use constant CAN_PACK_QUADS => !! eval { my $f = pack 'q'; 1 };
sub Int64  { unpack( ( CAN_PACK_QUADS  ? 'q<' : 'a8' ), $_[-1] ) }
sub UInt64 { unpack( ( CAN_PACK_QUADS  ? 'Q<' : 'a8' ), $_[-1] ) }