HDLbits: Mux9to1v

题目：Create a 16-bit wide, 9-to-1 multiplexer. sel=0 chooses a, sel=1 chooses b, etc. For the unused cases (sel=9 to 15), set all output bits to '1'.

我的答案：

module top_module( 
    input [15:0] a, b, c, d, e, f, g, h, i,
    input [3:0] sel,
    output [15:0] out );
    always@(*)
        case(sel)
            4'b0000: out = a;
            4'b0001: out = b;
            4'b0010: out = c;
            4'b0011: out = d;
            4'b0100: out = e;
            4'b0101: out = f;
            4'b0110: out = g;
            4'b0111: out = h;
            4'b1000: out = i;
            4'b1001: out = 16'b1111111111111111;
            4'b1010: out = 16'b1111111111111111;
            4'b1011: out = 16'b1111111111111111;
            4'b1100: out = 16'b1111111111111111;
            4'b1101: out = 16'b1111111111111111;
            4'b1110: out = 16'b1111111111111111;
            4'b1111: out = 16'b1111111111111111;
        endcase
endmodule

网站答案：

module top_module (
	input [15:0] a,
	input [15:0] b,
	input [15:0] c,
	input [15:0] d,
	input [15:0] e,
	input [15:0] f,
	input [15:0] g,
	input [15:0] h,
	input [15:0] i,
	input [3:0] sel,
	output logic [15:0] out
);

	// Case statements can only be used inside procedural blocks (always block)
	// This is a combinational circuit, so use a combinational always @(*) block.
	always @(*) begin
		out = '1;		// '1 is a special literal syntax for a number with all bits set to 1.
						// '0, 'x, and 'z are also valid.
						// I prefer to assign a default value to 'out' instead of using a
						// default case.
		case (sel)
			4'h0: out = a;
			4'h1: out = b;
			4'h2: out = c;
			4'h3: out = d;
			4'h4: out = e;
			4'h5: out = f;
			4'h6: out = g;
			4'h7: out = h;
			4'h8: out = i;
		endcase
	end
	
endmodule