code: private String getSegmentFileName(long currentId, long previousId) {
          return PbdSegmentName.createName(m_nonce, currentId, previousId, false);
      }
docs: Return a segment file name from m_nonce and current + previous segment ids.
  
  @see parseFiles for file name structure
  @param currentId   current segment id
  @param previousId  previous segment id
  @return  segment file name