.globl fac1
#####################################################################
# Returns factorial of parameter.
#
# Pre:
#    $a0 stores N
# Post:
#    $v0 stores N!
#
# Modifies: $t0, $t1, $v0, $a0
#
fac1:
        li    $t0, 1                 # check for base case
        bgt   $a0, $t0, recurse
        li    $v0, 1                 # if so, set $v0
        jr    $ra                    #        and return

recurse:
        move  $t1, $a0               # save N
        addi  $a0, $a0, -1           # calc N-1 for recursive call
        jal   fac1                   # calc (N-1)!
        mul   $v0, $v0, $t1          # multiply that by N

        jr    $ra                    #    and return