Subversion Repositories deflatecore

--------------------------------------------------------------------------------

-- Create Date:    03:46:54 10/31/05

-- Design Name:    

-- Module Name:    Hash - Behavioral

-- Project Name:   Deflate

-- Revision:

-- Revision 0.25 - Only one hash algorithm

-- Additional Comments:

-- The remarked comments for synchronous reser result in the use of more 192 slices witn a maximum frequency of 129 Mhz

--      But if the code is commented as it is now the number of slices utlised is 5 without a known clock , need to specifiy that as a compile time constraint.

-- TO DO: 

-- Wishbone interface

-- Concurrent Hashkey generation

--------------------------------------------------------------------------------

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity HashChain is

    Generic

              (                                                                                                                                                                   -- Data bus width currently set at 8

                         Data_Width : natural := 8;                                                                                               -- Width of the hash key generated now at 32 bits

                         Hash_Width : natural := 32

         );

    Port ( Hash_O   : inout std_logic_vector (Hash_Width - 1 downto 0);   -- Hash value of previous data

           Data_in  : in  std_logic_vector (Data_Width-1 downto 0);       -- Data input from byte stream

                          Clock,                                                                                                                            -- Clock

                          Reset,

                          Start,                                                                                                                            -- Reset

                          O_E : in  bit ;                                                                            -- Output Enable

           Busy,

                          Done : out bit                                                                                                                   -- Enabled when the hash key has been generated

                          );

end HashChain;

--An algorithm produced by Professor Daniel J. Bernstein and 

--shown first to the world on the usenet newsgroup comp.lang.c. 

--It is one of the most efficient hash functions ever published

--Actual function hash(i) = hash(i - 1) * 33 + str[i];

--Function now implemented using XOR hash(i) = hash(i - 1) * 33 ^ str[i];

architecture DJB2 of HashChain is

signal mode: integer := 0;

signal tempval, hash:std_logic_vector (Hash_Width - 1 downto 0):= X"00000000" ;

signal multiplier:std_logic_vector (39 downto 0):= X"0000000000" ;

begin

mealymachine: process (Clock)

begin

        if Reset = '1' and Clock = '1' then          -- Reset

                     mode <= 0;

        elsif start = '1' and Clock = '1' then    -- Start

                     mode <= 1;                                                                   -- Multiply previous key by 33          ( Clock = 1 )

                  elsif mode = 1 then

                     mode <= 2;                                                                   -- Ex-OR input with existing key ( Clock = 0 )

                  elsif mode = 2 then

                     mode <= 3;                                                                   -- Latch output                  ( Clock = 1 )

                  else

                     mode <= 4;

        end if;

end process mealymachine;

hash <= X"000016c7"  when mode = 0 else                     --initialise the hash key to 5831

                  multiplier(31 downto 0) xor tempval   when mode = 2 else          --Ex or with the current input

                  hash;                                                                                            --keep current value

multiplier <= hash * X"21" when mode = 1 else                 --Multiply by 33

                                  X"0000000000";

tempval <= X"00000000" when mode /= 1 else                 --Temporary value to be able to Exor the input with the hash key

           tempval+ Data_in;

busy <= '1' when mode > 0 and mode < 3 else                 --Indicates that the key is being generated

        '0' ;

Hash_O <= hash when mode = 3 and O_E = '1' else   --Output buffer

          Hash_O;                                 --Hash op bufffer

done <= '1' when mode = 3 else                    --1 after hash key has been calculated 

        '0';

end DJB2;

Configuration djb2_hash of hashchain is

for djb2

end for;

end djb2_hash;