code: public LongBigList signatures(final int signatureWidth, final ProgressLogger pl) throws IOException {
  		final LongBigList signatures = LongArrayBitVector.getInstance().asLongBigList(signatureWidth);
  		final long signatureMask = -1L >>> Long.SIZE - signatureWidth;
  		signatures.size(size());
  		pl.expectedUpdates = size();
  		pl.itemsName = "signatures";
  		pl.start("Signing...");
  		for (final ChunkedHashStore.Chunk chunk : this) {
  			final Iterator<long[]> chunkIterator = chunk.iterator();
  			for(int i = chunk.size(); i-- != 0;) {
  				final long[] quadruple = chunkIterator.next();
  				signatures.set(quadruple[3], signatureMask & quadruple[0]);
  				pl.lightUpdate();
  			}
  		}
  		pl.done();
  		return signatures;
  	}
docs: Generate a list of signatures using the lowest bits of the first hash in this store.
  
  <p>For this method to work, this store must contain ranks.
  
  @param signatureWidth the width in bits of the signatures.
  @param pl a progress logger.