for my $r ( [-123456789, 987654321], [1,2] ) {
   my $pp = pack 'ii', @{$r};
   my $jj = join ':', @{$r};
   my $pplen = length $pp;
   my $jjlen = length $jj;
   print "$r->[0]:$r->[1] packlen=$pplen joinlen=$jjlen\n";
   my ($xpp, $ypp) = unpack 'ii', $pp;
   my ($xjj, $yjj) = split /:/, $jj;
   $xpp == $r->[0] or die;
   $ypp == $r->[1] or die;
   $xjj == $r->[0] or die;
   $yjj == $r->[1] or die;
}