in tuple/tuple_sketch_int64.cpp [60:65]
void operator()(Summary& summary, const Summary& other) const {
if (mode_ == SUM) summary += other;
else if (mode_ == MIN) summary = std::min(summary, other);
else if (mode_ == MAX) summary = std::max(summary, other);
else if (mode_ == ONE) summary = 1;
}