demodulation.c

double carrier_phase[2];

double carrier_strength = fourier1p(dbuffer, (float) length * carrier / (float)rate, length, &carrier_phase[0], &carrier_phase[1]);

if(carrier_strength < threshold) continue;

double delta_re = carrier_phase[0] * old_carrier_phase[0] + carrier_phase[1]*old_carrier_phase[1];
double delta_im = -carrier_phase[1]*old_carrier_phase[0] + carrier_phase[0] * old_carrier_phase[1];


if(delta_re * delta_re > delta_im * delta_im) { /* Phase difference is a multiple of pi */
  if(delta_re > 0); /* No change */
  else {
    bit_data = bit_data * 2;
  }
} else {
  if(delta_im > 0) {
    bit_data = bit_data * 2 + 1;
  } else {
    if(isprint(bit_data)) printf("%c", bit_data);
    else printf("<%.2x>", bit_data);

    bit_data = 0;
  }
}

old_carrier_phase[0] = carrier_phase[0];
old_carrier_phase[1] = carrier_phase[1];