`include "../Defines.v"

module ex(input wire rst,
          input wire[`AluOpBus] aluop_i,
          input wire[`AluSelBus] alusel_i,
          input wire[`RegBus] reg1_i,
          input wire[`RegBus] reg2_i,
          input wire[`RegAddrBus] wd_i,
          input wire wreg_i,
          output reg[`RegAddrBus] wd_o,
          output reg wreg_o,
          output reg[`RegBus] wdata_o);
    
    reg[`RegBus] logicout;
    reg[`RegBus] shiftres;
    
    always @ (*) begin
        if (rst == `RstEnable) begin
            logicout <= `ZeroWord;
            end else begin
            case (aluop_i)
                `EXE_OR_OP:
                begin
                    logicout <= reg1_i | reg2_i;
                end
                `EXE_AND_OP:
                begin
                    logicout <= reg1_i & reg2_i;
                end
                `EXE_NOR_OP:
                begin
                    logicout <= ~(reg1_i |reg2_i);
                end
                `EXE_XOR_OP:
                begin
                    logicout <= reg1_i ^ reg2_i;
                end
                default:
                begin
                    logicout <= `ZeroWord;
                end
            endcase
        end
    end
    
    always @ (*) begin
        if (rst == `RstEnable) begin
            shiftres <= `ZeroWord;
            end else begin
            case (aluop_i)
                `EXE_SLL_OP:			begin
                    shiftres <= reg2_i << reg1_i[4:0] ;
                end
                `EXE_SRL_OP:		begin
                    shiftres <= reg2_i >> reg1_i[4:0];
                end
                `EXE_SRA_OP:		begin
                    shiftres <= ({32{reg2_i[31]}} << (6'd32-{1'b0, reg1_i[4:0]}))
                    | reg2_i >> reg1_i[4:0];
                end
                default:				begin
                    shiftres <= `ZeroWord;
                end
            endcase
        end
    end
    
    always @ (*) begin
        wd_o   <= wd_i;
        wreg_o <= wreg_i;
        case (alusel_i)
            `EXE_RES_LOGIC:		begin
                wdata_o <= logicout;
            end
            `EXE_RES_SHIFT:		begin
                wdata_o <= shiftres;
            end
            default:					begin
                wdata_o <= `ZeroWord;
            end
        endcase
    end
    
endmodule