// Copyright (c) 2012 The Chromium Authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. // This header defines cross-platform ByteSwap() implementations for 16, 32 and // 64-bit values, and NetToHostXX() / HostToNextXX() functions equivalent to // the traditional ntohX() and htonX() functions. // Use the functions defined here rather than using the platform-specific // functions directly. #ifndef BASE_SYS_BYTEORDER_H_ #define BASE_SYS_BYTEORDER_H_ #include #include "build/build_config.h" #if defined(COMPILER_MSVC) #include #endif #if defined(COMPILER_MSVC) && !defined(__clang__) // TODO(pkasting): See // https://developercommunity.visualstudio.com/t/Mark-some-built-in-functions-as-constexp/362558 // https://developercommunity.visualstudio.com/t/constexpr-byte-swapping-optimization/983963 #define BASE_BYTESWAPS_CONSTEXPR #else #define BASE_BYTESWAPS_CONSTEXPR constexpr #endif namespace base { // Returns a value with all bytes in |x| swapped, i.e. reverses the endianness. // TODO(pkasting): Once C++23 is available, replace with std::byteswap. inline BASE_BYTESWAPS_CONSTEXPR uint16_t ByteSwap(uint16_t x) { #if defined(COMPILER_MSVC) && !defined(__clang__) return _byteswap_ushort(x); #else return __builtin_bswap16(x); #endif } inline BASE_BYTESWAPS_CONSTEXPR uint32_t ByteSwap(uint32_t x) { #if defined(COMPILER_MSVC) && !defined(__clang__) return _byteswap_ulong(x); #else return __builtin_bswap32(x); #endif } inline BASE_BYTESWAPS_CONSTEXPR uint64_t ByteSwap(uint64_t x) { // Per build/build_config.h, clang masquerades as MSVC on Windows. If we are // actually using clang, we can rely on the builtin. // // This matters in practice, because on x86(_64), this is a single "bswap" // instruction. MSVC correctly replaces the call with an inlined bswap at /O2 // as of 2021, but clang as we use it in Chromium doesn't, keeping a function // call for a single instruction. #if defined(COMPILER_MSVC) && !defined(__clang__) return _byteswap_uint64(x); #else return __builtin_bswap64(x); #endif } inline BASE_BYTESWAPS_CONSTEXPR uintptr_t ByteSwapUintPtrT(uintptr_t x) { // We do it this way because some build configurations are ILP32 even when // defined(ARCH_CPU_64_BITS). Unfortunately, we can't use sizeof in #ifs. But, // because these conditionals are constexprs, the irrelevant branches will // likely be optimized away, so this construction should not result in code // bloat. static_assert(sizeof(uintptr_t) == 4 || sizeof(uintptr_t) == 8, "Unsupported uintptr_t size"); if (sizeof(uintptr_t) == 4) return ByteSwap(static_cast(x)); return ByteSwap(static_cast(x)); } // Converts the bytes in |x| from host order (endianness) to little endian, and // returns the result. inline BASE_BYTESWAPS_CONSTEXPR uint16_t ByteSwapToLE16(uint16_t x) { #if defined(ARCH_CPU_LITTLE_ENDIAN) return x; #else return ByteSwap(x); #endif } inline BASE_BYTESWAPS_CONSTEXPR uint32_t ByteSwapToLE32(uint32_t x) { #if defined(ARCH_CPU_LITTLE_ENDIAN) return x; #else return ByteSwap(x); #endif } inline BASE_BYTESWAPS_CONSTEXPR uint64_t ByteSwapToLE64(uint64_t x) { #if defined(ARCH_CPU_LITTLE_ENDIAN) return x; #else return ByteSwap(x); #endif } // Converts the bytes in |x| from network to host order (endianness), and // returns the result. inline BASE_BYTESWAPS_CONSTEXPR uint16_t NetToHost16(uint16_t x) { #if defined(ARCH_CPU_LITTLE_ENDIAN) return ByteSwap(x); #else return x; #endif } inline BASE_BYTESWAPS_CONSTEXPR uint32_t NetToHost32(uint32_t x) { #if defined(ARCH_CPU_LITTLE_ENDIAN) return ByteSwap(x); #else return x; #endif } inline BASE_BYTESWAPS_CONSTEXPR uint64_t NetToHost64(uint64_t x) { #if defined(ARCH_CPU_LITTLE_ENDIAN) return ByteSwap(x); #else return x; #endif } // Converts the bytes in |x| from host to network order (endianness), and // returns the result. inline BASE_BYTESWAPS_CONSTEXPR uint16_t HostToNet16(uint16_t x) { #if defined(ARCH_CPU_LITTLE_ENDIAN) return ByteSwap(x); #else return x; #endif } inline BASE_BYTESWAPS_CONSTEXPR uint32_t HostToNet32(uint32_t x) { #if defined(ARCH_CPU_LITTLE_ENDIAN) return ByteSwap(x); #else return x; #endif } inline BASE_BYTESWAPS_CONSTEXPR uint64_t HostToNet64(uint64_t x) { #if defined(ARCH_CPU_LITTLE_ENDIAN) return ByteSwap(x); #else return x; #endif } } // namespace base #undef BASE_BYTESWAPS_CONSTEXPR #endif // BASE_SYS_BYTEORDER_H_