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List:       kde-multimedia
Subject:    Re: Patch: Randomize Standard Playlist (Performance)
From:       Oliver Strutynski <olistrut () gmx ! net>
Date:       2001-11-11 17:22:50
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Here's another update for the randomize code (patch against cvs again). The 
first patch caused items at the end of the list to be pretty poorly 
randomized. The new code does fix this by exchanging two randomly chosen 
elements in the playlist - still much faster than the original 
implementation. Only problem is that chances are pretty high that _some_ of 
the elements at the end of the list remain there. While that does not look 
too random, it is exactly what ranomizing should be like. 

Now if there only were a better (=faster) way to exchange two listview items. 
Moving the items is still rather slow and should not be necessary.

Are there any objections to that patch, any problems? I understand that 
shuffle performance is not too high on your priority list, still it does make 
a significant difference in the handling of the noatun playlist, when dealing 
with a large number of audio files.

Index: playlist.cpp
===================================================================
RCS file: 
/home/kde/kdemultimedia/noatun/noatun/modules/splitplaylist/Attic/playlist.cpp,v
retrieving revision 1.28
diff -u -3 -p -r1.28 playlist.cpp
- --- playlist.cpp        2001/06/04 02:19:51     1.28
+++ playlist.cpp        2001/11/11 17:21:44
@@ -153,25 +153,18 @@ void SplitPlaylist::randomize()
        // otherwise, the list will get randomized and promptly sorted again
        view->setSorting(false);
        List *lview = view->listView();
- -       // eeeeevil :)
- -       QList<void> list;
- -       QList<QListViewItem> items;
- -       for ( int i = 0; i < lview->childCount(); i++ )
- -       {
- -               list.append( (void*) i );
- -               items.append( lview->itemAtIndex( i ) );
- -       }
+
+       // not so evil anymore :)

        KRandomSequence seq;
- -       seq.randomize( &list );
- -
        for ( int i = 0; i < lview->childCount(); i++ )
        {
- -               lview->moveItem( items.take(), 0L,
- -                                lview->itemAtIndex( (int) list.take() ) );
+               lview->moveItem( lview->itemAtIndex( (int) 
seq.getLong(lview->childCount()) ), 0L,
+                                lview->itemAtIndex( (int) 
seq.getLong(lview->childCount())));
        }

        setCurrent( currentItem );
+
}



- -- 
_____________________________________________________________________
 Oliver Strutynski                      oliver.strutynski@cs.tum.edu
                                                    olistrut@gmx.net
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