Subversion Repositories srdydrdy_lib

/*

 *  Simple parameterized hash function

 *

 * Takes an input item and folds it back upon itself using xor

 * as a reduction function.  Works only for hash tables with

 * a natural power of 2.

 */

module basic_hashfunc

  #(parameter input_sz=48,

    parameter table_sz=1024,

    parameter fsz=clogb2(table_sz))

  (

   input [input_sz-1:0]  hf_in,

   output reg [fsz-1:0]  hf_out);

  //localparam folds = (input_sz/fsz) + ( (input_sz%fsz) == 0) ? 0 : 1;

  localparam folds = num_folds(input_sz, fsz);

  wire [folds*fsz-1:0]   tmp_array;

  assign tmp_array = hf_in;

  integer                f, b;

  always @*

    begin

      for (b=0; b<fsz; b=b+1)

        begin

          hf_out[b] = 0;

          for (f=0; f<folds; f=f+1)

            hf_out[b] = hf_out[b]^tmp_array[f*fsz+b];

        end

    end

  function integer num_folds;

    input [31:0] in_sz;

    input [31:0] func_sz;

    integer      tmp_in_sz;

    begin

      num_folds = 0;

      tmp_in_sz = in_sz;

      while (tmp_in_sz > 0)

        begin

          tmp_in_sz = tmp_in_sz - func_sz;

          num_folds = num_folds + 1;

        end

    end

  endfunction

  function integer clogb2;

    input [31:0] depth;

    integer      i;

    begin

      i = depth;

      for (clogb2=0; i>0; clogb2=clogb2+1)

        i = i >> 1;

    end

  endfunction // for

endmodule // hashfunc