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library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use ieee.math_real.all;
entity tan_table is
generic(
Q : positive := 12;
INPUT_WIDTH : positive := 16;
OUTPUT_WIDTH: positive := 16;
STEPS : positive := 4;
ANGLE : real := MATH_PI*(45.0/180.0)
);
port(
reset : in std_logic;
clock : in std_logic;
phase : in signed(INPUT_WIDTH-1 downto 0);
phase_valid : in std_logic;
y : out signed(OUTPUT_WIDTH-1 downto 0);
y_valid : out std_logic
);
end entity;
architecture arch of tan_table is
type tan_table_t is array (natural range <>) of signed(OUTPUT_WIDTH-1 downto 0);
type tan_table_real_t is array (natural range <>) of real;
function generate_tan_table(steps, qscale : positive) return tan_table_t is
variable table : tan_table_t(0 to steps) := (others => (others => '0'));
begin
for i in table'range loop
table(i) := to_signed(integer(round(real(2**qscale)* tan(ANGLE * real(i)/real(steps)))),table(i)'length);
end loop;
return table;
end function;
function generate_tan_table_real(steps : positive) return tan_table_real_t is
variable table : tan_table_real_t(0 to steps) := (others => (0.0));
begin
for i in table'range loop
table(i) :=tan(ANGLE * real(i)/real(steps));
end loop;
return table;
end function;
constant table : tan_table_t(0 to STEPS) := generate_tan_table(STEPS,Q);
constant table_2 : tan_table_real_t(0 to STEPS) := generate_tan_table_real(STEPS);
begin
find_y : process(clock, reset)
begin
if reset = '1' then
--
y_valid <= '0';
y <= (others => '0');
elsif rising_edge(clock) then
y_valid <= '0';
if phase_valid = '1' then
if phase < 0 then
y <= table(to_integer(abs(phase)));
else
y <= -table(to_integer(abs(phase)));
end if;
y_valid <= '1';
end if;
--
end if;
end process;
end architecture;
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