fft4f.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       :4, 2
    data        :inplace
    table       :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, int, double *, int *, double *);
    void rdft(int, int, double *, int *, double *);
    void ddct(int, int, double *, int *, double *);
    void ddst(int, int, double *, int *, double *);
    void dfct(int, double *, double *, int *, double *);
    void dfst(int, double *, double *, int *, 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>
            ip[0] = 0; // first time only
            cdft(2*n, 1, a, ip, w);
        <case2>
            ip[0] = 0; // first time only
            cdft(2*n, -1, a, ip, w);
    [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
        ip[0...*]      :work area for bit reversal (int *)
                        length of ip >= 2+sqrt(n)  ; if n % 4 == 0
                                        2+sqrt(n/2); otherwise
                        ip[0],ip[1] are pointers of the cos/sin table.
        w[0...n/2-1]   :cos/sin table (double *)
                        w[],ip[] are initialized if ip[0] == 0.
    [remark]
        Inverse of 
            cdft(2*n, -1, a, ip, w);
        is 
            cdft(2*n, 1, a, ip, w);
            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>
            ip[0] = 0; // first time only
            rdft(n, 1, a, ip, w);
        <case2>
            ip[0] = 0; // first time only
            rdft(n, -1, a, ip, w);
    [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]
        ip[0...*]      :work area for bit reversal (int *)
                        length of ip >= 2+sqrt(n/2); if n % 4 == 2
                                        2+sqrt(n/4); otherwise
                        ip[0],ip[1] are pointers of the cos/sin table.
        w[0...n/2-1]   :cos/sin table (double *)
                        w[],ip[] are initialized if ip[0] == 0.
    [remark]
        Inverse of 
            rdft(n, 1, a, ip, w);
        is 
            rdft(n, -1, a, ip, w);
            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>
            ip[0] = 0; // first time only
            ddct(n, 1, a, ip, w);
        <case2>
            ip[0] = 0; // first time only
            ddct(n, -1, a, ip, w);
    [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
        ip[0...*]      :work area for bit reversal (int *)
                        length of ip >= 2+sqrt(n/2); if n % 4 == 2
                                        2+sqrt(n/4); otherwise
                        ip[0],ip[1] are pointers of the cos/sin table.
        w[0...n*5/4-1] :cos/sin table (double *)
                        w[],ip[] are initialized if ip[0] == 0.
    [remark]
        Inverse of 
            ddct(n, -1, a, ip, w);
        is 
            a[0] *= 0.5;
            ddct(n, 1, a, ip, w);
            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>
            ip[0] = 0; // first time only
            ddst(n, 1, a, ip, w);
        <case2>
            ip[0] = 0; // first time only
            ddst(n, -1, a, ip, w);
    [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]
        ip[0...*]      :work area for bit reversal (int *)
                        length of ip >= 2+sqrt(n/2); if n % 4 == 2
                                        2+sqrt(n/4); otherwise
                        ip[0],ip[1] are pointers of the cos/sin table.
        w[0...n*5/4-1] :cos/sin table (double *)
                        w[],ip[] are initialized if ip[0] == 0.
    [remark]
        Inverse of 
            ddst(n, -1, a, ip, w);
        is 
            a[0] *= 0.5;
            ddst(n, 1, a, ip, w);
            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]
        ip[0] = 0; // first time only
        dfct(n, a, t, ip, w);
    [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
        t[0...n/2]     :work area (double *)
        ip[0...*]      :work area for bit reversal (int *)
                        length of ip >= 2+sqrt(n/4); if n % 4 == 0
                                        2+sqrt(n/8); otherwise
                        ip[0],ip[1] are pointers of the cos/sin table.
        w[0...n*5/8-1] :cos/sin table (double *)
                        w[],ip[] are initialized if ip[0] == 0.
    [remark]
        Inverse of 
            a[0] *= 0.5;
            a[n] *= 0.5;
            dfct(n, a, t, ip, w);
        is 
            a[0] *= 0.5;
            a[n] *= 0.5;
            dfct(n, a, t, ip, w);
            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]
        ip[0] = 0; // first time only
        dfst(n, a, t, ip, w);
    [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)
        t[0...n/2-1]   :work area (double *)
        ip[0...*]      :work area for bit reversal (int *)
                        length of ip >= 2+sqrt(n/4); if n % 4 == 0
                                        2+sqrt(n/8); otherwise
                        ip[0],ip[1] are pointers of the cos/sin table.
        w[0...n*5/8-1] :cos/sin table (double *)
                        w[],ip[] are initialized if ip[0] == 0.
    [remark]
        Inverse of 
            dfst(n, a, t, ip, w);
        is 
            dfst(n, a, t, ip, w);
            for (j = 1; j <= n - 1; j++) {
                a[j] *= 2.0 / n;
            }
        .
*/


void cdft(int n, int isgn, double *a, int *ip, double *w)
{
    void makewt(int nw, int *ip, double *w);
    void bitrv2(int n, int *ip, double *a);
    void cftsub(int n, double *a, double *w);
    int j;
    
    if (n > (ip[0] << 2)) {
        makewt(n >> 2, ip, w);
    }
    if (n > 4) {
        bitrv2(n, ip + 2, a);
    }
    if (n > 4 && isgn < 0) {
        for (j = 1; j <= n - 1; j += 2) {
            a[j] = -a[j];
        }
        cftsub(n, a, w);
        for (j = 1; j <= n - 1; j += 2) {
            a[j] = -a[j];
        }
    } else {
        cftsub(n, a, w);
    }
}


