.title	getarg
;+
;	integer function getarg(narg, buf, size)
;-
ap=%5
narg=2
buf=4
size=6
;
;
	.psect	$r.roi,con,ro,rel,lcl,i
	.enabl	lsb
getarg::
	mov	#eof,r0			; assume invalid number
	clrb	@buf(ap)		; initialize user buffer to null str
	mov	@narg(ap),r1		; get argument number
	blt	10$			; return(EOF) if < 0
	cmp	r1,r$argc			; see if too large
	bge	10$			; YES, return (EOF)
	clc				; multiply by 2 for word offset
	rol	r1			; into argv
	mov	r$argv(r1),r1		; address of nth arg string
	mov	buf(ap),r2		; address of destination buffer
	mov	@size(ap),r0		; size of target buffer
	beq	10$			; if size is 0, done
1$:
	movb	(r1)+,(r2)+		; copy next character
	beq	2$			; just copied EOS - done
	sob	r0,1$			; decrement bytes left and try again
	clrb	-(r2)			; write EOS into last position
	inc	r0			; one less than max
2$:
	mov	r0,r1			; subtrahend in r1
	mov	@size(ap),r0		; minuend in r0
	sub	r1,r0			; number of characters in arg
10$:
	return
	.end