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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 // This header defines cross-platform ByteSwap() implementations for 16, 32 and
      6 // 64-bit values, and NetToHostXX() / HostToNextXX() functions equivalent to
      7 // the traditional ntohX() and htonX() functions.
      8 // Use the functions defined here rather than using the platform-specific
      9 // functions directly.
     10 
     11 #ifndef BASE_SYS_BYTEORDER_H_
     12 #define BASE_SYS_BYTEORDER_H_
     13 
     14 #include <stdint.h>
     15 
     16 #include "base/logging.h"
     17 #include "build/build_config.h"
     18 
     19 #if defined(COMPILER_MSVC)
     20 #include <stdlib.h>
     21 #endif
     22 
     23 namespace base {
     24 
     25 // Returns a value with all bytes in |x| swapped, i.e. reverses the endianness.
     26 inline uint16_t ByteSwap(uint16_t x) {
     27 #if defined(COMPILER_MSVC)
     28   return _byteswap_ushort(x);
     29 #else
     30   return __builtin_bswap16(x);
     31 #endif
     32 }
     33 
     34 inline uint32_t ByteSwap(uint32_t x) {
     35 #if defined(COMPILER_MSVC)
     36   return _byteswap_ulong(x);
     37 #else
     38   return __builtin_bswap32(x);
     39 #endif
     40 }
     41 
     42 inline uint64_t ByteSwap(uint64_t x) {
     43 #if defined(COMPILER_MSVC)
     44   return _byteswap_uint64(x);
     45 #else
     46   return __builtin_bswap64(x);
     47 #endif
     48 }
     49 
     50 inline uintptr_t ByteSwapUintPtrT(uintptr_t x) {
     51   // We do it this way because some build configurations are ILP32 even when
     52   // defined(ARCH_CPU_64_BITS). Unfortunately, we can't use sizeof in #ifs. But,
     53   // because these conditionals are constexprs, the irrelevant branches will
     54   // likely be optimized away, so this construction should not result in code
     55   // bloat.
     56   if (sizeof(uintptr_t) == 4) {
     57     return ByteSwap(static_cast<uint32_t>(x));
     58   } else if (sizeof(uintptr_t) == 8) {
     59     return ByteSwap(static_cast<uint64_t>(x));
     60   } else {
     61     NOTREACHED();
     62   }
     63 }
     64 
     65 // Converts the bytes in |x| from host order (endianness) to little endian, and
     66 // returns the result.
     67 inline uint16_t ByteSwapToLE16(uint16_t x) {
     68 #if defined(ARCH_CPU_LITTLE_ENDIAN)
     69   return x;
     70 #else
     71   return ByteSwap(x);
     72 #endif
     73 }
     74 inline uint32_t ByteSwapToLE32(uint32_t x) {
     75 #if defined(ARCH_CPU_LITTLE_ENDIAN)
     76   return x;
     77 #else
     78   return ByteSwap(x);
     79 #endif
     80 }
     81 inline uint64_t ByteSwapToLE64(uint64_t x) {
     82 #if defined(ARCH_CPU_LITTLE_ENDIAN)
     83   return x;
     84 #else
     85   return ByteSwap(x);
     86 #endif
     87 }
     88 
     89 // Converts the bytes in |x| from network to host order (endianness), and
     90 // returns the result.
     91 inline uint16_t NetToHost16(uint16_t x) {
     92 #if defined(ARCH_CPU_LITTLE_ENDIAN)
     93   return ByteSwap(x);
     94 #else
     95   return x;
     96 #endif
     97 }
     98 inline uint32_t NetToHost32(uint32_t x) {
     99 #if defined(ARCH_CPU_LITTLE_ENDIAN)
    100   return ByteSwap(x);
    101 #else
    102   return x;
    103 #endif
    104 }
    105 inline uint64_t NetToHost64(uint64_t x) {
    106 #if defined(ARCH_CPU_LITTLE_ENDIAN)
    107   return ByteSwap(x);
    108 #else
    109   return x;
    110 #endif
    111 }
    112 
    113 // Converts the bytes in |x| from host to network order (endianness), and
    114 // returns the result.
    115 inline uint16_t HostToNet16(uint16_t x) {
    116 #if defined(ARCH_CPU_LITTLE_ENDIAN)
    117   return ByteSwap(x);
    118 #else
    119   return x;
    120 #endif
    121 }
    122 inline uint32_t HostToNet32(uint32_t x) {
    123 #if defined(ARCH_CPU_LITTLE_ENDIAN)
    124   return ByteSwap(x);
    125 #else
    126   return x;
    127 #endif
    128 }
    129 inline uint64_t HostToNet64(uint64_t x) {
    130 #if defined(ARCH_CPU_LITTLE_ENDIAN)
    131   return ByteSwap(x);
    132 #else
    133   return x;
    134 #endif
    135 }
    136 
    137 }  // namespace base
    138 
    139 #endif  // BASE_SYS_BYTEORDER_H_
    140