Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/__algorithm/shift_right.h

@@ -0,0 +1,101 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_SHIFT_RIGHT_H
+#define _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
+
+#include <__algorithm/move.h>
+#include <__algorithm/move_backward.h>
+#include <__algorithm/swap_ranges.h>
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__utility/swap.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template <class _ForwardIterator>
+inline _LIBCPP_INLINE_VISIBILITY constexpr
+_ForwardIterator
+shift_right(_ForwardIterator __first, _ForwardIterator __last,
+            typename iterator_traits<_ForwardIterator>::difference_type __n)
+{
+    if (__n == 0) {
+        return __first;
+    }
+
+    if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value) {
+        decltype(__n) __d = __last - __first;
+        if (__n >= __d) {
+            return __last;
+        }
+        _ForwardIterator __m = __first + (__d - __n);
+        return _VSTD::move_backward(__first, __m, __last);
+    } else if constexpr (__has_bidirectional_iterator_category<_ForwardIterator>::value) {
+        _ForwardIterator __m = __last;
+        for (; __n > 0; --__n) {
+            if (__m == __first) {
+                return __last;
+            }
+            --__m;
+        }
+        return _VSTD::move_backward(__first, __m, __last);
+    } else {
+        _ForwardIterator __ret = __first;
+        for (; __n > 0; --__n) {
+            if (__ret == __last) {
+                return __last;
+            }
+            ++__ret;
+        }
+
+        // We have an __n-element scratch space from __first to __ret.
+        // Slide an __n-element window [__trail, __lead) from left to right.
+        // We're essentially doing swap_ranges(__first, __ret, __trail, __lead)
+        // over and over; but once __lead reaches __last we needn't bother
+        // to save the values of elements [__trail, __last).
+
+        auto __trail = __first;
+        auto __lead = __ret;
+        while (__trail != __ret) {
+            if (__lead == __last) {
+                _VSTD::move(__first, __trail, __ret);
+                return __ret;
+            }
+            ++__trail;
+            ++__lead;
+        }
+
+        _ForwardIterator __mid = __first;
+        while (true) {
+            if (__lead == __last) {
+                __trail = _VSTD::move(__mid, __ret, __trail);
+                _VSTD::move(__first, __mid, __trail);
+                return __ret;
+            }
+            swap(*__mid, *__trail);
+            ++__mid;
+            ++__trail;
+            ++__lead;
+            if (__mid == __ret) {
+                __mid = __first;
+            }
+        }
+    }
+}
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H