.define .exg

	! d0 : exchange size in bytes
	.text
.exg:
	move.l	(sp)+,.savret
	movem.l	d1/a1/a2,.savreg
	move.l	sp,a1
	sub.l	d0,sp
	move.l	sp,a2
	asr	#1,d0
	move.l	d0,d1
1:
	move.l	(a1)+,(a2)+
	sub	#1,d0
	bgt	1b
	move.l	sp,a1
	asr	#1,d1
1:
	move.l	(a1)+,(a2)+
	sub	#1,d1
	bgt	1b
	move.l	a1,sp
	movem.l	.savreg,d1/a1/a2
	move.l	.savret,-(sp)
	rts