//----------------------------------------------------------------
//	fifty.s	       (For you to 'debug' during our Final Exam)
//
//	This program adds the first fifty positive integers, 
//	then tells the user whether that sum is odd or even.
//----------------------------------------------------------------

	.equ	N, 50			# the maximum summand

sum:	.short	0			# holds running total
emsg:	.string	"The sum is even\n"	# reports an even sum
elen:	.int	. - emsg		# length of message
omsg:	.string	"The sum is odd\n"	# reports an odd sum
olen:	.int	. - olen		# length of message

	.text
_start:	# add up the first N positive integers
	movl	$1, %eax		# the initial summand 
nxadd:	addl	%eax, sum		# add current summand
	incl	%eax			# set up next summand
	cmpl	N, %eax			# does EAX exceed N? 
	jng	nxadd			# no, do another add 

	# ok, see whether the total is even or odd
	movl	sum, %eax		# copy total into EAX
	shrl	$1, %eax		# lowest bit to Carry 
	jnc	isevn			# CF == 0? yes, even 
	jmp	isodd			# otherwise, odd sum

isevn:	# report that the total was an even number	
	movl	emsg, %ecx		# message-address
	movl	elen, %edx		# message-length
	jmp	finis			# jump to finish

isodd:	# report that the total was an odd number
	movl	omsg, %ecx		# message-address
	movl	olen, %edx		# message-length
	jmp	finis			# jump to finish

finis:	# program shows report, then terminates
	movl	$4, %eax		# system-call ID-number
	movl	$1, %ebx		# device-file ID-number
	int	$0x80			# enter Linux kernel  
	.end				# end of program text
#-----------------------------------------------------------------