-- Copyright © 1993 by  McGraw-Hill, Inc. and Zainalabedin Navabi

-- FIGURE 5.3 




-- ENTITY DECLARATION OF NIBBLE-COMPARATOR  :

ENTITY nibble_comparator IS
  PORT (a, b : IN BIT_VECTOR (3 DOWNTO 0);  -- a and b data inputs
        gt,                                 -- previous greater than
        eq,                                 -- previous equal
        lt : IN BIT;                        -- previous less than
        a_gt_b,                             -- a > b
        a_eq_b,                             -- a = b
        a_lt_b : OUT BIT);                  -- a < b
END nibble_comparator;
--


-- STRUCTURAL ARCHITECTURE OF A NIBBLE-COMPARATOR :

ARCHITECTURE structural OF nibble_comparator IS
  COMPONENT comp1 
    PORT (a, b, gt, eq, lt : IN BIT; a_gt_b, a_eq_b, a_lt_b : OUT BIT);
  END COMPONENT;
  FOR ALL : comp1 USE ENTITY WORK.bit_comparator (functional);
  CONSTANT n : INTEGER := 4;
  SIGNAL im : BIT_VECTOR ( 0 TO (n-1)*3-1);
BEGIN
  c_all: FOR i IN 0 TO n-1 GENERATE
    l: IF i = 0 GENERATE
      least: comp1 PORT MAP (a(i), b(i), gt, eq, lt, im(0), im(1), im(2) );
    END GENERATE;
    m: IF i = n-1 GENERATE
      most: comp1 PORT MAP (a(i), b(i), im(i*3-3), im(i*3-2), im(i*3-1), a_gt_b, a_eq_b, a_lt_b);
    END GENERATE;
    r: IF i > 0 AND i < n-1 GENERATE
      rest: comp1 PORT MAP (a(i), b(i), im(i*3-3), im(i*3-2), im(i*3-1), im(i*3+0), im(i*3+1), im(i*3+2) );
    END GENERATE;
  END GENERATE;
END structural;
--