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- // 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 <stdint.h>
- #include "build/build_config.h"
- #if defined(COMPILER_MSVC)
- #include <stdlib.h>
- #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<uint32_t>(x));
- return ByteSwap(static_cast<uint64_t>(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_
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