sub aristotle {
	my $str = shift;
	my $rts = reverse $str;

	my $palindrome = '';
	for my $rotate_count ( 0 .. length( $str ) - 1 ) {
		my $mask = $str ^ $rts;

		# to distinguish adjacent palindromes
		substr $mask, $rotate_count, 0, "\1";

		while( $mask =~ /\0{3,}/g ) {
			my $len = $+[0] - $-[0];
			next if $len <= length $palindrome;
			my $offs = $-[0];
			--$offs if $offs > $rotate_count; # compensate for marker
			$palindrome = substr $str, $offs, $len;
		}

		substr $rts, 0, 0, chop $rts;
	}

	return $palindrome;
}