SYNOPSIS
        string xor_bits(string str1, string str2)

DESCRIPTION
        <str1> and <str2> are both bitstrings. The result of the function
        is a bitstring with the binary-xor of <str1> and <str2>,
        ie. a string in which a bit is set only if the corresponding
        bits in either <str1> or <str2> (but not both) is set.

EXAMPLES
        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 = xor_bits(s1, s2);

        -> s3 is now "0 (", ie. a bitstring with bits 4 and 15 set.

SEE ALSO
        clear_bit(E), set_bit(E), test_bit(E), next_bit(E), last_bit(E),
        count_bits(E), and_bits(E), or_bits(E), invert_bits(E), copy_bits(E)