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-- Authors :  

-- ***************************************************************************************************

--                     Juan Carlos Giraldo Carvajal M.Sc. : came up some morning with this idea.......

-- ***************************************************************************************************

--

--              Julian Andres Guarin Reyes : An easier one : encoded Juan's Idea in this RTL.

--

--

-- 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/>.

-- A 1 clock x 4 stage pipe square root.

-- The RTL encoding work was done by Julian Andres Guarin Reyes, however the real deal, was Juan Carlos Giraldo Carvajal, who came up with the idea.......

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use work.powerGrid.all;

entity sqrt is

        generic (

                W2 : integer := 64

        );

        port

        (

                clk,rst,ena : in std_logic;

                radical         : in std_logic_vector (W2-1 downto 0);

                root            : out std_logic_vector ((W2/2)-1 downto 0)

        );

end entity;

architecture rtl of sqrt is

        constant WP                             : integer:= W2/2;

        constant WP_2                   : integer:= WP/2;

        signal sa0,sb0,sx0,sy0,sb0_1            : std_logic_vector (WP-1 downto 0);

        signal sa1,sb1,sx1,sy1,sb1_1,muxs1      : std_logic_vector (WP-1 downto 0);

        signal sa2,sb2,sx2,sy2                          : std_logic_vector (WP-1 downto 0);

        signal localenc1                                        : integer range 0 to WP-1;

        signal localenc2                                        : integer range 0 to WP-1;

        signal sho                                                      : std_logic;

        signal a,b,x,y                                          : std_logic_vector ((W2/2)-1 downto 0);

        signal decoder                                          : integer range 0 to (W2/2)-1;

        signal ab,xy                                            : std_logic_vector (W2-1 downto 0);

        begin

        -- Logic function signals ...... if some day there's a paper of how this logic circuit works, it will be easier to comprehend this block of code

        sb0_1<=sa0(WP-2 downto 0) & '0';

        signalization : for i in 0 to WP-1 generate

                -- Stage 0. Functions for A,B,X and preliminar Y.

                sb0(i)<=radical(i*2);

                sa0(i)<=radical(i*2+1);

                sx0(i)<=sb0(i) or sa0(i);

                sy0(i)<=sb0(i) and sa0(i);

                -- Stage 1 : Function for signal Y.

                muxs1(i) <= sy1(i) or (not(sx1(i)) and sb1_1(i));

                -- Stage 3 :

                ab(i*2)         <= b(i);

                ab(i*2+1)       <= a(i);

                xy(i*2)         <= y(i);

                xy(i*2+1)       <= x(i);

        end generate signalization;

        stages: process (rst,clk,ena,sx0,sx1,localenc2)

                variable localenc0      : integer range 0 to WP-1;

        begin

                -- Highest signifcant pair enconder : look for the bit pair with the most significant bit.

                localenc0 := WP-1;

                stg0henc: while localenc0>0 loop

                        exit when (sx0(localenc0)='1');

                        localenc0:=localenc0-1;

                end loop;

                -- Clocking process;

                if rst='0' then

                        -- Stage 1

                        sa1<=(others => '0');

                        sb1<=(others => '0');

                        sx1<=(others => '0');

                        sy1<=(others => '0');

                        sb1_1<=(others => '0');

                        -- Stage 2

                        sx2<=(others => '0');

                        sa2<=(others => '0');

                        sb2<=(others => '0');

                        sy2<=(others => '0');

                        --Stage 3

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

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

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

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

                        --Stage 4

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

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

                        -- Stage01 

                        sa1<=sa0;

                        sb1<=sb0;

                        sx1<=sx0;

                        sy1<=sy0;

                        sb1_1<=sb0_1;

                        localenc1<=localenc0;

                        -- Stage12

                        sx2<=sx1;

                        sa2<=sa1;

                        sb2<=sb1;

                        sy2<= muxs1;

                        localenc2<=localenc1;

                        -- Stage 23 Shift 1 bit to right if the high bit in the highest significant pair is set.

                        if sa2(localenc2)='1' then

                                -- Shift Right

                                a <= '0' & sb2(WP-1 downto 1);

                                b <= sa2;

                                x <= '0' & sy2(WP-1 downto 1);

                                y <= sx2;

                        else

                                -- Leave me alone

                                x <= sx2;

                                y <= sy2;

                                a <= sa2;

                                b <= sb2;

                        end if;

                        decoder<=localenc2;

                        sho<=sa2(localenc2);

                        -- stage34

                        for i in 0 to WP-1 loop

                                if i>decoder then

                                        root(i)<='0';

                                elsif decoder-i>2 then

                                        root(i)<=ab(decoder+i+1);

                                elsif decoder-i=2 then

                                        root(i)<=(ab(decoder+i+1) and not(sho)) or (xy(decoder+i+1) and sho);

                                else

                                        root(i)<=xy(decoder+i+1);

                                end if;

                        end loop;

                end if;

        end process stages;

end rtl;