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--! Unsigned division circuit, based on slow division algorithm (Restoring division)

--! http://en.wikipedia.org/wiki/Division_%28digital%29

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.std_logic_arith.all;

--! Use CPU Definitions package

use work.pkgDefinitions.all;

entity divisor is

    Port ( rst : in  STD_LOGIC;

           clk : in  STD_LOGIC;

           quotient : out  STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

                          reminder : out  STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

           numerator : in  STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

           divident : in  STD_LOGIC_VECTOR ((nBitsLarge-1) downto 0);

           done : out  STD_LOGIC);

end divisor;

architecture Behavioral of divisor is

begin

        -- Division algorithm Q=N/D

        process (rst, clk, numerator, divident)

        variable Q : unsigned(quotient'length-1 downto 0);

        variable R : unsigned(reminder'length-1 downto 0);

        variable D : unsigned(reminder'length-1 downto 0);

        variable N : unsigned(reminder'length-1 downto 0);

        variable iteractions : integer;

        begin

                if (rst = '1') then

                        quotient <= (others => '0');

                        reminder <= (others => '0');

                        done <= '0';

                        -- Initialize variables

                        iteractions := quotient'length;

                        D := unsigned(divident);

                        N := unsigned(numerator);

                        -- initialize quotient and remainder to zero

                        Q := (others => '0');

                        R := (others => '0');

                elsif rising_edge(clk) then

                        if iteractions > 0 then

                                iteractions := iteractions - 1;

                                -- left-shift R by 1 bit 

                                R := (R((R'HIGH - 1) downto 0) & '0');

                                --set the least-significant bit of R equal to bit i of the numerator(dividend)

                                R(0)     := N(iteractions);

                                if (R >= D) then

                                        R := R - D;

                                        Q(iteractions) := '1';

                                end if;

                        else

                                done <= '1';

                                quotient <= CONV_STD_LOGIC_VECTOR(Q,32);

                                reminder <= CONV_STD_LOGIC_VECTOR(R,32);

                                -- Used to avoid transparent latch (Good practise)

                                D := unsigned(divident);

                                N := unsigned(numerator);

                        end if;

                end if;

        end process;

end Behavioral;