.. efun:: string and_bits(string str1, string str2)

  :arg:`str1` and :arg:`str2` are both bitstrings. The result of the function is a bitstring with the binary-and of :arg:`str1` and :arg:`str2`, ie. a string in which a bit is set only if both corresponding bits in the input strings are set, too.

  .. usage::

    ::

      string s1, s2, s3;

      s1 = set_bit("", 3); s1 = set_bit(s1, 15);  -> s1 is "( ("
      s2 = set_bit("", 3); s2 = set_bit(s2, 4);   -> s2 is "8"

      s3 = and_bits(s1, s2);

      -> s3 is now "8", ie. a bitstring with bit 3 set only.

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