2 Unix SMB/CIFS implementation.
3 some simple double linked list macros
5 Copyright (C) Andrew Tridgell 1998-2010
7 This program is free software; you can redistribute it and/or modify
8 it under the terms of the GNU General Public License as published by
9 the Free Software Foundation; either version 3 of the License, or
10 (at your option) any later version.
12 This program is distributed in the hope that it will be useful,
13 but WITHOUT ANY WARRANTY; without even the implied warranty of
14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 GNU General Public License for more details.
17 You should have received a copy of the GNU General Public License
18 along with this program. If not, see <http://www.gnu.org/licenses/>.
21 /* To use these macros you must have a structure containing a next and
28 February 2010 - changed list format to have a prev pointer from the
29 list head. This makes DLIST_ADD_END() O(1) even though we only have
32 The scheme is as follows:
34 1) with no entries in the list:
37 2) with 1 entry in the list:
38 list_head->next == NULL
39 list_head->prev == list_head
41 3) with 2 entries in the list:
42 list_head->next == element2
43 list_head->prev == element2
44 element2->prev == list_head
45 element2->next == NULL
47 4) with N entries in the list:
48 list_head->next == element2
49 list_head->prev == elementN
50 elementN->prev == element{N-1}
51 elementN->next == NULL
53 This allows us to find the tail of the list by using
54 list_head->prev, which means we can add to the end of the list in
58 Note that the 'type' arguments below are no longer needed, but
59 are kept for now to prevent an incompatible argument change
64 add an element at the front of a list
66 #define DLIST_ADD(list, p) \
69 (p)->prev = (list) = (p); \
72 (p)->prev = (list)->prev; \
80 remove an element from a list
81 Note that the element doesn't have to be in the list. If it
82 isn't then this is a no-op
84 #define DLIST_REMOVE(list, p) \
86 if ((p) == (list)) { \
87 if ((p)->next) (p)->next->prev = (p)->prev; \
89 } else if ((list) && (p) == (list)->prev) { \
90 (p)->prev->next = NULL; \
91 (list)->prev = (p)->prev; \
93 if ((p)->prev) (p)->prev->next = (p)->next; \
94 if ((p)->next) (p)->next->prev = (p)->prev; \
96 if ((p) != (list)) (p)->next = (p)->prev = NULL; \
100 find the head of the list given any element in it.
101 Note that this costs O(N), so you should avoid this macro
104 #define DLIST_HEAD(p, result_head) \
106 (result_head) = (p); \
107 while (DLIST_PREV(result_head)) (result_head) = (result_head)->prev; \
110 /* return the last element in the list */
111 #define DLIST_TAIL(list) ((list)?(list)->prev:NULL)
113 /* return the previous element in the list. */
114 #define DLIST_PREV(p) (((p)->prev && (p)->prev->next != NULL)?(p)->prev:NULL)
116 /* insert 'p' after the given element 'el' in a list. If el is NULL then
117 this is the same as a DLIST_ADD() */
118 #define DLIST_ADD_AFTER(list, p, el) \
120 if (!(list) || !(el)) { \
121 DLIST_ADD(list, p); \
124 (p)->next = (el)->next; \
126 if ((p)->next) (p)->next->prev = (p); \
127 if ((list)->prev == (el)) (list)->prev = (p); \
133 add to the end of a list.
135 #define DLIST_ADD_END(list, p) \
138 DLIST_ADD(list, p); \
140 DLIST_ADD_AFTER(list, p, (list)->prev); \
144 /* promote an element to the front of a list */
145 #define DLIST_PROMOTE(list, p) \
147 DLIST_REMOVE(list, p); \
148 DLIST_ADD(list, p); \
152 demote an element to the end of a list.
153 Note that 'type' is ignored
155 #define DLIST_DEMOTE(list, p, type) \
157 DLIST_REMOVE(list, p); \
158 DLIST_ADD_END(list, p); \
162 concatenate two lists - putting all elements of the 2nd list at the
163 end of the first list.
164 Note that 'type' is ignored
166 #define DLIST_CONCATENATE(list1, list2, type) \
171 (list1)->prev->next = (list2); \
173 void *_tmplist = (void *)(list1)->prev; \
174 (list1)->prev = (list2)->prev; \
175 (list2)->prev = _tmplist; \
180 #endif /* _DLINKLIST_H */