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playlist: implement Fisher-Yates shuffle properly

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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.
This commit is contained in:
Max Kellermann
2009-01-13 21:25:19 +01:00
parent e7c7e652a3
commit d8fc8ca7ba
1 changed files with 2 additions and 2 deletions
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4
src/playlist.c
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@@ -1118,7 +1118,7 @@ static void randomizeOrder(int start, int end)
clearPlayerQueue(); clearPlayerQueue();
for (i = start; i <= end; i++) { 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) if (ri == playlist.current)
playlist.current = i; playlist.current = i;
else if (i == playlist.current) else if (i == playlist.current)
@@ -1201,7 +1201,7 @@ void shufflePlaylist(void)
} }
/* shuffle the rest of the list */ /* shuffle the rest of the list */
for (; i < playlist.length; i++) { 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); swapSongs(i, ri);
} }