/ get user input and store it
input
store user_input

/ only find the factorial if the number is non-zero
skipcond 400
jns find_factorial

/ output the final factorial, or zero
load factorial_result
output

halt

/ initiate the factorial calculation
find_factorial, load user_input
subt one
store counter

load zero
add counter
store loop_counter

skipcond 400
jump calculate_factorial

jumpi find_factorial

/ calculate the factorial recursively
calculate_factorial, load user_input
add product
store product
store factorial_result

load counter
subt one
store counter

skipcond 400
jump calculate_factorial

jump reset_product

reset_product, load product
subt product
store product

load factorial_result
store user_input

jump decrement_loop

decrement_loop, load loop_counter
subt one
store counter

load zero
add counter
store loop_counter

/ continue calculating the factorial if further depth exists
skipcond 400
jump calculate_factorial

/ return to factorial calculation initialisation, a final stop
jumpi find_factorial

/ constants
zero, hex 0
one, dec 1

/ mutable variables
user_input, hex 0
factorial_result, hex 0
product, hex 0
counter, hex 0
loop_counter, hex 0