cc65/libsrc/cbm510/revers.s

;
; Ullrich von Bassewitz, 07.08.1998
;
; unsigned char revers (unsigned char onoff);
;

      	.export		_revers
        .import         RVS: zp


.proc   _revers

	ldx    	#$00		; Assume revers off
	tay			; Test onoff
	beq	L1		; Jump if off
	ldx	#$80		; Load on value
        ldy	#$00		; Assume old value is zero
L1:     lda    	RVS             ; Load old value
	stx	RVS             ; Set new value
	beq	L2		; Jump if old value zero
	iny			; Make old value = 1
L2:	ldx	#$00		; Load high byte of result
	tya			; Load low byte, set CC
	rts

.endproc