v1/__bit/byteswap.h

0001 // -*- C++ -*-
0002 //===----------------------------------------------------------------------===//
0003 //
0004 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0005 // See https://llvm.org/LICENSE.txt for license information.
0006 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0007 //
0008 //===----------------------------------------------------------------------===//
0009
0010 #ifndef _LIBCPP___BIT_BYTESWAP_H
0011 #define _LIBCPP___BIT_BYTESWAP_H
0012
0013 #include <__concepts/arithmetic.h>
0014 #include <__config>
0015 #include <cstdint>
0016
0017 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0018 #  pragma GCC system_header
0019 #endif
0020
0021 _LIBCPP_BEGIN_NAMESPACE_STD
0022
0023 #if _LIBCPP_STD_VER >= 23
0024
0025 template <integral _Tp>
0026 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp byteswap(_Tp __val) noexcept {
0027   if constexpr (sizeof(_Tp) == 1) {
0028     return __val;
0029   } else if constexpr (sizeof(_Tp) == 2) {
0030     return __builtin_bswap16(__val);
0031   } else if constexpr (sizeof(_Tp) == 4) {
0032     return __builtin_bswap32(__val);
0033   } else if constexpr (sizeof(_Tp) == 8) {
0034     return __builtin_bswap64(__val);
0035 #  if _LIBCPP_HAS_INT128
0036   } else if constexpr (sizeof(_Tp) == 16) {
0037 #    if __has_builtin(__builtin_bswap128)
0038     return __builtin_bswap128(__val);
0039 #    else
0040     return static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val))) << 64 |
0041            static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val >> 64)));
0042 #    endif // __has_builtin(__builtin_bswap128)
0043 #  endif   // _LIBCPP_HAS_INT128
0044   } else {
0045     static_assert(sizeof(_Tp) == 0, "byteswap is unimplemented for integral types of this size");
0046   }
0047 }
0048
0049 #endif // _LIBCPP_STD_VER >= 23
0050
0051 _LIBCPP_END_NAMESPACE_STD
0052
0053 #endif // _LIBCPP___BIT_BYTESWAP_H