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 20 namespace 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. 25 template < 26 typename To, typename From, 27 typename = std::enable_if_t<sizeof(To) == sizeof(From)> 28 #if (__has_feature(is_trivially_constructible) && defined(_LIBCPP_VERSION)) || \ 29 (defined(__GNUC__) && __GNUC__ >= 5) 30 , 31 typename = std::enable_if_t<std::is_trivially_constructible<To>::value> 32 #elif __has_feature(is_trivially_constructible) 33 , 34 typename = std::enable_if_t<__is_trivially_constructible(To)> 35 #else 36 // See comment below. 37 #endif 38 #if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) || \ 39 (defined(__GNUC__) && __GNUC__ >= 5) 40 , 41 typename = std::enable_if_t<std::is_trivially_copyable<To>::value>, 42 typename = std::enable_if_t<std::is_trivially_copyable<From>::value> 43 #elif __has_feature(is_trivially_copyable) 44 , 45 typename = std::enable_if_t<__is_trivially_copyable(To)>, 46 typename = std::enable_if_t<__is_trivially_copyable(From)> 47 #else 48 // This case is GCC 4.x. clang with libc++ or libstdc++ never get here. Unlike 49 // llvm/Support/type_traits.h's is_trivially_copyable we don't want to 50 // provide a good-enough answer here: developers in that configuration will hit 51 // compilation failures on the bots instead of locally. That's acceptable 52 // because it's very few developers, and only until we move past C++11. 53 #endif 54 > 55 inline To bit_cast(const From &from) noexcept { 56 To to; 57 std::memcpy(&to, &from, sizeof(To)); 58 return to; 59 } 60 61 } // namespace llvm 62 63 #endif 64