1//===-- llvm/ADT/bit.h - C++20 <bit> ----------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file implements the C++20 <bit> header.
10//
11//===----------------------------------------------------------------------===//
12
13#ifndef LLVM_ADT_BIT_H
14#define LLVM_ADT_BIT_H
15
16#include "llvm/Support/Compiler.h"
17#include <cstring>
18#include <type_traits>
19
20namespace llvm {
21
22// This implementation of bit_cast is different from the C++17 one in two ways:
23//  - It isn't constexpr because that requires compiler support.
24//  - It requires trivially-constructible To, to avoid UB in the implementation.
25template <typename To, typename From
26          , typename = typename std::enable_if<sizeof(To) == sizeof(From)>::type
27#if (__has_feature(is_trivially_constructible) && defined(_LIBCPP_VERSION)) || \
28    (defined(__GNUC__) && __GNUC__ >= 5)
29          , typename = typename std::is_trivially_constructible<To>::type
30#elif __has_feature(is_trivially_constructible)
31          , typename = typename std::enable_if<__is_trivially_constructible(To)>::type
32#else
33  // See comment below.
34#endif
35#if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \
36    (defined(__GNUC__) && __GNUC__ >= 5)
37          , typename = typename std::enable_if<std::is_trivially_copyable<To>::value>::type
38          , typename = typename std::enable_if<std::is_trivially_copyable<From>::value>::type
39#elif __has_feature(is_trivially_copyable)
40          , typename = typename std::enable_if<__is_trivially_copyable(To)>::type
41          , typename = typename std::enable_if<__is_trivially_copyable(From)>::type
42#else
43// This case is GCC 4.x. clang with libc++ or libstdc++ never get here. Unlike
44// llvm/Support/type_traits.h's is_trivially_copyable we don't want to
45// provide a good-enough answer here: developers in that configuration will hit
46// compilation failures on the bots instead of locally. That's acceptable
47// because it's very few developers, and only until we move past C++11.
48#endif
49>
50inline To bit_cast(const From &from) noexcept {
51  To to;
52  std::memcpy(&to, &from, sizeof(To));
53  return to;
54}
55
56} // namespace llvm
57
58#endif
59