This is to show how the pointers move in the buffer.
buffer_size = 32 * 1024;
period_size = 5.5 * 1024; /* intentionally odd number */
nfft = 2 * 1024;
double *audio_signal {nullptr};
double *signal_start {nullptr}; /* valid data in [start,end) */
double *signal_end {nullptr};
audio_signal = new double [large_enough];
signal_start = audio_signal;
signal_end = audio_signal;
for (int i = 0; i < period_size; i++) {
*signal_end++ = samples[i]; /* get new set of samples */
}
while(s->signal_end - s->signal_start >= nfft) {
auto p = signal_start;
for (int i = 0; i < nfft; i++) {
in_real[i] = *p++ * audio_window[i]; /* copy into FFT buffer */
}
fftw_execute(s->plan);
/* update waterfall, etc. */
signal_start += nfft/2; /* shift the FFT window for half the FFT size */
}
/* move a bulk of samples not used for FFT to the top of the buffer */
auto p = s->audio_signal;
auto q = s->signal_start;
while(q < s->signal_end) {
*p++ = *q++;
}
s->signal_start = s->audio_signal;
s->signal_end = p;
It seems that the buffer operation is stable.
