int8_t stage = 1;
int ntrig;
int32_t val;
int64_t rate;
int32_t cycles;

if (!inlet_EnvOn) { // Enveloppe can be switched off
  stage = 1;
  ntrig = 0;
} else {
  if ((inlet_Trigger > 0) &&
      !ntrig) { // pressing a key will start the enveloppe
    stage = 2;
    ntrig = 1;
  }

  if (!(inlet_Trigger > 0) && ntrig) { // releasing the key will start the final
                                       // (release) phase of the enveloppe
    stage = 9;
    ntrig = 0;
  }
}

switch (stage) {
case 1:
  val = (inlet_Level4 << 4); // phase 1: key is off, release is finnished
  break;
case 2: // phase 2: key is on, start of move to Level1 at Rate1
  cycles = (inlet_Duration1 + 134217728) >>
           21; // read duration and transfer to value range 0-127
  cycles = (11 * cycles * cycles - 234 * cycles) /
           10; // number of cycles is calculated based on the positive side of
               // parabolic formula y = 1.1*X^2 - 23.4 * x (-64 = 0 sec, 0 = 1
               // sec, +64 = 5 sec)
  rate = ((((inlet_Level1 << 4) - val)) /
          (cycles)); // the adjustment per cycle of the output value during this
                     // phase is calculated
  stage = 3;         // set the next stage and do not break
case 3:              // phase 2: key is on, moving to level1 at Rate1
  val += rate;       // the output value is adjusted
  cycles -= 1;       // opne cycle finnished
  if (cycles < 0) {
    stage = 4;
    val = (inlet_Level1 << 4);
  } // out of cycles move to the next phase
  else
    break;
case 4: // phase 3: key is on, start of move to Level2 at Rate2
  cycles = (inlet_Duration2 + 134217728) >> 21;
  cycles = (11 * cycles * cycles - 234 * cycles) / 10;
  rate = ((((inlet_Level2 << 4) - val)) / (cycles));
  stage = 5;
case 5: // phase 3: key is on, moving to level2 at Rate2
  val += rate;
  cycles -= 1;
  if (cycles < 0) {
    stage = 6;
    val = (inlet_Level2 << 4);
  } else
    break;
case 6: // phase 4: key is on, start of move to Level3 at Rate3
  cycles = (inlet_Duration3 + 134217728) >> 21;
  cycles = (11 * cycles * cycles - 234 * cycles) / 10;
  rate = ((((inlet_Level3 << 4) - val)) / (cycles));
  stage = 7;
case 7: // phase 4: key is on, moving to level3 at Rate3
  val += rate;
  cycles -= 1;
  if (cycles < 0) {
    stage = 8;
    val = (inlet_Level3 << 4);
  } else
    break;
case 8: // phase 5: key is on, staying at Level3
  val = (inlet_Level3 << 4);
  break;
case 9: // phase 6: key is off, start of move to Level4 at Rate4
  cycles = (inlet_Duration4 + 134217728) >> 21;
  cycles = (11 * cycles * cycles - 234 * cycles) / 10;
  rate = ((((inlet_Level4 << 4) - val)) / (cycles));
  stage = 10;
case 10: // phase 6: key is off, moving to level4 at Rate4
  val += rate;
  cycles -= 1;
  if (cycles < 0) {
    stage = 1;
    val = (inlet_Level4 << 4);
  } else
    break;
} // end switch

outlet_o = val >> 4;