doubler.lmasm

; Program to safely double the user input without erroring

entry	INP		    ; get user input

	    BRP	check	; check not negative
	    BRA	entry

; therefore the value is >= 0
check	SUB	max	    ; check if will exceed max allowed
        SUB	one
	    BRP	entry
	    ADD	one	    ; revert subtraction for range check
	    ADD	max

; therefore the value is within 0-999, so can be safely STA'd to double
	    STA	tmp
	    ADD	tmp
	    OUT
	    BRA	entry

tmp  	DAT	0
one	    DAT	1
max	    DAT	999