playlist: rewrite sorting so it's much less cryptic

src/mpdpp.cpp

@@ -916,7 +916,6 @@ bool MPD::Connection::AddRandomTag(mpd_tag_type tag, size_t number)
 	}
 	else
 	{
-		srand(time(0));
 		std::random_shuffle(tags.begin(), tags.end());
 		TagList::const_iterator it = tags.begin()+rand()%(tags.size()-number);
 		for (size_t i = 0; i < number && it != tags.end(); ++i)

src/ncmpcpp.cpp

@@ -94,6 +94,7 @@ namespace
 
 int main(int argc, char **argv)
 {
+	srand(time(0));
 	setlocale(LC_ALL, "");
 	
 	Config.CheckForCommandLineConfigFilePath(argv, argc);

src/playlist.cpp

@@ -182,39 +182,14 @@ void Playlist::EnterPressed()
 			return;
 		}
 		
-		ShowMessage("Sorting playlist...");
-		MPD::SongList playlist, cmp;
-		
+		MPD::SongList playlist;
 		playlist.reserve(end-beginning);
 		for (size_t i = beginning; i < end; ++i)
-		{
-			(*Items)[i].SetPosition(i);
 			playlist.push_back(&(*Items)[i]);
-		}
-		cmp = playlist;
-		sort(playlist.begin(), playlist.end(), Playlist::Sorting);
-		
-		if (playlist == cmp)
-		{
-			ShowMessage("Playlist is already sorted");
-			return;
-		}
 		
+		ShowMessage("Sorting...");
 		Mpd.StartCommandsList();
-		do
-		{
-			for (size_t i = 0, j = beginning; i < playlist.size(); ++i, ++j)
-			{
-				if (playlist[i]->GetPosition() > j)
-				{
-					Mpd.Swap(playlist[i]->GetPosition(), j);
-					std::swap(cmp[playlist[i]->GetPosition()-beginning], cmp[i]);
-					Items->Swap(playlist[i]->GetPosition(), j);
-				}
-				cmp[i]->SetPosition(j);
-			}
-		}
-		while (playlist != cmp);
+		QuickSort(playlist.begin(), playlist.end(), playlist.begin());
 		if (Mpd.CommitCommandsList())
 			ShowMessage("Playlist sorted");
 		w = Items;
@@ -445,13 +420,23 @@ void Playlist::EnableHighlighting()
 	UpdateTimer();
 }
 
-bool Playlist::Sorting(MPD::Song *a, MPD::Song *b)
+void Playlist::QuickSort(MPD::SongList::iterator first, MPD::SongList::iterator last, MPD::SongList::iterator begin)
 {
-	CaseInsensitiveStringComparison cmp;
-	for (size_t i = 0; i < SortOptions; ++i)
-		if (int ret = cmp(a->GetTags((*SortDialog)[i].second), b->GetTags((*SortDialog)[i].second)))
-			return ret < 0;
-	return a->GetPosition() < b->GetPosition();
+	if (last-first > 1)
+	{
+		MPD::SongList::iterator pivot = first+rand()%(last-first);
+		IterSwap(pivot, last-1, begin);
+		pivot = last-1;
+		
+		MPD::SongList::iterator tmp = first;
+		for (MPD::SongList::iterator i = first; i != pivot; ++i)
+			if (SongComp(*i, *pivot))
+				IterSwap(i, tmp++, begin);
+		IterSwap(tmp, pivot, begin);
+		
+		QuickSort(first, tmp, begin);
+		QuickSort(tmp+1, last, begin);
+	}
 }
 
 std::string Playlist::TotalLength()

src/playlist.h

@@ -105,7 +105,21 @@ class Playlist : public Screen<Window>
 		
 		time_t itsTimer;
 		
-		static bool Sorting(MPD::Song *a, MPD::Song *b);
+		// stuff for sorting playlist
+		static void QuickSort(MPD::SongList::iterator first, MPD::SongList::iterator last, MPD::SongList::iterator begin);
+		inline static void IterSwap(MPD::SongList::iterator a, MPD::SongList::iterator b, MPD::SongList::iterator begin)
+		{
+			iter_swap(a, b);
+			Mpd.Swap(a-begin, b-begin);
+		}
+		inline static bool SongComp(MPD::Song *a, MPD::Song *b)
+		{
+			CaseInsensitiveStringComparison cmp;
+			for (size_t i = 0; i < SortOptions; ++i)
+				if (int ret = cmp(a->GetTags((*SortDialog)[i].second), b->GetTags((*SortDialog)[i].second)))
+					return ret < 0;
+			return a->GetPosition() < b->GetPosition();
+		}
 		
 		static Menu< std::pair<std::string, MPD::Song::GetFunction> > *SortDialog;
 		static const size_t SortOptions;