If this was some generic checksum routine, you could add some validation (5.8+) 

sub checksum {
    my $s = shift;
    utf8::downgrade($s, 1)
        or croak("Wide character in subroutine entry");
    return unpack("%32C*", $s) % 65535;
}

[download]

For earlier backwards compatibility, that would be 

sub checksum {
    my $s = shift;
    if (defined(&utf8::downgrade)) {
        utf8::downgrade($s, 1)
            or croak("Wide character in subroutine entry");
    }
    return unpack("%32C*", $s) % 65535;
}

[download]

Update: Switched utf8->can() (method check) for defined(&) (sub check).

In reply to Re: Understanding pack and unpack changes for binary data between 5.8 and 5.10 by ikegami
in thread Understanding pack and unpack changes for binary data between 5.8 and 5.10 by dkg

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