; ** p13.stax ************************************************
; STAX program to add two base-2 integers, e.g., 100101+111=
; NOTE: If input string is valid this program returns 1, with
; the sum of the addition left on stack #2, most significant
; bit at the top of the stack.
;
; John Haskins, Jr., Ph.D.
; predator@cs.virginia.edu
; -----------------------------------------------------------

	.input_alphabet		"01+="
	.stack_alphabet		"01+"

qinit0:
	accept
	-, -, push[0]:$, qinit1

qinit1:
	deny
	-, -, push[1]:$, qinit2

qinit2:
	deny
	-, -, push[2]:$, q0

q0:
	deny
	'0', -, push[0]:'0', q1
	'1', -, push[0]:'1', q1

q1:
	deny
	'0', -, push[0]:'0', q1
	'1', -, push[0]:'1', q1
	'+', -, nop, q2

q2:
	deny
	'0', -, push[1]:'0', q3
	'1', -, push[1]:'1', q3

q3:
	deny
	'0', -, push[1]:'0', q3
	'1', -, push[1]:'1', q3
	'=', -, nop, q_0

q4:
	deny
	-, '+'[0], pop[0], q5

q5:
	deny
	-, '='[1], pop[1], q_0

q_0:
	deny
	-, '0'[0], pop[0], q_00
	-, '1'[0], pop[0], q_01
	-,   $[0], nop, q_0a

q_0a:
	deny
	-, '0'[1], nop, q_00
	-, '1'[1], nop, q_00
	-,   $[1], nop, qdone

q_00:
	deny
	-, '0'[1], pop[1], q_000
	-, '1'[1], pop[1], q_001
	-,   $[1], nop, q_000

q_01:
	deny
	-, '0'[1], pop[1], q_001
	-, '1'[1], pop[1], q_011
	-,   $[1], nop, q_001

q_000:
	deny
	-, -, push[2]:'0', q_0

q_001:
	deny
	-, -, push[2]:'1', q_0

q_011:
	deny
	-, -, push[2]:'0', q_1

q_1:
	deny
	-, '0'[0], pop[0], q_01
	-, '1'[0], pop[0], q_11
	-,   $[0], nop, q_01

q_11:
	deny
	-, '0'[1], pop[1], q_011
	-, '1'[1], pop[1], q_111
	-,   $[1], nop, q_011

q_111:
	deny
	-, -, push[2]:'1', q_1

qdone:
	accept
	halt

qerror:
	deny
	halt