Subversion Repositories iqcorrection

library ieee;

use ieee.std_logic_1164.all;

use ieee.math_real.all;

use ieee.numeric_std.all;

use work.random_int.all;

--by MEP 22 February 2011

--usage:

--this is a function, which means it can be on the right-hand side

--of an assignment. It returns a mean-zero random number from a

--normal distribution. The argument is a real number that indicates

--the standard deviation desired. 

--

--random_noise(sigma);

--

package normal_distribution_random_noise is

        function random_noise (

        sigma : real)

        return real;

end package normal_distribution_random_noise;

package body normal_distribution_random_noise is

        function random_noise (

        sigma : real

        )

        return real is

                --variables

                variable u_noise: real; --uniform distribution noise

                variable n_noise: real := 0.0; --normal distribution noise

                variable seed1 : positive;

                variable seed2 : positive;

        begin

                --obtain a uniformly distributed random number

                uniform(seed1, seed2, u_noise);

                --report "Random uniform noise is " & real'image(u_noise) & ".";

                for normal_count in 0 to 12 loop

                --Turn the uniform distributed number 

                --into a normally distributed number

                --by using the central limit theorem.

                --Make it mean zero and make it have

                --the range of the uniform numbers

                --that it is composed from. 

                n_noise := n_noise + u_noise;

                end loop;

                n_noise := n_noise - (0.5)*(real(12)); --normal distribution with a mean of zero

                --report "Random normal noise is " & real'image(n_noise) & ".";

                n_noise := n_noise/(real(12));

                --report "Random normal noise using range of uniform is " & real'image(n_noise) & ".";

                n_noise := sigma*n_noise;

                return n_noise;

        end function random_noise;

end package body normal_distribution_random_noise;