define ARRAY_SIZE() for everyone
diff --git a/include/compiler.h b/include/compiler.h
index e8ad80a..52a1fd1 100644
--- a/include/compiler.h
+++ b/include/compiler.h
@@ -9,4 +9,8 @@
 
 #define attribute_noreturn __attribute__((noreturn))
 
+#ifndef ARRAY_SIZE
+# define ARRAY_SIZE(arr) (sizeof(arr) / sizeof(arr[0]))
+#endif
+
 #endif