entity cos is
  port ( theta : in real;  result : out real );
end entity cos;

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architecture series of cos is
begin

  summation : process (theta) is
    variable sum, term : real;
    variable n : natural;
  begin
    sum := 1.0;
    term := 1.0;
    n := 0;
    while abs term > abs (sum / 1.0E6) loop
      n := n + 2;
      term := (-term) * theta**2 / real(((n-1) * n));
      sum := sum + term;
    end loop;
    result <= sum;
  end process summation;

end architecture series;