71. Arithmetic Logic Unit

How do you plan to solve it?

/*Write your code here*/
module alu4 (a,b,op,y,cf);
    input  [3:0] a,b;
    input  [2:0] op;
    output reg [3:0] y;
    output reg cf;
reg carry;
always @(*) begin
    y     = 4'b0000;
    cf    = 1'b0;
    carry = 1'b0;
    case (op)
        3'b000: begin // ADD
            {carry, y} = {1'b0, a} + {1'b0, b};
            cf = carry;
        end

    3'b001: begin // SUB
            {carry, y} = {1'b0, a} + {1'b0, ~b} + 1'b1;
            cf = ~carry;   // borrow
        end

    3'b010: begin // AND
            y  = a & b;
            cf = 1'b0;
        end

    3'b011: begin // OR
            y  = a | b;
            cf = 1'b0;
        end

    3'b100: begin // XOR
            y  = a ^ b;
            cf = 1'b0;
        end

    default: begin
            y  = 4'b0000;
            cf = 1'b0;
        end
    endcase
end

endmodule