code: public static byte[] buildRollupQualifier(final long timestamp,
                                              final short flags,
                                              final int aggregator_id,
                                              final RollupInterval interval) {
      return buildRollupQualifier(timestamp, 
          getRollupBasetime(timestamp, interval), flags, aggregator_id, interval);
    }
docs: Builds a rollup column qualifier, prepending the appender as a string
  then the offeset on 2 bytes for the interval after a colon with the last
  four bits reserved for the length and type flags. I.e.
  {@code <agg>:<offset(flag)>
  n  :  2 bytes }
  @param timestamp The data point timestamp
  @param flags The length and type (float || int) flags for the value
  @param aggregator_id The numeric ID of the aggregator the value maps to.
  @param interval The RollupInterval object with data about the interval
  @return An n byte array to use as the qualifier
  @throws IllegalArgumentException if the aggregator is null or empty or the
  timestamp is too far from the base time to fit within the interval.