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//////////////////////////////////////////////////////////////////

//                                                              //

//  Arithmetic Logic Unit (ALU) for Amber 25 Core               //

//                                                              //

//  This file is part of the Amber project                      //

//  http://www.opencores.org/project,amber                      //

//                                                              //

//  Description                                                 //

//  Supported functions: 32-bit add and subtract, AND, OR,      //

//  XOR, NOT, Zero extent 8-bit numbers                         //

//                                                              //

//  Author(s):                                                  //

//      - Conor Santifort, csantifort.amber@gmail.com           //

//                                                              //

//////////////////////////////////////////////////////////////////

//                                                              //

// Copyright (C) 2011 Authors and OPENCORES.ORG                 //

//                                                              //

// This source file may be used and distributed without         //

// restriction provided that this copyright statement is not    //

// removed from the file and that any derivative work contains  //

// the original copyright notice and the associated disclaimer. //

//                                                              //

// This source file is free software; you can redistribute it   //

// and/or modify it under the terms of the GNU Lesser General   //

// Public License as published by the Free Software Foundation; //

// either version 2.1 of the License, or (at your option) any   //

// later version.                                               //

//                                                              //

// This source 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 Lesser General Public License for more //

// details.                                                     //

//                                                              //

// You should have received a copy of the GNU Lesser General    //

// Public License along with this source; if not, download it   //

// from http://www.opencores.org/lgpl.shtml                     //

//                                                              //

//////////////////////////////////////////////////////////////////

module a25_alu (

input       [31:0]          i_a_in,

input       [31:0]          i_b_in,

input                       i_barrel_shift_carry,

input                       i_status_bits_carry,

input       [8:0]           i_function,

output      [31:0]          o_out,

output      [3:0]           o_flags

);

wire     [31:0]         a, b, b_not;

wire     [31:0]         and_out, or_out, xor_out;

wire     [31:0]         sign_ex8_out, sign_ex_16_out;

wire     [31:0]         zero_ex8_out, zero_ex_16_out;

wire     [32:0]         fadder_out;

wire                    swap_sel;

wire                    not_sel;

wire     [1:0]          cin_sel;

wire                    cout_sel;

wire     [3:0]          out_sel;

wire                    carry_in;

wire                    carry_out;

wire                    overflow_out;

wire                    fadder_carry_out;

assign  { swap_sel, not_sel, cin_sel, cout_sel, out_sel } = i_function;

// ========================================================

// A Select

// ========================================================

assign a     = (swap_sel ) ? i_b_in : i_a_in ;

// ========================================================

// B Select

// ========================================================

assign b     = (swap_sel ) ? i_a_in : i_b_in ;

// ========================================================

// Not Select

// ========================================================

assign b_not     = (not_sel ) ? ~b : b ;

// ========================================================

// Cin Select

// ========================================================

assign carry_in  = (cin_sel==2'd0 ) ? 1'd0                   :

                   (cin_sel==2'd1 ) ? 1'd1                   :

                                      i_status_bits_carry    ;  // add with carry

// ========================================================

// Cout Select

// ========================================================

assign carry_out = (cout_sel==1'd0 ) ? fadder_carry_out     :

                                       i_barrel_shift_carry ;

// For non-addition/subtractions that incorporate a shift 

// operation, C is set to the last bit

// shifted out of the value by the shifter.

// ========================================================

// Overflow out

// ========================================================

// Only assert the overflow flag when using the adder

assign  overflow_out    = out_sel == 4'd1 &&

                            // overflow if adding two positive numbers and get a negative number

                          ( (!a[31] && !b_not[31] && fadder_out[31]) ||

                            // or adding two negative numbers and get a positive number

                            (a[31] && b_not[31] && !fadder_out[31])     );

// ========================================================

// ALU Operations

// ========================================================

`ifdef XILINX_FPGA

    // XIlinx Spartan 6 DSP module

    `ifdef XILINX_SPARTAN6_FPGA

        xs6_addsub_n #(.WIDTH(33))

    `endif

    `ifdef XILINX_VIRTEX6_FPGA

        xv6_addsub_n #(.WIDTH(33))

    `endif

        u_xx_addsub_33(

        .i_a    ( {1'd0,a}      ),

        .i_b    ( {1'd0,b_not}  ),

        .i_cin  ( carry_in      ),

        .i_sub  ( 1'd0          ),

        .o_sum  ( fadder_out    ),

        .o_co   (               )

    );

`else

assign fadder_out       = { 1'd0,a} + {1'd0,b_not} + {32'd0,carry_in};

`endif

assign fadder_carry_out = fadder_out[32];

assign and_out          = a & b_not;

assign or_out           = a | b_not;

assign xor_out          = a ^ b_not;

assign zero_ex8_out     = {24'd0,  b_not[7:0]};

assign zero_ex_16_out   = {16'd0,  b_not[15:0]};

assign sign_ex8_out     = {{24{b_not[7]}},  b_not[7:0]};

assign sign_ex_16_out   = {{16{b_not[15]}}, b_not[15:0]};

// ========================================================

// Out Select

// ========================================================

assign o_out = out_sel == 4'd0 ? b_not            :

               out_sel == 4'd1 ? fadder_out[31:0] :

               out_sel == 4'd2 ? zero_ex_16_out   :

               out_sel == 4'd3 ? zero_ex8_out     :

               out_sel == 4'd4 ? sign_ex_16_out   :

               out_sel == 4'd5 ? sign_ex8_out     :

               out_sel == 4'd6 ? xor_out          :

               out_sel == 4'd7 ? or_out           :

                                 and_out          ;

assign o_flags       = {  o_out[31],      // negative

                         |o_out == 1'd0,  // zero

                         carry_out,       // carry

                         overflow_out     // overflow

                         };

endmodule