#**********************************************************************
#   CS 232: Comp. Arch. I
#   Written:  1/5/00, JP Mellor
#
#   This file contains procedure:
#     -- fib
#   
#   It expects one argument n stored in $a0 and return fib(n)
#   
#**********************************************************************

	.globl fib

#**********************************************************************

	.text

# $v0 - return value
# $a0 - counter
# $t0 - temp
# $t1 - fib(n-1)
# $t2 - fib(n)
	
fib:	mv	$v0, $a0		# put n in return value
	mv	$t1, 0			# put fib(0) in fib(n-1)
	mv	$t2, 1			# put fib(1) in fib(n)
	slt	$t3, $a0, 2		# check if n = 0 or 1
	bne	$t3, $zero, done	#	if so we're done
	add	$a0, $a0, -1		# decriment counter
loop:	add	$v0, $t1, $t2		# put fib(n+1) into return value
	mv	$t2, $t1		# put the old fib(n) in fib(n-1)
	mv	$v0, $t2		# put the new fib(n) in fib(n)
	add	$a0, $a0, -1		# decriment counter
	bne	$a0, $zero, loop	# check if we're done
done:	jr	$ra			# return