16QAM (De)Mapper using VHDL

RTL Code(Mapper)

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_signed.all;

entity QAM16mapper is
port(
	nrst, sclk : in std_logic;
	inbits : in std_logic_vector(3 downto 0);
	
	rdata : out std_logic_vector(5 downto 0);
	idata : out std_logic_vector(5 downto 0));
end entity;

architecture arch of QAM16mapper is

constant pvalue1 : std_logic_vector(5 downto 0) := "001000";
constant pvalue3 : std_logic_vector(5 downto 0) := "011000";
constant mvalue1 : std_logic_vector(5 downto 0) := "111000";
constant mvalue3 : std_logic_vector(5 downto 0) := "101000";

begin

process(nrst, sclk)
variable pr, pi : std_logic_vector(5 downto 0);
begin
if nrst = '0' then
	rdata <= (others => '0');
	idata <= (others => '0');
elsif sclk'event and sclk = '1' then
	if(inbits(1) = '0') then
		pr := pvalue3;
	else
		pr := pvalue1;
	end if;

	if(inbits(0) = '0') then
		pi := pvalue3;
	else
		pi := pvalue1;
	end if;


	if(inbits(3) = '0') then
		rdata <= pr;
	else
		rdata <= -pr;
	end if;


	if(inbits(2) = '0') then
		idata <= pi;
	else
		idata <= -pi;
	end if;
end if;
end process;

end arch;

---

RTL Code(DeMapper)

library ieee;
use ieee.std_logic_1164.all;
use ieee.std_logic_arith.all;
use ieee.std_logic_signed.all;

entity QAM16demapper is
port(
	nrst, sclk : in std_logic;
	rdata, idata : std_logic_vector(5 downto 0);

	outbits : out std_logic_vector(3 downto 0));
end entity;

architecture arch of QAM16demapper is

begin

process(nrst, sclk)
variable pr, pi : std_logic_vector(5 downto 0);
begin
	if nrst = '0' then
		outbits <= (others => '0');
	elsif sclk'event and sclk = '1' then
		if(rdata(5) = '0') then
			outbits(3) <= '0';
			pr := rdata;
		else
			outbits(3) <= '1';
			pr := -rdata;
		end if;


		if(idata(5) = '0') then
			outbits(2) <= '0';
			pi := idata;
		else
			outbits(2) <= '1';
			pi := -idata;
		end if;

		if(pr >= "010000") then
			outbits(1) <= '0';
		else
			outbits(1) <= '1';
		end if;

		if(pi >= "010000") then
			outbits(0) <= '0';
		else
			outbits(0) <= '1';
		end if;
end if;
end process;

end arch;