Flutter/Dart Google Maps API encoded polyline decoder

decodePolyline.dart

List _decode(String input) {
    var list=input.codeUnits;
    List lList = new List();
    int index=0;
    int len=input.length;
    int c=0;
    List<LatLng> positions = new List();
    // repeating until all attributes are decoded
    do {   
      var shift=0;
      int result=0;

      // for decoding value of one attribute
      do {
          c=list[index]-63;
          result|=(c & 0x1F)<<(shift*5);
          index++;
          shift++;
      } while(c>=32);
      /* if value is negetive then bitwise not the value */
      if(result & 1==1) {
          result=~result;
      }
      var result1 = (result >> 1) * 0.00001;
      lList.add(result1);
    } while(index<len);

    /*adding to previous value as done in encoding */
    for(int i=2;i<lList.length;i++) {
      lList[i]+=lList[i-2];
    }

    for(int i=0; i<lList.length; i+=2) {
      positions.add(LatLng(lList[i], lList[i+1]));
    }

    return positions;
  }