int32_t vC = 0;
bool sRS = true;

//           -2 +2    3.25/2 q27   -1 +1 q27

// f ~ 1/rc = param_rate/(3000/(20*32)); // => param_rate/4.68;
if (sRS) {
  vC = ___SMMLA(___SMMUL(param_rate, param_rate) << 4,
                2 * ((13 << 24) - param_pos) - vC, vC);
  if (vC > (1 << 27)) {
    sRS = false;
    vC = (1 << 28) - vC;
  }
} else {
  vC = ___SMMLA(___SMMUL(param_rate, param_rate) << 4,
                2 * (param_neg - (13 << 24)) - vC, vC);
  //                   RS change    vC subsample evolution ("mirror" against 1
  //                   or -1)
  if (vC < -(1 << 27)) {
    sRS = true;
    vC = -(1 << 28) - vC;
  }
}
outlet_out = vC;