# Non-recursive towers of hanoi solution.

# It does use a stack, of course, but with
# significantly fewer pushes and pops than
# a normal recursive subroutine would use.

MAIN:
   save 4 # number of disks.
   bsr HANOI
   end

HANOI:
   restore I0
   le I0, 0, end_of_sub
   save 0 # Sentinel
   set S0, "a"
   set S1, "b"
   set S2, "c"
   eq I0, 1, doprint
pushsome:
   dec I0
   exchange S1, S2
   push S2
   push S1
   push S0
   push I0
   gt I0, 1, pushsome
doprint:
   print "Move from tower "
   print S0
   print " to tower "
   print S2
   print ".\n"
   dec I0
   if I0, justswitch
   restore I0
   eq I0, 0, end_of_sub # sentinel?
   restore S0
   restore S1
   restore S2
   branch doprint
justswitch:
   exchange S0, S1
   gt I0, 1, pushsome
   branch doprint
end_of_sub:
   ret