Use compiler intrinsics to swap bytes

CMakeLists.txt

@@ -62,10 +62,16 @@ INCLUDE(ExternalProject)
 # Compilation options
 # *******************
 
+# Always check for C++ features
+INCLUDE(CheckCXXFeatures)
+
+IF(HAS_GCC_BUILTIN_SWAP)
+    SET(HAVE_GCC_BUILTIN_SWAP ON)
+ENDIF()
+
 # C++11 support
 OPTION(LIBTINS_ENABLE_CXX11 "Compile libtins with c++11 features" ON)
 IF(LIBTINS_ENABLE_CXX11)
-    INCLUDE(CheckCXXFeatures)
     # We only use declval and decltype on gcc/clang as VC fails to build that code,
     # at least on VC2013
     IF(HAS_CXX11_RVALUE_REFERENCES AND ((HAS_CXX11_DECLVAL AND HAS_CXX11_DECLTYPE) OR MSVC))

cmake/Modules/CheckCXXFeatures.cmake

@@ -142,3 +142,4 @@ cxx11_check_feature("decltype" HAS_CXX11_DECLTYPE)
 cxx11_check_feature("declval" HAS_CXX11_DECLVAL)
 cxx11_check_feature("initializer_list" HAS_CXX11_INITIALIZER_LIST)
 cxx11_check_feature("rvalue-references" HAS_CXX11_RVALUE_REFERENCES)
+cxx11_check_feature("builtin-swap" HAS_GCC_BUILTIN_SWAP)

cmake/Modules/CheckCXXFeatures/cxx-test-builtin-swap.cpp

@@ -0,0 +1,8 @@
+#include <stdint.h>
+
+int main() {
+    uint16_t u16 = __builtin_bswap16(0x9812U);
+    uint32_t u32 = __builtin_bswap32(0x9812ad81U);
+    uint64_t u64 = __builtin_bswap64(0x9812ad81f61a890dU);
+    return (u16 > 0 && u32 > 0 && u64 > 0) ? 0 : 1;
+}

include/tins/config.h.in

@@ -16,4 +16,7 @@
 /* Have TCP ACK tracking */
 #cmakedefine HAVE_ACK_TRACKER
 
+/* Have GCC builtin swap */
+#cmakedefine HAVE_GCC_BUILTIN_SWAP
+
 #endif // TINS_CONFIG_H

include/tins/endianness.h

@@ -42,6 +42,7 @@
     #define TINS_IS_LITTLE_ENDIAN (_BYTE_ORDER == _LITTLE_ENDIAN)
     #define TINS_IS_BIG_ENDIAN (_BYTE_ORDER == _BIG_ENDIAN)
 #elif defined(_WIN32)
+    #include <cstdlib>
     // Assume windows == little endian. fixme later
     #define TINS_IS_LITTLE_ENDIAN 1
     #define TINS_IS_BIG_ENDIAN 0
@@ -51,6 +52,19 @@
     #define TINS_IS_BIG_ENDIAN (__BYTE_ORDER == __BIG_ENDIAN)
 #endif
 
+// Define macros to swap bytes using compiler intrinsics when possible
+#if defined(_MSC_VER)
+    #define TINS_BYTE_SWAP_16(data) _byteswap_ushort(data)
+    #define TINS_BYTE_SWAP_32(data) _byteswap_ulong(data)
+    #define TINS_BYTE_SWAP_64(data) _byteswap_uint64(data)
+#elif defined(HAVE_GCC_BUILTIN_SWAP)
+    #define TINS_BYTE_SWAP_16(data) __builtin_bswap16(data)
+    #define TINS_BYTE_SWAP_32(data) __builtin_bswap32(data)
+    #define TINS_BYTE_SWAP_64(data) __builtin_bswap64(data)
+#else
+    #define TINS_NO_BYTE_SWAP_INTRINSICS
+#endif
+
 namespace Tins {
 namespace Endian {
 
@@ -70,7 +84,11 @@ inline uint8_t do_change_endian(uint8_t data) {
  * \param data The data to convert.
  */
 inline uint16_t do_change_endian(uint16_t data) {
-    return ((data & 0xff00) >> 8)  | ((data & 0x00ff) << 8);
+    #ifdef TINS_NO_BYTE_SWAP_INTRINSICS
+        return ((data & 0xff00) >> 8)  | ((data & 0x00ff) << 8);
+    #else
+        return TINS_BYTE_SWAP_16(data);
+    #endif
 }
 
 /**
@@ -79,8 +97,12 @@ inline uint16_t do_change_endian(uint16_t data) {
  * \param data The data to convert.
  */
 inline uint32_t do_change_endian(uint32_t data) {
-    return (((data & 0xff000000) >> 24) | ((data & 0x00ff0000) >> 8)  |
-            ((data & 0x0000ff00) << 8)  | ((data & 0x000000ff) << 24));
+    #ifdef TINS_NO_BYTE_SWAP_INTRINSICS
+        return (((data & 0xff000000) >> 24) | ((data & 0x00ff0000) >> 8)  |
+               ((data & 0x0000ff00) << 8)  | ((data & 0x000000ff) << 24));
+    #else
+        return TINS_BYTE_SWAP_32(data);
+    #endif
 }
 
 /**
@@ -89,8 +111,12 @@ inline uint32_t do_change_endian(uint32_t data) {
  * \param data The data to convert.
  */
  inline uint64_t do_change_endian(uint64_t data) {
-    return (((uint64_t)(do_change_endian((uint32_t)(data & 0xffffffff))) << 32) |
-            (do_change_endian(((uint32_t)(data >> 32)))));
+    #ifdef TINS_NO_BYTE_SWAP_INTRINSICS
+        return (((uint64_t)(do_change_endian((uint32_t)(data & 0xffffffff))) << 32) |
+               (do_change_endian(((uint32_t)(data >> 32)))));
+    #else
+        return TINS_BYTE_SWAP_64(data);
+    #endif
  }
  
 /**