my @zcells = ( ($k1 = pack 'i2', $x1, $y1) x !exists($cells->{$k1}), ($k2 = pack 'i2', $x1, $y0) x !exists($cells->{$k2}), ($k3 = pack 'i2', $x1, $y2) x !exists($cells->{$k3}), ($k4 = pack 'i2', $x0, $y1) x !exists($cells->{$k4}), ($k5 = pack 'i2', $x0, $y2) x !exists($cells->{$k5}), ($k6 = pack 'i2', $x2, $y1) x !exists($cells->{$k6}), ($k7 = pack 'i2', $x2, $y0) x !exists($cells->{$k7}), ($k8 = pack 'i2', $x2, $y2) x !exists($cells->{$k8}) );