1 files changed, 131 insertions, 0 deletions
diff --git a/contrib/llvm-project/libcxx/include/__ranges/drop_view.h b/contrib/llvm-project/libcxx/include/__ranges/drop_view.h
new file mode 100644
index 000000000000..099fd227111d
--- /dev/null
+++ b/contrib/llvm-project/libcxx/include/__ranges/drop_view.h
@@ -0,0 +1,131 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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___RANGES_DROP_VIEW_H
+#define _LIBCPP___RANGES_DROP_VIEW_H
+
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/next.h>
+#include <__ranges/access.h>
+#include <__ranges/all.h>
+#include <__ranges/concepts.h>
+#include <__ranges/enable_borrowed_range.h>
+#include <__ranges/non_propagating_cache.h>
+#include <__ranges/size.h>
+#include <__ranges/view_interface.h>
+#include <__utility/move.h>
+#include <concepts>
+#include <type_traits>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if !defined(_LIBCPP_HAS_NO_RANGES)
+
+namespace ranges {
+  template<view _View>
+  class drop_view
+    : public view_interface<drop_view<_View>>
+  {
+    // We cache begin() whenever ranges::next is not guaranteed O(1) to provide an
+    // amortized O(1) begin() method. If this is an input_range, then we cannot cache
+    // begin because begin is not equality preserving.
+    // Note: drop_view<input-range>::begin() is still trivially amortized O(1) because
+    // one can't call begin() on it more than once.
+    static constexpr bool _UseCache = forward_range<_View> && !(random_access_range<_View> && sized_range<_View>);
+    using _Cache = _If<_UseCache, __non_propagating_cache<iterator_t<_View>>, __empty_cache>;
+    [[no_unique_address]] _Cache __cached_begin_ = _Cache();
+    range_difference_t<_View> __count_ = 0;
+    _View __base_ = _View();
+
+public:
+    drop_view() requires default_initializable<_View> = default;
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr drop_view(_View __base, range_difference_t<_View> __count)
+      : __count_(__count)
+      , __base_(_VSTD::move(__base))
+    {
+      _LIBCPP_ASSERT(__count_ >= 0, "count must be greater than or equal to zero.");
+    }
+
+    _LIBCPP_HIDE_FROM_ABI constexpr _View base() const& requires copy_constructible<_View> { return __base_; }
+    _LIBCPP_HIDE_FROM_ABI constexpr _View base() && { return _VSTD::move(__base_); }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr auto begin()
+      requires (!(__simple_view<_View> &&
+                  random_access_range<const _View> && sized_range<const _View>))
+    {
+      if constexpr (_UseCache)
+        if (__cached_begin_.__has_value())
+          return *__cached_begin_;
+
+      auto __tmp = ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_));
+      if constexpr (_UseCache)
+        __cached_begin_.__set(__tmp);
+      return __tmp;
+    }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr auto begin() const
+      requires random_access_range<const _View> && sized_range<const _View>
+    {
+      return ranges::next(ranges::begin(__base_), __count_, ranges::end(__base_));
+    }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr auto end()
+      requires (!__simple_view<_View>)
+    { return ranges::end(__base_); }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr auto end() const
+      requires range<const _View>
+    { return ranges::end(__base_); }
+
+    _LIBCPP_HIDE_FROM_ABI
+    static constexpr auto __size(auto& __self) {
+      const auto __s = ranges::size(__self.__base_);
+      const auto __c = static_cast<decltype(__s)>(__self.__count_);
+      return __s < __c ? 0 : __s - __c;
+    }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr auto size()
+      requires sized_range<_View>
+    { return __size(*this); }
+
+    _LIBCPP_HIDE_FROM_ABI
+    constexpr auto size() const
+      requires sized_range<const _View>
+    { return __size(*this); }
+  };
+
+  template<class _Range>
+  drop_view(_Range&&, range_difference_t<_Range>) -> drop_view<views::all_t<_Range>>;
+
+  template<class _Tp>
+  inline constexpr bool enable_borrowed_range<drop_view<_Tp>> = enable_borrowed_range<_Tp>;
+} // namespace ranges
+
+#endif // !defined(_LIBCPP_HAS_NO_RANGES)
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___RANGES_DROP_VIEW_H