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--! @file shift.vhd

--! @brief RayTrac TestBench

--! @author Julián Andrés Guarín Reyes

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-- RAYTRAC

-- Author Julian Andres Guarin

-- shift.vhd

-- This file is part of raytrac.

-- 

--     raytrac 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.

-- 

--     raytrac 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 raytrac.  If not, see <http://www.gnu.org/licenses/>

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_signed.all;

use ieee.math_real.all;

--! \brief Dado que cualquier número entero A, se puede escribir 2^n * f, es importante obtener una representación del valor de f en base 2. Una vez hallado este valor y evaluado en una función bastara con realizar un corrimiento a la izquierda n bits del resultado, para calcular funciones como A^-1 o A^0.5.

entity shifter is

        generic (

                address_width   : integer       := 9;

                width                   : integer       := 32;

                --! Cuando even shifter es "YES" se hara la busqueda del primer bit con valor 1, de izquierda a derecha, pero NO de uno en uno.

                even_shifter    : string        := "YES"

        );

        port (

                data                    : in std_logic_vector(width - 1 downto 0);

                exp                             : out std_logic_vector(integer(ceil(log(real(width),2.0)))-1 downto 0);

                address                 : out std_logic_vector (address_width-1 downto 0);

                zero                    : out std_logic

        );

end shifter;

architecture shifter_arch of shifter is

begin

        sanityLost:

        process (data)

                variable index: integer range-1 to width+address_width-1:=width+address_width-1;

        begin

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

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

                zero<=data(0);

                if even_shifter="YES" then

                        index:=width-1;

                else

                        index:=width-2;

                end if;

                while index>=1 loop

                        if data(index)='1' then

                                zero<='0';

                                exp<=CONV_STD_LOGIC_VECTOR(index, exp'high+1);

                                if index>=address_width then

                                        address <= data (index-1 downto index-address_width);

                                else

                                        address(address_width-1 downto address_width-index) <= data (index-1 downto 0);

                                        address(address_width-index-1 downto 0) <= (others =>'0');

                                end if;

                                exit;

                        end if;

                        index:=index-2; --Boost

                end loop;

        end process sanityLost;

end shifter_arch;