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

//  This program is similar to "sum_of_constants.iml". 
//  The difference is that this program reads values for
//  the variables "first_number" and "second_number" from keyboard.
//  The user of the program may enter only single-digit numbers.
//  The calculated sum is printed with subroutine
//  "print_register_a_in_decimal_form".

beginning_of_main_program:
      call_subroutine                  read_and_echo_a_character
      subtract_value_from_register_a   '0'
      set_memory_pointer               first_number
      store_register_a_to_memory

      set_memory_pointer               plus_sign_text
      call_subroutine                  display_text

      call_subroutine                  read_and_echo_a_character
      subtract_value_from_register_a   '0'
      set_memory_pointer               second_number
      store_register_a_to_memory

      //  Now the two numbers have been read from keyboard.
      //  We can calculate their sum.

      set_memory_pointer               first_number
      load_register_a_from_memory
      set_memory_pointer               second_number
      load_register_b_from_memory

      add_register_b_to_a

      set_memory_pointer               sum_of_numbers
      store_register_a_to_memory

      set_memory_pointer               equal_sign_text
      call_subroutine                  display_text

      set_memory_pointer               sum_of_numbers
      load_register_a_from_memory
      call_subroutine                  print_register_a_in_decimal_form

end_of_main_program:
      stop_processing

first_number:              DATA        1
second_number:             DATA        1
sum_of_numbers:            DATA        1

plus_sign_text:            STRING      " + "

equal_sign_text:           STRING      " = "


read_and_echo_a_character:
      jump_if_input_not_ready            read_and_echo_a_character
      input_byte_to_register_a
      output_byte_from_register_a
      return_to_calling_program


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


print_register_a_in_decimal_form:

//  First we zero all the data-areas used by this subroutine.

      load_register_b_with_value       0
      set_memory_pointer               hundreds_in_byte
      store_register_b_to_memory
      set_memory_pointer               tens_in_byte
      store_register_b_to_memory
      set_memory_pointer               ones_in_byte
      store_register_b_to_memory      

find_hundreds_in_byte:
      load_register_b_with_value          100
      jump_if_register_a_smaller_than_b   find_tens_in_byte
      subtract_register_b_from_a
      set_memory_pointer                  hundreds_in_byte
      load_register_b_from_memory
      increment_register_b
      store_register_b_to_memory
      jump_to_address                     find_hundreds_in_byte

find_tens_in_byte:
      load_register_b_with_value          10
      jump_if_register_a_smaller_than_b   find_ones_in_byte
      subtract_register_b_from_a
      set_memory_pointer                  tens_in_byte
      load_register_b_from_memory
      increment_register_b
      store_register_b_to_memory
      jump_to_address                     find_tens_in_byte

find_ones_in_byte:
      set_memory_pointer                  ones_in_byte
      store_register_a_to_memory

print_hundreds_tens_and_ones:
      set_memory_pointer               hundreds_in_byte
      load_register_a_from_memory
      add_value_to_register_a          '0'
      output_byte_from_register_a

      set_memory_pointer               tens_in_byte
      load_register_a_from_memory
      add_value_to_register_a          '0'
      output_byte_from_register_a

      set_memory_pointer               ones_in_byte
      load_register_a_from_memory      
      add_value_to_register_a          '0'
      output_byte_from_register_a

end_of_print_register_a_in_decimal_form:
      return_to_calling_program

//  The following are the "local data" of subroutine
//  print_register_a_in_decimal_form. This data is local because
//  only this subroutine uses them.

hundreds_in_byte:    DATA        1
tens_in_byte:        DATA        1
ones_in_byte:        DATA        1