Delphi32 - PosEx or system.pos wiht position

//Inf=Delphi32 - PosEx or system.pos wiht position
Function Sho_PosInt(substr : ShortString;StartIndex:Integer;Const largeString : String;LimMax:Integer): Integer;
Var nlen,nth:Integer;
Begin Result:=RTCAN;
      if (length(LargeString)<1) then exit;
      Result:=RTREJ;
      if (length(substr)<1) then exit;
      if (StartIndex<1) then StartIndex:=1 else
      if (StartIndex>length(LargeString)) then
                  StartIndex:=1;
      if (LimMax<1) then LimMax:=kMaxInt;
      nth:=pos(substr,copy(LargeString,StartIndex,LimMax));
      result:=if_int(nth<1,0,StartIndex+nth);
End;