in src/main/java/org/apache/datasketches/quantiles/ItemsUnion.java [270:342]
static <T> ItemsSketch<T> updateLogic(final int myMaxK, final Comparator<? super T> comparator,
final ItemsSketch<T> myQS, final ItemsSketch<T> 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
}
ItemsSketch<T> ret = null;
switch (outCase) {
case 0: break;
case 1: ret = myQS; break;
case 2: { //myQS = null, other = valid; stream or downsample to myMaxK
assert other != null;
if (!other.isEstimationMode()) { //other is exact, stream items in
ret = ItemsSketch.getInstance(other.getClassOfT(), myMaxK, comparator);
final int otherCnt = other.getBaseBufferCount();
final Object[] combBuf = other.getCombinedBuffer();
for (int i = 0; i < otherCnt; i++) {
ret.update((T) combBuf[i]);
}
}
else { //myQS = null, other is est mode
ret = (myMaxK < other.getK())
? other.downSample(myMaxK)
: ItemsSketch.copy(other); //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;
final int otherCnt = other.getBaseBufferCount();
final Object[] combBuf = other.getCombinedBuffer();
for (int i = 0; i < otherCnt; i++) {
ret.update((T) combBuf[i]);
}
}
else { //myQS = empty/valid, other = valid and in est mode
if (myQS.getK() <= other.getK()) { //I am smaller or equal, thus the target
ItemsMergeImpl.mergeInto(other, myQS);
ret = myQS;
}
else { //Bigger: myQS.getK() > other.getK(), must reverse roles
//must copy other as it will become mine and can't have any externally owned handles.
ret = ItemsSketch.copy(other);
ItemsMergeImpl.mergeInto(myQS, ret);
}
}
break;
}
case 4: {
assert other != null;
ret = ItemsSketch.getInstance(other.getClassOfT(), Math.min(myMaxK, other.getK()), comparator);
break;
}
default: break; //This cannot happen
}
return ret;
}