static long indexOfBytesInFile(File f, byte[] data) ctex {
  int b, l = l(data);
  CircularByteBuffer buf = new(l);
  temp BufferedInputStream in = bufferedFileInputStream(f);
  long counter = 0;
  bigLoop: while ((b = in.read()) >= 0) {
    buf.add((byte) b);
    ++counter;
    if (buf.size() >= l) {
      long start = counter-l;
      for i to l: {
        if (buf.get(start+i) != data[i])
          continue bigLoop;
      }
      ret start;
    }
  }
  ret -1;
}