src/undo.c

   1 /*
   2  * Sylpheed -- a GTK+ based, lightweight, and fast e-mail client
   3  * Copyright (C) 1999-2001 Hiroyuki Yamamoto
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program; if not, write to the Free Software
  17  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
  18  */
  19
  20 /* code ported from gedit */
  21 /* This is for my patient girlfirend Regina */
  22
  23 #ifdef HAVE_CONFIG_H
  24 #  include "config.h"
  25 #endif
  26
  27 #include <glib.h>
  28
  29 #include <string.h> /* for strlen */
  30 #include <stdlib.h> /* for mbstowcs */
  31
  32 #include "undo.h"
  33 #include "utils.h"
  34 #include "prefs_common.h"
  35
  36 typedef struct _UndoInfo UndoInfo;
  37
  38 struct _UndoInfo
  39 {
  40         UndoAction action;
  41         gchar *text;
  42         gint start_pos;
  43         gint end_pos;
  44         gfloat window_position;
  45         gint mergeable;
  46 };
  47
  48 static void undo_free_list      (GList         **list_pointer);
  49 static void undo_check_size     (UndoMain       *undostruct);
  50 static gint undo_merge          (GList          *list,
  51                                  guint           start_pos,
  52                                  guint           end_pos,
  53                                  gint            action,
  54                                  const guchar   *text);
  55 static void undo_add            (const gchar    *text,
  56                                  gint            start_pos,
  57                                  gint            end_pos,
  58                                  UndoAction      action,
  59                                  UndoMain       *undostruct);
  60 static gint undo_get_selection  (GtkTextView    *textview,
  61                                  guint          *start,
  62                                  guint          *end);
  63 static void undo_insert_text_cb (GtkTextBuffer  *textbuf,
  64                                  GtkTextIter    *iter,
  65                                  gchar          *new_text,
  66                                  gint           new_text_length,
  67                                  UndoMain       *undostruct);
  68 static void undo_delete_text_cb (GtkTextBuffer  *textbuf,
  69                                  GtkTextIter    *start,
  70                                  GtkTextIter    *end,
  71                                  UndoMain       *undostruct);
  72
  73 static void undo_paste_clipboard_cb     (GtkTextView    *textview,
  74                                          UndoMain       *undostruct);
  75
  76 void undo_undo                  (UndoMain       *undostruct);
  77 void undo_redo                  (UndoMain       *undostruct);
  78
  79
  80 UndoMain *undo_init(GtkWidget *text)
  81 {
  82         UndoMain *undostruct;
  83         GtkTextView *textview = GTK_TEXT_VIEW(text);
  84         GtkTextBuffer *textbuf = gtk_text_view_get_buffer(textview);
  85
  86         g_return_val_if_fail(text != NULL, NULL);
  87
  88         undostruct = g_new(UndoMain, 1);
  89         undostruct->textview = textview;
  90         undostruct->undo = NULL;
  91         undostruct->redo = NULL;
  92         undostruct->paste = 0;
  93         undostruct->undo_state = FALSE;
  94         undostruct->redo_state = FALSE;
  95
  96         g_signal_connect(G_OBJECT(textbuf), "insert-text",
  97                          G_CALLBACK(undo_insert_text_cb), undostruct);
  98         g_signal_connect(G_OBJECT(textbuf), "delete-range",
  99                          G_CALLBACK(undo_delete_text_cb), undostruct);
 100         g_signal_connect(G_OBJECT(textview), "paste-clipboard",
 101                          G_CALLBACK(undo_paste_clipboard_cb), undostruct);
 102
 103         return undostruct;
 104 }
 105
 106 void undo_destroy (UndoMain *undostruct)
 107 {
 108         undo_free_list(&undostruct->undo);
 109         undo_free_list(&undostruct->redo);
 110         g_free(undostruct);
 111 }
 112
 113 static UndoInfo *undo_object_new(gchar *text, gint start_pos, gint end_pos,
 114                                  UndoAction action, gfloat window_position)
 115 {
 116         UndoInfo *undoinfo;
