code: public double lookupPosterior( int value ) {
  		TldFernFeature found = table[value];
  		if( found == null ) {
  			return 0;
  		}
  		return found.posterior;
  	}
docs: Looks up the posterior probability of the specified fern.  If a fern is found its posterior is returned
  otherwise -1 is returned.
  
  NOTE: How unknown values are handled is a deviation from the paper.
  
  @param value The fern's value
  @return Fern's posterior probability.  If the value is known then return -1