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;* GetVidOffset - Macro to determine offset in video segment that corresponds
;* to given screen coordinates.
;*
;* Params:  row - Screen row (top line = 0)
;*          col - Screen column (leftmost column = 0)
 
GetVidOffset MACRO row, col             ;; Macro definition
    mov ax, row
    mov bl, 80                          ;; Number of columns per row *
    mul bl                              ;;   current row + current column =
    add ax, col                         ;;   character byte #
    shl ax, 1                           ;; Double to account for cell size
ENDM                                    ;; Result in AX register
                                    -♦-