code: public static LongBigArrayBigList index(final InputStream in, final ProgressLogger pl) throws IOException {
  		final LongBigArrayBigList pointers = new LongBigArrayBigList();
  		long current = 0;
  		final GZIPArchiveReader gzar = new GZIPArchiveReader(in);
  		GZIPArchive.ReadEntry re;
  		for (;;) {
  			re = gzar.skipEntry();
  			if (re == null) break;
  			pointers.add(current);
  			current += re.compressedSkipLength;
  			if (pl != null) pl.lightUpdate();
  		}
  		in.close();
  		return pointers;
  	}
docs: Returns a list of pointers to a GZIP archive entries positions (including the end of file).
  
  @param in the stream from which to read the GZIP archive.
  @param pl a progress logger.
  @return a list of longs where the <em>i</em>-th long is the offset in the stream of the first byte of the <em>i</em>-th archive entry.