module bin2gray4(bin_in,gray_out);
input [3:0]bin_in;
output wire [3:0]gray_out;
// assign gray_out[3:0]={bin_in[3],bin_in[3]^bin_in[2],bin_in[2]^bin_in[1],bin_in[1]^bin_in[0]}
assign gray_out[3]=bin_in[3];
assign gray_out[2]=bin_in[3]^bin_in[2];
assign gray_out[1]=bin_in[2]^bin_in[1];
assign gray_out[0]=bin_in[1]^bin_in[0];
endmodule