; -- strlen(s) returns the length of null terminated string s
;    version 3, using pointer difference to compute length of string

STRLEN:	; expects R3 = s,   a pointer to a string
	; returns R3        the length of s
	; uses    R4 = s',  working copy of s
	;         R5 = *s', successive values

	MOVE	R4,R3		; s' = s
STRLLP:				; loop {
	LOADS	R5,R4		;   -- get word holding *s'
	EXTB	R5,R5,R4	;   -- get *s'
	BZS	STRLQT		;   if (*s' == 0) break

	ADDSI	R4,1		;   s++

	BR	STRLLP
STRLQT:				; }
	SUB	R3,R4,R3
	JUMPS	R1		; return s - s'