[libcxx-commits] [libcxx] [libc++] Introduce one-sided binary search for set_intersection so that it can be completed in sub-linear time for a large class of inputs. (PR #75230)

[Louis Dionne via libcxx-commits]

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@@ -85,6 +86,56 @@ struct _IterOps<_ClassicAlgPolicy> {
     std::advance(__iter, __count);
   }
 
+  // advance with sentinel, a la std::ranges::advance
+  // it's unclear whether _Iter has a difference_type and whether that's signed, so we play it safe:
+  // use the incoming type for returning and steer clear of negative overflows
+  template <class _Iter, class _Distance>
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 static _Distance
+  advance(_Iter& __iter, _Distance __count, const _Iter& __sentinel) {
+    return _IterOps::__advance(__iter, __count, __sentinel, typename iterator_traits<_Iter>::iterator_category());
+  }
+
+private:
+  // advance with sentinel, a la std::ranges::advance -- InputIterator specialization
+  template <class _InputIter, class _Distance>
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ldionne wrote:

Is there a way that we could share the same code between this and the implementation of `ranges::advance` in `libcxx/include/__iterator/advance.h`?

https://github.com/llvm/llvm-project/pull/75230