Add original unix v6

source/s4/getc.s

@@ -0,0 +1,83 @@
+/ getw/getc -- get words/characters from input file
+/ fopen -- open a file for use by get(c|w)
+
+indir = 0
+
+.globl	_getc, _getw, _fopen
+.globl	cerror
+.comm	_errno,2
+
+_fopen:
+	mov	r5,-(sp)
+	mov	sp,r5
+	mov	4(r5),0f
+	sys	0; 9f
+	.data
+9:	sys	open; 0:..; 0
+	.text
+	bes	badret
+	mov	6(r5),r1
+	mov	r0,(r1)+
+	clr	(r1)+
+	clr	r0
+	mov	(sp)+,r5
+	rts	pc
+
+_getw:
+	clr	_errno
+	mov	r5,-(sp)
+	mov	sp,r5
+	mov	4(r5),r1
+	sub	$2,2(r1)
+	bge	1f
+	cmp	2(r1),$-1
+	blt	2f
+	movb	*4(r1),-(sp)
+	jsr	pc,fill
+	mov	4(r1),r0
+	br	3f
+2:
+	jsr	pc,fill
+	dec	2(r1)
+1:
+	mov	4(r1),r0
+	movb	(r0)+,-(sp)
+3:
+	movb	(r0)+,1(sp)
+	mov	r0,4(r1)
+	mov	(sp)+,r0
+	mov	(sp)+,r5
+	rts	pc
+
+_getc:
+	mov	r5,-(sp)
+	mov	sp,r5
+	mov	4(r5),r1
+	dec	2(r1)
+	bge	1f
+	jsr	pc,fill
+1:
+	clr	r0
+	bisb	*4(r1),r0
+	inc	4(r1)
+	mov	(sp)+,r5
+	rts	pc
+
+fill:
+	mov	r1,r0
+	add	$6,r0
+	mov	r0,0f
+	mov	r0,4(r1)
+	mov	(r1),r0
+	sys	0; 9f
+.data
+9:	sys	read; 0:..; 512.
+.text
+	bes	badret
+	dec	r0
+	bmi	badret
+	mov	r0,2(r1)
+	rts	pc
+
+badret:
+	jmp	cerror