PI/n/2), sin(M_PI/n/2), a);
        <case2>
            ddst(n, cos(M_PI/n/2), -sin(M_PI/n/2), a);
    [parameters]
        n            :data length (int)
                      n >= 2, n = power of 2
        a[0...n-1]   :input/output data (double *)
                      <case1>
                          input data
                              a[j] = A[j], 0<j<n
                              a[0] = A[n]
                          output data
                              a[k] = S[k], 0<=k<n
                      <case2>
                          output data
                              a[k] = S[k], 0<k<n
                              a[0] = S[n]
    [remark]
        Inverse of 
            ddst(n, cos(M_PI/n/2), -sin(M_PI/n/2), a);
        is 
            a[0] *= 0.5;
            ddst(n, cos(M_PI/n/2), sin(M_PI/n/2), a);
            for (j = 0; j <= n - 1; j++) {
                a[j] *= 2.0 / n;
            }
        .


-------- Cosine Transform of RDFT (Real Symmetric DFT) --------
    [definition]
        C[k] = sum_j=0^n a[j]*cos(pi*j*k/n), 0<=k<=n
    [usage]
        dfct(n, cos(M_PI/n), sin(M_PI/n), a);
    [parameters]
        n            :data length - 1 (int)
                      n >= 2, n = power of 2
        a[0...n]     :input/output data (double *)
                      output data
                          a[k] = C[k], 0<=k<=n
    [remark]
        Inverse of 
            a[0] *= 0.5;
            a[n] *= 0.5;
            dfct(n, cos(M_PI/n), sin(M_PI/n), a);
        is 
            a[0] *= 0.5;
            a[n] *= 0.5;
            dfct(n, cos(M_PI/n), sin(M_PI/n), a);
            for (j = 0; j <= n; j++) {
                a[j] *= 2.0 / n;
            }
        .


-------- Sine Transform of RDFT (Real Anti-symmetric DFT) --------
    [definition]
        S[k] = sum_j=1^n-1 a[j]*sin(pi*j*k/n), 0<k<n
    [usage]
        dfst(n, cos(M_PI/n), sin(M_PI/n), a);
    [parameters]
        n            :data length + 1 (int)
                      n >= 2, n = power of 2
        a[0...n-1]   :input/output data (double *)
                      output data
                          a[k] = S[k], 0<k<n
                      (a[0] is used for work area)
    [remark]
        Inverse of 
            dfst(n, cos(M_PI/n), sin(M_PI/n), a);
        is 
            dfst(n, cos(M_PI/n), sin(M_PI/n), a);
            for (j = 1; j <= n - 1; j++) {
                a[j] *= 2.0 / n;
            }
        .
*/


void bitrv2(int n, double *a)
{
    int j, j1, k, k1, l, m, m2, n2;
    double xr, xi;
    
    m = n >> 2;
    m2 = m << 1;
    n2 = n - 2;
    k = 0;
    for (j = 0; j <= m2 - 4; j += 4) {
        if (j < k) {
            xr = a[j];
            xi = a[j + 1];
            a[j] = a[k];
            a[j + 1] = a[k + 1];
            a[k] = xr;
            a[k + 1] = xi;
        } else if (j > k) {
            j1 = n2 - j;
            k1 = n2 - k;
            xr = a[j1];
            xi = a[j1 + 1];
            a[j1] = a[k1];
            a[j1 + 1] = a[k1 + 1];
            a[k1] = xr;
            a[k1 + 1] = xi;
        }
        k1 = m2 + k;
        xr = a[j + 2];
        xi = a[j + 3];
        a[j + 2] = a[k1];
        a[j + 3] = a[k1 + 1];
        a[k1] = xr;
        a[k1 + 1] = xi;
        l = m;
        while (k >= l) {
            k -= l;
            l >>= 1;
        }
        k += l;
    }
}


void cdft(int n, double wr, double wi, double *a)
{
    void bitrv2(int n, double *a);
    int i, j, k, l, m;
    double wkr, wki, wdr, wdi, ss, xr, xi;
    
    m = n;
    while (m > 4) {
        l = m >> 1;
        wkr = 1;
        wki = 0;
        wdr = 1 - 2 * wi * wi;
        wdi = 2 * wi * wr;
        ss = 2 * wdi;
        wr = wdr;
        wi = wdi;
        for (j = 0; j <= n - m; j += m) {
            i = j + l;
            xr = a[j] - a[i];
            xi = a[j + 1] - a[i + 1];
            a[j] += a[i];
            a[j + 1] += a[i + 1];
            a[i] = xr;
            a[i + 1] = xi;
            xr = a[j + 2] - a[i + 2];
            xi = a[j + 3] - a[i + 3];
            a[j + 2] += a[i + 2];
            a[j + 3] += a[i + 3];
            a[i + 2] = wdr * xr - wdi * xi;
            a[i + 3] = wdr * xi + wdi * xr;
        }
        for (k = 4; k <= l - 4; k += 4) {
            wkr -= ss * wdi;
            wki += ss * wdr;
            wdr -= ss * wki;
            wdi += ss * wkr;
            for (j = k; j <= n - m + k; j += m) {
                i = j + l;
                xr = a[j] - a[i];
                xi = a[j + 1] - a[i + 1];
                a[j] += a[i];
                a[j + 1] += a[i + 1];
                a[i] = wkr * xr - wki * xi;
                a[i + 1] = wkr * xi + wki * xr;
                xr = a[j + 2] - a[i + 2];
                xi = a[j + 3] - a[i + 3];
                a[j + 2] += a[i + 2];
                a[j + 3] += a[i + 3];
                a[i + 2] = wdr * xr - wdi * xi;
                a[i + 3] = wdr * xi + wdi * xr;
            }
        }
        m = l;
    }
    if (m > 2) {
        for (j = 0; j <= n - 4; j += 4) {
            xr = a[j] - a[j + 2];
            xi = a[j + 1] - a[j + 3];
            a[j] += a[j + 2];
            a[j + 1] += a[j + 3];
            a[j + 2] = xr;
            a[j + 3] = xi;
        }
    }
    if (n > 4) {
        bitrv2(n, a);
    }
}


void rdft(int n, double wr, double wi, double *a)
{
    void cdft(int n, double wr, double wi, double *a);
    int j, k;
    double wkr, wki, wdr, wdi, ss, xr, xi, yr, yi;
    
    if (n > 4) {
        wkr = 0;
        wki = 0;