sandbox: add double linked-list data structure

sandbox/queue/queue.c

@@ -0,0 +1,104 @@
+#include <socks/queue.h>
+
+void queue_insert_before(queue_t *q, queue_entry_t *entry, queue_entry_t *before)
+{
+	queue_entry_t *x = before->qe_prev;
+	if (x) {
+		x->qe_next = entry;
+	} else {
+		q->q_first = entry;
+	}
+
+	entry->qe_prev = x;
+
+	before->qe_prev = entry;
+	entry->qe_next = before;
+}
+	 
+void queue_insert_after(queue_t *q, queue_entry_t *entry, queue_entry_t *after)
+{
+	queue_entry_t *x = after->qe_next;
+	if (x) {
+		x->qe_prev = entry;
+	} else {
+		q->q_last = entry;
+	}
+
+	entry->qe_prev = x;
+
+	after->qe_next = entry;
+	entry->qe_prev = after;
+	q->q_length++;
+}
+
+void queue_push_front(queue_t *q, queue_entry_t *entry)
+{
+	if (q->q_first) {
+		q->q_first->qe_prev = entry;
+	}
+	    
+	entry->qe_next = q->q_first;
+	entry->qe_prev = NULL;
+
+	q->q_first = entry;
+
+	if (!q->q_last) {
+		q->q_last = entry;
+	}
+	
+	q->q_length++;
+}
+
+void queue_push_back(queue_t *q, queue_entry_t *entry)
+{
+	if (q->q_last) {
+		q->q_last->qe_next = entry;
+	}
+
+	entry->qe_prev = q->q_last;
+	entry->qe_next = NULL;
+
+	q->q_last = entry;
+
+	if (!q->q_first) {
+		q->q_first = entry;
+	}
+	
+	q->q_length++;
+}
+
+queue_entry_t *queue_pop_front(queue_t *q)
+{
+	queue_entry_t *x = q->q_first;
+	queue_delete(q, x);
+	return x;
+}
+
+queue_entry_t *queue_pop_back(queue_t *q)
+{
+	queue_entry_t *x = q->q_last;
+	queue_delete(q, x);
+	return x;
+}
+
+void queue_delete(queue_t *q, queue_entry_t *entry)
+{
+	if (entry == q->q_first) {
+		q->q_first = q->q_first->qe_next;
+	}
+
+	if (entry == q->q_last) {
+		q->q_last = q->q_last->qe_prev;
+	}
+
+	if (entry->qe_next) {
+		entry->qe_next->qe_prev = entry->qe_prev;
+	}
+
+	if (entry->qe_prev) {
+		entry->qe_prev->qe_next = entry->qe_next;
+	}
+
+	entry->qe_next = entry->qe_prev = NULL;
+	q->q_length--;
+}