Question

I got this example code for 1D Deconvolution from http://rosettacode.org/wiki/Deconvolution/1D#C, and it doesn’t seem to work right. When trying to build this project, I am first getting this error, ‘_fft’ : illegal use of type ‘void’. If it helps, this code was initially meant for C, and I had to make some changes like changing the include from complex.h to complex, and using namespace std. Thanks for the help

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <complex>
using namespace std;

double PI;
complex<double> cplx;




void _fft(cplx buf[], cplx out[], int n, int step)
 {
if (step < n) {
    _fft(out, buf, n, step * 2);
    _fft(out + step, buf + step, n, step * 2);

    for (int i = 0; i < n; i += 2 * step) {
        cplx t = cexp(-I * PI * i / n) * out[i + step];
        buf[i / 2]     = out[i] + t;
        buf[(i + n)/2] = out[i] - t;
    }
}
}

void fft(cplx buf[], int n)
{
cplx out[n];
for (int i = 0; i < n; i++) out[i] = buf[i];
_fft(buf, out, n, 1);
}

cplx *pad_two(double g[], int len, int *ns)
{
int n = 1;
if (*ns) n = *ns;
else while (n < len) n *= 2;

cplx *buf = calloc(sizeof(cplx), n);
for (int i = 0; i < len; i++) buf[i] = g[i];
*ns = n;
return buf;
}

void deconv(double g[], int lg, double f[], int lf, double out[]) {
int ns = 0;
cplx *g2 = pad_two(g, lg, &ns);
cplx *f2 = pad_two(f, lf, &ns);

fft(g2, ns);
fft(f2, ns);

cplx h[ns];
for (int i = 0; i < ns; i++) h[i] = g2[i] / f2[i];
fft(h, ns);

for (int i = 0; i >= lf - lg; i--)
    out[-i] = h[(i + ns) % ns]/32;
free(g2);
free(f2);
}

int main()
{
PI = atan2(1,1) * 4;
double g[] = {24,75,71,-34,3,22,-45,23,245,25,52,25,-67,-96,96,31,55,36,29,-43,-7};
double f[] = { -3,-6,-1,8,-6,3,-1,-9,-9,3,-2,5,2,-2,-7,-1 };
double h[] = { -8,-9,-3,-1,-6,7 };

int lg = sizeof(g)/sizeof(double);
int lf = sizeof(f)/sizeof(double);
int lh = sizeof(h)/sizeof(double);

double h2[lh];
double f2[lf];

printf("f[] data is : ");
for (int i = 0; i < lf; i++) printf(" %g", f[i]);
printf("\n");

printf("deconv(g, h): ");
deconv(g, lg, h, lh, f2);
for (int i = 0; i < lf; i++) printf(" %g", f2[i]);
printf("\n");

printf("h[] data is : ");
for (int i = 0; i < lh; i++) printf(" %g", h[i]);
printf("\n");

printf("deconv(g, f): ");
deconv(g, lg, f, lf, h2);
for (int i = 0; i < lh; i++) printf(" %g", h2[i]);
printf("\n");
}

Answer 1

Without running this, cplx is being used as a class, when it is actually a variable. Can you change this line:

complex<double> cplx;

like this

typedef complex<double> cplx;