static S md5(String text) ctex {
  if (text == null) ret "-";
  return bytesToHex(md5_impl(text.getBytes("UTF-8"))); // maybe different than the way PHP does it...
}

static S md5(byte[] data) {
  if (data == null) ret "-";
  ret bytesToHex(md5_impl(data));
}

static MessageDigest md5_md;

/*static byte[] md5_impl(byte[] data) ctex {
  if (md5_md == null)
    md5_md = MessageDigest.getInstance("MD5");
  return ((MessageDigest) md5_md.clone()).digest(data);
}*/

static byte[] md5_impl(byte[] data) ctex {
  return MessageDigest.getInstance("MD5").digest(data);
}

static S md5(File file) {
  ret md5OfFile(file);
}