    # File lib/gettext/mo.rb, line 208
      def save_to_stream(io)
        #Save data as little endian format.
        header_size = 4 * 7
        table_size  = 4 * 2 * size

        hash_table_size = next_prime((size * 4) / 3)
        hash_table_size = 3 if hash_table_size <= 2
        header = Header.new(
          MAGIC_LITTLE_ENDIAN,          # magic
          0,                            # revision
          size,                         # nstrings
          header_size,                  # orig_table_offset
          header_size + table_size,     # translated_table_offset
          hash_table_size,              # hash_table_size
          header_size + table_size * 2  # hash_table_offset
        )
        io.write(header.to_a.pack('a4V*'))

        ary = to_a
        ary.sort!{|a, b| a[0] <=> b[0]} # sort by original string

        pos = header.hash_table_size * 4 + header.hash_table_offset

        orig_table_data = Array.new()
        ary.each{|item, _|
          orig_table_data.push(item.size)
          orig_table_data.push(pos)
          pos += item.size + 1 # +1 is <NUL>
        }
        io.write(orig_table_data.pack('V*'))

        trans_table_data = Array.new()
        ary.each{|_, item|
          trans_table_data.push(item.size)
          trans_table_data.push(pos)
          pos += item.size + 1 # +1 is <NUL>
        }
        io.write(trans_table_data.pack('V*'))

        hash_tab = Array.new(hash_table_size)
        j = 0
        ary[0...size].each {|key, _|
          hash_val = hash_string(key)
          idx = hash_val % hash_table_size
          if hash_tab[idx] != nil
            incr = 1 + (hash_val % (hash_table_size - 2))
            begin
              if (idx >= hash_table_size - incr)
                idx -= hash_table_size - incr
              else
                idx += incr
              end
            end until (hash_tab[idx] == nil)
          end
          hash_tab[idx] = j + 1
          j += 1
        }
        hash_tab.collect!{|i| i ? i : 0}

        io.write(hash_tab.pack('V*'))

        ary.each{|item, _| io.write(item); io.write("\0") }
        ary.each{|_, item| io.write(item); io.write("\0") }

        self
      end