CLN: simplify core.algorithms
thanks This seems to have caused a small but consistent performance regression: https://pandas.pydata.org/speed/pandas/#index_object.IntervalIndexMethod.time_intersection?p-param1=1000&commits=f58b07e0 (might be worth investigating)

(to be clear: just reporting here what ASV reports, didn't do any sanity check of the validity of the report) I'll take a look, thanks