Merge pull request #16292 from kaspar030/clist_is_empty

core: add clist_is_empty()

core/include/clist.h

@@ -33,6 +33,7 @@
  * clist_remove()       | O(n)    | remove and return node
  * clist_sort()         | O(NlogN)| sort list (stable)
  * clist_count()        | O(n)    | count the number of elements in a list
+ * clist_is_empty()     | O(1)    | returns true if the list contains no elements
  *
  * clist can be used as a traditional list, a queue (FIFO) and a stack (LIFO) using
  * fast O(1) operations.
@@ -87,6 +88,7 @@
 #ifndef CLIST_H
 #define CLIST_H
 
+#include <stdbool.h>
 #include <stddef.h>
 #include "list.h"
 
@@ -102,6 +104,20 @@ extern "C" {
  */
 typedef list_node_t clist_node_t;
 
+/**
+ * @brief Checks if *list is empty
+ *
+ * @note Complexity: O(1)
+ *
+ * @param[in]   list        Pointer to clist
+ *
+ * @returns     true if list contains no elements, false otherwise
+ */
+static inline bool clist_is_empty(const clist_node_t *list)
+{
+    return list->next == NULL;
+}
+
 /**
  * @brief Appends *new_node* at the end of *list
  *

tests/unittests/tests-core/tests-core-clist.c

@@ -331,6 +331,23 @@ static void test_clist_count(void)
     }
 }
 
+static void test_clist_is_empty(void)
+{
+    TEST_ASSERT(clist_is_empty(&test_clist));
+
+    for (unsigned i = 1; i <= TEST_CLIST_LEN; i++) {
+        clist_rpush(&test_clist, &tests_clist_buf[i - 1]);
+        TEST_ASSERT(!clist_is_empty(&test_clist));
+    }
+    for (unsigned i = TEST_CLIST_LEN; i > 0; i--) {
+        clist_lpop(&test_clist);
+        /* when i == 1 at the beginning of the iteration, there's one element
+           left, which is then dropped in the line above.
+           So in all cases but that last one, the list is not empty. */
+        TEST_ASSERT(clist_is_empty(&test_clist) == (i == 1));
+    }
+}
+
 Test *tests_core_clist_tests(void)
 {
     EMB_UNIT_TESTFIXTURES(fixtures) {
@@ -349,6 +366,7 @@ Test *tests_core_clist_tests(void)
         new_TestFixture(test_clist_sort_empty),
         new_TestFixture(test_clist_sort),
         new_TestFixture(test_clist_count),
+        new_TestFixture(test_clist_is_empty),
     };
 
     EMB_UNIT_TESTCALLER(core_clist_tests, set_up, NULL,