 117         undoinfo = g_new (UndoInfo, 1);
 118         undoinfo->text      = text;
 119         undoinfo->start_pos = start_pos;
 120         undoinfo->end_pos   = end_pos;
 121         undoinfo->action    = action;
 122         undoinfo->window_position = window_position;
 123         return undoinfo;
 124 }
 125
 126 static void undo_object_free(UndoInfo *undo)
 127 {
 128         g_free (undo->text);
 129         g_free (undo);
 130 }
 131
 132 /**
 133  * undo_free_list:
 134  * @list_pointer: list to be freed
 135  *
 136  * frees and undo structure list
 137  **/
 138 static void undo_free_list(GList **list_pointer)
 139 {
 140         UndoInfo *undo;
 141         GList *cur, *list = *list_pointer;
 142
 143         if (list == NULL) return;
 144
 145         for (cur = list; cur != NULL; cur = cur->next) {
 146                 undo = (UndoInfo *)cur->data;
 147                 undo_object_free(undo);
 148         }
 149
 150         g_list_free(list);
 151         *list_pointer = NULL;
 152 }
 153
 154 void undo_set_change_state_func(UndoMain *undostruct, UndoChangeStateFunc func,
 155                                 gpointer data)
 156 {
 157         g_return_if_fail(undostruct != NULL);
 158
 159         undostruct->change_state_func = func;
 160         undostruct->change_state_data = data;
 161 }
 162
 163 /**
 164  * undo_check_size:
 165  * @compose: document to check
 166  *
 167  * Checks that the size of compose->undo does not excede settings->undo_levels and
 168  * frees any undo level above sett->undo_level.
 169  *
 170  **/
 171 static void undo_check_size(UndoMain *undostruct)
 172 {
 173         UndoInfo *last_undo;
 174         guint length;
 175
 176         if (prefs_common.undolevels < 1) return;
 177
 178         /* No need to check for the redo list size since the undo
 179            list gets freed on any call to compose_undo_add */
 180         length = g_list_length(undostruct->undo);
 181         if (length >= prefs_common.undolevels && prefs_common.undolevels > 0) {
 182                 last_undo = (UndoInfo *)g_list_last(undostruct->undo)->data;
 183                 undostruct->undo = g_list_remove(undostruct->undo, last_undo);
 184                 undo_object_free(last_undo);
 185         }
 186 }
 187
 188 /**
 189  * undo_merge:
 190  * @last_undo:
 191  * @start_pos:
 192  * @end_pos:
 193  * @action:
 194  *
 195  * This function tries to merge the undo object at the top of
 196  * the stack with a new set of data. So when we undo for example
 197  * typing, we can undo the whole word and not each letter by itself
 198  *
 199  * Return Value: TRUE is merge was sucessful, FALSE otherwise
 200  **/
 201 static gint undo_merge(GList *list, guint start_pos, guint end_pos,
 202                        gint action, const guchar *text)
 203 {
 204         guchar *temp_string;
 205         UndoInfo *last_undo;
 206
 207         /* This are the cases in which we will NOT merge :
 208            1. if (last_undo->mergeable == FALSE)
 209            [mergeable = FALSE when the size of the undo data was not 1.
 210            or if the data was size = 1 but = '\n' or if the undo object
 211            has been "undone" already ]
 212            2. The size of text is not 1
 213            3. If the new merging data is a '\n'
 214            4. If the last char of the undo_last data is a space/tab
 215            and the new char is not a space/tab ( so that we undo
 216            words and not chars )
 217            5. If the type (action) of undo is different from the last one
 218            Chema */
 219
 220         if (list == NULL) return FALSE;
 221
 222         last_undo = list->data;
 223
 224         if (!last_undo->mergeable) return FALSE;
 225
 226         if (end_pos - start_pos != 1 ||
 227             text[0] == '\n' ||
 228             action != last_undo->action ||
 229             action == UNDO_ACTION_REPLACE_INSERT ||
 230             action == UNDO_ACTION_REPLACE_DELETE) {
 231                 last_undo->mergeable = FALSE;
 232                 return FALSE;
 233         }
 234
 235         if (action == UNDO_ACTION_DELETE) {
 236                 gboolean checkit = TRUE;
