/* GLIB - Library of useful routines for C programming
 * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * 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 2.1 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/>.
 */

/*
 * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
 * file for a list of people on the GLib Team.  See the ChangeLog
 * files for a list of changes.  These files are distributed with
 * GLib at ftp://ftp.gtk.org/pub/gtk/.
 */

/*
 * MT safe
 */

#include "config.h"

#include "gslist.h"

#include "gtestutils.h"
#include "gslice.h"

/**
 * SECTION:linked_lists_single
 * @title: Singly-Linked Lists
 * @short_description: linked lists that can be iterated in one direction
 *
 * The #GSList structure and its associated functions provide a
 * standard singly-linked list data structure. The benefit of this
 * data-structure is to provide insertion/deletion operations in O(1)
 * complexity where access/search operations are in O(n). The benefit
 * of #GSList over #GList (doubly linked list) is that they are lighter
 * in space as they only need to retain one pointer but it double the
 * cost of the worst case access/search operations.
 *
 * Each element in the list contains a piece of data, together with a
 * pointer which links to the next element in the list. Using this
 * pointer it is possible to move through the list in one direction
 * only (unlike the [double-linked lists][glib-Doubly-Linked-Lists],
 * which allow movement in both directions).
 *
 * The data contained in each element can be either integer values, by
 * using one of the [Type Conversion Macros][glib-Type-Conversion-Macros],
 * or simply pointers to any type of data.
 *
 * List elements are allocated from the [slice allocator][glib-Memory-Slices],
 * which is more efficient than allocating elements individually.
 *
 * Note that most of the #GSList functions expect to be passed a
 * pointer to the first element in the list. The functions which insert
 * elements return the new start of the list, which may have changed.
 *
 * There is no function to create a #GSList. %NULL is considered to be
 * the empty list so you simply set a #GSList* to %NULL.
 *
 * To add elements, use g_slist_append(), g_slist_prepend(),
 * g_slist_insert() and g_slist_insert_sorted().
 *
 * To remove elements, use g_slist_remove().
 *
 * To find elements in the list use g_slist_last(), g_slist_next(),
 * g_slist_nth(), g_slist_nth_data(), g_slist_find() and
 * g_slist_find_custom().
 *
 * To find the index of an element use g_slist_position() and
 * g_slist_index().
 *
 * To call a function for each element in the list use
 * g_slist_foreach().
 *
 * To free the entire list, use g_slist_free().
 **/

/**
 * GSList:
 * @data: holds the element's data, which can be a pointer to any kind
 *        of data, or any integer value using the
 *        [Type Conversion Macros][glib-Type-Conversion-Macros]
 * @next: contains the link to the next element in the list.
 *
 * The #GSList struct is used for each element in the singly-linked
 * list.
 **/

/**
 * g_slist_next:
 * @slist: an element in a #GSList.
 *
 * A convenience macro to get the next element in a #GSList.
 * Note that it is considered perfectly acceptable to access
 * @slist->next directly.
 *
 * Returns: the next element, or %NULL if there are no more elements.
 **/

#define _g_slist_alloc0()       g_slice_new0 (GSList)
#define _g_slist_alloc()        g_slice_new (GSList)
#define _g_slist_free1(slist)   g_slice_free (GSList, slist)

/**
 * g_slist_alloc:
 *
 * Allocates space for one #GSList element. It is called by the
 * g_slist_append(), g_slist_prepend(), g_slist_insert() and
 * g_slist_insert_sorted() functions and so is rarely used on its own.
 *
 * Returns: a pointer to the newly-allocated #GSList element.
 **/
GSList*
g_slist_alloc (void)
{
  return _g_slist_alloc0 ();
}

/**
 * g_slist_free:
 * @list: the first link of a #GSList
 *
 * Frees all of the memory used by a #GSList.
 * The freed elements are returned to the slice allocator.
 *
 * If list elements contain dynamically-allocated memory,
 * you should either use g_slist_free_full() or free them manually
 * first.
 *
 * It can be combined with g_steal_pointer() to ensure the list head pointer
 * is not left dangling:
 * |[<!-- language="C" -->
 * GSList *list_of_borrowed_things = …;  /<!-- -->* (transfer container) *<!-- -->/
 * g_slist_free (g_steal_pointer (&list_of_borrowed_things));
 * ]|
 */
void
g_slist_free (GSList *list)
{
  g_slice_free_chain (GSList, list, next);
}

