- improve performance, by not iterating for each entry through all entries,...

- improve performance, by not iterating for each entry through all entries, but initially create an associative array of old entries indexed by their key and then iterating through the new entries once identifying new, modfied or removed entries
(this makes a hugh difference eg. for addressbooks with a couple of thousand entries more then a factor of 10)
- it drops the requirement that ids need to be in ascending order, new diff code works also if $new contains smaller ids. That happens eg. for us when a users unsubscribs from a mail folder and subscribes again

src/lib/default/diffbackend/diffstate.php

@@ -110,20 +110,6 @@ class DiffState implements IChanges {
      * DiffState specific stuff
      */
 
-    /**
-     * Comparing function used for sorting of the differential engine
-     *
-     * @param array        $a
-     * @param array        $b
-     *
-     * @access public
-     * @return boolean
-     */
-    static public function RowCmp($a, $b) {
-        // TODO implement different comparing functions
-        return $a["id"] < $b["id"] ? 1 : -1;
-    }
-
     /**
      * Differential mechanism
      * Compares the current syncstate to the sent $new
@@ -134,74 +120,51 @@ class DiffState implements IChanges {
      * @return array
      */
     protected function getDiffTo($new) {
-        $changes = array();
+        $changes = $old = array();
 
-        // Sort both arrays in the same way by ID
-        usort($this->syncstate, array("DiffState", "RowCmp"));
-        usort($new, array("DiffState", "RowCmp"));
-
-        $inew = 0;
-        $iold = 0;
+        // create associative array of old items with id as key
+        foreach($this->syncstate as &$item) {
+            $old[$item['id']] =& $item;
+        }
 
-        // Get changes by comparing our list of messages with
-        // our previous state
-        while(1) {
-            $change = array();
+        // iterate through new items to identify new or changed items
+        foreach($new as &$item) {
+            $id = $item['id'];
+            $change = array("id" => $id);
 
-            if($iold >= count($this->syncstate) || $inew >= count($new))
-                break;
+            if (!isset($old[$id])) {
+                // Message in new seems to be new (add)
+                $change["type"] = "change";
+                $change['flags'] = SYNC_NEWMESSAGE;
+                $changes[] = $change;
+            } else {
+                $old_item =& $old[$id];
 
-            if($this->syncstate[$iold]["id"] == $new[$inew]["id"]) {
                 // Both messages are still available, compare flags and mod
-                if(isset($this->syncstate[$iold]["flags"]) && isset($new[$inew]["flags"]) && $this->syncstate[$iold]["flags"] != $new[$inew]["flags"]) {
+                if(isset($old_item["flags"]) && isset($item["flags"]) && $old_item["flags"] != $item["flags"]) {
                     // Flags changed
                     $change["type"] = "flags";
-                    $change["id"] = $new[$inew]["id"];
-                    $change["flags"] = $new[$inew]["flags"];
+                    $change["flags"] = $item["flags"];
                     $changes[] = $change;
                 }
 
-                if($this->syncstate[$iold]["mod"] != $new[$inew]["mod"]) {
+                if ($old_item['mod'] != $item['mod']) {
                     $change["type"] = "change";
-                    $change["id"] = $new[$inew]["id"];
                     $changes[] = $change;
                 }
 
-                $inew++;
-                $iold++;
-            } else {
-                if($this->syncstate[$iold]["id"] > $new[$inew]["id"]) {
-                    // Message in state seems to have disappeared (delete)
-                    $change["type"] = "delete";
-                    $change["id"] = $this->syncstate[$iold]["id"];
-                    $changes[] = $change;
-                    $iold++;
-                } else {
-                    // Message in new seems to be new (add)
-                    $change["type"] = "change";
-                    $change["flags"] = SYNC_NEWMESSAGE;
-                    $change["id"] = $new[$inew]["id"];
-                    $changes[] = $change;
-                    $inew++;
-                }
+                // unset in $old, so $old contains only the deleted items
+                unset($old[$id]);
             }
         }
 
-        while($iold < count($this->syncstate)) {
-            // All data left in 'syncstate' have been deleted
-            $change["type"] = "delete";
-            $change["id"] = $this->syncstate[$iold]["id"];
-            $changes[] = $change;
-            $iold++;
-        }
-
-        while($inew < count($new)) {
-            // All data left in new have been added
-            $change["type"] = "change";
-            $change["flags"] = SYNC_NEWMESSAGE;
-            $change["id"] = $new[$inew]["id"];
-            $changes[] = $change;
-            $inew++;
+        // now $old contains only deleted items
+        foreach($old as $id => &$item) {
+            // Message in state seems to have disappeared (delete)
+            $changes[] = array(
+                "type" => "delete",
+                "id"   => $id,
+            );
         }
 
         return $changes;