org	100h
	jmp	demo
	;;;	Given an 0-terminated ASCII string containing digits in [DE],
	;;;	see if it matches its check digit. Returns with zero flag set
	;;;	if the string matches.
damm:	mvi	c,0	; Interim digit in C, starts off at 0.
	ldax	d	; Get current byte from string
	inx	d 	; Advance the pointer
	ana	a	; Is the byte zero?
	jnz	$+5	; If not, go look up interim digit
	cmp	c	; But if so, see if the interim digit is also zero
	ret		; And return whether this was the case
	sui	'0'	; Subtract ASCII 0
	mov	b,a	; Keep digit to be processed in B
	mov	a,c	; Calculate C*10 (interim digit row index)
	add	a	; * 2
	add	a	; * 4
	add	c	; * 5
	add	a	; * 10
	add	b	; Add column index
	lxi	h,dammit
	add	l	; Table lookup (assuming H doesn't change, i.e. it
	mov	l,a	; doesn't cross a page boundary).
	mov	c,m	; Get new interim digit from table
	jmp	damm+2	; And check next character
	;;;	Table of interim digits
	;;;	NOTE: must not cross page boundary
dammit:	db	0,3,1,7,5,9,8,6,4,2
	db	7,0,9,2,1,5,4,8,6,3
	db	4,2,0,6,8,7,1,3,5,9
	db	1,7,5,0,9,8,3,4,2,6
	db	6,1,2,3,0,4,5,9,7,8
	db	3,6,7,4,2,0,9,5,8,1
	db	5,8,6,9,7,2,0,1,3,4
	db	8,9,4,5,3,6,2,0,1,7
	db	9,4,3,8,6,1,7,2,0,5
	db	2,5,8,1,4,3,6,7,9,0
	;;;	Demo code: see if the argument on the CP/M command line
	;;;	matches its input.
demo:	lxi	h,80h	; Zero-terminate input
	mov	e,m
	mvi	d,0
	inx	d
	dad	d
	mov	m,d
	lxi	d,82h	; Command line argument, skipping first space
	call	damm	; See if it validates
	mvi	c,9
	lxi	d,ok	; Print OK...
	jz	5	; ...if the checksum matches,
	lxi	d,no	; Print NOT OK otherwise.
	jmp	5
no:	db	'NOT '
ok:	db	'OK$'