[PATCH 2/4] comctl32/listbox: Implement LBS_NODATA for multi-selection listboxes

[Gabriel Ivăncescu]

Use a byte array to store selection state of items, since we don't need any
other data for LBS_NODATA multi-selection listboxes. This improves memory
usage dramatically for large lists, and performance boosts are nice too.

Signed-off-by: Gabriel Ivăncescu <gabrielopcode at gmail.com>
---

For now, this should be good enough (byte array). Unfortunately, using
other storage representations in the future (like selection ranges, or bit
arrays) would probably need the avoided NODATA helpers to split the functions
(in order to be easier maintainable), so for now this will suffice.

 dlls/comctl32/listbox.c | 48 +++++++++++++++++++++++++++++++++++------
 1 file changed, 41 insertions(+), 7 deletions(-)

diff --git a/dlls/comctl32/listbox.c b/dlls/comctl32/listbox.c
index b6024c3..5afdf5c 100644
--- a/dlls/comctl32/listbox.c
+++ b/dlls/comctl32/listbox.c
@@ -18,8 +18,6 @@
  * License along with this library; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
  *
- * TODO:
- *    - LBS_NODATA for multi-selection listboxes
  */
 
 #include <string.h>
@@ -127,6 +125,15 @@ static TIMER_DIRECTION LISTBOX_Timer = LB_TIMER_NONE;
 
 static LRESULT LISTBOX_GetItemRect( const LB_DESCR *descr, INT index, RECT *rect );
 
+/*
+   Resize the item storage array if needed.
+
+   For single-selection LBS_NODATA listboxes, no storage is allocated,
+   and thus descr->items will always be NULL.
+
+   For multi-selection LBS_NODATA listboxes, one byte per item is stored
+   for the item's selection state, instead of the usual LB_ITEMDATA.
+*/
 static BOOL resize_storage(LB_DESCR *descr, UINT items_size)
 {
     LB_ITEMDATA *items;
@@ -137,7 +144,10 @@ static BOOL resize_storage(LB_DESCR *descr, UINT items_size)
         items_size = (items_size + LB_ARRAY_GRANULARITY - 1) & ~(LB_ARRAY_GRANULARITY - 1);
         if ((descr->style & (LBS_NODATA | LBS_MULTIPLESEL | LBS_EXTENDEDSEL)) != LBS_NODATA)
         {
-            items = heap_realloc(descr->items, items_size * sizeof(LB_ITEMDATA));
+            size_t size = items_size;
+            if (!(descr->style & LBS_NODATA)) size *= sizeof(LB_ITEMDATA);
+
+            items = heap_realloc(descr->items, size);
             if (!items)
             {
                 SEND_NOTIFICATION(descr, LBN_ERRSPACE);
@@ -150,8 +160,7 @@ static BOOL resize_storage(LB_DESCR *descr, UINT items_size)
 
     if ((descr->style & LBS_NODATA) && descr->items && items_size > descr->nb_items)
     {
-        memset(&descr->items[descr->nb_items], 0,
-               (items_size - descr->nb_items) * sizeof(LB_ITEMDATA));
+        memset((BYTE*)descr->items + descr->nb_items, 0, items_size - descr->nb_items);
     }
     return TRUE;
 }
@@ -180,13 +189,21 @@ static BOOL is_item_selected( const LB_DESCR *descr, UINT index )
 {
     if (!(descr->style & (LBS_MULTIPLESEL | LBS_EXTENDEDSEL)))
         return index == descr->selected_item;
-    return descr->items[index].selected;
+    if (descr->style & LBS_NODATA)
+        return ((BYTE*)descr->items)[index];
+    else
+        return descr->items[index].selected;
 }
 
 static void set_item_selected_state(LB_DESCR *descr, UINT index, BOOL state)
 {
     if (descr->style & (LBS_MULTIPLESEL | LBS_EXTENDEDSEL))
-        descr->items[index].selected = state;
+    {
+        if (descr->style & LBS_NODATA)
+            ((BYTE*)descr->items)[index] = state;
+        else
+            descr->items[index].selected = state;
+    }
 }
 
 static void insert_item_data(LB_DESCR *descr, UINT index, WCHAR *str, ULONG_PTR data)
@@ -194,6 +211,15 @@ static void insert_item_data(LB_DESCR *descr, UINT index, WCHAR *str, ULONG_PTR
     LB_ITEMDATA *item;
 
     if (!descr->items) return;
+    if (descr->style & LBS_NODATA)
+    {
+        BYTE *item = (BYTE*)descr->items + index;
+
+        if (index < descr->nb_items)
+            memmove(item + 1, item, descr->nb_items - index);
+        *item = FALSE;
+        return;
+    }
 
     item = descr->items + index;
     if (index < descr->nb_items)
@@ -210,6 +236,14 @@ static void remove_item_data(LB_DESCR *descr, UINT index)
     LB_ITEMDATA *item;
 
     if (!descr->items) return;
+    if (descr->style & LBS_NODATA)
+    {
+        BYTE *item = (BYTE*)descr->items + index;
+
+        if (index < descr->nb_items)
+            memmove(item, item + 1, descr->nb_items - index);
+        return;
+    }
 
     item = descr->items + index;
     if (index < descr->nb_items)
-- 
2.20.1