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library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
entity func_test2 is
generic (NBITS: natural := 6);
end entity;
architecture fum of func_test2 is
signal dividend: std_logic_vector (NBITS - 1 downto 0);
function mod5 (dividend: std_logic_vector) return std_logic is
type remains is (r0, r1, r2, r3, r4); -- remainder values
type remain_array is array (NBITS downto 0) of remains;
type branch is array (remains, bit) of remains;
constant br_table: branch := ( r0 => ('0' => r0, '1' => r1),
r1 => ('0' => r2, '1' => r3),
r2 => ('0' => r4, '1' => r0),
r3 => ('0' => r1, '1' => r2),
r4 => ('0' => r3, '1' => r4)
);
variable remaind: remain_array := (others => r0);
variable tbit: bit_vector (NBITS - 1 downto 0);
begin
tbit := to_bitvector(dividend); -- little endian
for i in dividend'length - 1 downto 0 loop
remaind(i) := br_table(remaind(i + 1),tbit(i));
end loop;
if remaind(0) = r0 then
return '1';
else
return '0';
end if;
end function;
begin
process
variable errors: natural;
begin
errors := 0;
for i in 0 to 2 ** NBITS - 1 loop
dividend <= std_logic_vector(to_unsigned(i, NBITS));
wait for 0 ns;
report "mod5(" & integer'image(i) &") = " &
std_ulogic'image(mod5(dividend));
end loop;
wait;
end process;
end architecture;
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