1 files changed, 53 insertions, 0 deletions
diff --git a/contrib/llvm-project/libcxx/include/__bit/byteswap.h b/contrib/llvm-project/libcxx/include/__bit/byteswap.h
new file mode 100644
index 000000000000..6225ecf2f92d
--- /dev/null
+++ b/contrib/llvm-project/libcxx/include/__bit/byteswap.h
@@ -0,0 +1,53 @@
+// -*- 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___BIT_BYTESWAP_H
+#define _LIBCPP___BIT_BYTESWAP_H
+
+#include <__concepts/arithmetic.h>
+#include <__config>
+#include <cstdint>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 23
+
+template <integral _Tp>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp byteswap(_Tp __val) noexcept {
+  if constexpr (sizeof(_Tp) == 1) {
+    return __val;
+  } else if constexpr (sizeof(_Tp) == 2) {
+    return __builtin_bswap16(__val);
+  } else if constexpr (sizeof(_Tp) == 4) {
+    return __builtin_bswap32(__val);
+  } else if constexpr (sizeof(_Tp) == 8) {
+    return __builtin_bswap64(__val);
+#  ifndef _LIBCPP_HAS_NO_INT128
+  } else if constexpr (sizeof(_Tp) == 16) {
+#    if __has_builtin(__builtin_bswap128)
+    return __builtin_bswap128(__val);
+#    else
+    return static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val))) << 64 |
+           static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val >> 64)));
+#    endif // __has_builtin(__builtin_bswap128)
+#  endif   // _LIBCPP_HAS_NO_INT128
+  } else {
+    static_assert(sizeof(_Tp) == 0, "byteswap is unimplemented for integral types of this size");
+  }
+}
+
+#endif // _LIBCPP_STD_VER >= 23
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___BIT_BYTESWAP_H