Implement list sorting.

* include/mailutils/list.h (mu_list_sort): New proto.
* libmailutils/list/sort.c: New file.
* libmailutils/list/Makefile.am (liblist_la_SOURCES): Add sort.c
* libmailutils/tests/listop.c: Implement the sort command.
* libmailutils/tests/list.at: Test list sorting.

@@ -274,7 +274,9 @@ int mu_list_map (mu_list_t _list, mu_list_mapper_t _map,
 		 void *_data, size_t _nelem,
 		 mu_list_t *_res);
 
-  /* List fold */
+  /* ************************************************* */
+  /* List folding                                      */
+  /* ************************************************* */
 
 typedef int (*mu_list_folder_t) (void *_item, void *_data,
 				 void *_prev, void **_ret);
@@ -316,6 +318,18 @@ int mu_list_fold (mu_list_t _list, mu_list_folder_t _fold, void *_data,
 int mu_list_rfold (mu_list_t _list, mu_list_folder_t _fold, void *_data,
 		   void *_init, void *_return_value);
 
+  /* ************************************************* */
+  /* Sorting                                           */
+  /* ************************************************* */
+
+  /* Sort _list using quicksort algorithm.  Use _comp to compare elements.
+     If it is NULL, use the comparator method of _list.
+
+     Comparator must return 0 if the two elements are equal, -1 if
+     first of them is less than the second, and +1 otherwise.
+  */
+void mu_list_sort (mu_list_t _list, mu_list_comparator_t _comp);
+  
 #ifdef __cplusplus
 }
 #endif

@@ -45,6 +45,7 @@ liblist_la_SOURCES = \
  setdestr.c\
  slice.c\
  slice2.c\
+ sort.c\
  tail.c
 
 INCLUDES = @MU_LIB_COMMON_INCLUDES@ -I/libmailutils

+/* GNU Mailutils -- a suite of utilities for electronic mail
+   Copyright (C) 2011 Free Software Foundation, Inc.
+
+   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/>. */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+#include <stdlib.h>
+#include <string.h>
+#include <mailutils/errno.h>
+#include <mailutils/sys/list.h>
+
+static void
+_list_append_entry (struct _mu_list *list, struct list_data *ent)
+{
+  ent->prev = list->head.prev ? list->head.prev : &list->head;
+  ent->next = &list->head;
+  if (list->head.prev)
+    list->head.prev->next = ent;
+  else
+    list->head.next = ent;
+  list->head.prev = ent;
+  list->count++;
+}
+
+static void
+_list_qsort (mu_list_t list, mu_list_comparator_t cmp)
+{
+  struct list_data *cur, *middle;
+  struct _mu_list high_list, low_list;
+  int rc;
+
+  if (list->count < 2)
+    return;
+  if (list->count == 2)
+    {
+      if (cmp (list->head.prev->item, list->head.next->item) < 0)
+	{
+	  cur = list->head.prev;
+	  list->head.prev = list->head.next;
+	  list->head.next = cur;
+	  
+	  list->head.next->prev = &list->head;
+	  list->head.next->next = list->head.prev;
+	  
+	  list->head.prev->next = &list->head;
+	  list->head.prev->prev = list->head.next;
+	}
+      return;
+    }
+  
+  cur = list->head.next;
+  do {
+    cur = cur->next;
+    if (!cur)
+      return;
+  } while ((rc = cmp (list->head.next->item, cur->item)) == 0);
+
+  /* Select the lower of the two as the middle value */
+  middle = (rc > 0) ? cur : list->head.next;
+
+  /* Split into two sublists */
+  memset (&high_list, 0, sizeof (high_list));
+  memset (&low_list, 0, sizeof (low_list));
+
+  for (cur = list->head.next; cur != &list->head; )
+    {
+      struct list_data *next = cur->next;
+      cur->next = NULL;
+
+      if (cmp (middle->item, cur->item) < 0)
+	_list_append_entry (&high_list, cur);
+      else
+	_list_append_entry (&low_list, cur);
+      cur = next;
+    }
+
+  /* Sort both sublists recursively */
+  _list_qsort (&low_list, cmp);
+  _list_qsort (&high_list, cmp);
+
+  /* Join both lists in order */
+  if (low_list.head.prev)
+    cur = low_list.head.prev;
+  else
+    cur = &low_list.head;
+  cur->next = high_list.head.next;
+  if (high_list.head.next)
+    high_list.head.next->prev = cur;
+  
+  low_list.head.prev = high_list.head.prev;
+  high_list.head.prev = &low_list.head;
+  low_list.count += high_list.count;
+    
+  /* Return the resulting list */
+  list->head = low_list.head;
+  if (list->head.next)
+    list->head.next->prev = &list->head;
+  if (list->head.prev)
+    list->head.prev->next = &list->head;
+}
+
+void
+mu_list_sort (mu_list_t list, mu_list_comparator_t comp)
+{
+  if (list)
+    _list_qsort (list, comp ? comp : list->comp);
+}

@@ -445,6 +445,68 @@ rfold
 
 m4_popdef([MU_TEST_KEYWORDS])
 
+# ------------------------------------------------------------
+# Sort
+# ------------------------------------------------------------
+
+m4_define([MU_TEST_GROUP],[Sort])
+m4_pushdef([MU_TEST_KEYWORDS],MU_TEST_KEYWORDS[ sort])
+
+TESTLIST([empty list],[],
+[sort
+print
+],
+[# items: 0
+])
+
+TESTLIST([sorted list asc],[],
+[add a b c d e f
+sort
+print
+],
+[# items: 6
+a
+b
+c
+d
+e
+f
+])
+
+TESTLIST([sorted list desc],[],
+[add f e d c b a
+sort
+print
+],
+[# items: 6
+a
+b
+c
+d
+e
+f
+])
+
+TESTLIST([unsorted list],[],
+[add en to tre fire fem seks syv atte ni ti
+sort
+print
+],
+[# items: 10
+atte
+en
+fem
+fire
+ni
+seks
+syv
+ti
+to
+tre
+])
+
+m4_popdef([MU_TEST_KEYWORDS])
+
 dnl ------------------------------------------------------------
 dnl Cleanup
 m4_popdef([TESTLIST])

@@ -775,6 +775,12 @@ rfold (mu_list_t list)
 }
 
 void
+sort (mu_list_t list)
+{
+  mu_list_sort (list, NULL);
+}
+
+void
 help ()
 {
   printf ("count\n");
@@ -802,6 +808,7 @@ help ()
   printf ("help\n");
   printf ("head\n");
   printf ("tail\n");
+  printf ("sort\n");
   printf ("NUMBER\n");
 }
 
@@ -921,6 +928,14 @@ shell (mu_list_t list)
 	    head (ws.ws_wordc, list);
 	  else if (strcmp (ws.ws_wordv[0], "tail") == 0)
 	    tail (ws.ws_wordc, list);
+	  else if (strcmp (ws.ws_wordv[0], "sort") == 0)
+	    {
+	      int i;
+	      sort (list);
+
+	      for (i = 0; i < NITR; i++)
+		mu_iterator_destroy (&itr[i]);
+	    }
 	  else if (ws.ws_wordc == 1)
 	    {
 	      char *p;