def add_global(message)
      unless (slot = @entries.index { |e| e.nil? })
        # No more free slots. We have to find the least recently used one.
        slot = 0
        0.upto(15) do |i|
          if i != slot && @entries[slot].last_use > @entries[i].last_use
            slot = i
          end
        end
      end
      @entries[slot] = Entry.new(message, Time.now)

      slot
    end
def add_global(message)
      unless (slot = @entries.index { |e| e.nil? })
        # No more free slots. We have to find the least recently used one.
        slot = 0
        0.upto(15) do |i|
          if i != slot && @entries[slot].last_use > @entries[i].last_use
            slot = i
          end
        end
      end
      @entries[slot] = Entry.new(message, Time.now)

      slot
    end
Add a new GlobalFitMessage to the mapper and return the local message
 number.