svoid saveBinaryFilePart(S path, long start, byte[] data) {
  saveBinaryFilePart(newFile(path), start, data);
}

svoid saveBinaryFilePart(File f, long start, byte[] data) {
  RandomAccessFile raf = new RandomAccessFile(f, "rw");
  try {
    raf.seek(start);
    raf.write(data);
  } finally {
    raf.close();
  }
}