static final CompactSketch heapify2to3()

in src/main/java/org/apache/datasketches/theta/ForwardCompatibility.java [94:151]
56 lines of code
11 McCabe index (conditional complexity)

  static final CompactSketch heapify2to3(final Memory srcMem, final short seedHash) {
    final int memCap = (int) srcMem.getCapacity();
    final int preLongs = extractPreLongs(srcMem); //1,2 or 3
    final int familyId = extractFamilyID(srcMem); //1,2,3,4
    if ((familyId < 1) || (familyId > 4)) {
      throw new SketchesArgumentException("Family (Sketch Type) must be 1 to 4: " + familyId);
    }
    int reqBytesIn = 8;
    int curCount = 0;
    long thetaLong = Long.MAX_VALUE;
    if (preLongs == 1) {
      reqBytesIn = 8;
      validateInputSize(reqBytesIn, memCap);
      return EmptyCompactSketch.getInstance();
    }
    if (preLongs == 2) { //includes pre0 + count, no theta (== 1.0)
      reqBytesIn = preLongs << 3;
      validateInputSize(reqBytesIn, memCap);
      curCount = extractCurCount(srcMem);
      if (curCount == 0) {
        return EmptyCompactSketch.getInstance();
      }
      if (curCount == 1) {
        reqBytesIn = (preLongs + 1) << 3;
        validateInputSize(reqBytesIn, memCap);
        final long hash = srcMem.getLong(preLongs << 3);
        return new SingleItemSketch(hash, seedHash);
      }
      //curCount > 1
      reqBytesIn = (curCount + preLongs) << 3;
      validateInputSize(reqBytesIn, memCap);
      final long[] compactOrderedCache = new long[curCount];
      srcMem.getLongArray(preLongs << 3, compactOrderedCache, 0, curCount);
      return new HeapCompactSketch(compactOrderedCache, false, seedHash, curCount, thetaLong,true);
    }
    if (preLongs == 3) { //pre0 + count + theta
      reqBytesIn = (preLongs) << 3; //
      validateInputSize(reqBytesIn, memCap);
      curCount = extractCurCount(srcMem);
      thetaLong = extractThetaLong(srcMem);
      if ((curCount == 0) && (thetaLong == Long.MAX_VALUE)) {
        return EmptyCompactSketch.getInstance();
      }
      if ((curCount == 1) && (thetaLong == Long.MAX_VALUE)) {
        reqBytesIn = (preLongs + 1) << 3;
        validateInputSize(reqBytesIn, memCap);
        final long hash = srcMem.getLong(preLongs << 3);
        return new SingleItemSketch(hash, seedHash);
      }
      //curCount > 1 and/or theta < 1.0
      reqBytesIn = (curCount + preLongs) << 3;
      validateInputSize(reqBytesIn, memCap);
      final long[] compactOrderedCache = new long[curCount];
      srcMem.getLongArray(preLongs << 3, compactOrderedCache, 0, curCount);
      return new HeapCompactSketch(compactOrderedCache, false, seedHash, curCount, thetaLong, true);
    }
    throw new SketchesArgumentException("PreLongs must be 1,2, or 3: " + preLongs);
  }