timsort: Add gtk_tim_sort_set_runs()

... and use it in the SortListModel

Setting runs allows declaring already sorted regions so the sort does
not attempt to sort them again.

This massively speeds up partial inserts where we can reuse the sorted
model as a run and only resort the newly inserted parts.

Benchmarks:

    appending half the model
                    qsort  timsort
    128,000 items    94ms     69ms
    256,000 items   202ms    143ms
    512,000 items   488ms    328ms

    appending 1 item
                    qsort  timsort
      8,000 items   1.5ms    0.0ms
     16,000 items   3.1ms    0.0ms
              ...
    512,000 items     ---    1.8ms

gtk/gtksortlistmodel.c

@@ -175,13 +175,22 @@ sort_func (gconstpointer a,
 }
 
 static void
-gtk_sort_list_model_resort (GtkSortListModel *self)
+gtk_sort_list_model_resort (GtkSortListModel *self,
+                            guint             already_sorted)
 {
-  gtk_tim_sort (sort_array_get_data (&self->items),
-                sort_array_get_size (&self->items),
-                sizeof (SortItem),
-                sort_func,
-                self->sorter);
+  GtkTimSort sort;
+
+  gtk_tim_sort_init (&sort,
+                     sort_array_get_data (&self->items),
+                     sort_array_get_size (&self->items),
+                     sizeof (SortItem),
+                     sort_func,
+                     self->sorter);
+  gtk_tim_sort_set_runs (&sort, (gsize[2]) { already_sorted, 0 });
+
+  while (gtk_tim_sort_step (&sort));
+
+  gtk_tim_sort_finish (&sort);
 }
 
 static void
@@ -252,7 +261,7 @@ gtk_sort_list_model_items_changed_cb (GListModel       *model,
         {
           sort_array_append (&self->items, &(SortItem) { g_list_model_get_item (self->model, i), i });
         }
-      gtk_sort_list_model_resort (self);
+      gtk_sort_list_model_resort (self, sort_array_get_size (&self->items) - added);
 
       for (i = 0; i < start; i++)
         {
@@ -339,7 +348,7 @@ gtk_sort_list_model_sorter_changed_cb (GtkSorter        *sorter,
   else if (sort_array_is_empty (&self->items))
     gtk_sort_list_model_create_items (self);
 
-  gtk_sort_list_model_resort (self);
+  gtk_sort_list_model_resort (self, 0);
 
   n_items = g_list_model_get_n_items (G_LIST_MODEL (self));
   if (n_items > 1)
@@ -476,7 +485,7 @@ gtk_sort_list_model_set_model (GtkSortListModel *self,
       added = g_list_model_get_n_items (model);
 
       gtk_sort_list_model_create_items (self);
-      gtk_sort_list_model_resort (self);
+      gtk_sort_list_model_resort (self, 0);
     }
   else
     added = 0;

gtk/gtktimsort-impl.c

@@ -215,10 +215,6 @@ gtk_tim_sort(merge_append) (GtkTimSort *self)
   /* Push run onto pending-run stack, and maybe merge */
   gtk_tim_sort_push_run (self, self->base, run_len);
 
-  /* Advance to find next run */
-  self->base = ELEM (self->base, run_len);
-  self->size -= run_len;
-
   return TRUE;
 }
 

gtk/gtktimsort.c

@@ -125,10 +125,15 @@ gtk_tim_sort_push_run (GtkTimSort *self,
                        gsize       len)
 {
   g_assert (self->pending_runs < GTK_TIM_SORT_MAX_PENDING);
+  g_assert (len <= self->size);
 
   self->run[self->pending_runs].base = base;
   self->run[self->pending_runs].len = len;
   self->pending_runs++;
+
+  /* Advance to find next run */
+  self->base = ((char *) self->base) + len * self->element_size;
+  self->size -= len;
 }
 
 /**
@@ -167,6 +172,54 @@ gtk_tim_sort_ensure_capacity (GtkTimSort *self,
   return self->tmp;
 }
 
+/*<private>
+ * gtk_tim_sort_get_runs:
+ * @self: a #GtkTimSort
+ * @runs: (out) (caller-allocates): Place to store the 0-terminated list of
+ *     runs
+ *
+ * Stores the already presorted list of runs - ranges of items that are
+ * known to be sorted among themselves.
+ *
+ * This can be used with gtk_tim_sort_set_runs() when resuming a sort later.
+ **/
+void
+gtk_tim_sort_get_runs (GtkTimSort *self,
+                       gsize       runs[GTK_TIM_SORT_MAX_PENDING + 1])
+{
+  gsize i;
+
+  g_return_if_fail (self);
+  g_return_if_fail (runs);
+
+  for (i = 0; i < self->pending_runs; i++)
+    runs[i] = self->run[i].len;
+}
+
+/*<private>
+ * gtk_tim_sort_set_runs:
+ * @self: a freshly initialized #GtkTimSort
+ * @runs: (array length=zero-terminated): a 0-terminated list of runs
+ *
+ * Sets the list of runs. A run is a range of items that are already
+ * sorted correctly among themselves. Runs must appear at the beginning of
+ * the array.
+ *
+ * Runs can only be set at the beginning of the sort operation.
+ **/
+void
+gtk_tim_sort_set_runs (GtkTimSort *self,
+                       gsize      *runs)
+{
+  gsize i;
+
+  g_return_if_fail (self);
+  g_return_if_fail (self->pending_runs == 0);
+
+  for (i = 0; runs[i] != 0; i++)
+    gtk_tim_sort_push_run (self, self->base, runs[i]);
+}
+
 #if 1
 #define WIDTH 4
 #include "gtktimsort-impl.c"

gtk/gtktimsortprivate.h

@@ -95,6 +95,11 @@ void            gtk_tim_sort_init                               (GtkTimSort
                                                                  gpointer                data);
 void            gtk_tim_sort_finish                             (GtkTimSort             *self);
 
+void            gtk_tim_sort_get_runs                           (GtkTimSort             *self,
+                                                                 gsize                   runs[GTK_TIM_SORT_MAX_PENDING + 1]);
+void            gtk_tim_sort_set_runs                           (GtkTimSort             *self,
+                                                                 gsize                  *runs);
+
 gboolean        gtk_tim_sort_step                               (GtkTimSort             *self);
 
 void            gtk_tim_sort                                    (gpointer                base,