// next-state logic for read and write pointers
always @*
    begin
    // successive pointer values
    w_ptr_succ = w_ptr_reg + 1;
    r_ptr_succ = r_ptr_reg + 1;
    // default: keep old values
    w_ptr_next = w_ptr_reg;
    r_ptr_next = r_ptr_reg;
    full_next = full_reg;
    empty_next = empty_reg;
    case ({wr, rd})
    // 2'b00: no op
        2'b01: // read
        if (~empty_reg) // not empty
            begin
            r_ptr_next = r_ptr_succ;
            full_next = 1'b0;
            if (r_ptr_succ==w_ptr_reg)
                empty_next = 1'b1;
            end
        2'b10: // write
        if (~full_reg) // not full
            begin
            w_ptr_next = w_ptr_succ ;
            empty_next = 1'b0;
            if (w_ptr_succ==r_ptr_reg)
                full_next = 1'b1;
            end
        2'b11: // write and read
            begin
            w_ptr_next = w_ptr_succ;
            r_ptr_next = r_ptr_succ;
            end
    endcase
end
// output
assign full = full_reg;
assign empty = empty_reg;

endmodule