/* DLIFE Copyright (C) 2000 Richard W.M. Jones <rich@annexia.org>
 * and other authors listed in the ``AUTHORS'' file.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 *
 * $Id: dlink.h,v 1.1 2002/04/05 14:40:26 rich Exp $
 */

#ifndef dlink_h
#define dlink_h

/* This was snarfed from the source for Python 1.5. */
#ifdef HAVE_STDDEF_H
#include <stddef.h>
#endif

#ifndef offsetof
#define offsetof(type, member) ( (int) & ((type*)0) -> member )
#endif

typedef struct dlink_list_element
{
  void *next;
  void *prev;
} dlink_list_element_t;

typedef struct dlink_list
{
  void *first;
  void *last;
  int offset;
} dlink_list_t;

#define DLINK_LIST_INIT(offset) { 0, 0, (offset) }

#define _DLINK_ELEMENT_PTRS(element,list) ((dlink_list_element_t *) ((element) + (list)->offset))
#define _DLINK_FIRST_PTRS(list) _DLINK_ELEMENT_PTRS((list)->first,(list))
#define _DLINK_LAST_PTRS(list) _DLINK_ELEMENT_PTRS((list)->last,(list))

extern inline void
dlink_list_init (dlink_list_t *list, int offset)
{
  list->first = list->last = 0;
  list->offset = offset;
}

extern inline void
insert_before_first (void *element, dlink_list_t *list)
{
  dlink_list_element_t *eptrs = _DLINK_ELEMENT_PTRS (element, list);

  eptrs->prev = 0;
  eptrs->next = list->first;
  if (list->first)
    _DLINK_FIRST_PTRS(list)->prev = element;
  else
    list->last = element;
  list->first = element;
}

extern inline void
insert_before_last (void *element, dlink_list_t *list)
{
  dlink_list_element_t *eptrs = _DLINK_ELEMENT_PTRS (element, list);

  eptrs->next = 0;
  eptrs->prev = list->last;
  if (list->last)
    _DLINK_LAST_PTRS(list)->next = element;
  else
    list->first = element;
  list->last = element;
}

extern inline void
move_towards_last (void *e, dlink_list_t *list)
{
  dlink_list_element_t *eptrs = _DLINK_ELEMENT_PTRS (e, list);

  void *e0 = eptrs->prev;
  dlink_list_element_t *e0ptrs = _DLINK_ELEMENT_PTRS (e0, list);

  void *e1 = eptrs->next;
  dlink_list_element_t *e1ptrs = _DLINK_ELEMENT_PTRS (e1, list);

  void *e2 = e1ptrs->next;
  dlink_list_element_t *e2ptrs = _DLINK_ELEMENT_PTRS (e2, list);

  /* The elements are:   e0 <---> e <---> e1 <---> e2.
   *
   * We know that e and e1 exist, but e0 and e2 may or may not exist.
   *
   * We want the arrangement to be:
   *                     e0 <---> e1 <---> e <---> e2.
   */
  e1ptrs->prev = e0;
  if (e0)
    e0ptrs->next = e1;
  else
    list->first = e1;

  e1ptrs->next = e;
  eptrs->prev = e1;

  eptrs->next = e2;
  if (e2)
    e2ptrs->prev = e;
  else
    list->last = e;
}

extern inline void
remove_element (void *element, dlink_list_t *list)
{
  dlink_list_element_t *eptrs = _DLINK_ELEMENT_PTRS (element, list);

  void *eprev = eptrs->prev;
  dlink_list_element_t *eprevptrs = _DLINK_ELEMENT_PTRS (eprev, list);

  void *enext = eptrs->next;
  dlink_list_element_t *enextptrs = _DLINK_ELEMENT_PTRS (enext, list);

  if (eptrs->next)
    enextptrs->prev = eprev;
  else
    list->last = eprev;

  if (eptrs->prev)
    eprevptrs->next = enext;
  else
    list->first = enext;
}

#endif /* dlink_h */