code: @VisibleForTesting
    static File getFile(String[] localDirs, int subDirsPerLocalDir, String filename) {
      int hash = JavaUtils.nonNegativeHash(filename);
      String localDir = localDirs[hash % localDirs.length];
      int subDirId = (hash / localDirs.length) % subDirsPerLocalDir;
      return new File(createNormalizedInternedPathname(
          localDir, String.format("%02x", subDirId), filename));
    }
docs: Hashes a filename into the corresponding local directory, in a manner consistent with
  Spark's DiskBlockManager.getFile().