-static inline uint16_t __u_bswap16(uint16_t val)
-{
- return ((val >> 8) & 0xffu) | ((val & 0xffu) << 8);
-}
+#define __eval_once(func, x) \
+ ({ __typeof__(x) __x = x; func(__x); })
+
+#ifdef __cplusplus
+/*
+ * g++ does not support __builtin_choose_expr, so always use __eval_once.
+ * Unfortunately this means that the byte order functions can't be used
+ * as a constant expression anymore
+ */
+#define __eval_safe(func, x) __eval_once(func, x)
+#else
+#define __eval_safe(func, x) \
+ __builtin_choose_expr(__is_constant(x), \
+ func(x), __eval_once(func, x))
+#endif