How to "rove across time" with trim path

I think this expression for the End property will level out the speed:

val = value;
if (numKeys > 2){
  if (time < key(1).time){
    val = key(1).value;
  }else if (time > key(numKeys).time){
    val = key(numKeys).value;
  }else{
    dTot = 0;
    for (i = 2; i <= numKeys; i++){
      dTot += Math.abs(key(i).value - key(i-1).value);
    }
    tTot = key(numKeys).time - key(1).time;
    tCur = key(1).time;
    i = 2;
    while(tCur <= time && i <= numKeys){
      tPrev = tCur;
      tCur += (Math.abs(key(i).value - key(i-1).value)/dTot)*tTot;
      i++;
    }
    i--;
    val = linear(time,tPrev,tCur,key(i-1).value,key(i).value);
  } 
}
val