Make for_each segmented iterator optimization valid for C++03

Author: winner245

libcxx/include/__algorithm/for_each.h

@@ -14,7 +14,7 @@
 #include <__algorithm/iterator_operations.h>
 #include <__config>
 #include <__iterator/segmented_iterator.h>
-#include <__ranges/movable_box.h>
+#include <__type_traits/enable_if.h>
 #include <__utility/in_place.h>
 #include <__utility/move.h>
 
@@ -27,32 +27,37 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _InputIterator, class _Function>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Function
-for_each(_InputIterator __first, _InputIterator __last, _Function __f);
-
-template <class, class _InputIterator, class _Function>
+template <class, class _InputIterator, class _Sent, class _Function>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Function
-__for_each(_InputIterator __first, _InputIterator __last, _Function& __f) {
+__for_each(_InputIterator __first, _Sent __last, _Function& __f) {
   for (; __first != __last; ++__first)
     __f(*__first);
   return std::move(__f);
 }
 
-// __movable_box is available in C++20, but is actually a copyable-box, so optimization is only correct in C++23
-#if _LIBCPP_STD_VER >= 23
-template <class, class _SegmentedIterator, class _Function>
-  requires __is_segmented_iterator<_SegmentedIterator>::value
+template <class _InputIterator, class _Function>
+struct _ForeachSegment {
+  using _Traits _LIBCPP_NODEBUG = __segmented_iterator_traits<_InputIterator>;
+
+  _Function& __func_;
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 explicit _ForeachSegment(_Function& __func) : __func_(__func) {}
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
+  operator()(typename _Traits::__local_iterator __lfirst, typename _Traits::__local_iterator __llast) {
+    std::__for_each<_ClassicAlgPolicy>(__lfirst, __llast, __func_);
+  }
+};
+
+template <class,
+          class _SegmentedIterator,
+          class _Function,
+          __enable_if_t<__is_segmented_iterator<_SegmentedIterator>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI constexpr _Function
-for_each(_SegmentedIterator __first, _SegmentedIterator __last, _Function& __func) {
-  ranges::__movable_box<_Function> __wrapped_func(in_place, std::move(__func));
-  std::__for_each_segment(__first, __last, [&](auto __lfirst, auto __llast) {
-    __wrapped_func =
-        ranges::__movable_box<_Function>(in_place, std::for_each(__lfirst, __llast, std::move(*__wrapped_func)));
-  });
-  return std::move(*__wrapped_func);
+__for_each(_SegmentedIterator __first, _SegmentedIterator __last, _Function& __func) {
+  std::__for_each_segment(__first, __last, _ForeachSegment<_SegmentedIterator, _Function>(__func));
+  return std::move(__func);
 }
-#endif // _LIBCPP_STD_VER >= 23
 
 template <class _InputIterator, class _Function>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Function

libcxx/include/__algorithm/for_each_n.h

@@ -14,6 +14,7 @@
 #include <__algorithm/iterator_operations.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
+#include <__iterator/next.h>
 #include <__iterator/segmented_iterator.h>
 #include <__type_traits/enable_if.h>
 #include <__utility/convert_to_integral.h>
@@ -30,8 +31,7 @@ template <class _InputIterator,
           class _Size,
           class _Function,
           __enable_if_t<!__is_segmented_iterator<_InputIterator>::value ||
-                            (__has_input_iterator_category<_InputIterator>::value &&
-                             !__has_random_access_iterator_category<_InputIterator>::value),
+                            __has_exactly_input_iterator_category<_InputIterator>::value,
                         int> = 0>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
 for_each_n(_InputIterator __first, _Size __orig_n, _Function __f) {
@@ -49,11 +49,13 @@ template <class _InputIterator,
           class _Size,
           class _Function,
           __enable_if_t<__is_segmented_iterator<_InputIterator>::value &&
-                            __has_random_access_iterator_category<_InputIterator>::value,
+                            __has_forward_iterator_category<_InputIterator>::value,
                         int> = 0>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
 for_each_n(_InputIterator __first, _Size __orig_n, _Function __f) {
-  _InputIterator __last = __first + __orig_n;
+  typedef decltype(std::__convert_to_integral(__orig_n)) _IntegralSize;
+  _IntegralSize __n     = __orig_n;
+  _InputIterator __last = std::next(__first, __n);
   std::__for_each<_ClassicAlgPolicy>(__first, __last, __f);
   return __last;
 }

libcxx/include/__algorithm/ranges_for_each_n.h

@@ -18,6 +18,7 @@
 #include <__iterator/concepts.h>
 #include <__iterator/incrementable_traits.h>
 #include <__iterator/iterator_traits.h>
+#include <__iterator/next.h>
 #include <__iterator/projected.h>
 #include <__ranges/concepts.h>
 #include <__utility/move.h>
@@ -42,8 +43,8 @@ struct __for_each_n {
   template <input_iterator _Iter, class _Proj = identity, indirectly_unary_invocable<projected<_Iter, _Proj>> _Func>
   _LIBCPP_HIDE_FROM_ABI constexpr for_each_n_result<_Iter, _Func>
   operator()(_Iter __first, iter_difference_t<_Iter> __count, _Func __func, _Proj __proj = {}) const {
-    if constexpr (random_access_iterator<_Iter>) {
-      auto __last = __first + __count;
+    if constexpr (forward_iterator<_Iter>) {
+      auto __last = std::ranges::next(__first, __count);
       auto __f    = [&](auto&& __val) { std::invoke(__func, std::invoke(__proj, __val)); };
       std::__for_each<_RangeAlgPolicy>(__first, __last, __f);
       return {std::move(__last), std::move(__func)};