.. efun:: int last_bit(string str)

  Return the number of the last set bit in bitstring :arg:`str`.

  Each character contains 6 bits. So you can store a value between 0 and 63 in one character (2^6=64). Starting character is the blank :char:`SPACE` which has the value 0. The first character in the string is the one with the lowest bits (0-5).

  .. usage::

    ::

      string s;

      s = set_bit("", 4);
      s = set_bit(s, 2);

      last_bit(s) // returns 4

  .. seealso:: :efun:`set_bit`, :efun:`clear_bit`, :efun:`next_bit`, :efun:`test_bit`, :efun:`count_bits`, :efun:`and_bits`, :efun:`or_bits`, :efun:`xor_bits`, :efun:`invert_bits`, :efun:`copy_bits`