# The Towers Of Hanoi
# Parrot VM
# Copyright (C) 2003 Amit Singh. All Rights Reserved.
# http://hanoi.kernelthread.com
#
# Last tested under Parrot version 0.0.0-10devel
# http://www.parrotcode.org
#
# Usage:
#
# % assemble.pl hanoi.pasm -o hanoi.pbc
# % parrot hanoi.pbc 3

main:
	set	I0, P0[1]	# I0 = argv[1] (n)
	lt	I0, 1,  error	# if (argv[1] < 1) ... error
	gt	I0, 10, error	# if (argv[1] > 10) .. error
	set	I1, 1		# I1 = 1 (f)
	set	I2, 2		# I2 = 2 (u)
	set	I3, 3		# I3 = 3 (t)
	bsr	hanoi		# hanoi(n, f, u, t)
	branch	done		# OK
error:
	print	"usage: hanoi n, where 0 < n <= 10\n"
done:
	end

hanoi:				# hanoi(n, f, u, t)
	pushi			# input
	save	I0		# n
	save	I1		# f
	save	I2		# u
	save	I3		# t
	gt	I0, 0, run	# if (n > 0)
	branch	out		# if (n <= 0) GOTO out
run:
	dec	I0		# n = n - 1
	set	I4, I3		# tmp = t
	set	I3, I2		# t = u
	set	I2, I4		# u = tmp
	bsr	hanoi		# hanoi(n - 1, f, t, u)
	print	I1		# printf("%d", f)
	print	" --> "		# printf(" --> ")
	print	I2		# printf("%d", t)
	print	"\n"		# printf("\n")
	set	I4, I1		# tmp = f
	set	I1, I3		# f = u
	set	I5, I2		# tmp1 = t
	set	I2, I4		# u = f
	set	I3, I5		# t = tmp1
	bsr	hanoi		# hanoi(n - 1, u, f, t)
out:
	popi			# input
	restore I3		# t
	restore I2		# u
	restore I1		# f
	restore I0		# n
	ret