Algorithms for ranges shift left and shift right

Author: xevor11

libcxx/include/__algorithm/ranges_shift_left.h

@@ -0,0 +1,74 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_SHIFT_LEFT_H
+#define _LIBCPP___ALGORITHM_RANGES_SHIFT_LEFT_H
+
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/subrange.h>
+#include <__utility/move.h>
+#include <__utility/forward.h>
+#include <__iterator/advance.h>
+#include <__iterator/distance.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+namespace __shift_left {
+
+struct __fn {
+  template <std::permutable _Iter, std::sentinel_for<_Iter> _Sent>
+  _LIBCPP_HIDE_FROM_ABI constexpr subrange<_Iter>
+  operator()(_Iter __first, _Sent __last, iter_difference_t<_Iter> __n) const {
+    if (__n <= 0) {
+      return {__first, __first};
+    }
+
+    auto __dist = std::ranges::distance(__first, __last);
+    if (__n >= __dist) {
+      return {__first, __first};
+    }
+
+    auto __mid = std::ranges::next(__first, __n);
+    auto __new_last = std::move(__mid, __last, __first);
+    return {__first, __new_last};
+  }
+
+  template <std::ranges::forward_range _Range>
+  requires std::permutable<iterator_t<_Range>>
+  _LIBCPP_HIDE_FROM_ABI constexpr borrowed_subrange_t<_Range>
+  operator()(_Range&& __range, range_difference_t<_Range> __n) const {
+    return (*this)(std::ranges::begin(__range), std::ranges::end(__range), __n);
+  }
+};
+
+} // namespace __shift_left
+
+inline namespace __cpo {
+  inline constexpr auto shift_left = __shift_left::__fn{};
+} // namespace __cpo
+
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___ALGORITHM_RANGES_SHIFT_LEFT_H

libcxx/include/__algorithm/ranges_shift_right.h

@@ -0,0 +1,75 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_SHIFT_RIGHT_H
+#define _LIBCPP___ALGORITHM_RANGES_SHIFT_RIGHT_H
+
+#include <__config>
+#include <__iterator/concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__ranges/access.h>
+#include <__ranges/concepts.h>
+#include <__ranges/subrange.h>
+#include <__utility/move.h>
+#include <__utility/forward.h>
+#include <__iterator/advance.h>
+#include <__iterator/distance.h>
+#include <algorithm>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace ranges {
+
+namespace __shift_right {
+
+struct __fn {
+  template <std::permutable _Iter, std::sentinel_for<_Iter> _Sent>
+  _LIBCPP_HIDE_FROM_ABI constexpr subrange<_Iter>
+  operator()(_Iter __first, _Sent __last, iter_difference_t<_Iter> __n) const {
+    if (__n <= 0) {
+      return {__last, __last};
+    }
+
+    auto __dist = std::ranges::distance(__first, __last);
+    if (__n >= __dist) {
+      return {__last, __last};
+    }
+
+    auto __new_first = std::ranges::next(__first, __dist - __n);
+    std::move_backward(__first, __new_first, __last);
+    return {__new_first, __last};
+  }
+
+  template <std::ranges::forward_range _Range>
+  requires std::permutable<iterator_t<_Range>>
+  _LIBCPP_HIDE_FROM_ABI constexpr borrowed_subrange_t<_Range>
+  operator()(_Range&& __range, range_difference_t<_Range> __n) const {
+    return (*this)(std::ranges::begin(__range), std::ranges::end(__range), __n);
+  }
+};
+
+} // namespace __shift_right
+
+inline namespace __cpo {
+  inline constexpr auto shift_right = __shift_right::__fn{};
+} // namespace __cpo
+
+} // namespace ranges
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___ALGORITHM_RANGES_SHIFT_RIGHT_H