 237
 238                 if (last_undo->start_pos != end_pos &&
 239                     last_undo->start_pos != start_pos) {
 240                         last_undo->mergeable = FALSE;
 241                         return FALSE;
 242                 } else if (last_undo->start_pos == start_pos) {
 243                         /* Deleted with the delete key */
 244                         if (text[0] != ' ' && text[0] != '\t' &&
 245                             (last_undo->text[last_undo->end_pos - last_undo->start_pos - 1] == ' ' ||
 246                              last_undo->text[last_undo->end_pos - last_undo->start_pos - 1] == '\t'))
 247                                 checkit = FALSE;
 248
 249                         temp_string = g_strdup_printf("%s%s", last_undo->text, text);
 250                         last_undo->end_pos++;
 251                         g_free(last_undo->text);
 252                         last_undo->text = temp_string;
 253                 } else {
 254                         /* Deleted with the backspace key */
 255                         if (text[0] != ' ' && text[0] != '\t' &&
 256                             (last_undo->text[0] == ' ' ||
 257                              last_undo->text[0] == '\t'))
 258                                 checkit = FALSE;
 259
 260                         temp_string = g_strdup_printf("%s%s", text, last_undo->text);
 261                         last_undo->start_pos = start_pos;
 262                         g_free(last_undo->text);
 263                         last_undo->text = temp_string;
 264                 }
 265
 266                 if (!checkit) {
 267                         last_undo->mergeable = FALSE;
 268                         return FALSE;
 269                 }
 270         } else if (action == UNDO_ACTION_INSERT) {
 271                 if (last_undo->end_pos != start_pos) {
 272                         last_undo->mergeable = FALSE;
 273                         return FALSE;
 274                 } else {
 275                         temp_string = g_strdup_printf("%s%s", last_undo->text, text);
 276                         g_free(last_undo->text);
 277                         last_undo->end_pos = end_pos;
 278                         last_undo->text = temp_string;
 279                 }
 280         } else
 281                 debug_print("Unknown action [%i] inside undo merge encountered", action);
 282
 283         return TRUE;
 284 }
 285
 286 /**
 287  * compose_undo_add:
 288  * @text:
 289  * @start_pos:
 290  * @end_pos:
 291  * @action: either UNDO_ACTION_INSERT or UNDO_ACTION_DELETE
 292  * @compose:
 293  * @view: The view so that we save the scroll bar position.
 294  *
 295  * Adds text to the undo stack. It also performs test to limit the number
 296  * of undo levels and deltes the redo list
 297  **/
 298
 299 static void undo_add(const gchar *text,
 300                      gint start_pos, gint end_pos,
 301                      UndoAction action, UndoMain *undostruct)
 302 {
 303         UndoInfo *undoinfo;
 304         GtkAdjustment *vadj;
 305
 306         g_return_if_fail(text != NULL);
 307         g_return_if_fail(end_pos >= start_pos);
 308
 309         undo_free_list(&undostruct->redo);
 310
 311         /* Set the redo sensitivity */
 312         undostruct->change_state_func(undostruct,
 313                                       UNDO_STATE_UNCHANGED, UNDO_STATE_FALSE,
 314                                       undostruct->change_state_data);
 315
 316         if (undostruct->paste != 0) {
 317                 if (action == UNDO_ACTION_INSERT)
 318                         action = UNDO_ACTION_REPLACE_INSERT;
 319                 else
 320                         action = UNDO_ACTION_REPLACE_DELETE;
 321                 undostruct->paste = undostruct->paste + 1;
 322                 if (undostruct->paste == 3)
 323                         undostruct->paste = 0;
 324         }
 325
 326         if (undo_merge(undostruct->undo, start_pos, end_pos, action, text))
 327                 return;
 328
 329         undo_check_size(undostruct);
 330
 331         vadj = GTK_ADJUSTMENT(GTK_TEXT_VIEW(undostruct->textview)->vadjustment);
