Bugfix/bacnet real endian simplify (#89)

* Remove dependence on endian define

* Make use of existing big_endian function if BACNET_BIG_ENDIAN is not defined

* Add efficient endian macro option if available

Co-authored-by: Steve Karg <skarg@users.sourceforge.net>

src/bacnet/basic/sys/bigend.c

@@ -3,8 +3,9 @@
 
 /** @file bigend.c  Determination of Endianess */
 
-#include "bigend.h"
+#include "bacnet/basic/sys/bigend.h"
 
+#ifndef BACNET_BIG_ENDIAN
 /* Big-Endian systems save the most significant byte first.  */
 /* Sun and Motorola processors, IBM-370s and PDP-10s are big-endian. */
 /* "Network Byte Order" is also know as "Big-Endian Byte Order" */
@@ -46,3 +47,4 @@ int big_endian(void)
 
     return (u.c[sizeof(long) - 1] == 1);
 }
+#endif

src/bacnet/basic/sys/bigend.h

@@ -29,26 +29,24 @@
 #ifdef __cplusplus
 extern "C" {
 #endif /* __cplusplus */
+    #ifndef BACNET_BIG_ENDIAN
+        /* GCC */
+        #ifdef __BYTE_ORDER__
+            #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+                #define BACNET_BIG_ENDIAN 1
+            #else
+                #define BACNET_BIG_ENDIAN 0
+            #endif
+        #endif
+    #endif
 
-/* Big-Endian systems save the most significant byte first.  */
-/* Sun and Motorola processors, IBM-370s and PDP-10s are big-endian. */
-/* for example, a 4 byte integer 67305985 is 0x04030201 in hexidecimal. */
-/* x[0] = 0x04 */
-/* x[1] = 0x03 */
-/* x[2] = 0x02 */
-/* x[3] = 0x01 */
-
-/* Little-Endian systems save the least significant byte first.  */
-/* The entire Intel x86 family, Vaxes, Alphas and PDP-11s are little-endian. */
-/* for example, a 4 byte integer 67305985 is 0x04030201 in hexidecimal. */
-/* x[0] = 0x01 */
-/* x[1] = 0x02 */
-/* x[2] = 0x03 */
-/* x[3] = 0x04 */
-
+    #ifdef BACNET_BIG_ENDIAN
+        #define big_endian() BACNET_BIG_ENDIAN
+    #else
     BACNET_STACK_EXPORT
     int big_endian(
         void);
+    #endif
 
 #ifdef __cplusplus
 }