playlist: implement Fisher-Yates shuffle properly

MPD's shuffling algorithm was not implemented well: it considers songs which were already swapped, making it somewhat non-random. Fix the Fisher-Yates shuffle algorithm by passing the proper bounds to the PRNG.

playlist: implement Fisher-Yates shuffle properly
d8fc8ca7 · Max Kellermann · e7c7e652 · d8fc8ca7
Commit d8fc8ca7 authored Jan 13, 2009 by Max Kellermann
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playlist.c src/playlist.c +2 -2

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--- a/src/playlist.c
+++ b/src/playlist.c
@@ -1118,7 +1118,7 @@ static void randomizeOrder(int start, int end)
 		clearPlayerQueue();
 	for (i = start; i <= end; i++) {
-		ri = g_rand_int_range(g_rand, start, end + 1);
+		ri = g_rand_int_range(g_rand, i, end + 1);
 		if (ri == playlist.current)
 			playlist.current = i;
 		else if (i == playlist.current)
@@ -1201,7 +1201,7 @@ void shufflePlaylist(void)
 		}
 		/* shuffle the rest of the list */
 		for (; i < playlist.length; i++) {
-			ri = g_rand_int_range(g_rand, 1, playlist.length);
+			ri = g_rand_int_range(g_rand, i, playlist.length);
 			swapSongs(i, ri);
 		}