multiplication in fixed_pkg

to convert std_logic_Vector there is a function called

function to_sfixed (     
arg                  : STD_ULOGIC_VECTOR;  -- shifted vector     
constant left_index  : INTEGER; 
    constant right_index : INTEGER)     
return UNRESOLVED_sfixed; 

or there is this version:

function to_sfixed (     
arg      : STD_ULOGIC_VECTOR;       -- shifted vector     size_res : UNRESOLVED_sfixed)       -- for size only     return UNRESOLVED_sfixed; 

where you can use another signal for sizing information

so for example, to convert a 14 bit slv to an sfixed with 6 integer bits and 8 fractional, use the function like this:

output <= to_sfixed(my_slv, 5, -8);

or you can do this:

output <= to_sfixed(my_slv, output);