equal_range in LLVM

equal_range.h

template <class _AlgPolicy, class _Compare, class _Iter, class _Sent, class _Tp, class _Proj>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_Iter, _Iter>
__equal_range(_Iter __first, _Sent __last, const _Tp& __value, _Compare&& __comp, _Proj&& __proj) {
  auto __len  = _IterOps<_AlgPolicy>::distance(__first, __last);
  _Iter __end = _IterOps<_AlgPolicy>::next(__first, __last);
  while (__len != 0) {
    auto __half_len = std::__half_positive(__len);
    _Iter __mid     = _IterOps<_AlgPolicy>::next(__first, __half_len);
    if (std::__invoke(__comp, std::__invoke(__proj, *__mid), __value)) {
      __first = ++__mid;
      __len -= __half_len + 1;
    } else if (std::__invoke(__comp, __value, std::__invoke(__proj, *__mid))) {
      __end = __mid;
      __len = __half_len;
    } else {
      _Iter __mp1 = __mid;
      return pair<_Iter, _Iter>(
          std::__lower_bound<_AlgPolicy>(__first, __mid, __value, __comp, __proj),
          std::__upper_bound<_AlgPolicy>(++__mp1, __end, __value, __comp, __proj));
    }
  }
  return pair<_Iter, _Iter>(__first, __first);
}