 332         undoinfo = undo_object_new(g_strdup(text), start_pos, end_pos, action,
 333                                    vadj->value);
 334
 335         if (end_pos - start_pos != 1 || text[0] == '\n')
 336                 undoinfo->mergeable = FALSE;
 337         else
 338                 undoinfo->mergeable = TRUE;
 339
 340         undostruct->undo = g_list_prepend(undostruct->undo, undoinfo);
 341
 342         undostruct->change_state_func(undostruct,
 343                                       UNDO_STATE_TRUE, UNDO_STATE_UNCHANGED,
 344                                       undostruct->change_state_data);
 345 }
 346
 347 /**
 348  * undo_undo:
 349  * @w: not used
 350  * @data: not used
 351  *
 352  * Executes an undo request on the current document
 353  **/
 354 void undo_undo(UndoMain *undostruct)
 355 {
 356         UndoInfo *undoinfo;
 357         GtkTextView *textview;
 358         GtkTextBuffer *buffer;
 359         GtkTextIter iter, start_iter, end_iter;
 360         GtkTextMark *mark;
 361
 362         g_return_if_fail(undostruct != NULL);
 363
 364         if (undostruct->undo == NULL) return;
 365
 366         /* The undo data we need is always at the top op the
 367            stack. So, therefore, the first one */
 368         undoinfo = (UndoInfo *)undostruct->undo->data;
 369         g_return_if_fail(undoinfo != NULL);
 370         undoinfo->mergeable = FALSE;
 371         undostruct->redo = g_list_prepend(undostruct->redo, undoinfo);
 372         undostruct->undo = g_list_remove(undostruct->undo, undoinfo);
 373
 374         textview = undostruct->textview;
 375         buffer = gtk_text_view_get_buffer(textview);
 376
 377         undo_block(undostruct);
 378
 379         /* Check if there is a selection active */
 380         mark = gtk_text_buffer_get_insert(buffer);
 381         gtk_text_buffer_get_iter_at_mark(buffer, &iter, mark);
 382         gtk_text_buffer_place_cursor(buffer, &iter);
 383
 384         /* Move the view (scrollbars) to the correct position */
 385         gtk_adjustment_set_value
 386                 (GTK_ADJUSTMENT(textview->vadjustment),
 387                  undoinfo->window_position);
 388
 389         switch (undoinfo->action) {
 390         case UNDO_ACTION_DELETE:
 391                 gtk_text_buffer_get_iter_at_offset(buffer, &iter, undoinfo->start_pos);
 392                 gtk_text_buffer_insert(buffer, &iter, undoinfo->text, -1);
 393                 break;
 394         case UNDO_ACTION_INSERT:
 395                 gtk_text_buffer_get_iter_at_offset(buffer, &start_iter, undoinfo->start_pos);
 396                 gtk_text_buffer_get_iter_at_offset(buffer, &end_iter, undoinfo->end_pos);
 397                 gtk_text_buffer_delete(buffer, &start_iter, &end_iter);
 398                 break;
 399         case UNDO_ACTION_REPLACE_INSERT:
 400                 gtk_text_buffer_get_iter_at_offset(buffer, &start_iter, undoinfo->start_pos);
 401                 gtk_text_buffer_get_iter_at_offset(buffer, &end_iter, undoinfo->end_pos);
 402                 gtk_text_buffer_delete(buffer, &start_iter, &end_iter);
 403                 /* "pull" another data structure from the list */
 404                 undoinfo = (UndoInfo *)undostruct->undo->data;
 405                 g_return_if_fail(undoinfo != NULL);
 406                 undostruct->redo = g_list_prepend(undostruct->redo, undoinfo);
 407                 undostruct->undo = g_list_remove(undostruct->undo, undoinfo);
 408                 g_return_if_fail(undoinfo->action == UNDO_ACTION_REPLACE_DELETE);
 409                 gtk_text_buffer_insert(buffer, &start_iter, undoinfo->text, -1);
 410                 break;
 411         case UNDO_ACTION_REPLACE_DELETE:
 412                 g_warning("This should not happen. UNDO_REPLACE_DELETE");
 413                 break;
 414         default:
 415                 g_assert_not_reached();
 416                 break;
 417         }
 418
 419         undostruct->change_state_func(undostruct,
 420                                       UNDO_STATE_UNCHANGED, UNDO_STATE_TRUE,
 421                                       undostruct->change_state_data);
 422
 423         if (undostruct->undo == NULL)
