Add original unix v6

source/s3/sqrt.s

@@ -0,0 +1,58 @@
+ldfps = 170100^tst
+stfps = 170200^tst
+/
+/	sqrt replaces the f.p. number in fr0 by its
+/	square root.  newton's method
+/
+.globl	sqrt, _sqrt
+/
+/
+_sqrt:
+	mov	r5,-(sp)
+	mov	sp,r5
+	movf	4(r5),fr0
+	jsr	pc,sqrt
+	mov	(sp)+,r5
+	rts	pc
+
+sqrt:
+	tstf	fr0
+	cfcc
+	bne	1f
+	clc
+	rts	pc		/sqrt(0)
+1:
+	bgt	1f
+	clrf	fr0
+	sec
+	rts	pc		/ sqrt(-a)
+1:
+	mov	r0,-(sp)
+	stfps	-(sp)
+	mov	(sp),r0
+	bic	$!200,r0		/ retain mode
+	ldfps	r0
+	movf	fr1,-(sp)
+	movf	fr2,-(sp)
+/
+	movf	fr0,fr1
+	movf	fr0,-(sp)
+	asr	(sp)
+	add	$20100,(sp)
+	movf	(sp)+,fr0	/initial guess
+	mov	$4,r0
+1:
+	movf	fr1,fr2
+	divf	fr0,fr2
+	addf	fr2,fr0
+	mulf	$half,fr0	/ x = (x+a/x)/2
+	sob	r0,1b
+2:
+	movf	(sp)+,fr2
+	movf	(sp)+,fr1
+	ldfps	(sp)+
+	mov	(sp)+,r0
+	clc
+	rts	pc
+/
+half	= 40000