libcxx/include/__bit/byteswap.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___BIT_BYTESWAP_H
  11 #define _LIBCPP___BIT_BYTESWAP_H
  12
  13 #include <__concepts/arithmetic.h>
  14 #include <__config>
  15 #include <cstdint>
  16
  17 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  18 #  pragma GCC system_header
  19 #endif
  20
  21 _LIBCPP_BEGIN_NAMESPACE_STD
  22
  23 #if _LIBCPP_STD_VER >= 23
  24
  25 template <integral _Tp>
  26 [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Tp byteswap(_Tp __val) noexcept {
  27   if constexpr (sizeof(_Tp) == 1) {
  28     return __val;
  29   } else if constexpr (sizeof(_Tp) == 2) {
  30     return __builtin_bswap16(__val);
  31   } else if constexpr (sizeof(_Tp) == 4) {
  32     return __builtin_bswap32(__val);
  33   } else if constexpr (sizeof(_Tp) == 8) {
  34     return __builtin_bswap64(__val);
  35 #  if _LIBCPP_HAS_INT128
  36   } else if constexpr (sizeof(_Tp) == 16) {
  37 #    if __has_builtin(__builtin_bswap128)
  38     return __builtin_bswap128(__val);
  39 #    else
  40     return static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val))) << 64 |
  41            static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val >> 64)));
  42 #    endif // __has_builtin(__builtin_bswap128)
  43 #  endif   // _LIBCPP_HAS_INT128
  44   } else {
  45     static_assert(sizeof(_Tp) == 0, "byteswap is unimplemented for integral types of this size");
  46   }
  47 }
  48
  49 #endif // _LIBCPP_STD_VER >= 23
  50
  51 _LIBCPP_END_NAMESPACE_STD
  52
  53 #endif // _LIBCPP___BIT_BYTESWAP_H