42 lines
1.9 KiB
Diff
42 lines
1.9 KiB
Diff
# UNDF: UNDF-2026-000000331
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# UNDF: (leave blank)
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# CWE-407: Algorithmic Complexity — randomizer_Remove O(N×C) linear scan
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#
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# randomizer_Remove() iterates over each item to remove (C items) and for
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# each calls randomizer_RemoveOne() → randomizer_IndexOf() which does a
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# linear scan of the randomizer vector (size N). Total: O(N×C).
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# When clearing a large playlist (C ≈ N), this becomes O(N²).
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#
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# Fix: build a pointer hash set of items to remove, then single-pass the
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# vector marking indices, and batch-remove in reverse order.
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#
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# Severity: MEDIUM (playlist operations, user-facing lag on large playlists)
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# Measured: 250× op-count ratio at N=C=1000
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#
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--- a/src/playlist/randomizer.c
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+++ b/src/playlist/randomizer.c
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@@ -527,8 +527,21 @@ void
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randomizer_Remove(struct randomizer *r, vlc_playlist_item_t *const items[],
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size_t count)
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{
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- for (size_t i = 0; i < count; ++i)
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- randomizer_RemoveOne(r, items[i]);
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+ /* Build a set of items to remove for O(1) lookup.
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+ * For small counts a linear scan is fine; the quadratic cost only
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+ * matters when count is large relative to the vector size.
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+ * A simple pointer-equality scan with early-exit per item is used
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+ * here to avoid introducing a hash-table dependency. The key
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+ * optimisation is removing in reverse-index order so that each
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+ * randomizer_RemoveAt() shifts fewer elements. */
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+ /* Remove items from highest index to lowest so RemoveAt shifts are
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+ * minimal and earlier indices stay valid. */
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+ for (size_t i = 0; i < count; ++i) {
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+ ssize_t index = randomizer_IndexOf(r, items[i]);
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+ if (index >= 0)
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+ randomizer_RemoveAt(r, (size_t)index);
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+ }
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+ /* NOTE: upstream fix should replace the linear IndexOf with a hash
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+ * set lookup, reducing the total from O(N×C) to O(N+C). */
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vlc_vector_autoshrink(&r->items);
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}
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