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 #include <cstdlib>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #  pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_BEGIN_NAMESPACE_STD
  23
  24 #if _LIBCPP_STD_VER > 20 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
  25
  26 template <integral _Tp>
  27 _LIBCPP_HIDE_FROM_ABI constexpr _Tp byteswap(_Tp __val) noexcept {
  28
  29   if constexpr (sizeof(_Tp) == 1) {
  30     return __val;
  31   } else if constexpr (sizeof(_Tp) == 2) {
  32     return __builtin_bswap16(__val);
  33   } else if constexpr (sizeof(_Tp) == 4) {
  34     return __builtin_bswap32(__val);
  35   } else if constexpr (sizeof(_Tp) == 8) {
  36     return __builtin_bswap64(__val);
  37 #ifndef _LIBCPP_HAS_NO_INT128
  38   } else if constexpr (sizeof(_Tp) == 16) {
  39 #if __has_builtin(__builtin_bswap128)
  40     return __builtin_bswap128(__val);
  41 #else
  42     return static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val))) << 64 |
  43            static_cast<_Tp>(byteswap(static_cast<uint64_t>(__val >> 64)));
  44 #endif // __has_builtin(__builtin_bswap128)
  45 #endif // _LIBCPP_HAS_NO_INT128
  46   } else {
  47     static_assert(sizeof(_Tp) == 0, "byteswap is unimplemented for integral types of this size");
  48   }
  49 }
  50
  51 #endif // _LIBCPP_STD_VER > 20 && !defined(_LIBCPP_HAS_NO_CONCEPTS)
  52
  53 _LIBCPP_END_NAMESPACE_STD
  54
  55 #endif // _LIBCPP___BIT_BYTESWAP_H