/**
 * g_slist_free_1:
 * @list: a #GSList element
 *
 * Frees one #GSList element.
 * It is usually used after g_slist_remove_link().
 */
/**
 * g_slist_free1:
 *
 * A macro which does the same as g_slist_free_1().
 *
 * Since: 2.10
 **/
void
g_slist_free_1 (GSList *list)
{
  _g_slist_free1 (list);
}

/**
 * g_slist_free_full:
 * @list: the first link of a #GSList
 * @free_func: the function to be called to free each element's data
 *
 * Convenience method, which frees all the memory used by a #GSList, and
 * calls the specified destroy function on every element's data.
 *
 * @free_func must not modify the list (eg, by removing the freed
 * element from it).
 *
 * It can be combined with g_steal_pointer() to ensure the list head pointer
 * is not left dangling ­— this also has the nice property that the head pointer
 * is cleared before any of the list elements are freed, to prevent double frees
 * from @free_func:
 * |[<!-- language="C" -->
 * GSList *list_of_owned_things = …;  /<!-- -->* (transfer full) (element-type GObject) *<!-- -->/
 * g_slist_free_full (g_steal_pointer (&list_of_owned_things), g_object_unref);
 * ]|
 *
 * Since: 2.28
 **/
void
g_slist_free_full (GSList         *list,
		   GDestroyNotify  free_func)
{
  g_slist_foreach (list, (GFunc) free_func, NULL);
  g_slist_free (list);
}

/**
 * g_slist_append:
 * @list: a #GSList
 * @data: the data for the new element
 *
 * Adds a new element on to the end of the list.
 *
 * The return value is the new start of the list, which may
 * have changed, so make sure you store the new value.
 *
 * Note that g_slist_append() has to traverse the entire list
 * to find the end, which is inefficient when adding multiple
 * elements. A common idiom to avoid the inefficiency is to prepend
 * the elements and reverse the list when all elements have been added.
 *
 * |[<!-- language="C" --> 
 * // Notice that these are initialized to the empty list.
 * GSList *list = NULL, *number_list = NULL;
 *
 * // This is a list of strings.
 * list = g_slist_append (list, "first");
 * list = g_slist_append (list, "second");
 *
 * // This is a list of integers.
 * number_list = g_slist_append (number_list, GINT_TO_POINTER (27));
 * number_list = g_slist_append (number_list, GINT_TO_POINTER (14));
 * ]|
 *
 * Returns: the new start of the #GSList
 */
GSList*
g_slist_append (GSList   *list,
                gpointer  data)
{
  GSList *new_list;
  GSList *last;

  new_list = _g_slist_alloc ();
  new_list->data = data;
  new_list->next = NULL;

  if (list)
    {
      last = g_slist_last (list);
      /* g_assert (last != NULL); */
      last->next = new_list;

      return list;
    }
  else
    return new_list;
}

/**
 * g_slist_prepend:
 * @list: a #GSList
 * @data: the data for the new element
 *
 * Adds a new element on to the start of the list.
 *
 * The return value is the new start of the list, which
 * may have changed, so make sure you store the new value.
 *
 * |[<!-- language="C" --> 
 * // Notice that it is initialized to the empty list.
 * GSList *list = NULL;
 * list = g_slist_prepend (list, "last");
 * list = g_slist_prepend (list, "first");
 * ]|
 *
 * Returns: the new start of the #GSList
 */
GSList*
g_slist_prepend (GSList   *list,
                 gpointer  data)
{
  GSList *new_list;

  new_list = _g_slist_alloc ();
  new_list->data = data;
  new_list->next = list;

  return new_list;
}

/**
 * g_slist_insert:
 * @list: a #GSList
 * @data: the data for the new element
 * @position: the position to insert the element.
 *     If this is negative, or is larger than the number
 *     of elements in the list, the new element is added on
 *     to the end of the list.
 *
 * Inserts a new element into the list at the given position.
 *
 * Returns: the new start of the #GSList
 */
GSList*
g_slist_insert (GSList   *list,
                gpointer  data,
                gint      position)
{
  GSList *prev_list;
  GSList *tmp_list;
  GSList *new_list;

  if (position < 0)
    return g_slist_append (list, data);
  else if (position == 0)
    return g_slist_prepend (list, data);

  new_list = _g_slist_alloc ();
  new_list->data = data;

  if (!list)
    {
      new_list->next = NULL;
      return new_list;
    }

  prev_list = NULL;
  tmp_list = list;

  while ((position-- > 0) && tmp_list)
    {
      prev_list = tmp_list;
      tmp_list = tmp_list->next;
    }

