MINOR: tools: add a DEFNULL() macro to use NULL for empty args

It's sometimes convenient for debugging macros not to be forced to
explicitly pass NULL in an unused argument. This macro does this, it
replaces a missing arg with NULL.

diff --git a/include/common/standard.h b/include/common/standard.h
index cdefc9f5b3ebbbd8538e99762b7d84c852f62bc3..ffebac8ee7fb7db0f08e2eb60ad8ae3a59b54b83 100644 (file)
--- a/include/common/standard.h
+++ b/include/common/standard.h
@@ -61,6 +61,12 @@
  * power of 2, and 0 otherwise */
 #define POWEROF2(x) (((x) & ((x)-1)) == 0)
 
+/* DEFNULL() returns either the argument as-is, or NULL if absent. This is for
+ * use in macros arguments.
+ */
+#define DEFNULL(...) _FIRST_ARG(NULL, ##__VA_ARGS__, NULL)
+#define _FIRST_ARG(a, b, ...) b
+
 /* operators to compare values. They're ordered that way so that the lowest bit
  * serves as a negation for the test and contains all tests that are not equal.
  */