static UpdateDoublesSketch updateLogic()

in src/main/java/org/apache/datasketches/quantiles/DoublesUnionImpl.java [159:247]
83 lines of code
28 McCabe index (conditional complexity)

  static UpdateDoublesSketch updateLogic(final int myMaxK, final UpdateDoublesSketch myQS,
                                         final DoublesSketch other) {
    int sw1 = ((myQS  == null) ? 0 :  myQS.isEmpty() ? 4 : 8);
    sw1 |=    ((other == null) ? 0 : other.isEmpty() ? 1 : 2);
    int outCase = 0; //0=null, 1=NOOP, 2=copy, 3=merge

    switch (sw1) {
      case 0:  outCase = 0; break; //myQS = null,  other = null ; return null
      case 1:  outCase = 4; break; //myQS = null,  other = empty; create empty-heap(myMaxK)
      case 2:  outCase = 2; break; //myQS = null,  other = valid; stream or downsample to myMaxK
      case 4:  outCase = 1; break; //myQS = empty, other = null ; no-op
      case 5:  outCase = 1; break; //myQS = empty, other = empty; no-op
      case 6:  outCase = 3; break; //myQS = empty, other = valid; merge
      case 8:  outCase = 1; break; //myQS = valid, other = null ; no-op
      case 9:  outCase = 1; break; //myQS = valid, other = empty: no-op
      case 10: outCase = 3; break; //myQS = valid, other = valid; merge
      default: break; //This cannot happen
    }
    UpdateDoublesSketch ret = null;

    switch (outCase) {
      case 0: break; //return null
      case 1: ret = myQS; break; //no-op
      case 2: { //myQS = null,  other = valid; stream or downsample to myMaxK
        assert other != null;
        if (!other.isEstimationMode()) { //other is exact, stream items in
          ret = HeapUpdateDoublesSketch.newInstance(myMaxK);
          // exact mode, only need copy base buffer
          final DoublesSketchAccessor otherAccessor = DoublesSketchAccessor.wrap(other);
          for (int i = 0; i < otherAccessor.numItems(); ++i) {
            ret.update(otherAccessor.get(i));
          }
        }
        else { //myQS = null, other is est mode
          ret = (myMaxK < other.getK())
              ? other.downSampleInternal(other, myMaxK, null) //null mem
              : DoublesUtil.copyToHeap(other); //copy required because caller has handle
        }
        break;
      }
      case 3: { //myQS = empty/valid, other = valid; merge
        assert other != null;
        assert myQS != null;
        if (!other.isEstimationMode()) { //other is exact, stream items in
          ret = myQS;
          // exact mode, only need copy base buffer
          final DoublesSketchAccessor otherAccessor = DoublesSketchAccessor.wrap(other);
          for (int i = 0; i < otherAccessor.numItems(); ++i) {
            ret.update(otherAccessor.get(i));
          }
        }
        else { //myQS = empty/valid, other = valid and in est mode
          if (myQS.getK() <= other.getK()) { //I am smaller or equal, thus the target
            DoublesMergeImpl.mergeInto(other, myQS);
            ret = myQS;
          }
          else { //Bigger: myQS.getK() > other.getK(), must effectively downsize me or swap
            if (myQS.isEmpty()) {
              if (myQS.hasMemory()) {
                final WritableMemory mem = myQS.getMemory(); //myQS is empty, ok to reconfigure
                other.putMemory(mem, false); // not compact, but BB ordered
                ret = DirectUpdateDoublesSketch.wrapInstance(mem);
              } else { //myQS is empty and on heap
                ret = DoublesUtil.copyToHeap(other);
              }
            }
            else { //Not Empty: myQS has data, downsample to tmp
              final UpdateDoublesSketch tmp = DoublesSketch.builder().setK(other.getK()).build();

              DoublesMergeImpl.downSamplingMergeInto(myQS, tmp); //myData -> tmp
              ret = (myQS.hasMemory())
                  ? DoublesSketch.builder().setK(other.getK()).build(myQS.getMemory())
                  : DoublesSketch.builder().setK(other.getK()).build();

              DoublesMergeImpl.mergeInto(tmp, ret);
              DoublesMergeImpl.mergeInto(other, ret);
            }
          }
        }
        break;
      }
      case 4: { //myQS = null,  other = empty; create empty-heap(myMaxK)
        ret = HeapUpdateDoublesSketch.newInstance(myMaxK);
        break;
      }
      default: break; //This cannot happen
    }
    return ret;
  }