  new_list->next = prev_list->next;
  prev_list->next = new_list;

  return list;
}

/**
 * g_slist_insert_before:
 * @slist: a #GSList
 * @sibling: node to insert @data before
 * @data: data to put in the newly-inserted node
 *
 * Inserts a node before @sibling containing @data.
 *
 * Returns: the new head of the list.
 */
GSList*
g_slist_insert_before (GSList  *slist,
                       GSList  *sibling,
                       gpointer data)
{
  if (!slist)
    {
      slist = _g_slist_alloc ();
      slist->data = data;
      slist->next = NULL;
      g_return_val_if_fail (sibling == NULL, slist);
      return slist;
    }
  else
    {
      GSList *node, *last = NULL;

      for (node = slist; node; last = node, node = last->next)
        if (node == sibling)
          break;
      if (!last)
        {
          node = _g_slist_alloc ();
          node->data = data;
          node->next = slist;

          return node;
        }
      else
        {
          node = _g_slist_alloc ();
          node->data = data;
          node->next = last->next;
          last->next = node;

          return slist;
        }
    }
}

/**
 * g_slist_concat:
 * @list1: a #GSList
 * @list2: the #GSList to add to the end of the first #GSList
 *
 * Adds the second #GSList onto the end of the first #GSList.
 * Note that the elements of the second #GSList are not copied.
 * They are used directly.
 *
 * Returns: the start of the new #GSList
 */
GSList *
g_slist_concat (GSList *list1, GSList *list2)
{
  if (list2)
    {
      if (list1)
        g_slist_last (list1)->next = list2;
      else
        list1 = list2;
    }

  return list1;
}

static GSList*
_g_slist_remove_data (GSList        *list,
                      gconstpointer  data,
                      gboolean       all)
{
  GSList *tmp = NULL;
  GSList **previous_ptr = &list;

  while (*previous_ptr)
    {
      tmp = *previous_ptr;
      if (tmp->data == data)
        {
          *previous_ptr = tmp->next;
          g_slist_free_1 (tmp);
          if (!all)
            break;
        }
      else
        {
          previous_ptr = &tmp->next;
        }
    }

  return list;
}
/**
 * g_slist_remove:
 * @list: a #GSList
 * @data: the data of the element to remove
 *
 * Removes an element from a #GSList.
 * If two elements contain the same data, only the first is removed.
 * If none of the elements contain the data, the #GSList is unchanged.
 *
 * Returns: the new start of the #GSList
 */
GSList*
g_slist_remove (GSList        *list,
                gconstpointer  data)
{
  return _g_slist_remove_data (list, data, FALSE);
}

/**
 * g_slist_remove_all:
 * @list: a #GSList
 * @data: data to remove
 *
 * Removes all list nodes with data equal to @data.
 * Returns the new head of the list. Contrast with
 * g_slist_remove() which removes only the first node
 * matching the given data.
 *
 * Returns: new head of @list
 */
GSList*
g_slist_remove_all (GSList        *list,
                    gconstpointer  data)
{
  return _g_slist_remove_data (list, data, TRUE);
}

static inline GSList*
_g_slist_remove_link (GSList *list,
                      GSList *link)
{
  GSList *tmp = NULL;
  GSList **previous_ptr = &list;

  while (*previous_ptr)
    {
      tmp = *previous_ptr;
      if (tmp == link)
        {
          *previous_ptr = tmp->next;
          tmp->next = NULL;
          break;
        }

      previous_ptr = &tmp->next;
    }

  return list;
}

/**
 * g_slist_remove_link:
 * @list: a #GSList
 * @link_: an element in the #GSList
 *
 * Removes an element from a #GSList, without
 * freeing the element. The removed element's next
 * link is set to %NULL, so that it becomes a
 * self-contained list with one element.
 *
 * Removing arbitrary nodes from a singly-linked list
 * requires time that is proportional to the length of the list
 * (ie. O(n)). If you find yourself using g_slist_remove_link()
 * frequently, you should consider a different data structure,
 * such as the doubly-linked #GList.
 *
 * Returns: the new start of the #GSList, without the element
 */
GSList*
g_slist_remove_link (GSList *list,
                     GSList *link_)
{
  return _g_slist_remove_link (list, link_);
}

