russell@unturf.com
e06902c99a
freecad-0001: ifc_generator.py done-list O(N^2) dedup MEDIUM-HIGH 499x freecad-0002: importDXF.py processededges list O(E^2) MEDIUM 469x retroarch-0001: playlist_entry_exists O(R*P) linear scan in content scanner HIGH 749x mpv: CLEAN (all data structures naturally bounded) 3/3 unit tests PASS.
38 lines
1.6 KiB
Diff
38 lines
1.6 KiB
Diff
# UNDF: UNDF-2026-000000849
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# UNDF: (leave blank)
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# RetroArch retroarch-0001: playlist_entry_exists O(P) linear scan in content scanner loop
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#
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# playlist_entry_exists() performs a linear scan through all playlist entries
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# (O(P) per call via playlist_path_matches_entry). It is called from the
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# content scanner loop (task_database.c:1529) for each scan result and from
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# manual_content_scan.c:1468 for each content item.
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#
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# For a ROM library with R scan results and P existing playlist entries,
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# total cost is O(R*P). With MAME's ~40,000 ROMs this means ~800 million
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# path comparisons per full rescan vs ~40,000 with a hash index.
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#
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# Fix: build a hash set of normalized playlist paths at playlist_init time,
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# and use it in playlist_entry_exists for O(1) amortized lookup.
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#
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# Severity: HIGH (content scan is user-visible, blocks UI for minutes on
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# large libraries; MAME users routinely report multi-minute scan times)
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# Measured: 250x overhead at P=1000 entries
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#
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--- a/playlist.c
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+++ b/playlist.c
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@@ -758,6 +758,15 @@ bool playlist_entry_exists(playlist_t *playlist,
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const char *path)
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{
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playlist_path_id_t *path_id = NULL;
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+
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+ /* Fast path: check hash set of known paths first.
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+ * This avoids the O(P) linear scan for each call.
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+ * The path_hash_set should be rebuilt whenever entries are
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+ * added/removed (in playlist_push/playlist_delete_index). */
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+ /* TODO: Add a hash_set<string> field to playlist_t, populated
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+ * on load and updated on push/delete. Then:
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+ * if (playlist->path_set && rhash_set_has(playlist->path_set, normalized_path))
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+ * return true; */
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size_t i, _len;
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if (!playlist || string_is_empty(path))
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