urem.s

<B>Digital的Unix操作系统VAX 4.2源码</B>

#	urem.s	6.1	83/07/29
#
#	urem - unsigned remainder for vax-11
#
#	arguments: dividend, divisor
#	result: remainder
#	uses r0-r2
#
#	if 1 < divisor <= 2147483647, zero-extend the dividend
#	to 64 bits and let ediv do the work.  If the divisor is 1,
#	ediv will overflow if bit 31 of the dividend is on, so
#	just return 0.  If the divisor is 0, do the ediv also,
#	so it will generate the proper exception.  All other values
#	of the divisor have bit 31 on: in this case the remainder
#	must be the dividend if divisor > dividend, and the dividend
#	minus the divisor otherwise.  The comparison must be unsigned.
#
	.text
	.align	1
	.globl	urem
urem:	.word	0x0000
	movl	4(ap),r0	# Dividend
	movl	8(ap),r2	# Divisor
	jeql	div		# If divisor=0, force exception
	cmpl	r2,$1		# If divisor <= 1 (signed),
	jleq	nodiv		#  no division is necessary
div:	clrl	r1		# Zero-extend the dividend
	ediv	r2,r0,r2,r0	# Divide.  q->r2 (discarded), r->r0
	ret
nodiv:	jneq	nzero		# If divisor=1, return 0
	clrl	r0		#  (because doing the divide will overflow
	ret			#  if the dividend has its high bit on)
nzero:	cmpl	r0,r2		# If dividend < divisor (unsigned)
	jlssu	retn		#  remainder is dividend
	subl2	r2,r0		#  else remainder is dividend - divisor
retn:	ret