Multiplication on floating point format

Sorry to ask this, how to create an interface to the megafunction? I never use this function.

for example this is my previous codes:

library ieee;

use ieee.std_logic_1164.all;

library floatfixlib;

use floatfixlib.fixed_pkg.all;

entity my_mult is

port (

clk : in std_logic;

a,b : in sfixed(3 downto -4);

c : out sfixed(7 downto -8)

);

end entity my_mult;

architecture rtl of my_mult is

begin

mult_proc : process(clk)

begin

if rising_edge(clk) then

c <= a * b;

end if;

end process;