Subversion Repositories lzrw1-compressor-core

--/**************************************************************************************************************

--*

--*    L Z R W 1   E N C O D E R   C O R E

--*

--*  A high throughput loss less data compression core.

--* 

--* Copyright 2012-2013   Lukas Schrittwieser (LS)

--*

--*    This program 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 2 of the License, or

--*    (at your option) any later version.

--*

--*    This program 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 this program; if not, write to the Free Software

--*    Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

--*    Or see <http://www.gnu.org/licenses/>

--*

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

--*

--* Change Log:

--*

--* Version 1.0 - 2012/6/30 - LS

--*   started file

--*

--* Version 1.0 - 2013/04/05 - LS

--*   release

--*

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

--*

--* Naming convention:  http://dz.ee.ethz.ch/en/information/hdl-help/vhdl-naming-conventions.html

--*

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

--*

--* Compares a the look ahead buffer to a candidate and returns the number of bytes before the first

--* non-matching pair. The counting starts at the least significant end of the look ahead and the candidate

--*

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

library IEEE;

use IEEE.STD_LOGIC_1164.all;

use IEEE.NUMERIC_STD.all;

library UNISIM;

use UNISIM.VComponents.all;

entity comparator is

  port (

    -- ClkxCI          : in  std_logic;

    -- RstxRI          : in  std_logic;

    -- EnxSI           : in  std_logic;

    LookAheadxDI    : in  std_logic_vector(16*8-1 downto 0);

    LookAheadLenxDI : in  integer range 0 to 16;  -- how many bytes of LookAheadxDI are valid 

    CandidatexDI    : in  std_logic_vector(16*8-1 downto 0);

    CandidateLenxDI : in  integer range 0 to 16;  -- how many bytes of CandidatexDI are valid

    MatchLenxDO     : out integer range 0 to 16);  -- length of the match in bytes

end comparator;

architecture Behavioral of comparator is

  signal MatchVectorxS : std_logic_vector(15 downto 0);  -- match signals for the individual bytes

  signal RawMatchLenxD : integer range 0 to 16;  -- number of matching bytes (before further processing)

  signal MaxLengthxD   : integer range 0 to 16;  -- smaller of the two input signal length;

begin

  -- implement 16 byte wide comparators

  genByteComps : for i in 0 to 15 generate

    MatchVectorxS(i) <= '1' when CandidatexDI((i+1)*8-1 downto i*8) = LookAheadxDI((i+1)*8-1 downto i*8) else '0';

  end generate genByteComps;

  -- count the number of leading bytes to determine the match length

  process (MatchVectorxS)

    variable cnt : integer range 0 to 16 := 0;

  begin  -- process

    cnt := 0;

    cntLoop : for i in 0 to 15 loop

      if MatchVectorxS(i) = '1' then

        cnt := cnt + 1;

      else

        exit cntLoop;

      end if;

    end loop;  -- i

    RawMatchLenxD <= cnt;

  end process;

-- the match length can not be longer than the shorter of the two data inputs

  MaxLengthxD <= CandidateLenxDI when CandidateLenxDI < LookAheadLenxDI else LookAheadLenxDI;

-- make sure the match length is not bigger than the max length

  MatchLenxDO <= RawMatchLenxD when RawMatchLenxD <= MaxLengthxD else MaxLengthxD;

end Behavioral;