/**
 * g_slist_delete_link:
 * @list: a #GSList
 * @link_: node to delete
 *
 * Removes the node link_ from the list and frees it.
 * Compare this to g_slist_remove_link() which removes the node
 * without freeing it.
 *
 * Removing arbitrary nodes from a singly-linked list requires time
 * that is proportional to the length of the list (ie. O(n)). If you
 * find yourself using g_slist_delete_link() frequently, you should
 * consider a different data structure, such as the doubly-linked
 * #GList.
 *
 * Returns: the new head of @list
 */
GSList*
g_slist_delete_link (GSList *list,
                     GSList *link_)
{
  list = _g_slist_remove_link (list, link_);
  _g_slist_free1 (link_);

  return list;
}

/**
 * g_slist_copy:
 * @list: a #GSList
 *
 * Copies a #GSList.
 *
 * Note that this is a "shallow" copy. If the list elements
 * consist of pointers to data, the pointers are copied but
 * the actual data isn't. See g_slist_copy_deep() if you need
 * to copy the data as well.
 *
 * Returns: a copy of @list
 */
GSList*
g_slist_copy (GSList *list)
{
  return g_slist_copy_deep (list, NULL, NULL);
}

/**
 * g_slist_copy_deep:
 * @list: a #GSList
 * @func: a copy function used to copy every element in the list
 * @user_data: user data passed to the copy function @func, or #NULL
 *
 * Makes a full (deep) copy of a #GSList.
 *
 * In contrast with g_slist_copy(), this function uses @func to make a copy of
 * each list element, in addition to copying the list container itself.
 *
 * @func, as a #GCopyFunc, takes two arguments, the data to be copied
 * and a @user_data pointer. On common processor architectures, it's safe to
 * pass %NULL as @user_data if the copy function takes only one argument. You
 * may get compiler warnings from this though if compiling with GCC’s
 * `-Wcast-function-type` warning.
 *
 * For instance, if @list holds a list of GObjects, you can do:
 * |[<!-- language="C" --> 
 * another_list = g_slist_copy_deep (list, (GCopyFunc) g_object_ref, NULL);
 * ]|
 *
 * And, to entirely free the new list, you could do:
 * |[<!-- language="C" --> 
 * g_slist_free_full (another_list, g_object_unref);
 * ]|
 *
 * Returns: a full copy of @list, use g_slist_free_full() to free it
 *
 * Since: 2.34
 */
GSList*
g_slist_copy_deep (GSList *list, GCopyFunc func, gpointer user_data)
{
  GSList *new_list = NULL;

  if (list)
    {
      GSList *last;

      new_list = _g_slist_alloc ();
      if (func)
        new_list->data = func (list->data, user_data);
      else
        new_list->data = list->data;
      last = new_list;
      list = list->next;
      while (list)
        {
          last->next = _g_slist_alloc ();
          last = last->next;
          if (func)
            last->data = func (list->data, user_data);
          else
            last->data = list->data;
          list = list->next;
        }
      last->next = NULL;
    }

  return new_list;
}

/**
 * g_slist_reverse:
 * @list: a #GSList
 *
 * Reverses a #GSList.
 *
 * Returns: the start of the reversed #GSList
 */
GSList*
g_slist_reverse (GSList *list)
{
  GSList *prev = NULL;

  while (list)
    {
      GSList *next = list->next;

      list->next = prev;

      prev = list;
      list = next;
    }

  return prev;
}

/**
 * g_slist_nth:
 * @list: a #GSList
 * @n: the position of the element, counting from 0
 *
 * Gets the element at the given position in a #GSList.
 *
 * Returns: the element, or %NULL if the position is off
 *     the end of the #GSList
 */
GSList*
g_slist_nth (GSList *list,
             guint   n)
{
  while (n-- > 0 && list)
    list = list->next;

  return list;
}

/**
 * g_slist_nth_data:
 * @list: a #GSList
 * @n: the position of the element
 *
 * Gets the data of the element at the given position.
 *
 * Returns: the element's data, or %NULL if the position
 *     is off the end of the #GSList
 */
gpointer
g_slist_nth_data (GSList   *list,
                  guint     n)
{
  while (n-- > 0 && list)
    list = list->next;

  return list ? list->data : NULL;
}

/**
 * g_slist_find:
 * @list: a #GSList
 * @data: the element data to find
 *
 * Finds the element in a #GSList which
 * contains the given data.
 *
 * Returns: the found #GSList element,
 *     or %NULL if it is not found
 */
GSList*
g_slist_find (GSList        *list,
              gconstpointer  data)
{
  while (list)
    {
      if (list->data == data)
        break;
      list = list->next;
    }

