include: sys: util: add note and test for NUM_VA_ARGS_LESS_1

Notes that `NUM_VA_ARGS_LESS_1` support up to 64 arguments,
and added test for it in `tests/lib/sys_util`.

Signed-off-by: Yong Cong Sin <[email protected]>

Author: ycsin

include/zephyr/sys/util_macro.h

@@ -623,6 +623,8 @@ extern "C" {
 /**
  * @brief Number of arguments in the variable arguments list minus one.
  *
+ * @note Supports up to 64 arguments.
+ *
  * @param ... List of arguments
  * @return  Number of variadic arguments in the argument list, minus one
  */

tests/lib/sys_util/src/main.c

@@ -52,6 +52,21 @@ ZTEST(sys_util, test_NUM_VA_ARGS)
 	/* support up to 63 args */
 	zassert_equal(63, NUM_VA_ARGS(LISTIFY(63, ~, (,))));
 }
+
+/**
+ * @brief Test NUM_VA_ARGS_LESS_1 works as expected with typical use cases
+ *
+ * @see NUM_VA_ARGS_LESS_1()
+ */
+
+ZTEST(sys_util, test_NUM_VA_ARGS_LESS_1)
+{
+	zassert_equal(0, NUM_VA_ARGS_LESS_1());
+	zassert_equal(0, NUM_VA_ARGS_LESS_1(_1));
+	zassert_equal(1, NUM_VA_ARGS_LESS_1(_1, _2));
+	/* support up to 64 args */
+	zassert_equal(63, NUM_VA_ARGS_LESS_1(LISTIFY(64, ~, (,))));
+}
 /**
  * @}
  */