private SargIntervalSequence evaluateIntersection(List<SargIntervalSequence> list) {
SargIntervalSequence seq = null;
if (list.isEmpty()) {
// Counterintuitive but true: intersection of no sets is the
// universal set (kinda like 2^0=1). One way to prove this to
// yourself is to apply DeMorgan's law. The union of no sets is
// certainly the empty set. So the complement of that union is the
// universal set. That's equivalent to the intersection of the
// complements of no sets, which is the intersection of no sets.
// QED.
seq = new SargIntervalSequence();
seq.addInterval(new SargInterval(factory, getDataType()));
return seq;
}
// The way we evaluate the intersection is to start with the first
// entry as a baseline, and then keep deleting stuff from it by
// intersecting the other entrie in turn. Whatever makes it through
// this filtering remains as the final result.
for (SargIntervalSequence newSeq : list) {
if (seq == null) {
// first child
seq = newSeq;
continue;
}
intersectSequences(seq, newSeq);
}
return seq;
}
private SargIntervalSequence evaluateUnion(List<SargIntervalSequence> list) {
SargIntervalSequence seq = new SargIntervalSequence();
// Toss all entries from each sequence in the list into one big sorted
// set.
SortedSet<SargInterval> intervals = new TreeSet<SargInterval>(new IntervalComparator());
for (SargIntervalSequence childSeq : list) {
intervals.addAll(childSeq.getList());
}
// Now, overlapping ranges are consecutive in the set. Merge them by
// increasing the upper bound of the first; discard the others. In the
// example, [4, 6] and [5, 7) are combined to form [4, 7). (7, 8] is
// not merged with the new range because neither range contains the
// value 7.
//
// Input:
// 1 2 3 4 5 6 7 8 9
// 1 [1, 3] [-----]
// 2 [4, 6] [-----]
// 3 [5, 7) [-----)
// 4 (7, 8] (--]
//
// Output:
// 1 [1, 3] [-----]
// 2 [4, 7) [--------)
// 3 (7, 8] (--]
SargInterval accumulator = null;
for (SargInterval interval : intervals) {
// Empty intervals should have been previously filtered out.
assert (!interval.isEmpty());
if (accumulator == null) {
// The very first interval: start accumulating.
accumulator = new SargInterval(factory, getDataType());
accumulator.copyFrom(interval);
seq.addInterval(accumulator);
continue;
}
if (accumulator.contains(interval)) {
// Just drop new interval because it's already covered
// by accumulator.
continue;
}
// Test for overlap.
int c = interval.getLowerBound().compareTo(accumulator.getUpperBound());
// If no overlap, test for touching instead.
if (c > 0) {
if (interval.getLowerBound().isTouching(accumulator.getUpperBound())) {
// Force test below to pass.
c = -1;
}
}
if (c <= 0) {
// Either touching or overlap: grow the accumulator.
accumulator.upperBound.copyFrom(interval.getUpperBound());
} else {
// Disjoint: start accumulating a new interval
accumulator = new SargInterval(factory, getDataType());
accumulator.copyFrom(interval);
seq.addInterval(accumulator);
}
}
return seq;
}