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//
// fft_example.c
//
// This example demonstrates the interface to the fast discrete Fourier
// transform (FFT).
// SEE ALSO: mdct_example.c
// fct_example.c
//
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <getopt.h>
#include "liquid.h"
// print usage/help message
void usage()
{
printf("fft_example [options]\n");
printf(" h : print help\n");
printf(" v/q : verbose/quiet\n");
printf(" n : fft size, default: 16\n");
}
int main(int argc, char*argv[])
{
// options
unsigned int nfft = 16; // transform size
int method = 0; // fft method (ignored)
int verbose = 0; // verbose output?
int dopt;
while ((dopt = getopt(argc,argv,"hvqn:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'v': verbose = 1; break;
case 'q': verbose = 0; break;
case 'n': nfft = atoi(optarg); break;
default:
exit(1);
}
}
// allocate memory arrays
float complex * x = (float complex*) fft_malloc(nfft*sizeof(float complex));
float complex * y = (float complex*) fft_malloc(nfft*sizeof(float complex));
float complex * z = (float complex*) fft_malloc(nfft*sizeof(float complex));
// initialize input
unsigned int i;
for (i=0; i<nfft; i++)
x[i] = (float)i - _Complex_I*(float)i;
// create fft plans
fftplan pf = fft_create_plan(nfft, x, y, LIQUID_FFT_FORWARD, method);
fftplan pr = fft_create_plan(nfft, y, z, LIQUID_FFT_BACKWARD, method);
// print fft plans
fft_print_plan(pf);
//fft_print_plan(pr);
// execute fft plans
fft_execute(pf);
fft_execute(pr);
// destroy fft plans
fft_destroy_plan(pf);
fft_destroy_plan(pr);
// normalize inverse
for (i=0; i<nfft; i++)
z[i] /= (float) nfft;
if (verbose) {
// print results
printf("original signal, x[n]:\n");
for (i=0; i<nfft; i++)
printf(" x[%3u] = %8.4f + j%8.4f\n", i, crealf(x[i]), cimagf(x[i]));
printf("y[n] = fft( x[n] ):\n");
for (i=0; i<nfft; i++)
printf(" y[%3u] = %8.4f + j%8.4f\n", i, crealf(y[i]), cimagf(y[i]));
printf("z[n] = ifft( y[n] ):\n");
for (i=0; i<nfft; i++)
printf(" z[%3u] = %8.4f + j%8.4f\n", i, crealf(z[i]), cimagf(z[i]));
}
// compute RMSE between original and result
float rmse = 0.0f;
for (i=0; i<nfft; i++) {
float complex d = x[i] - z[i];
rmse += crealf(d * conjf(d));
}
rmse = sqrtf( rmse / (float)nfft );
printf("rmse = %12.4e\n", rmse);
// free allocated memory
fft_free(x);
fft_free(y);
fft_free(z);
printf("done.\n");
return 0;
}
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