 424                 undostruct->change_state_func(undostruct,
 425                                               UNDO_STATE_FALSE,
 426                                               UNDO_STATE_UNCHANGED,
 427                                               undostruct->change_state_data);
 428
 429         undo_unblock(undostruct);
 430 }
 431
 432 /**
 433  * undo_redo:
 434  * @w: not used
 435  * @data: not used
 436  *
 437  * executes a redo request on the current document
 438  **/
 439 void undo_redo(UndoMain *undostruct)
 440 {
 441         UndoInfo *redoinfo;
 442         GtkTextView *textview;
 443         GtkTextBuffer *buffer;
 444         GtkTextIter iter, start_iter, end_iter;
 445         GtkTextMark *mark;
 446
 447         g_return_if_fail(undostruct != NULL);
 448
 449         if (undostruct->redo == NULL) return;
 450
 451         redoinfo = (UndoInfo *)undostruct->redo->data;
 452         g_return_if_fail (redoinfo != NULL);
 453         undostruct->undo = g_list_prepend(undostruct->undo, redoinfo);
 454         undostruct->redo = g_list_remove(undostruct->redo, redoinfo);
 455
 456         textview = undostruct->textview;
 457         buffer = gtk_text_view_get_buffer(textview);
 458
 459         undo_block(undostruct);
 460
 461         /* Check if there is a selection active */
 462         mark = gtk_text_buffer_get_insert(buffer);
 463         gtk_text_buffer_get_iter_at_mark(buffer, &iter, mark);
 464         gtk_text_buffer_place_cursor(buffer, &iter);
 465
 466         /* Move the view to the right position. */
 467         gtk_adjustment_set_value(textview->vadjustment,
 468                                  redoinfo->window_position);
 469
 470         switch (redoinfo->action) {
 471         case UNDO_ACTION_INSERT:
 472                 gtk_text_buffer_get_iter_at_offset(buffer, &iter, redoinfo->start_pos);
 473                 gtk_text_buffer_insert(buffer, &iter, redoinfo->text, -1);
 474                 break;
 475         case UNDO_ACTION_DELETE:
 476                 gtk_text_buffer_get_iter_at_offset(buffer, &start_iter, redoinfo->start_pos);
 477                 gtk_text_buffer_get_iter_at_offset(buffer, &end_iter, redoinfo->end_pos);
 478                 gtk_text_buffer_delete(buffer, &start_iter, &end_iter);
 479                 break;
 480         case UNDO_ACTION_REPLACE_DELETE:
 481                 gtk_text_buffer_get_iter_at_offset(buffer, &start_iter, redoinfo->start_pos);
 482                 gtk_text_buffer_get_iter_at_offset(buffer, &end_iter, redoinfo->end_pos);
 483                 gtk_text_buffer_delete(buffer, &start_iter, &end_iter);
 484                 debug_print("UNDO_ACTION_REPLACE %s\n", redoinfo->text);
 485                 /* "pull" another data structure from the list */
 486                 redoinfo = (UndoInfo *)undostruct->redo->data;
 487                 g_return_if_fail(redoinfo != NULL);
 488                 undostruct->undo = g_list_prepend(undostruct->redo, redoinfo);
 489                 undostruct->redo = g_list_remove(undostruct->undo, redoinfo);
 490                 g_return_if_fail(redoinfo->action == UNDO_ACTION_REPLACE_DELETE);
 491                 gtk_text_buffer_insert(buffer, &start_iter, redoinfo->text, -1);
 492                 break;
 493         case UNDO_ACTION_REPLACE_INSERT:
 494                 g_warning("This should not happen. Redo: UNDO_REPLACE_INSERT");
 495                 break;
 496         default:
 497                 g_assert_not_reached();
 498                 break;
 499         }
 500
 501         undostruct->change_state_func(undostruct,
 502                                       UNDO_STATE_TRUE, UNDO_STATE_UNCHANGED,
 503                                       undostruct->change_state_data);
 504
 505         if (undostruct->redo == NULL)
 506                 undostruct->change_state_func(undostruct,
 507                                               UNDO_STATE_UNCHANGED,
 508                                               UNDO_STATE_FALSE,
 509                                               undostruct->change_state_data);
 510
 511         undo_unblock(undostruct);
 512 }
 513
 514 void undo_block(UndoMain *undostruct)
 515 {
 516         GtkTextBuffer *buffer;
