Land #998, Windows: Improve check for endianness when using Visual St…

…udio

CMakeLists.txt

@@ -140,6 +140,15 @@ endif()
 if(MSVC)
 	add_definitions(-Dinline=__inline)
 	message(STATUS "Using [${CMAKE_C_COMPILER_ID}] compiler")
+
+	include(TestBigEndian)
+	TEST_BIG_ENDIAN(HAVE_BIG_ENDIAN)
+	if(HAVE_BIG_ENDIAN)
+		add_definitions(-DHAVE_BIG_ENDIAN)
+	else()
+		add_definitions(-DHAVE_LITTLE_ENDIAN)
+	endif()
+
 	if(CMAKE_C_COMPILER_ID MATCHES "MSVC" OR CMAKE_C_COMPILER_ID MATCHES "Clang")
 		set(MSVC_DISABLED_WARNINGS_LIST
 			"C4018" # 'expression' : signed/unsigned mismatch

include/compat/endian.h

@@ -13,13 +13,28 @@
 #define PDP_ENDIAN 3412
 
 /*
- * Use GCC and Visual Studio compiler defines to determine endian.
+ * Use GCC compiler defines to determine endianness.
  */
+#if defined(__BYTE_ORDER__)
 #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define BYTE_ORDER LITTLE_ENDIAN
 #else
 #define BYTE_ORDER BIG_ENDIAN
 #endif
+#endif
+
+/*
+ * Use build system defines to determine endianness.
+ */
+#if !defined(BYTE_ORDER)
+#if defined(HAVE_LITTLE_ENDIAN)
+#define BYTE_ORDER LITTLE_ENDIAN
+#elif defined(HAVE_BIG_ENDIAN)
+#define BYTE_ORDER BIG_ENDIAN
+#else
+#error "Could not detect endianness."
+#endif
+#endif
 
 #elif defined(HAVE_ENDIAN_H)
 #include_next <endian.h>