pack("Yv", -1);      # yields "ffff"
  pack("YN", -1);      # yields "ffffffff"
  pack("Y[X]v", -1);   # maybe yields "FFFF"
  pack("Y[o]v", -1);   # maybe yields "177777"
  pack("Y[b]c", 15);   # maybe yields "00001111"