private static void mergeInto()

in src/main/java/org/apache/datasketches/cpc/CpcUnion.java [278:338]
48 lines of code
16 McCabe index (conditional complexity)

  private static void mergeInto(final CpcUnion union, final CpcSketch source) {
    if (source == null) { return; }
    checkSeeds(union.seed, source.seed);

    final int sourceFlavorOrd = source.getFlavor().ordinal();
    if (sourceFlavorOrd == 0) { return; } //EMPTY

    //Accumulator and bitMatrix must be mutually exclusive,
    //so bitMatrix != null => accumulator == null and visa versa
    //if (Accumulator != null) union must be EMPTY or SPARSE,
    checkUnionState(union);

    if (source.lgK < union.lgK) { reduceUnionK(union, source.lgK); }

    // if source is past SPARSE mode, make sure that union is a bitMatrix.
    if ((sourceFlavorOrd > 1) && (union.accumulator != null)) {
      union.bitMatrix = CpcUtil.bitMatrixOfSketch(union.accumulator);
      union.accumulator = null;
    }

    final int state = ((sourceFlavorOrd - 1) << 1) | ((union.bitMatrix != null) ? 1 : 0);
    switch (state) {
      case 0 : { //A: Sparse, bitMatrix == null, accumulator valid
        if (union.accumulator == null) {
          //CodeQL could not figure this out so I have to insert this.
          throw new SketchesStateException("union.accumulator can never be null here.");
        }
        if ((union.accumulator.getFlavor() == EMPTY)
            && (union.lgK == source.lgK)) {
          union.accumulator = source.copy();
          break;
        }
        walkTableUpdatingSketch(union.accumulator, source.pairTable);
        // if the accumulator has graduated beyond sparse, switch union to a bitMatrix
        if (union.accumulator.getFlavor().ordinal() > 1) {
          union.bitMatrix = CpcUtil.bitMatrixOfSketch(union.accumulator);
          union.accumulator = null;
        }
        break;
      }
      case 1 : { //B: Sparse, bitMatrix valid, accumulator == null
        orTableIntoMatrix(union.bitMatrix, union.lgK, source.pairTable);
        break;
      }
      case 3 :   //C: Hybrid, bitMatrix valid, accumulator == null
      case 5 : { //C: Pinned, bitMatrix valid, accumulator == null
        orWindowIntoMatrix(union.bitMatrix, union.lgK, source.slidingWindow,
            source.windowOffset, source.lgK);
        orTableIntoMatrix(union.bitMatrix, union.lgK, source.pairTable);
        break;
      }
      case 7 : { //D: Sliding, bitMatrix valid, accumulator == null
        // SLIDING mode involves inverted logic, so we can't just walk the source sketch.
        // Instead, we convert it to a bitMatrix that can be OR'ed into the destination.
        final long[] sourceMatrix = CpcUtil.bitMatrixOfSketch(source);
        orMatrixIntoMatrix(union.bitMatrix, union.lgK, sourceMatrix, source.lgK);
        break;
      }
      default: throw new SketchesStateException("Illegal Union state: " + state);
    }
  }