[gnome-photos] selection-toolbar: Avoid O(n) logic

[Debarshi Ray <debarshir src gnome org>]

commit a795b5b292791b7b22614fb43be57b1d619ec259
Author: Debarshi Ray <debarshir gnome org>
Date:   Fri Oct 30 14:09:29 2015 +0100

    selection-toolbar: Avoid O(n) logic
    
    To check whether a GList is non-empty, it is faster to check it against
    NULL. We can similarly check if there is only one element by looking at
    the pointers. In those cases where we really do need the length, we can
    calculate it ourselves if we are already iterating over the list.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=757363

 src/photos-selection-toolbar.c |   16 +++++++---------
 1 files changed, 7 insertions(+), 9 deletions(-)
---
diff --git a/src/photos-selection-toolbar.c b/src/photos-selection-toolbar.c
index 449fd1c..bb4b87e 100644
--- a/src/photos-selection-toolbar.c
+++ b/src/photos-selection-toolbar.c
@@ -218,7 +218,7 @@ photos_selection_toolbar_print_clicked (GtkButton *button, gpointer user_data)
   const gchar *urn;
 
   selection = photos_selection_controller_get_selection (priv->sel_cntrlr);
-  if (g_list_length (selection) != 1)
+  if (selection != NULL && selection->next == NULL) /* length == 1 */
     return;
 
   urn = (gchar *) selection->data;
@@ -280,14 +280,12 @@ photos_selection_toolbar_set_item_visibility (PhotosSelectionToolbar *self)
   gchar *favorite_label;
   gchar *open_label;
   guint fav_count = 0;
-  guint apps_length;
-  guint sel_length;
+  guint sel_length = 0;
 
   priv->inside_refresh = TRUE;
 
   selection = photos_selection_controller_get_selection (priv->sel_cntrlr);
-  sel_length = g_list_length (selection);
-  has_selection = sel_length > 0;
+  has_selection = selection != NULL;
 
   show_collection = has_selection;
   show_favorite = has_selection;
@@ -313,12 +311,12 @@ photos_selection_toolbar_set_item_visibility (PhotosSelectionToolbar *self)
 
       show_trash = show_trash && photos_base_item_can_trash (item);
       show_print = show_print && !photos_base_item_is_collection (item);
+
+      sel_length++;
     }
 
   show_favorite = show_favorite && ((fav_count == 0) || (fav_count == sel_length));
-
-  apps_length = g_list_length (apps);
-  show_open = (apps_length > 0);
+  show_open = apps != NULL;
 
   if (sel_length > 1)
     {
@@ -326,7 +324,7 @@ photos_selection_toolbar_set_item_visibility (PhotosSelectionToolbar *self)
       show_properties = FALSE;
     }
 
-  if (apps_length == 1)
+  if (apps != NULL && apps->next == NULL) /* length == 1 */
     /* Translators: this is the Open action in a context menu */
     open_label = g_strdup_printf (_("Open with %s"), (gchar *) apps->data);
   else