问错误:表达式“000000000000000000000000000000”有32个元素；预期有33个元素

EN

architecture sm1 of SM is

...
signal sum_1 : float (5 downto -27);
...

begin   

N_PROCESS: process (N, j, CLK)

    ...

begin
    if rising_edge(CLK) then
        ...

        sum_1 <= to_float(0);

        ...
    end if;
end process;

end sm1;