PM123 shuffle mode

From PM123 1.41 a new shuffle algorithm has been implemented. It provides the following properties:

• Shuffle is deterministic. I.e. using previous/next song results in repeatable behavior. This includes nested playlists.
• The deterministic shuffle sequence changes only if the top level playlist has been completed or if a new (or the same) object is loaded into the player.
• Items in different, nested playlists are never exchanged. I.e. all items of one nested playlists are played before another (random) item of the parent playlist is taken.
• It keeps the order of unmodified items when the playlist is altered. Even reloading a playlist from disk does not change the shuffle sequence for items that still exist somewhere in the list.
• It inserts new playlist items at a random location. This implies that new items might not be played if the playback is already active.
• Moving playlist item inside a list does not change the shuffle sequence.
• Changing properties of playlist items does not change the shuffle sequence.
• The shuffle mode can be enabled or disabled in playlist references. This overrides the user setting for a nested playlist.

How does it work?

• PM123 gives each playlist item a unique id.
• A random seed is created when shuffle is enabled.
• A hash value is calculated for each playlist item from the random seed an the unique id.
• The items in each playlist are ordered by this hash.