  return list;
}


/**
 * g_slist_find_custom:
 * @list: a #GSList
 * @data: user data passed to the function
 * @func: the function to call for each element.
 *     It should return 0 when the desired element is found
 *
 * Finds an element in a #GSList, using a supplied function to
 * find the desired element. It iterates over the list, calling
 * the given function which should return 0 when the desired
 * element is found. The function takes two #gconstpointer arguments,
 * the #GSList element's data as the first argument and the
 * given user data.
 *
 * Returns: the found #GSList element, or %NULL if it is not found
 */
GSList*
g_slist_find_custom (GSList        *list,
                     gconstpointer  data,
                     GCompareFunc   func)
{
  g_return_val_if_fail (func != NULL, list);

  while (list)
    {
      if (! func (list->data, data))
        return list;
      list = list->next;
    }

  return NULL;
}

/**
 * g_slist_position:
 * @list: a #GSList
 * @llink: an element in the #GSList
 *
 * Gets the position of the given element
 * in the #GSList (starting from 0).
 *
 * Returns: the position of the element in the #GSList,
 *     or -1 if the element is not found
 */
gint
g_slist_position (GSList *list,
                  GSList *llink)
{
  gint i;

  i = 0;
  while (list)
    {
      if (list == llink)
        return i;
      i++;
      list = list->next;
    }

  return -1;
}

/**
 * g_slist_index:
 * @list: a #GSList
 * @data: the data to find
 *
 * Gets the position of the element containing
 * the given data (starting from 0).
 *
 * Returns: the index of the element containing the data,
 *     or -1 if the data is not found
 */
gint
g_slist_index (GSList        *list,
               gconstpointer  data)
{
  gint i;

  i = 0;
  while (list)
    {
      if (list->data == data)
        return i;
      i++;
      list = list->next;
    }

  return -1;
}

/**
 * g_slist_last:
 * @list: a #GSList
 *
 * Gets the last element in a #GSList.
 *
 * This function iterates over the whole list.
 *
 * Returns: the last element in the #GSList,
 *     or %NULL if the #GSList has no elements
 */
GSList*
g_slist_last (GSList *list)
{
  if (list)
    {
      while (list->next)
        list = list->next;
    }

  return list;
}

/**
 * g_slist_length:
 * @list: a #GSList
 *
 * Gets the number of elements in a #GSList.
 *
 * This function iterates over the whole list to
 * count its elements. To check whether the list is non-empty, it is faster to
 * check @list against %NULL.
 *
 * Returns: the number of elements in the #GSList
 */
guint
g_slist_length (GSList *list)
{
  guint length;

  length = 0;
  while (list)
    {
      length++;
      list = list->next;
    }

  return length;
}

/**
 * g_slist_foreach:
 * @list: a #GSList
 * @func: the function to call with each element's data
 * @user_data: user data to pass to the function
 *
 * Calls a function for each element of a #GSList.
 *
 * It is safe for @func to remove the element from @list, but it must
 * not modify any part of the list after that element.
 */
void
g_slist_foreach (GSList   *list,
                 GFunc     func,
                 gpointer  user_data)
{
  while (list)
    {
      GSList *next = list->next;
      (*func) (list->data, user_data);
      list = next;
    }
}

static GSList*
g_slist_insert_sorted_real (GSList   *list,
                            gpointer  data,
                            GFunc     func,
                            gpointer  user_data)
{
  GSList *tmp_list = list;
  GSList *prev_list = NULL;
  GSList *new_list;
  gint cmp;

  g_return_val_if_fail (func != NULL, list);

  if (!list)
    {
      new_list = _g_slist_alloc ();
      new_list->data = data;
      new_list->next = NULL;
      return new_list;
    }

  cmp = ((GCompareDataFunc) func) (data, tmp_list->data, user_data);

  while ((tmp_list->next) && (cmp > 0))
    {
      prev_list = tmp_list;
      tmp_list = tmp_list->next;

      cmp = ((GCompareDataFunc) func) (data, tmp_list->data, user_data);
    }

  new_list = _g_slist_alloc ();
  new_list->data = data;

  if ((!tmp_list->next) && (cmp > 0))
    {
      tmp_list->next = new_list;
      new_list->next = NULL;
      return list;
    }

  if (prev_list)
    {
      prev_list->next = new_list;
      new_list->next = tmp_list;
      return list;
    }
  else
    {
      new_list->next = list;
      return new_list;
    }
}

