Add original unix v6

source/s1/diff2.s

@@ -0,0 +1,56 @@
+/	hash routine for diff
+/	effectively spreads the string out into 7-bit
+/	bytes, then sums the result 1's-complement
+/	by 16-bit bytes and adds 1 to avoid zero answer
+
+/	r4 hash accumulator
+/	r3 current offset
+/	r2 first time flag
+.globl	_readhash
+.globl getc
+
+.data
+_readhash:
+	mov	2(sp),0f
+	mov	r5,-(sp)
+	mov	r4,-(sp)
+	mov	r3,-(sp)
+	mov	r2,-(sp)
+	mov	$1,r4
+	mov	r4,r2
+	clr	r3
+1:
+	jsr	r5,getc; 0: 0
+	bes	2f
+	clr	r2
+	cmp	r0,$'\n
+	beq	1f
+	ashc	$-16.,r0
+	ashc	r3,r0
+	add	r0,r4
+	adc	r4
+	add	r1,r4
+	adc	r4
+	add	$7,r3
+	cmp	r3,$16.
+	blt	1b
+	sub	$16.,r3
+	br	1b
+2:
+	tst	r2
+	bne	2f
+	mov	$2,r0
+	sys	write; 3f; 4f-3f
+2:
+	clr	r4
+1:
+	mov	r4,r0
+	mov	(sp)+,r2
+	mov	(sp)+,r3
+	mov	(sp)+,r4
+	mov	(sp)+,r5
+	rts	pc
+3:
+	<incomplete line omitted\n>
+4:
+.even