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-- Declare an eight_bit subtype, taking values in the range -128 to 127. 
-------------------------------------------------------------------------

PACKAGE new_types IS 
BEGIN
   SUBTYPE eight_bit IS integer RANGE -128 TO 127;
END PACKAGE new_type;

USE WORK.new_types.ALL;      
ENTITY eight_bit_adder IS 
   PORT( a,b: IN eight_bit;   
         s: OUT eight_bit); 
END  ENTITY eight_bit_adder;

ARCHITECTURE adder OF eight_bit_adder IS 
BEGIN
   s <= a + b;
END ARCHITECTURE adder;