//2024-1-11 姜青羊
//case语句实现多路选择逻辑

`timescale 1ns/10ps
module fn_sw (
                        a,
                        b,
                        sel,
                        y
                    );

input                   a,b;
input[1:0]              sel;

output                  y;
reg                     y;

always @(*)
begin
    case (sel)
    2'b00: begin  y<=a&b;    end
    2'b01: begin  y<=a|b;    end
    2'b10: begin  y<=a^b;    end
    2'b11: begin  y<=~(a^b); end
    endcase
end
    
endmodule


//---------testbench----------
module tb_fn_sw ();

reg                     aa,bb;
reg[1:0]                ss;

initial begin
                        ss=00; aa=0; bb=0;
                #10     ss=00; aa=0; bb=1;
                #10     ss=00; aa=1; bb=0;
                #10     ss=00; aa=1; bb=1;
                #10     ss=01; aa=0; bb=0;
                #10     ss=01; aa=0; bb=1;
                #10     ss=01; aa=1; bb=0;
                #10     ss=01; aa=1; bb=1;
                #10     ss=10; aa=0; bb=0;
                #10     ss=10; aa=0; bb=1;
                #10     ss=10; aa=1; bb=0;
                #10     ss=10; aa=1; bb=1;
                #10     ss=11; aa=0; bb=0;
                #10     ss=11; aa=0; bb=1;
                #10     ss=11; aa=1; bb=0;
                #10     ss=11; aa=1; bb=1;
                        $stop;
end

fn_sw u_fn_sw (
                        .a(aa),
                        .b(bb),
                        .sel(ss),
                        .y(yy)
                    );

endmodule