Cursor wrap when editing files

The cursor always appears in the top left hand corner when editing so if to want to edit data in the lower right corner you must do a lot of cursor movement. This routine allows you to move from the top line to the bottom by moving the cursor UP and from the left side of the screen to the right by moving the cursor LEFT. The reverse is also true!

5108 LET C=C-U+(Q AND C=O): GO TO VAL "5040"
5109 LET C=(C+U)*(C<Q-U): GO TO VAL "5040"
5110 LET L=(L+U)*(L<G+G): GO TO VAL "5040"
5111 LET L=L-U+(J AND L=O): GO TO "5040"
5112 LET E$(L+U)=E$(L+U, TO C)+E$(L+U,C+H TO ): PRINT AT L,O;E$(L+U): GO TO VAL "5040"+(VAL "68" AND C>O)