void rdft(int n, int isgn, double *a, int *ip, double *w)
{
    void makewt(int nw, int *ip, double *w);
    void makect(int nc, int *ip, double *c);
    void bitrv2(int n, int *ip, double *a);
    void cftsub(int n, double *a, double *w);
    void rftsub(int n, double *a, int nc, double *c);
    int j, nw, nc;
    double xi;
    
    nw = ip[0];
    if (n > (nw << 2)) {
        nw = n >> 2;
        makewt(nw, ip, w);
    }
    nc = ip[1];
    if (n > (nc << 2)) {
        nc = n >> 2;
        makect(nc, ip, w + nw);
    }
    if (isgn < 0) {
        a[1] = 0.5 * (a[1] - a[0]);
        a[0] += a[1];
        for (j = 3; j <= n - 1; j += 2) {
            a[j] = -a[j];
        }
        if (n > 4) {
            rftsub(n, a, nc, w + nw);
            bitrv2(n, ip + 2, a);
        }
        cftsub(n, a, w);
        for (j = 1; j <= n - 1; j += 2) {
            a[j] = -a[j];
        }
    } else {
        if (n > 4) {
            bitrv2(n, ip + 2, a);
        }
        cftsub(n, a, w);
        if (n > 4) {
            rftsub(n, a, nc, w + nw);
        }
        xi = a[0] - a[1];
        a[0] += a[1];
        a[1] = xi;
    }
}


void ddct(int n, int isgn, double *a, int *ip, double *w)
{
    void makewt(int nw, int *ip, double *w);
    void makect(int nc, int *ip, double *c);
    void bitrv2(int n, int *ip, double *a);
    void cftsub(int n, double *a, double *w);
    void rftsub(int n, double *a, int nc, double *c);
    void dctsub(int n, double *a, int nc, double *c);
    int j, nw, nc;
    double xr;
    
    nw = ip[0];
    if (n > (nw << 2)) {
        nw = n >> 2;
        makewt(nw, ip, w);
    }
    nc = ip[1];
    if (n > nc) {
        nc = n;
        makect(nc, ip, w + nw);
    }
    if (isgn < 0) {
        xr = a[n - 1];
        for (j = n - 2; j >= 2; j -= 2) {
            a[j + 1] = a[j - 1] - a[j];
            a[j] += a[j - 1];
        }
        a[1] = xr - a[0];
        a[0] += xr;
        if (n > 4) {
            rftsub(n, a, nc, w + nw);
            bitrv2(n, ip + 2, a);
        }
        cftsub(n, a, w);
        for (j = 1; j <= n - 1; j += 2) {
            a[j] = -a[j];
        }
    }
    dctsub(n, a, nc, w + nw);
    if (isgn >= 0) {
        if (n > 4) {
            bitrv2(n, ip + 2, a);
        }
        cftsub(n, a, w);
        if (n > 4) {
            rftsub(n, a, nc, w + nw);
        }
        xr = a[0] - a[1];
        a[0] += a[1];
        for (j = 2; j <= n - 2; j += 2) {
            a[j - 1] = a[j] - a[j + 1];
            a[j] += a[j + 1];
        }
        a[n - 1] = xr;
    }
}


void ddst(int n, int isgn, double *a, int *ip, double *w)
{
    void makewt(int nw, int *ip, double *w);
    void makect(int nc, int *ip, double *c);
    void bitrv2(int n, int *ip, double *a);
    void cftsub(int n, double *a, double *w);
    void rftsub(int n, double *a, int nc, double *c);
    void dstsub(int n, double *a, int nc, double *c);
    int j, nw, nc;
    double xr;
    
    nw = ip[0];
    if (n > (nw << 2)) {
        nw = n >> 2;
        makewt(nw, ip, w);
    }
    nc = ip[1];
    if (n > nc) {
        nc = n;
        makect(nc, ip, w + nw);
    }
    if (isgn < 0) {
        xr = a[n - 1];
        for (j = n - 2; j >= 2; j -= 2) {
            a[j + 1] = a[j - 1] + a[j];
            a[j] -= a[j - 1];
        }
        a[1] = -xr - a[0];
        a[0] -= xr;
        if (n > 4) {
            rftsub(n, a, nc, w + nw);
            bitrv2(n, ip + 2, a);
        }
        cftsub(n, a, w);
        for (j = 1; j <= n - 1; j += 2) {
            a[j] = -a[j];
        }
    }
    dstsub(n, a, nc, w + nw);
    if (isgn >= 0) {
        if (n > 4) {
            bitrv2(n, ip + 2, a);
        }
        cftsub(n, a, w);
        if (n > 4) {
            rftsub(n, a, nc, w + nw);
        }
        xr = a[0] - a[1];
        a[0] += a[1];
        for (j = 2; j <= n - 2; j += 2) {
            a[j - 1] = -a[j] - a[j + 1];
            a[j] -= a[j + 1];
        }
        a[n - 1] = -xr;
    }
}


void dfct(int n, double *a, double *t, int *ip, double *w)
{
    void makewt(int nw, int *ip, double *w);
    void makect(int nc, int *ip, double *c);
    void bitrv2(int n, int *ip, double *a);
    void cftsub(int n, double *a, double *w);
    void rftsub(int n, double *a, int nc, double *c);
    void dctsub(int n, double *a, int nc, double *c);