.title	isatty
;+
;	stat = isatty(int)
;
;	status returns are YES/NO
;-
ap=%5
int=2
	.psect	$r.roi,con,ro,rel,lcl,i
	.enabl	lsb
isatty::
	mov	@int(ap),r0		; rat4 unit number
	call	r$gfbk			; get RFDB address
	mov	#no,r0			; assume not
	bcs	100$			; c set => invalid unit
	bit	#rf.clo,(r1)		; is file open on unit?
	bne	100$			; NO
	bit	#rf.tty,(r1)		; is it a terminal?
	beq	100$			; NO
	mov	#yes,r0			; return YES
100$:
	return
	.end