.title	fold
;+
;	subroutine fold(buf)
;
;	character buf(ARB)
;
;	any characters found in the range A-Z are folded to the corresponding
;	lower case character
;-
buf=4
biga=65
bigz=90
leta=97
letz=122
dif=leta-biga
	.psect	st_pure_code	rel,con,lcl,exe,nowrt,rd,pic,shr,usr,novec,long
	.entry	fold	^m<>
	movl	buf(ap),r1		; address of buf(1)
10$:
	movzbl	(r1),r0			; fetch next character
	beql	20$			; if == 0, done
	cmpb	r0,#biga		; >= A?
	blss	30$			; NO
	cmpb	r0,#bigz		; <= Z?
	bgtr	30$			; NO
	addl2	#dif,r0			; make lower case
30$:
	movb	r0,(r1)+		; copy character back into string
	brb	10$			; try again
20$:
	ret
	.end