USE work.multiplier_types.all;
USE work.bv_arithmetic.all;
USE std.textio.all;


ENTITY adder IS
  PORT ( a :          in  word;
         b :          in  word;
         c_in :       in  bit;
         s :          out word;
         c_out :      out bit);
END adder;


ARCHITECTURE behaviour OF adder IS

BEGIN  --  behaviour 
  
  add : PROCESS (a, b, c_in)
    CONSTANT Tpd : Time := 8 ns;
    VARIABLE c : bit;
    VARIABLE sum : word;
    VARIABLE L : line;
    
  BEGIN  --  PROCESS add 
    c := c_in;
    FOR i IN 0 to word_size-1 LOOP
      sum(i) := (a(i) XOR b(i)) XOR c;
      c := (a(i) AND b(i)) OR ((a(i) XOR b(i)) AND c);
    END LOOP;
    s <= sum after Tpd;
    c_out <= c after Tpd;
    --write(L, string'("adder:"));
    --write_hex(L, a);
    --write(L, string'(" + "));
    --write_hex(L, b);
    --write(L, string'(" -> "));
    --write_hex(L, sum);
    --writeline(output, L);
  END PROCESS add;

END behaviour;