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-- Company: 

-- Engineer:

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

-- Design Name:    

-- Module Name:    Hash - Behavioral

-- Project Name:   Deflate

-- Revision:

-- Revision 0.01 - File Created

-- Additional Comments:

-- 

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library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.STD_LOGIC_ARITH.ALL;

use IEEE.STD_LOGIC_UNSIGNED.ALL;

use IEEE.std_logic_unsigned.all;

---- Uncomment the following library declaration if instantiating

---- any Xilinx primitives in this code.

--library UNISIM;

--use UNISIM.VComponents.all;

entity HashChain is

    Port ( Data_in  : in std_logic_vector (7 downto 0);   -- Data input from byte stream

           Hash_o   : out real;                          -- Hash value of previous data

           Clock,                                                                                                          -- Clock

                          Reset,                                                                                                           -- Reset

                          Output_E : in bit                                                                        -- Output Enable

           );

end HashChain;

--From Robert Sedgwicks Algorithms in C

architecture RSHash of HashChain is

signal mode,

       data : integer;

begin

mode <= 0 when clock = '1' and reset = '0' and Output_E = '1' else  -- Active data being latched to output

        1 when clock = '0' and reset = '0' and Output_E = '1' else  -- No change to output till thge next clock

                  2 when clock = '1' and reset = '1' and Output_E = '1' else  -- Reset active

                  2 when clock = '1' and reset = '1' and Output_E = '0' else  -- Reset active

                  3 when clock = '1' and reset = '0' and Output_E = '0' else  -- Disable output

                  4;

--data <= Data_in; --Need to convert the input standard logic input to a form that can be processed using arthimetic

Process (mode)

variable a, b, hash : real ; -- Variables for calculating the output

begin

case mode is

when 0 =>                    --Calculate the hash key of the current input value using the Data on the input vector

   hash := hash * a;

   hash := hash + data;

        a    := a * b;

when 2 =>

    hash := 0.0;                                        -- Reset 

         a:=378551.0;                                   -- Reset 

         b:=63689.0;                                    -- Reset

when 3=>                                                                -- Need to implement a disable output section

when OTHERS =>                                          -- Do nothing 

End case;

hash_o<= hash;                                          -- Assign the clculated hash value to the output

end process;

end RSHash;

--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 DJB of HashChain is

signal mode,

       data : integer;

begin

mode <= 0 when clock = '1' and reset = '0' and Output_E = '1' else  -- Active data being latched to output

        1 when clock = '0' and reset = '0' and Output_E = '1' else  -- No change to output till thge next clock

                  2 when clock = '1' and reset = '1' and Output_E = '1' else  -- Reset active

                  2 when clock = '1' and reset = '1' and Output_E = '0' else  -- Reset active

                  3 when clock = '1' and reset = '0' and Output_E = '0' else  -- Disable output

                  4;

--data <= Data_in; --Need to convert the input standard logic input to a form that can be processed using arthimetic

Process (mode)

variable a, b, hash : real ; -- Variables for calculating the output

begin

case mode is

when 0 =>                    --Calculate the hash key of the current input value using the Data on the input vector

        a := hash * 33.0;

   hash := a + hash + data;

when 2 =>

    hash := 5831.0;                             -- Reset 

when 3=>                                                                -- Need to implement a disable output section

when OTHERS =>                                          -- Do nothing 

End case;

hash_o<= hash;                                          -- Assign the clculated hash value to the output

end process;

end DJB;

--This algorithm was created for sdbm (a public-domain reimplementation of ndbm) database library.

--it was found to do well in scrambling bits, causing better distribution of the keys and fewer splits.

--it also happens to be a good general hashing function with good distribution. 

--the actual function is hash(i) = hash(i - 1) * 65599 + str[i];

architecture sdbm of HashChain is

signal mode,

       data : integer;

begin

mode <= 0 when clock = '1' and reset = '0' and Output_E = '1' else  -- Active data being latched to output

        1 when clock = '0' and reset = '0' and Output_E = '1' else  -- No change to output till thge next clock

                  2 when clock = '1' and reset = '1' and Output_E = '1' else  -- Reset active

                  2 when clock = '1' and reset = '1' and Output_E = '0' else  -- Reset active

                  3 when clock = '1' and reset = '0' and Output_E = '0' else  -- Disable output

                  4;

--data <= Data_in;           --Need to convert the input standard logic input to a form that can be processed using arthimetic

Process (mode)

variable a, b, hash : real ; -- Variables for calculating the output

begin

case mode is

when 0 =>                    --Calculate the hash key of the current input value using the Data on the input vector

        a := hash * 65599.0;

   hash := a + hash + data;

when 2 =>

    hash := 0.0;                                      -- Reset 

when 3=>                                                                -- Need to implement a disable output section

when OTHERS =>                                          -- Do nothing 

End case;

hash_o<= hash;                                          -- Assign the clculated hash value to the output

end process;

end sdbm;