public ImmutableBitSet getFactorsRefByFactor(int factIdx) {
    return requireNonNull(factorsRefByFactor, "factorsRefByFactor")[factIdx];
  }
Returns a bitmap corresponding to the factors referenced by the specified
factor in the various join filters that correspond to comparisons.

@param factIdx Factor for which information will be returned
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/rules/HiveLoptMultiJoin.java