FreeBSD support in endian.h (dmlc#476)

* FreeBSD support in endian.h

* Better endian detection logic

* Fix typo

* Add attribution to Boost Library for detection logic

* Fix typo

* Fix style error

* Simplify detection logic; offload corner cases to CMake

CMakeLists.txt

@@ -96,6 +96,15 @@ endif()
 
 check_symbol_exists(nanosleep time.h DMLC_NANOSLEEP_PRESENT)
 
+# Check endianness
+include(TestBigEndian)
+test_big_endian(BIG_ENDIAN)
+if(BIG_ENDIAN)
+  set(DMLC_CMAKE_LITTLE_ENDIAN 0)
+else()
+  set(DMLC_CMAKE_LITTLE_ENDIAN 1)
+endif()
+
 message(STATUS "${CMAKE_LOCAL}/build_config.h.in -> ${INCLUDE_DMLC_DIR}/build_config.h")
 configure_file("${CMAKE_LOCAL}/build_config.h.in" "${INCLUDE_DMLC_DIR}/build_config.h")
 

cmake/build_config.h.in

@@ -25,4 +25,6 @@
 
 #cmakedefine DMLC_NANOSLEEP_PRESENT
 
+#cmakedefine DMLC_CMAKE_LITTLE_ENDIAN ${DMLC_CMAKE_LITTLE_ENDIAN}
+
 #endif  // DMLC_BUILD_CONFIG_H_

include/dmlc/endian.h

@@ -8,11 +8,21 @@
 
 #include "./base.h"
 
-#if defined(__APPLE__) || defined(_WIN32)
-#define DMLC_LITTLE_ENDIAN 1
+#ifdef DMLC_CMAKE_LITTLE_ENDIAN
+  // If compiled with CMake, use CMake's endian detection logic
+  #define DMLC_LITTLE_ENDIAN DMLC_CMAKE_LITTLE_ENDIAN
 #else
-#include <endian.h>
-#define DMLC_LITTLE_ENDIAN (__BYTE_ORDER == __LITTLE_ENDIAN)
+  #if defined(__APPLE__) || defined(_WIN32)
+    #define DMLC_LITTLE_ENDIAN 1
+  #elif defined(__GLIBC__)
+    #include <endian.h>
+    #define DMLC_LITTLE_ENDIAN (__BYTE_ORDER == __LITTLE_ENDIAN)
+  #elif defined(__FreeBSD__)
+    #include <sys/endian.h>
+    #define DMLC_LITTLE_ENDIAN (_BYTE_ORDER == _LITTLE_ENDIAN)
+  #else
+    #error "Unable to determine endianness of your machine; use CMake to compile"
+  #endif
 #endif
 
 /*! \brief whether serialize using little endian */