; -- strlen(s) returns the length of null terminated string s
;    version 1, using array indexing to each s[i]

STRLEN:	; expects R3 = s, a pointer to a string
	; returns R3 = i, the length of s
	; uses    R4 = address of s[i]
	;         R5 = s[i], successive values
	;         R6 = i, during the code

	LIS	R6,0		; i = 0
STRLLP:				; loop {
	ADD	R4,R3,R6	;   -- compute address of s[i]
	LOADS	R5,R4		;   -- get word holding s[i]
	EXTB	R5,R5,R4	;   -- get s[i]
	BZS	STRLQT		;   if (s[i] == 0) break

	ADDSI	R6,1		;   i = i + 1

	BR	STRLLP
STRLQT:				; }
	MOVE	R3,R6		; -- move return value into place
	JUMPS	R1		; return i