Procedure AdjustPtr(Var P:Pointer;Amount:LongInt);

    Adjusts the pointer by Amount where

    - 64 k + 15 <= Amount <= + 64 k - 15

    Example

    P:=Ptr(0,$FFFF);  AdjustPtr(P, 1); = P:=Ptr($FFF,$F);
    P:=Ptr(0,$FFFF);  AdjustPtr(P,-1); = P:=Ptr(0,$FFFE);