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LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
USE ieee.numeric_std.ALL;
-- full 4-bit adder entity
entity add4b is
port (
A: in std_logic_vector(3 downto 0);
B: in std_logic_vector(3 downto 0);
Cin: in std_logic;
X: out std_logic_vector(3 downto 0);
Cout: out std_logic);
end add4b;
architecture Behavioral of add4b is
signal C0: std_logic; -- Cout0 -> Cin1
signal C1: std_logic; -- Cout1 -> Cin2
signal C2: std_logic; -- Cout2 -> Cin3
component add1b
port (
A: in std_logic;
B: in std_logic;
Cin: in std_logic;
X: out std_logic;
Cout: out std_logic);
end component;
begin
-- full adder ladder (e.g. Cin -> Cin0, Cout0 -> Cin1, ..., Cout3 -> Cout)
add0: component add1b
port map (
A => A(0),
B => B(0),
Cin => Cin,
X => X(0),
Cout => C0);
add1: component add1b
port map (
A => A(1),
B => B(1),
Cin => C0,
X => X(1),
Cout => C1);
add2: component add1b
port map (
A => A(2),
B => B(2),
Cin => C1,
X => X(2),
Cout => C2);
add3: component add1b
port map (
A => A(3),
B => B(3),
Cin => C2,
X => X(3),
Cout => Cout);
end Behavioral;
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