Add original unix v6

source/salloc/altch.s

@@ -0,0 +1,63 @@
+.globl	alterchar
+.globl	plausible
+.globl	stats
+.globl	allocate, release
+.globl	copy
+.globl	bufchar, getbuf
+.globl	swap
+.globl	w, r, a, l
+.globl	w1, flag, u1, fixct
+/
+/	routine to rewrite the character pointer to by
+/	read pointer.  The read pointer is advanced.
+/	the string is extended if necessary.
+/	there is no error return.
+/
+/	movb	ch,r0
+/	mov	...,r1
+/	jsr	pc,alterchar
+/	mov	r1,...
+/
+alterchar:
+	mov	r2,-(sp)
+	mov	r1,-(sp)
+	mov	r0,nchar
+	jsr	pc,plausible
+	inc	stats+8.
+1:	cmp	r(r1),l(r1)	/W,L
+	blt	3f
+	mov	l(r1),r0
+	inc	r0
+	sub	a(r1),r0	/W-A+1
+	jsr	pc,allocate
+	mov	(sp),r0
+	jsr	pc,copy
+	jsr	pc,swap
+	jsr	pc,release
+	mov	(sp),r1
+/
+3:	mov	r(r1),r0
+	jsr	pc,bufchar
+	bec	2f
+	jsr	pc,getbuf
+
+2:	movb	nchar,(r0)
+	mov	nchar,r0	/to preserve r0 for user
+	inc	r(r1)
+	mov	$1,w1(r2)
+	cmp	r(r1),w(r1)
+	ble	3f
+	mov	r(r1),w(r1)
+3:
+	inc	flag
+	bne	1f
+	jsr	pc,fixct
+	br	2f
+1:
+	mov	flag,u1(r2)
+2:
+	mov	(sp)+,r1
+	mov	(sp)+,r2
+	rts	pc
+/
+nchar:	.=.+2