1 files changed, 142 insertions, 0 deletions
diff --git a/libcxx/include/__algorithm/ranges_merge.h b/libcxx/include/__algorithm/ranges_merge.h
new file mode 100644
index 000000000000..c73e09e94ccc
--- /dev/null
+++ b/libcxx/include/__algorithm/ranges_merge.h
@@ -0,0 +1,142 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___ALGORITHM_RANGES_MERGE_H
+#define _LIBCPP___ALGORITHM_RANGES_MERGE_H
+
+#include <__algorithm/in_in_out_result.h>
+#include <__algorithm/ranges_copy.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__functional/ranges_operations.h>
+#include <__iterator/concepts.h>
+#include <__iterator/mergeable.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/dangling.h>
+#include <__utility/move.h>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+template <class _InIter1, class _InIter2, class _OutIter>
+using merge_result = in_in_out_result<_InIter1, _InIter2, _OutIter>;
+
+namespace __merge {
+
+template <
+    class _InIter1,
+    class _Sent1,
+    class _InIter2,
+    class _Sent2,
+    class _OutIter,
+    class _Comp,
+    class _Proj1,
+    class _Proj2>
+_LIBCPP_HIDE_FROM_ABI constexpr merge_result<__uncvref_t<_InIter1>, __uncvref_t<_InIter2>, __uncvref_t<_OutIter>>
+__merge_impl(
+    _InIter1&& __first1,
+    _Sent1&& __last1,
+    _InIter2&& __first2,
+    _Sent2&& __last2,
+    _OutIter&& __result,
+    _Comp&& __comp,
+    _Proj1&& __proj1,
+    _Proj2&& __proj2) {
+  for (; __first1 != __last1 && __first2 != __last2; ++__result) {
+    if (std::invoke(__comp, std::invoke(__proj2, *__first2), std::invoke(__proj1, *__first1))) {
+      *__result = *__first2;
+      ++__first2;
+    } else {
+      *__result = *__first1;
+      ++__first1;
+    }
+  }
+  auto __ret1 = ranges::copy(std::move(__first1), std::move(__last1), std::move(__result));
+  auto __ret2 = ranges::copy(std::move(__first2), std::move(__last2), std::move(__ret1.out));
+  return {std::move(__ret1.in), std::move(__ret2.in), std::move(__ret2.out)};
+}
+
+struct __fn {
+  template <
+      input_iterator _InIter1,
+      sentinel_for<_InIter1> _Sent1,
+      input_iterator _InIter2,
+      sentinel_for<_InIter2> _Sent2,
+      weakly_incrementable _OutIter,
+      class _Comp  = less,
+      class _Proj1 = identity,
+      class _Proj2 = identity>
+    requires mergeable<_InIter1, _InIter2, _OutIter, _Comp, _Proj1, _Proj2>
+  _LIBCPP_HIDE_FROM_ABI constexpr merge_result<_InIter1, _InIter2, _OutIter> operator()(
+      _InIter1 __first1,
+      _Sent1 __last1,
+      _InIter2 __first2,
+      _Sent2 __last2,
+      _OutIter __result,
+      _Comp __comp   = {},
+      _Proj1 __proj1 = {},
+      _Proj2 __proj2 = {}) const {
+    return __merge::__merge_impl(__first1, __last1, __first2, __last2, __result, __comp, __proj1, __proj2);
+  }
+
+  template <
+      input_range _Range1,
+      input_range _Range2,
+      weakly_incrementable _OutIter,
+      class _Comp  = less,
+      class _Proj1 = identity,
+      class _Proj2 = identity>
+    requires mergeable<
+        iterator_t<_Range1>,
+        iterator_t<_Range2>,
+        _OutIter,
+        _Comp,
+        _Proj1,
+        _Proj2> 
+  _LIBCPP_HIDE_FROM_ABI constexpr merge_result<borrowed_iterator_t<_Range1>, borrowed_iterator_t<_Range2>, _OutIter>
+        operator()(
+            _Range1&& __range1,
+            _Range2&& __range2,
+            _OutIter __result,
+            _Comp __comp   = {},
+            _Proj1 __proj1 = {},
+            _Proj2 __proj2 = {}) const {
+    return __merge::__merge_impl(
+        ranges::begin(__range1),
+        ranges::end(__range1),
+        ranges::begin(__range2),
+        ranges::end(__range2),
+        __result,
+        __comp,
+        __proj1,
+        __proj2);
+  }
+};
+
+} // namespace __merge
+
+inline namespace __cpo {
+  inline constexpr auto merge = __merge::__fn{};
+} // namespace __cpo
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+
+#endif // _LIBCPP___ALGORITHM_RANGES_MERGE_H