root/ossiedev/branches/mcarrick/VHDL/carry_lookahead_adder/carry_lookahead_adder_logic.vhd @ 8216

-- Carry Look Ahead Logic
--
-- This implements the carry look head logic for the
-- carry look ahead adder. The minimum requirement
-- for the number of bits is 2.
--

library ieee;
use ieee.std_logic_1164.all;

entity carry_lookahead_logic is
        generic (       numBits : integer := 4
        );
        port (  p               : in    std_logic_vector(numBits-1 downto 0);
                        g               : in    std_logic_vector(numBits-1 downto 0);
                        cIn             : in    std_logic;
                        c               : out   std_logic_vector(numBits-1 downto 0)
        );
end entity carry_lookahead_logic;

architecture carry_lookahead_logic_behav of carry_lookahead_logic is

        -- internal signal for carry values
        signal carry : std_logic_vector(numBits-1 downto 0);

        begin

                -- determine if numBits is large enough
                valid_numBits : if (numBits > 1) generate

                        -- calculate all of the carry signals
                        calculate_carry : for i in 0 to numBits-1 generate

                                -- case for first signal
                                first_carry : if (i = 0) generate
                                begin
                                        carry(i) <= g(i) or (p(i) and cIn);
                                end generate first_carry;
                                
                                -- case for other carries
                                other_carries : if (i > 0) generate
                                begin
                                        carry(i) <= g(i) or (p(i) and carry(i-1));
                                end generate other_carries;

                        end generate calculate_carry;

                end generate valid_numBits;

                -- assign output value
                c <= carry;



end architecture carry_lookahead_logic_behav;