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-- Author : Julian Andres Guarin Reyes.

-- Project : JART, Just Another Ray Tracer.

-- email : jguarin2002 at gmail.com, j.guarin at javeriana.edu.co

-- This code was entirely written by Julian Andres Guarin Reyes.

-- The following code is licensed under GNU Public License

-- http://www.gnu.org/licenses/gpl-3.0.txt.

 -- This file is part of JART (Just Another Ray Tracer).

    -- JART (Just Another Ray Tracer) is free software: you can redistribute it and/or modify

    -- it under the terms of the GNU General Public License as published by

    -- the Free Software Foundation, either version 3 of the License, or

    -- (at your option) any later version.

    -- JART (Just Another Ray Tracer) is distributed in the hope that it will be useful,

    -- but WITHOUT ANY WARRANTY; without even the implied warranty of

    -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

    -- GNU General Public License for more details.

    -- You should have received a copy of the GNU General Public License

    -- along with JART (Just Another Ray Tracer).  If not, see <http://www.gnu.org/licenses/>.

-- This is a discriminant proof cell.   

library ieee;

use ieee.std_logic_1164.all;

use work.powerGrid.all;

entity kComparisonCell is

        generic (       W               : integer := 32 );

        port (

                                clk,rst         : in std_logic;

                                nxtSphere       : in std_logic; -- Controls when the sphere goes to the next Row. 

                                pipeOn          : in std_logic; -- Enables / Disable the upwarding flow.

                                kinput          : in std_logic_vector (W-1 downto 0);

                                koutput         : out std_logic_vector (W-1 downto 0);

                                vdinput         : in std_logic_vector (W-1 downto 0);    -- V.D input.

                                vdoutput        : out std_logic_vector (W-1 downto 0)    -- Selected dot product.

        );

        end port;

end entity;

architecture rtl of kComparisonCell is

        signal ssge32   : std_logic;    -- Signed "Greater or equal  than" signal.

begin

        comparison : sge32 port map (

                dataa   => vdinput,

                datab   => kinput,

                AgeB    => ssge32

                );

        -- When ssge32 (greater or equal signal) is set then V.D > kte, therefore intersection is confirmed and  V.D is to be shifted to the distance comparison grid.

        selector : process (rst,clk,ssg32,pipeOn)

        begin

                if rst='0' then

                        -- At the beginning set the Maximum over Maximum distance.

                        vdoutput <= '0' & (others =>'1');

                elsif rising_edge(clk) and pipeOn ='1' then

                        if ssge32 = '1' then -- If VD ids grater or equal than K .....

                                vdoutput <= vdinput;

                        else

                                vdoutput <= '0' & (others =>'1');

                        end if;

                end if;

        end process;

        -- Behavioral : When nxtSphere is set, the Sphere and its K constant should go the the next row

        kPipeStage : process (clk,rst,nxtSphere)

        begin

                if rst='0' then

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

                elsif rising_edge(clk) and nxtSphere ='1' then

                        koutput <= kinput;

                end if;

        end process;

end rtl;