use Encode qw( encode_utf8 );
my $x = chr(1 << 63);
print length($x), "\n";
print length(encode_utf8($x)), "\n";
print "yep\n" if $x gt chr(255);

##</code><code>##

Use of code point 0x8000000000000000 is deprecated; the permissible max is 0x7FFFFFFFFFFFFFFF at foo line 2.
1
13
yep