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;