# UNDF: UNDF-2026-000000795
# UNDF: (leave blank)
# darktable-0001: dt_map_location_update_images g_list_find O(N*M) image diff
#
# In src/common/map_locations.c, dt_map_location_update_images() computes the
# symmetric difference between old images (imgs) and new images (new_imgs) by
# calling g_list_find() inside two sequential for-loops. Each g_list_find() is
# O(M) on a GList, making each loop O(N*M). For a location covering N=1000
# geotagged images with M=1000 new images, this is O(N*M) = 1,000,000
# pointer comparisons instead of O(N+M) with a hash set.
#
# Similarly, dt_map_location_update_locations() does the same pattern with
# old_tags vs tags lists: two loops with g_list_find() inside each.
#
# Fix: build a GHashTable from one list, then iterate the other with O(1)
# hash lookups.
#
# Severity: MEDIUM — triggered on every map location update; scales with
# collection size.
--- a/src/common/map_locations.c
+++ b/src/common/map_locations.c
@@ -535,14 +535,22 @@
   // clean up locations which are not valid anymore
+  GHashTable *tag_set = g_hash_table_new(g_direct_hash, g_direct_equal);
+  for(GList *tag = (GList *)tags; tag; tag = g_list_next(tag))
+    g_hash_table_add(tag_set, tag->data);
+
   for(GList *tag = old_tags; tag; tag = g_list_next(tag))
   {
-    if(!g_list_find((GList *)tags, tag->data))
+    if(!g_hash_table_contains(tag_set, tag->data))
     {
       dt_tag_detach(GPOINTER_TO_INT(tag->data), imgid,
       FALSE, FALSE);
     }
   }
+  g_hash_table_destroy(tag_set);

   // add new locations
+  GHashTable *old_set = g_hash_table_new(g_direct_hash, g_direct_equal);
+  for(GList *tag = old_tags; tag; tag = g_list_next(tag))
+    g_hash_table_add(old_set, tag->data);
+
   for(GList *tag = (GList *)tags; tag; tag = g_list_next(tag))
   {
-    if(!g_list_find(old_tags, tag->data))
+    if(!g_hash_table_contains(old_set, tag->data))
     {
       dt_tag_attach(GPOINTER_TO_INT(tag->data), imgid,
                     FALSE, FALSE);
     }
   }
+  g_hash_table_destroy(old_set);
   g_list_free(old_tags);
 }

@@ -558,14 +566,22 @@
   gboolean res = FALSE;
   // detach images which are not in location anymore
+  GHashTable *new_set = g_hash_table_new(g_direct_hash, g_direct_equal);
+  for(GList *img = new_imgs; img; img = g_list_next(img))
+    g_hash_table_add(new_set, img->data);
+
   for(GList *img = imgs; img; img = g_list_next(img))
   {
-    if(!g_list_find(new_imgs, img->data))
+    if(!g_hash_table_contains(new_set, img->data))
     {
       dt_tag_detach(ld->id, GPOINTER_TO_INT(img->data), FALSE, FALSE);
       res = TRUE;
     }
   }
+  g_hash_table_destroy(new_set);

   // add new images to location
+  GHashTable *old_img_set = g_hash_table_new(g_direct_hash, g_direct_equal);
+  for(GList *img = imgs; img; img = g_list_next(img))
+    g_hash_table_add(old_img_set, img->data);
+
   for(GList *img = new_imgs; img; img = g_list_next(img))
   {
-    if(!g_list_find(imgs, img->data))
+    if(!g_hash_table_contains(old_img_set, img->data))
     {
       dt_tag_attach(ld->id, GPOINTER_TO_INT(img->data), FALSE, FALSE);
       res = TRUE;
     }
   }
+  g_hash_table_destroy(old_img_set);
   g_list_free(new_imgs);