macros.h: Implement SIDE_PARAM_SELECT_ARG1

[libside.git] / include / side / macros.h

diff --git a/include/side/macros.h b/include/side/macros.h
index af6ba1152252be219666160c18e010ebbb2d17fe..aea7b9ca5e71c12de16afb752213572515cffff3 100644 (file)
--- a/include/side/macros.h
+++ b/include/side/macros.h
@@ -6,6 +6,9 @@
 #ifndef _SIDE_MACROS_H
 #define _SIDE_MACROS_H
 
+#include <stddef.h>
+#include <limits.h>
+
 /* Helper macros */
 
 #define SIDE_ARRAY_SIZE(arr)   (sizeof(arr) / sizeof((arr)[0]))
@@ -27,6 +30,30 @@
 
 #define SIDE_PARAM(...)        __VA_ARGS__
 
+/*
+ * SIDE_PARAM_SELECT_ARG1
+ *
+ * Select second argument. Use inside macros to implement optional last
+ * macro argument, such as:
+ *
+ * #define macro(_a, _b, _c, _optional...) \
+ *     SIDE_PARAM_SELECT_ARG1(_, ##_optional, do_default_macro())
+ *
+ * This macro is far from pretty, but attempts to create a cleaner layer
+ * on top fails for various reasons:
+ *
+ * - The libside API needs to use the default argument selection as an
+ *   argument to itself (recursively), e.g. for fields and for types, so
+ *   using the argument selection within an extra layer of macro fails
+ *   because the extra layer cannot expand recursively.
+ * - Attempts to make the extra layer of macro support recursion through
+ *   another layer of macros which expands all arguments failed because
+ *   the optional argument may contain commas, and is therefore expanded
+ *   into multiple arguments before argument selection, which fails to
+ *   select the optional argument content after its first comma.
+ */
+#define SIDE_PARAM_SELECT_ARG1(_arg0, _arg1, ...) _arg1
+
 /*
  * side_container_of - Get the address of an object containing a field.
  *
@@ -41,4 +68,17 @@
                (type *)((char *)__ptr - offsetof(type, member));       \
        })
 
+#define side_struct_field_sizeof(_struct, _field) \
+       sizeof(((_struct * )NULL)->_field)
+
+#if defined(__SIZEOF_LONG__)
+#define SIDE_BITS_PER_LONG     (__SIZEOF_LONG__ * 8)
+#elif defined(_LP64)
+#define SIDE_BITS_PER_LONG     64
+#else
+#define SIDE_BITS_PER_LONG     32
+#endif
+
+#define SIDE_PACKED    __attribute__((packed))
+
 #endif /* _SIDE_MACROS_H */