; make a char uppercase
	; IN	al	char
	; OUT	al	char
	; do nothing if >z
ucase	cmp al, 0x7B
	jnc .ret
	; do nothing if <a
	cmp al, 0x61
	jc .ret
	; do it!
	sub al, 0x20
.ret	ret

	; read integer from ascii string
	; default dec but allows 0x for hex
	; bogus result if larger than 16 bit
	; IN	ds:si	source string
	;	cx	max number of chars
	; OUT	ax	number
	;	ds:si	first rejected char
	;	cx	chars ignored
lodnum	xor di, di
	mov bx, 10
	cmp cx, 2
	jc .loop
	; test for 0x prefix
	mov ax, [si]
	cmp al, 0x30
	jne .loop
	mov al, ah
	call ucase
	cmp al, 0x58
	jne .loop
	; apply 0x prefix
.hex	add si, 2
	sub cx, 2
	mov bx, 0x10
	; check if there are chars left
.loop	test cx, cx
	jnz .do
.ret	mov ax, di
	ret
.do	mov al, [si]
	call ucase
	; check if in range
	sub al, 0x30
	jc .ret
	cmp al, 0x10
	jc .skip
	sub al, 7
	; must be smaller than base
	; necessary to prevent hex digits in decimals
.skip	mov ah, 0
	cmp ax, bx
	jnc .ret
	; mark as read
	inc si
	dec cx
	; add digit to number
	xchg ax, di
	mul bx
	add di, ax
	jmp .loop