-- Copyright (C) 1996 Morgan Kaufmann Publishers, Inc

-- This file is part of VESTs (Vhdl tESTs).

-- VESTs 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. 

-- VESTs 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 VESTs; if not, write to the Free Software Foundation,
-- Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 

-- ---------------------------------------------------------------------
--
-- $Id: ch_15_alu-b.vhd,v 1.3 2001-10-26 16:29:35 paw Exp $
-- $Revision: 1.3 $
--
-- ---------------------------------------------------------------------

library bv_utilities;
use bv_utilities.bv_arithmetic.all;

architecture behavior of alu is

begin

  alu_op: process ( s1, s2, func ) is

                                     variable bv_s1, bv_s2 : dlx_bv_word;
                                   variable temp_result : dlx_bv_word;
                                   variable temp_overflow : boolean;

                                   type boolean_to_X01_table is array (boolean) of X01;
                                   constant boolean_to_X01 : boolean_to_X01_table := ( '0', '1' );

  begin
    bv_s1 := To_bitvector(s1);
    bv_s2 := To_bitvector(s2);
    temp_overflow := false;
    case func is
      when alu_pass_s1 =>
        temp_result := bv_s1;
      when alu_pass_s2 =>
        temp_result := bv_s2;
      when alu_and =>
        temp_result := bv_s1 and bv_s2;
      when alu_or =>
        temp_result := bv_s1 or bv_s2;
      when alu_xor =>
        temp_result := bv_s1 xor bv_s2;
      when alu_sll =>
        temp_result := bv_s1 sll bv_to_natural(bv_s2(27 to 31));
      when alu_srl =>
        temp_result := bv_s1 srl bv_to_natural(bv_s2(27 to 31));
      when alu_sra =>
        temp_result := bv_s1 sra bv_to_natural(bv_s2(27 to 31));
      when alu_add =>
        bv_add(bv_s1, bv_s2, temp_result, temp_overflow);
      when alu_addu =>
        bv_addu(bv_s1, bv_s2, temp_result, temp_overflow);
      when alu_sub =>
        bv_sub(bv_s1, bv_s2, temp_result, temp_overflow);
      when alu_subu =>
        bv_subu(bv_s1, bv_s2, temp_result, temp_overflow);
      when others =>
	report "illegal function code" severity error;
	temp_result := X"0000_0000";
    end case;
    result <= To_X01(temp_result) after Tpd;
    zero <= boolean_to_X01(temp_result = X"0000_0000") after Tpd;
    negative <= To_X01(temp_result(0)) after Tpd;
    overflow <= boolean_to_X01(temp_overflow) after Tpd;
  end process alu_op;

end architecture behavior;