func mergeHlltoHLLmode()

in hll/union.go [365:455]
88 lines of code
14 McCabe index (conditional complexity)

func mergeHlltoHLLmode(src HllSketch, tgt HllSketch, srcLgK int, tgtLgK int) error {
	sw := 0
	if srcLgK > tgtLgK {
		sw |= 4
	}
	if src.GetTgtHllType() != TgtHllTypeHll8 {
		sw |= 8
	}
	srcK := 1 << srcLgK

	switch sw {
	case 0: //HLL_8, srcLgK=tgtLgK, src=heap, tgt=heap
		{
			srcArr := src.(*hllSketchState).sketch.(*hll8ArrayImpl).hllByteArr
			tgtArr := tgt.(*hllSketchState).sketch.(*hll8ArrayImpl).hllByteArr
			// Hack to trigger the bound check only once on tgtArr
			_ = tgtArr[len(srcArr)-1]
			for i, srcV := range srcArr {
				if srcV > tgtArr[i] {
					tgtArr[i] = srcV
				}
			}
		}
	case 8, 9: //!HLL_8, srcLgK=tgtLgK, src=heap, tgt=heap/mem
		{
			tgtAbsHllArr := tgt.(*hllSketchState).sketch.(*hll8ArrayImpl)
			if src.GetTgtHllType() == TgtHllTypeHll4 {
				src4 := src.(*hllSketchState).sketch.(*hll4ArrayImpl)
				auxHashMap := src4.auxHashMap
				curMin := src4.curMin
				i := 0
				j := 0
				for j < srcK {
					b := src4.hllByteArr[i]
					i++
					value := uint(b) & loNibbleMask
					if value == auxToken {
						v, err := auxHashMap.mustFindValueFor(j)
						if err != nil {
							return err
						}
						tgtAbsHllArr.updateSlotNoKxQ(j, v)
					} else {
						tgtAbsHllArr.updateSlotNoKxQ(j, int(value)+curMin)
					}
					j++
					value = uint(b) >> 4
					if value == auxToken {
						v, err := auxHashMap.mustFindValueFor(j)
						if err != nil {
							return err
						}
						tgtAbsHllArr.updateSlotNoKxQ(j, v)
					} else {
						tgtAbsHllArr.updateSlotNoKxQ(j, int(value)+curMin)
					}
					j++
				}
			} else {
				src6 := src.(*hllSketchState).sketch.(*hll6ArrayImpl)
				i := 0
				j := 0
				for j < srcK {
					b1 := src6.hllByteArr[i]
					b2 := src6.hllByteArr[i+1]
					b3 := src6.hllByteArr[i+2]
					i += 3
					value := uint(b1) & 0x3f
					tgtAbsHllArr.updateSlotNoKxQ(j, int(value))
					j++
					value = uint(b1) >> 6
					value |= (uint(b2) & 0x0f) << 2
					tgtAbsHllArr.updateSlotNoKxQ(j, int(value))
					j++
					value = uint(b2) >> 4
					value |= (uint(b3) & 3) << 4
					tgtAbsHllArr.updateSlotNoKxQ(j, int(value))
					j++
					value = uint(b3) >> 2
					tgtAbsHllArr.updateSlotNoKxQ(j, int(value))
					j++
				}
			}
		}
		// TODO continue implementing
	default:
		return fmt.Errorf("not implemented")
	}
	tgt.(*hllSketchState).sketch.putRebuildCurMinNumKxQFlag(true)
	return nil
}