 517
 518         g_return_if_fail(GTK_IS_TEXT_VIEW(undostruct->textview));
 519
 520         buffer = gtk_text_view_get_buffer(undostruct->textview);
 521         g_signal_handlers_block_by_func(buffer, undo_insert_text_cb, undostruct);
 522         g_signal_handlers_block_by_func(buffer, undo_delete_text_cb, undostruct);
 523         g_signal_handlers_block_by_func(buffer, undo_paste_clipboard_cb,
 524                                           undostruct);
 525 }
 526
 527 void undo_unblock(UndoMain *undostruct)
 528 {
 529         GtkTextBuffer *buffer;
 530
 531         g_return_if_fail(GTK_IS_TEXT_VIEW(undostruct->textview));
 532
 533         buffer = gtk_text_view_get_buffer(undostruct->textview);
 534         g_signal_handlers_unblock_by_func(buffer, undo_insert_text_cb, undostruct);
 535         g_signal_handlers_unblock_by_func(buffer, undo_delete_text_cb, undostruct);
 536         g_signal_handlers_unblock_by_func(buffer, undo_paste_clipboard_cb,
 537                                           undostruct);
 538 }
 539
 540 void undo_insert_text_cb(GtkTextBuffer *textbuf, GtkTextIter *iter,
 541                          gchar *new_text, gint new_text_length,
 542                          UndoMain *undostruct)
 543 {
 544         gchar *text_to_insert;
 545         gint pos;
 546
 547         if (prefs_common.undolevels <= 0) return;
 548
 549         pos = gtk_text_iter_get_offset(iter);
 550
 551         Xstrndup_a(text_to_insert, new_text, new_text_length, return);
 552         undo_add(text_to_insert, pos, pos + g_utf8_strlen(text_to_insert, -1),
 553                  UNDO_ACTION_INSERT, undostruct);
 554 }
 555
 556 void undo_delete_text_cb(GtkTextBuffer *textbuf, GtkTextIter *start,
 557                          GtkTextIter *end, UndoMain *undostruct)
 558 {
 559         gchar *text_to_delete;
 560         gint start_pos, end_pos;
 561
 562         if (prefs_common.undolevels <= 0) return;
 563
 564         text_to_delete = gtk_text_buffer_get_text(textbuf, start, end, FALSE);
 565         if (!text_to_delete || !*text_to_delete) return;
 566
 567         start_pos = gtk_text_iter_get_offset(start);
 568         end_pos   = gtk_text_iter_get_offset(end);
 569
 570         undo_add(text_to_delete, start_pos, end_pos, UNDO_ACTION_DELETE,
 571                  undostruct);
 572         g_free(text_to_delete);
 573 }
 574
 575 void undo_paste_clipboard_cb(GtkTextView *textview, UndoMain *undostruct)
 576 {
 577 #if 0
 578         if (editable->clipboard_text == NULL) return;
 579 #endif
 580
 581         if (prefs_common.undolevels > 0)
 582                 if (undo_get_selection(textview, NULL, NULL))
 583                         undostruct->paste = TRUE;
 584 }
 585
 586 /**
 587  * undo_get_selection:
 588  * @text: Text to get the selection from
 589  * @start: return here the start position of the selection
 590  * @end: return here the end position of the selection
 591  *
 592  * Gets the current selection for View
 593  *
 594  * Return Value: TRUE if there is a selection active, FALSE if not
 595  **/
 596 static gint undo_get_selection(GtkTextView *textview, guint *start, guint *end)
 597 {
 598         GtkTextBuffer *buffer;
 599         GtkTextIter start_iter, end_iter;
 600         guint start_pos, end_pos;
 601
 602         buffer = gtk_text_view_get_buffer(textview);
 603         gtk_text_buffer_get_selection_bounds(buffer, &start_iter, &end_iter);
 604
 605         start_pos = gtk_text_iter_get_offset(&start_iter);
 606         end_pos   = gtk_text_iter_get_offset(&end_iter);
 607
 608         /* The user can select from end to start too. If so, swap it*/
 609         if (end_pos < start_pos) {
 610                 guint swap_pos;
 611                 swap_pos  = end_pos;
 612                 end_pos   = start_pos;
 613                 start_pos = swap_pos;
 614         }
 615
 616         if (start != NULL)
 617                 *start = start_pos;
 618
 619         if (end != NULL)
 620                 *end = end_pos;
 621
 622         if ((start_pos > 0 || end_pos > 0) && (start_pos != end_pos))
 623                 return TRUE;
 624         else
 625                 return FALSE;
 626 }