VHDL for FPGA Design/4-Bit Adder

library ieee; use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all use ieee.std_logic_arith.all;

Entity Adder4 Is port ( a,b:in integer Range -8 to 7; sum:out integer Range -16 to 15 ); end Adder4;

Architecture Adder4arch of Adder4 Is Begin sum<=a+b;

end Adder4arch;

Simulation Waveform

library ieee;
use ieee.std_logic_1164.all;
use work.all;

entity adder4b is
  port (a,b,c:in std_logic_vector(3 downto 0);
        cin:in std_logic;
        cout:out std_logic;
        s:out std_logic_vector(3 downto 0));
END adder4b;

architecture arch12 of adder is
  signal y:std_logic_vector(4 downto 0);
begin
  y(0)<= cin;
  cout<=y(4);
  --u:for i in 0 to 3 generate
  --p:entity work.FA(arch) port map(a,b,c,s,r=>y(i+1));
  p0:entity work.FA(arch) port map(a=>a(0),b=>b(0),c=>y(0),s=>s(0),r=>y(1));
  p1:entity work.FA(arch) port map(a=>a(1),b=>b(1),c=>y(1),s=>s(1),r=>y(2));
  p2:entity work.FA(arch) port map(a=>a(2),b=>b(2),c=>y(2),s=>s(2),r=>y(3));
  p3:entity work.FA(arch) port map(a=>a(3),b=>b(3),c=>y(3),s=>s(3),r=>y(4));
--end generate;