Subversion Repositories special_functions_unit

-- Log2 IEEE754 case detect

library ieee;

        use ieee.std_logic_1164.all;

        use ieee.numeric_std.all;

entity exp2_ieee is

        generic (BX                                             :               natural := 7);

        port      (i_data                                       : in    std_logic_vector(31 downto 0);

                                o_case                                  : out std_logic_vector(31 downto 0);

                                o_case_en                               : out std_logic);

end entity;

architecture rtl of exp2_ieee is

        signal s_sgn    : std_logic;

        signal s_exp    : std_logic_vector(7 downto 0);

        signal s_mantis: std_logic_vector(22 downto 0);

begin

        s_sgn   <= i_data(i_data'left);

        s_exp   <= i_data(i_data'left-1 downto 23);

        s_mantis        <= i_data(22 downto 0);

        process(s_sgn, s_exp, s_mantis)

        begin

                if to_integer(unsigned(s_exp)) < (127 - BX) then -- -subn, -0.0, +0.0, +subn and exp<127-BX

                        o_case          <= X"3F800000"; -- +1

                        o_case_en       <= '1';

                elsif s_exp > X"86" then

                        o_case_en       <= '1';

                        if s_mantis /= "00000000000000000000000" and s_exp = X"FF" then -- NaN

                                o_case <= X"FFFFFFFF"; -- NaN

                        else

                                if s_sgn = '0' then-- +inf

                                        o_case <= X"7F800000"; -- +inf

                                else -- -inf

                                        o_case <= X"00000000"; -- 0     

                                end if;

                        end if;

                else

                        o_case_en       <= '0';

                        o_case <= X"00000000";

                end if;

        end process;

end rtl;