// adding a zip64 extra in the local header (too late anyway).
	var buf []byte
	if w.isZip64() {
		buf = make([]byte, dataDescriptor64Len)
	} else {
		buf = make([]byte, dataDescriptorLen)
	}
	b := writeBuf(buf)
	b.uint32(dataDescriptorSignature) // de-facto standard, required by OS X
	b.uint32(w.CRC32)
	if w.isZip64() {
		b.uint64(w.CompressedSize64)
		b.uint64(w.UncompressedSize64)
	} else {

	if mode&fs.ModeDir != 0 {
		h.ExternalAttrs |= msdosDir
	}
	if mode&0200 == 0 {
		h.ExternalAttrs |= msdosReadOnly
	}
}

// isZip64 reports whether the file size exceeds the 32 bit limit
func (h *FileHeader) isZip64() bool {
	return h.CompressedSize64 >= uint32max || h.UncompressedSize64 >= uint32max
}

func (h *FileHeader) hasDataDescriptor() bool {
	return h.Flags&0x8 != 0
}