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