/* stack used: 60 bytes */
void fir_fft_init(const short *coeffs, Complex *fft_coeffs, Complex *result, \
short *trail, int ncoeffs, int fft_N, int log_fft_N, \
fir_fft_state *s)
{
int i; int *hlp;
s->c = fft_coeffs; /* set up pointers */
s->r = result;
s->d = trail;
s->k = ncoeffs;
s->l = log_fft_N;
s->n = fft_N;
for(i = 0; i < ncoeffs-1; i++) trail[i] = 0; /* clear trail */
hlp = (int *) fft_coeffs;
for(i = 0; i < ncoeffs; i++) hlp[i] = coeffs[i]; /* copy coeffs */
for(i = ncoeffs; i < fft_N; i++) hlp[i] = 0; /* add zero padding */
while(REALFFT(hlp, fft_coeffs, log_fft_N-1)) ; /* error */
}
void Helmholtz::autocorrelation()
{
int n;
int fftsize = framesize * 2;
REALFFT(fftsize, processbuf);
// compute power spectrum
processbuf[0] *= processbuf[0]; // DC
processbuf[framesize] *= processbuf[framesize]; // Nyquist
for(n=1; n<framesize; n++)
{
processbuf[n] = processbuf[n] * processbuf[n]
+ processbuf[fftsize-n] * processbuf[fftsize-n]; // imag coefficients appear reversed
processbuf[fftsize-n] = 0.;
}
REALIFFT(fftsize, processbuf);
}
