/* 
   Unix SMB/CIFS implementation.
   some simple double linked list macros

   Copyright (C) Andrew Tridgell 1998-2010

     ** NOTE! The following LGPL license applies to the ldb
     ** library. This does NOT imply that all of Samba is released
     ** under the LGPL
   
   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/

/* To use these macros you must have a structure containing a next and
   prev pointer */

#ifndef _DLINKLIST_H
#define _DLINKLIST_H

/*
  February 2010 - changed list format to have a prev pointer from the
  list head. This makes DLIST_ADD_END() O(1) even though we only have
  one list pointer.

  The scheme is as follows:

     1) with no entries in the list:
          list_head == NULL

     2) with 1 entry in the list:
          list_head->next == NULL
          list_head->prev == list_head

     3) with 2 entries in the list:
          list_head->next == element2
          list_head->prev == element2
	  element2->prev == list_head
	  element2->next == NULL

     4) with N entries in the list:
          list_head->next == element2
          list_head->prev == elementN
	  elementN->prev == element{N-1}
	  elementN->next == NULL

  This allows us to find the tail of the list by using
  list_head->prev, which means we can add to the end of the list in
  O(1) time
 */


/*
   add an element at the front of a list
*/
#define DLIST_ADD(list, p) \
do { \
        if (!(list)) { \
		(p)->prev = (list) = (p);  \
		(p)->next = NULL; \
	} else { \
		(p)->prev = (list)->prev; \
		(list)->prev = (p); \
		(p)->next = (list); \
		(list) = (p); \
	} \
} while (0)

/*
   remove an element from a list
   Note that the element doesn't have to be in the list. If it
   isn't then this is a no-op
*/
#define DLIST_REMOVE(list, p) \
do { \
	if ((p) == (list)) { \
		if ((p)->next) (p)->next->prev = (p)->prev; \
		(list) = (p)->next; \
	} else if ((p)->prev && (list) && (p) == (list)->prev) {	\
		(p)->prev->next = NULL; \
		(list)->prev = (p)->prev; \
	} else { \
		if ((p)->prev) (p)->prev->next = (p)->next; \
		if ((p)->next) (p)->next->prev = (p)->prev; \
	} \
	if ((p) != (list)) (p)->next = (p)->prev = NULL;	\
} while (0)

/*
   find the head of the list given any element in it.
   Note that this costs O(N), so you should avoid this macro
   if at all possible!
*/
#define DLIST_HEAD(p, result_head) \
do { \
       (result_head) = (p); \
       while (DLIST_PREV(result_head)) (result_head) = (result_head)->prev; \
} while(0)

/* return the last element in the list */
#define DLIST_TAIL(list) ((list)?(list)->prev:NULL)

/* return the previous element in the list. */
#define DLIST_PREV(p) (((p)->prev && (p)->prev->next != NULL)?(p)->prev:NULL)

/* insert 'p' after the given element 'el' in a list. If el is NULL then
   this is the same as a DLIST_ADD() */
#define DLIST_ADD_AFTER(list, p, el) \
do { \
        if (!(list) || !(el)) { \
		DLIST_ADD(list, p); \
	} else { \
		(p)->prev = (el);   \
		(p)->next = (el)->next;		\
		(el)->next = (p);		\
		if ((p)->next) (p)->next->prev = (p);	\
		if ((list)->prev == (el)) (list)->prev = (p); \
	}\
} while (0)


/*
   add to the end of a list.
*/
#define DLIST_ADD_END(list, p) \
do { \
	if (!(list)) { \
		DLIST_ADD(list, p); \
	} else { \
		DLIST_ADD_AFTER(list, p, (list)->prev); \
	} \
} while (0)

/* promote an element to the front of a list */
#define DLIST_PROMOTE(list, p) \
do { \
          DLIST_REMOVE(list, p); \
          DLIST_ADD(list, p); \
} while (0)

/*
   demote an element to the end of a list.
*/
#define DLIST_DEMOTE(list, p) \
do { \
	DLIST_REMOVE(list, p); \
	DLIST_ADD_END(list, p); \
} while (0)

/*
   concatenate two lists - putting all elements of the 2nd list at the
   end of the first list.
*/
#define DLIST_CONCATENATE(list1, list2) \
do { \
	if (!(list1)) { \
		(list1) = (list2); \
	} else { \
		(list1)->prev->next = (list2); \
		if (list2) { \
			void *_tmplist = (void *)(list1)->prev; \
			(list1)->prev = (list2)->prev; \
			(list2)->prev = _tmplist; \
		} \
	} \
} while (0)

#endif /* _DLINKLIST_H */
