code: public DenseHll mergeWith(DenseHll other)
      {
          if (indexBitLength != other.indexBitLength) {
              throw new IllegalArgumentException(String.format(
                      "Cannot merge HLLs with different number of buckets: %s vs %s",
                      numberOfBuckets(indexBitLength),
                      numberOfBuckets(other.indexBitLength)));
          }
  
          int baseline = Math.max(this.baseline, other.baseline);
          int baselineCount = 0;
  
          int overflows = 0;
          int[] overflowBuckets = new int[OVERFLOW_GROW_INCREMENT];
          byte[] overflowValues = new byte[OVERFLOW_GROW_INCREMENT];
  
          int numberOfBuckets = numberOfBuckets(indexBitLength);
          for (int i = 0; i < numberOfBuckets; i++) {
              int value = Math.max(getValue(i), other.getValue(i));
  
              int delta = value - baseline;
              if (delta == 0) {
                  baselineCount++;
              }
              else if (delta > MAX_DELTA) {
                  // grow overflows arrays if necessary
                  overflowBuckets = Ints.ensureCapacity(overflowBuckets, overflows + 1, OVERFLOW_GROW_INCREMENT);
                  overflowValues = Bytes.ensureCapacity(overflowValues, overflows + 1, OVERFLOW_GROW_INCREMENT);
  
                  overflowBuckets[overflows] = i;
                  overflowValues[overflows] = (byte) (delta - MAX_DELTA);
  
                  overflows++;
  
                  delta = MAX_DELTA;
              }
  
              setDelta(i, delta);
          }
  
          this.baseline = (byte) baseline;
          this.baselineCount = baselineCount;
          this.overflows = overflows;
          this.overflowBuckets = overflowBuckets;
          this.overflowValues = overflowValues;
  
          // all baseline values in one of the HLLs lost to the values
          // in the other HLL, so we need to adjust the final baseline
          adjustBaselineIfNeeded();
  
          return this;
      }
docs: Returns "this" for chaining