endian: Be able to detect endian on GNU and BSD

On GNU __BYTE_ORDER and __LITTLE_ENDIAN is defined and
the include is "endian.h" on FreeBSD it is "sys/endian.h"
and LITTLE_ENDIAN/_LITTLE_ENDIAN and BYTE_ORDER/_BYTE_ORDER
is defined.

Create a header file that defines OSMO_IS_LITTLE_ENDIAN
and OSMO_IS_BIG_ENDIAN and can be used as

 #if OSMO_IS_LITTLE_ENDIAN
   do_little_endian
 #elif OSMO_IS_BIG_ENDIAN
   do_big_endian
 #else
   #error "Unknown endian"
 #endif

1 files changed, 38 insertions, 0 deletions

diff --git a/include/osmocom/core/endian.h b/include/osmocom/core/endian.h
new file mode 100644
index 00000000..c890fd72
--- /dev/null
+++ b/include/osmocom/core/endian.h
@@ -0,0 +1,38 @@
+#pragma once
+
+/**
+ * GNU and FreeBSD have various ways to express the
+ * endianess but none of them is similiar enough. This
+ * will create two defines that allows to decide on the
+ * endian. The following will be defined to either 0 or
+ * 1 at the end of the file.
+ *
+ *      OSMO_IS_LITTLE_ENDIAN
+ *      OSMO_IS_BIG_ENDIAN
+ *
+ */
+
+#if defined(__FreeBSD__)
+#include <sys/endian.h>
+        #if BYTE_ORDER == LITTLE_ENDIAN
+                #define OSMO_IS_LITTLE_ENDIAN           1
+                #define OSMO_IS_BIG_ENDIAN              0
+        #elif BYTE_ORDER == BIG_ENDIAN
+                #define OSMO_IS_LITTLE_ENDIAN           0
+                #define OSMO_IS_BIG_ENDIAN              1
+        #else
+                #error "Unknown endian"
+        #endif
+#else
+#include <endian.h>
+        #if __BYTE_ORDER == __LITTLE_ENDIAN
+                #define OSMO_IS_LITTLE_ENDIAN           1
+                #define OSMO_IS_BIG_ENDIAN              0
+        #elif __BYTE_ORDER == __BIG_ENDIAN
+                #define OSMO_IS_LITTLE_ENDIAN           0
+                #define OSMO_IS_BIG_ENDIAN              1
+        #else
+                #error "Unknown endian"
+        #endif
+#endif
+