core: queue: implement moving queue entries

this works exactly the same as moving btree nodes.

core/include/blue/core/queue.h

@@ -35,24 +35,24 @@ static inline void b_queue_init(b_queue *q)
 }
 static inline bool b_queue_empty(const b_queue *q)
 {
-	return q->q_first == NULL;
+	return q ? (q->q_first == NULL) : true;
 }
 
 static inline b_queue_entry *b_queue_first(const b_queue *q)
 {
-	return q->q_first;
+	return q ? q->q_first : NULL;
 }
 static inline b_queue_entry *b_queue_last(const b_queue *q)
 {
-	return q->q_last;
+	return q ? q->q_last : NULL;
 }
 static inline b_queue_entry *b_queue_next(const b_queue_entry *entry)
 {
-	return entry->qe_next;
+	return entry ? entry->qe_next : NULL;
 }
 static inline b_queue_entry *b_queue_prev(const b_queue_entry *entry)
 {
-	return entry->qe_prev;
+	return entry ? entry->qe_prev : NULL;
 }
 
 BLUE_API b_type b_queue_iterator_get_type(void);
@@ -70,6 +70,7 @@ BLUE_API void b_queue_push_back(b_queue *q, b_queue_entry *entry);
 BLUE_API b_queue_entry *b_queue_pop_front(b_queue *q);
 BLUE_API b_queue_entry *b_queue_pop_back(b_queue *q);
 
+BLUE_API void b_queue_move(b_queue *q, b_queue_entry *dest, b_queue_entry *src);
 BLUE_API void b_queue_delete(b_queue *q, b_queue_entry *entry);
 BLUE_API void b_queue_delete_all(b_queue *q);
 

core/queue.c

@@ -102,6 +102,27 @@ struct b_queue_entry *b_queue_pop_back(struct b_queue *q)
 	return x;
 }
 
+void b_queue_move(b_queue *q, b_queue_entry *dest, b_queue_entry *src)
+{
+	if (src->qe_next) {
+		src->qe_next->qe_prev = dest;
+	}
+
+	if (src->qe_prev) {
+		src->qe_prev->qe_next = dest;
+	}
+
+	if (q->q_first == src) {
+		q->q_first = dest;
+	}
+
+	if (q->q_last == src) {
+		q->q_last = dest;
+	}
+
+	memmove(dest, src, sizeof *src);
+}
+
 void b_queue_delete(struct b_queue *q, struct b_queue_entry *entry)
 {
 	if (!entry) {