/**
 * g_slist_insert_sorted:
 * @list: a #GSList
 * @data: the data for the new element
 * @func: the function to compare elements in the list.
 *     It should return a number > 0 if the first parameter
 *     comes after the second parameter in the sort order.
 *
 * Inserts a new element into the list, using the given
 * comparison function to determine its position.
 *
 * Returns: the new start of the #GSList
 */
GSList*
g_slist_insert_sorted (GSList       *list,
                       gpointer      data,
                       GCompareFunc  func)
{
  return g_slist_insert_sorted_real (list, data, (GFunc) func, NULL);
}

/**
 * g_slist_insert_sorted_with_data:
 * @list: a #GSList
 * @data: the data for the new element
 * @func: the function to compare elements in the list.
 *     It should return a number > 0 if the first parameter
 *     comes after the second parameter in the sort order.
 * @user_data: data to pass to comparison function
 *
 * Inserts a new element into the list, using the given
 * comparison function to determine its position.
 *
 * Returns: the new start of the #GSList
 *
 * Since: 2.10
 */
GSList*
g_slist_insert_sorted_with_data (GSList           *list,
                                 gpointer          data,
                                 GCompareDataFunc  func,
                                 gpointer          user_data)
{
  return g_slist_insert_sorted_real (list, data, (GFunc) func, user_data);
}

static GSList *
g_slist_sort_merge (GSList   *l1,
                    GSList   *l2,
                    GFunc     compare_func,
                    gpointer  user_data)
{
  GSList list, *l;
  gint cmp;

  l=&list;

  while (l1 && l2)
    {
      cmp = ((GCompareDataFunc) compare_func) (l1->data, l2->data, user_data);

      if (cmp <= 0)
        {
          l=l->next=l1;
          l1=l1->next;
        }
      else
        {
          l=l->next=l2;
          l2=l2->next;
        }
    }
  l->next= l1 ? l1 : l2;

  return list.next;
}

static GSList *
g_slist_sort_real (GSList   *list,
                   GFunc     compare_func,
                   gpointer  user_data)
{
  GSList *l1, *l2;

  if (!list)
    return NULL;
  if (!list->next)
    return list;

  l1 = list;
  l2 = list->next;

  while ((l2 = l2->next) != NULL)
    {
      if ((l2 = l2->next) == NULL)
        break;
      l1=l1->next;
    }
  l2 = l1->next;
  l1->next = NULL;

  return g_slist_sort_merge (g_slist_sort_real (list, compare_func, user_data),
                             g_slist_sort_real (l2, compare_func, user_data),
                             compare_func,
                             user_data);
}

/**
 * g_slist_sort:
 * @list: a #GSList
 * @compare_func: the comparison function used to sort the #GSList.
 *     This function is passed the data from 2 elements of the #GSList
 *     and should return 0 if they are equal, a negative value if the
 *     first element comes before the second, or a positive value if
 *     the first element comes after the second.
 *
 * Sorts a #GSList using the given comparison function. The algorithm
 * used is a stable sort.
 *
 * Returns: the start of the sorted #GSList
 */
GSList *
g_slist_sort (GSList       *list,
              GCompareFunc  compare_func)
{
  return g_slist_sort_real (list, (GFunc) compare_func, NULL);
}

/**
 * g_slist_sort_with_data:
 * @list: a #GSList
 * @compare_func: comparison function
 * @user_data: data to pass to comparison function
 *
 * Like g_slist_sort(), but the sort function accepts a user data argument.
 *
 * Returns: new head of the list
 */
GSList *
g_slist_sort_with_data (GSList           *list,
                        GCompareDataFunc  compare_func,
                        gpointer          user_data)
{
  return g_slist_sort_real (list, (GFunc) compare_func, user_data);
}

/**
 * g_clear_slist: (skip)
 * @slist_ptr: (not nullable): a #GSList return location
 * @destroy: (nullable): the function to pass to g_slist_free_full() or %NULL to not free elements
 *
 * Clears a pointer to a #GSList, freeing it and, optionally, freeing its elements using @destroy.
 *
 * @slist_ptr must be a valid pointer. If @slist_ptr points to a null #GSList, this does nothing.
 *
 * Since: 2.64
 */
void
(g_clear_slist) (GSList         **slist_ptr,
                 GDestroyNotify   destroy)
{
  GSList *slist;

  slist = *slist_ptr;
  if (slist)
    {
      *slist_ptr = NULL;

      if (destroy)
        g_slist_free_full (slist, destroy);
      else
        g_slist_free (slist);
    }
}