/*
 * This block chooses max value from inputs
 * and assigns it to the output.
 */
module poolling_layer_unit(in, out);
    input[7:0] in[0:3];
    output[7:0] out;

    /*
     * 8-digit comparator with only one output b>=a.
     */
    module comparator(a, b, out);
        input[7:0] a;
        input[7:0] b;
        output out;

        assign out = ~a[7]&b[7]|(~(a[7]^b[7]))&
                         (~a[6]&b[6]|(~(a[6]^b[6]))&
                         (~a[5]&b[5]|(~(a[5]^b[5]))&
                         (~a[4]&b[4]|(~(a[4]^b[4]))&
                         (~a[3]&b[3]|(~(a[3]^b[3]))&
                         (~a[2]&b[2]|(~(a[2]^b[2]))&
                         (~a[1]&b[1]|(~(a[1]^b[1]))&
                         (~a[0]&b[0]|(~(a[0]^b[0])))))))));

    endmodule //comparator

    wire out_01;
    wire out_23;
    wire out_0123;
    wire[7:0] in_01;
    wire[7:0] in_23;

    comparator cmp01(in[0], in[1], out_01);
    comparator cmp34(in[2], in[3], out_23);
    comparator cmp(in_01, in_23, out_0123);

    always @ (in[0], in[1], in[2], in[3]) begin
        in_01 = in[0] & ~out_01 | in[1] & out_01;
        in_23 = in[2] & ~out_23 | in[3] & out_23;
        out = in[0] & ~out_0123 & ~in_01 |
                in[1] & ~out_0123 & in_01 |
                in[2] & out_0123 & ~in_23 |
                in[3] & out_0123 & in_23;
    end

endmodule //poolling_layer_unit