private String getSubdirectoryPath(String resourceId) {
    String subdirectory = String.valueOf(Math.abs(resourceId.hashCode() % SHARDING_BUCKET_COUNT));
    return mVersionDirectory + File.separator + subdirectory;
  }
Gets the directory to use to store the given key

@param resourceId the id of the file we're going to store
@return the directory to store the file in
imagepipeline-base/src/main/java/com/facebook/cache/disk/DefaultDiskStorage.java