http-walker: reduce O(n) ops with doubly-linked list
[git/git.git] / list.h
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94e99012
EW
1/*
2 * Copyright (C) 2002 Free Software Foundation, Inc.
3 * (originally part of the GNU C Library and Userspace RCU)
4 * Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
5 *
6 * Copyright (C) 2009 Pierre-Marc Fournier
7 * Conversion to RCU list.
8 * Copyright (C) 2010 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
9 *
10 * This library is free software; you can redistribute it and/or
11 * modify it under the terms of the GNU Lesser General Public
12 * License as published by the Free Software Foundation; either
13 * version 2.1 of the License, or (at your option) any later version.
14 *
15 * This library is distributed in the hope that it will be useful,
16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 * Lesser General Public License for more details.
19 *
20 * You should have received a copy of the GNU Lesser General Public
21 * License along with this library; if not, see
22 * <http://www.gnu.org/licenses/>.
23 */
24
25#ifndef LIST_H
26#define LIST_H 1
27
28/*
29 * The definitions of this file are adopted from those which can be
30 * found in the Linux kernel headers to enable people familiar with the
31 * latter find their way in these sources as well.
32 */
33
34/* Basic type for the double-link list. */
35struct list_head {
36 struct list_head *next, *prev;
37};
38
39/* Define a variable with the head and tail of the list. */
40#define LIST_HEAD(name) \
41 struct list_head name = { &(name), &(name) }
42
43/* Initialize a new list head. */
44#define INIT_LIST_HEAD(ptr) \
45 (ptr)->next = (ptr)->prev = (ptr)
46
47#define LIST_HEAD_INIT(name) { &(name), &(name) }
48
49/* Add new element at the head of the list. */
50static inline void list_add(struct list_head *newp, struct list_head *head)
51{
52 head->next->prev = newp;
53 newp->next = head->next;
54 newp->prev = head;
55 head->next = newp;
56}
57
58/* Add new element at the tail of the list. */
59static inline void list_add_tail(struct list_head *newp, struct list_head *head)
60{
61 head->prev->next = newp;
62 newp->next = head;
63 newp->prev = head->prev;
64 head->prev = newp;
65}
66
67/* Remove element from list. */
68static inline void __list_del(struct list_head *prev, struct list_head *next)
69{
70 next->prev = prev;
71 prev->next = next;
72}
73
74/* Remove element from list. */
75static inline void list_del(struct list_head *elem)
76{
77 __list_del(elem->prev, elem->next);
78}
79
80/* Remove element from list, initializing the element's list pointers. */
81static inline void list_del_init(struct list_head *elem)
82{
83 list_del(elem);
84 INIT_LIST_HEAD(elem);
85}
86
87/* Delete from list, add to another list as head. */
88static inline void list_move(struct list_head *elem, struct list_head *head)
89{
90 __list_del(elem->prev, elem->next);
91 list_add(elem, head);
92}
93
94/* Replace an old entry. */
95static inline void list_replace(struct list_head *old, struct list_head *newp)
96{
97 newp->next = old->next;
98 newp->prev = old->prev;
99 newp->prev->next = newp;
100 newp->next->prev = newp;
101}
102
103/* Join two lists. */
104static inline void list_splice(struct list_head *add, struct list_head *head)
105{
106 /* Do nothing if the list which gets added is empty. */
107 if (add != add->next) {
108 add->next->prev = head;
109 add->prev->next = head->next;
110 head->next->prev = add->prev;
111 head->next = add->next;
112 }
113}
114
115/* Get typed element from list at a given position. */
116#define list_entry(ptr, type, member) \
117 ((type *) ((char *) (ptr) - offsetof(type, member)))
118
119/* Get first entry from a list. */
120#define list_first_entry(ptr, type, member) \
121 list_entry((ptr)->next, type, member)
122
123/* Iterate forward over the elements of the list. */
124#define list_for_each(pos, head) \
125 for (pos = (head)->next; pos != (head); pos = pos->next)
126
127/*
128 * Iterate forward over the elements list. The list elements can be
129 * removed from the list while doing this.
130 */
131#define list_for_each_safe(pos, p, head) \
132 for (pos = (head)->next, p = pos->next; \
133 pos != (head); \
134 pos = p, p = pos->next)
135
136/* Iterate backward over the elements of the list. */
137#define list_for_each_prev(pos, head) \
138 for (pos = (head)->prev; pos != (head); pos = pos->prev)
139
140/*
141 * Iterate backwards over the elements list. The list elements can be
142 * removed from the list while doing this.
143 */
144#define list_for_each_prev_safe(pos, p, head) \
145 for (pos = (head)->prev, p = pos->prev; \
146 pos != (head); \
147 pos = p, p = pos->prev)
148
149static inline int list_empty(struct list_head *head)
150{
151 return head == head->next;
152}
153
154static inline void list_replace_init(struct list_head *old,
155 struct list_head *newp)
156{
157 struct list_head *head = old->next;
158
159 list_del(old);
160 list_add_tail(newp, head);
161 INIT_LIST_HEAD(old);
162}
163
164#endif /* LIST_H */