1
2 /* Copyright 1998 by the Massachusetts Institute of Technology.
3 *
4 * Permission to use, copy, modify, and distribute this
5 * software and its documentation for any purpose and without
6 * fee is hereby granted, provided that the above copyright
7 * notice appear in all copies and that both that copyright
8 * notice and this permission notice appear in supporting
9 * documentation, and that the name of M.I.T. not be used in
10 * advertising or publicity pertaining to distribution of the
11 * software without specific, written prior permission.
12 * M.I.T. makes no representations about the suitability of
13 * this software for any purpose. It is provided "as is"
14 * without express or implied warranty.
15 */
16
17 #include "ares_setup.h"
18
19 #include "ares.h"
20 #include "ares_private.h"
21
22 /* Routines for managing doubly-linked circular linked lists with a
23 * dummy head.
24 */
25
26 /* Initialize a new head node */
ares__init_list_head(struct list_node * head)27 void ares__init_list_head(struct list_node* head) {
28 head->prev = head;
29 head->next = head;
30 head->data = NULL;
31 }
32
33 /* Initialize a list node */
ares__init_list_node(struct list_node * node,void * d)34 void ares__init_list_node(struct list_node* node, void* d) {
35 node->prev = NULL;
36 node->next = NULL;
37 node->data = d;
38 }
39
40 /* Returns true iff the given list is empty */
ares__is_list_empty(struct list_node * head)41 int ares__is_list_empty(struct list_node* head) {
42 return ((head->next == head) && (head->prev == head));
43 }
44
45 /* Inserts new_node before old_node */
ares__insert_in_list(struct list_node * new_node,struct list_node * old_node)46 void ares__insert_in_list(struct list_node* new_node,
47 struct list_node* old_node) {
48 new_node->next = old_node;
49 new_node->prev = old_node->prev;
50 old_node->prev->next = new_node;
51 old_node->prev = new_node;
52 }
53
54 /* Removes the node from the list it's in, if any */
ares__remove_from_list(struct list_node * node)55 void ares__remove_from_list(struct list_node* node) {
56 if (node->next != NULL) {
57 node->prev->next = node->next;
58 node->next->prev = node->prev;
59 node->prev = NULL;
60 node->next = NULL;
61 }
62 }
63
64 /* Swap the contents of two lists */
ares__swap_lists(struct list_node * head_a,struct list_node * head_b)65 void ares__swap_lists(struct list_node* head_a,
66 struct list_node* head_b) {
67 int is_a_empty = ares__is_list_empty(head_a);
68 int is_b_empty = ares__is_list_empty(head_b);
69 struct list_node old_a = *head_a;
70 struct list_node old_b = *head_b;
71
72 if (is_a_empty) {
73 ares__init_list_head(head_b);
74 } else {
75 *head_b = old_a;
76 old_a.next->prev = head_b;
77 old_a.prev->next = head_b;
78 }
79 if (is_b_empty) {
80 ares__init_list_head(head_a);
81 } else {
82 *head_a = old_b;
83 old_b.next->prev = head_a;
84 old_b.prev->next = head_a;
85 }
86 }
87