russell@unturf.com
25c2bafdee
New UNDF assignments (693→720): elixir-0002 → UNDF-2026-000000698 (typespec used_type_pairs O(T²)) r-source-0002 → UNDF-2026-000000711 (.walkClassGraph match dedup O(S²)) ruby-0003 → UNDF-2026-000000712 (RubyGems dependent_gems O(N²×D)) victoria-metrics-0002 → UNDF-2026-000000717 (MetricName tag-filter O(T×I)) Total: 720 UNDF assigned
70 lines
2.4 KiB
Diff
70 lines
2.4 KiB
Diff
# UNDF: UNDF-2026-000000684
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--- a/libavcodec/gif.c
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+++ b/libavcodec/gif.c
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@@ -67,18 +67,53 @@ static void shrink_palette(const uint32_t *src, uint8_t *map,
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uint32_t *dst, size_t *palette_count)
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{
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- size_t colors_seen = 0;
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-
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- for (size_t i = 0; i < AVPALETTE_COUNT; i++) {
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- int seen = 0;
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- for (size_t c = 0; c < colors_seen; c++) {
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- if (src[i] == dst[c]) {
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- seen = 1;
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- break;
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- }
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- }
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- if (!seen) {
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- dst[colors_seen] = src[i];
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- map[i] = colors_seen;
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- colors_seen++;
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- }
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- }
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-
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- *palette_count = colors_seen;
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+ /*
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+ * CWE-407 fix: replace O(P²) nested scan with an open-addressing hash
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+ * table over the 256-entry colour space.
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+ *
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+ * Original: for each of P=256 entries, scan all previously-seen entries →
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+ * O(0+1+…+255) = 32,640 comparisons worst-case per frame.
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+ *
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+ * Fix: Knuth multiplicative hash folds 32-bit ARGB to an 8-bit slot;
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+ * linear probing resolves collisions. Total work: O(P) = 256 hash ops.
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+ * Speedup: ~127× worst-case (all 256 colours unique).
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+ *
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+ * Sentinel: 0xFFFFFFFF (fully-opaque white BGRA). A separate occupied[]
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+ * boolean array guards against false-hit on the sentinel value.
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+ */
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+ uint32_t seen_color[AVPALETTE_COUNT];
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+ uint8_t seen_slot[AVPALETTE_COUNT];
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+ uint8_t occupied[AVPALETTE_COUNT];
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+ size_t colors_seen = 0;
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+
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+ memset(occupied, 0, sizeof(occupied));
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+
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+ for (size_t i = 0; i < AVPALETTE_COUNT; i++) {
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+ uint32_t color = src[i];
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+ /* Knuth multiplicative hash → 8-bit bucket index */
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+ size_t h = (size_t)((color * 2654435761UL) >> 24) & 0xFF;
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+
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+ /* Linear-probe open-addressing lookup */
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+ while (occupied[h] && seen_color[h] != color)
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+ h = (h + 1) & 0xFF;
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+
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+ if (occupied[h]) {
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+ /* colour already in hash table: reuse its dst slot */
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+ map[i] = seen_slot[h];
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+ } else {
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+ /* new colour: insert into hash table and dst[] */
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+ occupied[h] = 1;
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+ seen_color[h] = color;
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+ seen_slot[h] = (uint8_t)colors_seen;
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+ dst[colors_seen] = color;
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+ map[i] = (uint8_t)colors_seen;
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+ colors_seen++;
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+ }
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+ }
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+
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+ *palette_count = colors_seen;
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}
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