//  simplesum.iml  (c) 1997 - 2000  Kari Laitinen

//  The following program displays twice the text
//  " + ", and expects the user of the imaginary computer
//  to use the keyboard and type in two single-digit numbers.
//  The program calculates the sum of the numbers the user
//  typed and displays it on the screen after the sign =.
//  When the program is executed with numbers 7 and 9
//  the screen should show    + 7 + 9 = 16

beginning_of_program:
      set_memory_pointer                  text_for_number_input
      call_subroutine                     display_text

first_number_not_given:
      jump_if_input_not_ready             first_number_not_given
      input_byte_to_register_a
      output_byte_from_register_a         // Echo the number to screen
      subtract_value_from_register_a      '0'
      move_content_of_register_a_to_b

      set_memory_pointer                  text_for_number_input
      call_subroutine                     display_text

second_number_not_given:
      jump_if_input_not_ready             second_number_not_given
      input_byte_to_register_a
      output_byte_from_register_a         // Echo the number to screen
      subtract_value_from_register_a      '0'
 
      add_register_b_to_a
      push_register_a_to_stack            // Save the result of adding

      set_memory_pointer                  text_for_result
      call_subroutine                     display_text

      pop_register_a_from_stack           // the result back to a
      load_register_b_with_value          9
      jump_if_register_a_greater_than_b   display_two_numbers

display_one_number:
      add_value_to_register_a             '0'
      output_byte_from_register_a
      jump_to_address                     end_of_program

display_two_numbers:

      //  The result is more than 9, but it cannot be more than 18.

      load_register_b_with_value          '1'
      output_byte_from_register_b
      subtract_value_from_register_a      10
      add_value_to_register_a             '0'
      output_byte_from_register_a

end_of_program:
      stop_processing


display_text:
      load_register_a_from_memory
      jump_if_register_a_zero               end_of_display_text
      output_byte_from_register_a
      increment_memory_pointer
      jump_to_address                       display_text
end_of_display_text:
      return_to_calling_program

text_for_number_input:       STRING    " + "

text_for_result:             STRING    " = "