Hue value to RGB color in pure VHDL

hue2rgb.vhd

-- Loosely based off https://stackoverflow.com/a/34663498
-- but implemented with fixed arithmatic
-- to fit the 12-bit value of a VGA color

signal color : std_logic_vector (12-1 downto 1-1);

color_proc : process (clk, clk_en) is
begin
	if rising_edge(clk) then
		if clk_en = '1' then
			if hue < 15 then
				hue <= hue + 1;
			else
				hue <= 0;
			end if;
		end if;
	end if;
end process;

color <= hue2rgb(hue);

pure function floor(hue : integer) return integer is
begin
	if hue < 15 then
		return 0;
	elsif hue < 30 then
		return 15;
	elsif hue < 45 then
		return 30;
	else
		return 45;
	end if;
end function;

pure function clamp(val : integer; lo : integer; hi : integer) return integer is
begin
	if val < lo then
		return lo;
	elsif val > hi then
		return hi;
	else
		return val;
	end if;
end function;

pure function channel(hue : integer; ch : integer) return std_logic_vector is
begin
	return std_logic_vector(to_unsigned(
		clamp(
			6 * abs((hue + (5 * ch)) - floor((hue + (5 * ch))) - 8) - 15,
			0,
			15
		), 4
	));
end function;

pure function hue2rgb(hue : integer) return std_logic_vector is
begin
	return channel(hue, 0) & channel(hue, 1) & channel(hue, 2);
end function;