[ccan] [PATCH 2/1] list: list_swap to exchange elements
Eric Wong
normalperson at yhbt.net
Wed Sep 10 11:58:47 EST 2014
This allows deleting and re-inserting an element in place
of the deleted element without branching.
Signed-off-by: Eric Wong <normalperson at yhbt.net>
---
Applies on top of my list_add_after/list_add_before patch.
ccan/list/list.h | 33 +++++++++++++++++++++++++++++++++
ccan/list/test/run.c | 23 +++++++++++++++++++++--
2 files changed, 54 insertions(+), 2 deletions(-)
diff --git a/ccan/list/list.h b/ccan/list/list.h
index 5c1159f..983675b 100644
--- a/ccan/list/list.h
+++ b/ccan/list/list.h
@@ -369,6 +369,39 @@ static inline void list_del_from(struct list_head *h, struct list_node *n)
}
/**
+ * list_swap - swap out an entry from an (unknown) linked list for a new one.
+ * @o: the list_node to replace from the list.
+ * @n: the list_node to insert in place of the old one.
+ *
+ * Note that this leaves @o in an undefined state; it can be added to
+ * another list, but not deleted/swapped again.
+ *
+ * See also:
+ * list_del()
+ *
+ * Example:
+ * struct child x1, x2;
+ * LIST_HEAD(xh);
+ *
+ * list_add(&xh, &x1.list);
+ * list_swap(&x1.list, &x2.list);
+ */
+#define list_swap(o, n) list_swap_(o, n, LIST_LOC)
+static inline void list_swap_(struct list_node *o,
+ struct list_node *n,
+ const char* abortstr)
+{
+ (void)list_debug_node(o, abortstr);
+ *n = *o;
+ n->next->prev = n;
+ n->prev->next = n;
+#ifdef CCAN_LIST_DEBUG
+ /* Catch use-after-del. */
+ o->next = o->prev = NULL;
+#endif
+}
+
+/**
* list_entry - convert a list_node back into the structure containing it.
* @n: the list_node
* @type: the type of the entry
diff --git a/ccan/list/test/run.c b/ccan/list/test/run.c
index 2f1acc7..3067445 100644
--- a/ccan/list/test/run.c
+++ b/ccan/list/test/run.c
@@ -19,13 +19,13 @@ static LIST_HEAD(static_list);
int main(int argc, char *argv[])
{
struct parent parent;
- struct child c1, c2, c3, *c, *n;
+ struct child c1, c2, c3, x1, *c, *n;
unsigned int i;
struct list_head list = LIST_HEAD_INIT(list);
opaque_t *q, *nq;
struct list_head opaque_list = LIST_HEAD_INIT(opaque_list);
- plan_tests(79);
+ plan_tests(84);
/* Test LIST_HEAD, LIST_HEAD_INIT, list_empty and check_list */
ok1(list_empty(&static_list));
ok1(list_check(&static_list, NULL));
@@ -253,5 +253,24 @@ int main(int argc, char *argv[])
}
ok1(i == 3);
+ /* test list_swap */
+ list_swap(&c3.list, &x1.list);
+ ok1(list_check(&parent.children, "list_swap"));
+ i = 0;
+ list_for_each(&parent.children, c, list) {
+ switch (i++) {
+ case 0:
+ ok1(c == &c1);
+ break;
+ case 1:
+ ok1(c == &x1);
+ break;
+ case 2:
+ ok1(c == &c2);
+ break;
+ }
+ }
+ ok1(i == 3);
+
return exit_status();
}
--
EW
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