src/llist.c: Add llist_next_filter()

This convenience function can be used to return the successor of a list
item if it is matched by a filter callback and return NULL otherwise.

We will use this for an improved version of the LLIST_FIND_FOREACH macro
that can be used whenever results are known to be continuous.

Signed-off-by: Lukas Fleischer <calcurse@cryptocrack.de>

src/llist.c

@@ -114,6 +114,19 @@ llist_next (llist_item_t *i)
   return i ? i->next : NULL;
 }
 
+/*
+ * Return the successor of a list item if it is matched by some filter
+ * callback. Return NULL otherwise.
+ */
+llist_item_t *
+llist_next_filter (llist_item_t *i, long data, llist_fn_match_t fn_match)
+{
+  if (i && i->next && fn_match (i->next->data, data))
+    return i->next;
+  else
+    return NULL;
+}
+
 /*
  * Get the actual data of an item.
  */