Procedure QuickSort(FList: PPointerList; L, R : Longint;
                     Compare: TListSortCompare);
var
  I, J : Longint;
  P, Q : Pointer;
begin
 repeat
   I := L;
   J := R;
   P := FList^[ (L + R) div 2 ];
   repeat
     while Compare(P, FList^[i]) > 0 do
       I := I + 1;
     while Compare(P, FList^[J]) < 0 do
       J := J - 1;
     If I <= J then
     begin
       Q := FList^[I];
       Flist^[I] := FList^[J];
       FList^[J] := Q;
       I := I + 1;
       J := J - 1;
     end;
   until I > J;
   // sort the smaller range recursively
   // sort the bigger range via the loop
   // Reasons: memory usage is O(log(n)) instead of O(n) and loop is faster than recursion
   if J - L < R - I then
   begin
     if L < J then
       QuickSort(FList, L, J, Compare);
     L := I;
   end
   else
   begin
     if I < R then
       QuickSort(FList, I, R, Compare);
     R := J;
   end;
 until L >= R;
end;