base: Use compiler builtins for byte swapping

base/sys_byteorder.h

 // 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
+
 namespace base {
 
 // Returns a value with all bytes in |x| swapped, i.e. reverses the endianness.
 inline uint16_t ByteSwap(uint16_t x) {
-  return ((x & 0x00ff) << 8) | ((x & 0xff00) >> 8);
+#if defined(COMPILER_MSVC)
+  return _byteswap_ushort(x);
+#else
+  return __builtin_bswap16(x);
+#endif
 }
 
 inline uint32_t ByteSwap(uint32_t x) {
-  return ((x & 0x000000fful) << 24) | ((x & 0x0000ff00ul) << 8) |
-      ((x & 0x00ff0000ul) >> 8) | ((x & 0xff000000ul) >> 24);
+#if defined(COMPILER_MSVC)
+  return _byteswap_ulong(x);
+#else
+  return __builtin_bswap32(x);
+#endif
 }
 
 inline uint64_t ByteSwap(uint64_t x) {
-  return ((x & 0x00000000000000ffull) << 56) |
-      ((x & 0x000000000000ff00ull) << 40) |
-      ((x & 0x0000000000ff0000ull) << 24) |
-      ((x & 0x00000000ff000000ull) << 8) |
-      ((x & 0x000000ff00000000ull) >> 8) |
-      ((x & 0x0000ff0000000000ull) >> 24) |
-      ((x & 0x00ff000000000000ull) >> 40) |
-      ((x & 0xff00000000000000ull) >> 56);
+#if defined(COMPILER_MSVC)
+  return _byteswap_uint64(x);
+#else
+  return __builtin_bswap64(x);
+#endif
 }
 
 // Converts the bytes in |x| from host order (endianness) to little endian, and
 // returns the result.
 inline uint16_t ByteSwapToLE16(uint16_t x) {
 #if defined(ARCH_CPU_LITTLE_ENDIAN)
   return x;
 #else
   return ByteSwap(x);
 #endif
@@ skipping 57 matching lines @@
 #if defined(ARCH_CPU_LITTLE_ENDIAN)
   return ByteSwap(x);
 #else
   return x;
 #endif
 }
 
 }  // namespace base
 
 #endif  // BASE_SYS_BYTEORDER_H_