llvm-mirror/include/llvm/ADT/bit.h

//===-- llvm/ADT/bit.h - C++20 <bit> ----------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the C++20 <bit> header.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_BIT_H
#define LLVM_ADT_BIT_H

#include "llvm/Support/Compiler.h"
#include <cstring>
#include <type_traits>

namespace llvm {

template <typename To, typename From
          , typename = typename std::enable_if<sizeof(To) == sizeof(From)>::type
#if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \
    (defined(__GNUC__) && __GNUC__ >= 5)
          , typename = typename std::enable_if<std::is_trivially_copyable<To>::value>::type
          , typename = typename std::enable_if<std::is_trivially_copyable<From>::value>::type
#elif __has_feature(is_trivially_copyable)
          , typename = typename std::enable_if<__is_trivially_copyable(To>>::type
          , typename = typename std::enable_if<__is_trivially_copyable(From)>::type
#else
  // This case is GCC 4.x. clang with libc++ or libstdc++ never get here. Unlike
  // llvm/Support/type_traits.h's isPodLike we don't want to provide a
  // good-enough answer here: developers in that configuration will hit
  // compilation failures on the bots instead of locally. That's acceptable
  // because it's very few developers, and only until we move past C++11.
#endif
>
inline To bit_cast(const From &from) noexcept {
  alignas(To) unsigned char storage[sizeof(To)];
  std::memcpy(&storage, &from, sizeof(To));
#if defined(__GNUC__)
  // Before GCC 7.2, GCC thought that this violated strict aliasing.
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wstrict-aliasing"
#endif
  return reinterpret_cast<To &>(storage);
#if defined(__GNUC__)
#pragma GCC diagnostic pop
#endif
}

} // namespace llvm

#endif