private int toPageIndex(final long offsetInFile) {
    final int pageIndex = (int)(offsetInFile / pageSize);
    if (pageIndex < 0) {
      throw new AssertionError("pageIndex(offset: " + offsetInFile + ") = " + pageIndex + ", but must be >=0");
    }
    return pageIndex;
  }
private int toPageIndex(final long offsetInFile)