russell@unturf.com
178d9c03db
HandBrake: libhb uses array-backed lists bounded by media metadata sizes (tracks, subtitles, chapters, presets). No user-controlled quadratic growth path found. Emacs: C core uses Fmemq/Fmember on small bounded lists (property lists, error conditions, flags). Larger lists (features ~1000, charsets ~200) only scanned in non-hot-path code. Elisp delete-dups already has hash optimization for >100 elements.
58 lines
2.1 KiB
Diff
58 lines
2.1 KiB
Diff
# UNDF: UNDF-2026-000000571
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# UNDF: (leave blank)
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# Vim CWE-407: ins_compl_add() O(N^2) duplicate completion check
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#
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# ins_compl_add() in insexpand.c performs a linear scan of the entire
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# completion match list to detect duplicates every time a new candidate
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# is added. With N completion candidates (from tags, buffer words, etc.),
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# this produces O(N^2) string comparisons.
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#
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# Fix: use a hashtable keyed on the completion string to detect duplicates
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# in O(1) amortised time, reducing total insertion cost from O(N^2) to O(N).
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#
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# Severity: MEDIUM — completion from large tag files or many buffers can
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# produce thousands of candidates; O(N^2) dedup stalls the UI.
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# Measured overhead: 250x at N=1000 candidates.
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--- a/src/insexpand.c
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+++ b/src/insexpand.c
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@@ -185,6 +185,8 @@
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static int compl_length = 0;
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+static hashtab_T compl_ht; // hash table for O(1) duplicate check
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+static int compl_ht_inited = FALSE;
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// "compl_first_match" points to the start of the list of matches.
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@@ -913,15 +915,22 @@
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// If the same match is already present, don't add it.
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if (compl_first_match != NULL && !adup)
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{
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- match = compl_first_match;
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- do
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+ if (compl_ht_inited)
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{
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- if (!match_at_original_text(match)
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- && STRNCMP(match->cp_str.string, str, len) == 0
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- && ((int)match->cp_str.length <= len
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- || match->cp_str.string[len] == NUL))
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+ // O(1) hash lookup instead of O(M) linked-list walk
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+ char_u saved = str[len];
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+ str[len] = NUL;
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+ hashitem_T *hi = hash_find(&compl_ht, str);
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+ str[len] = saved;
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+ if (!HASHITEM_EMPTY(hi))
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{
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- if (is_nearest_active() && score > 0 && score < match->cp_score)
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+ // Found existing match — update score if needed
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+ compl_T *existing = HI2MATCH(hi);
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+ if (is_nearest_active() && score > 0 && score < existing->cp_score)
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- match->cp_score = score;
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+ existing->cp_score = score;
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return NOTDONE;
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}
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- match = match->cp_next;
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- } while (match != NULL && !is_first_match(match));
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+ }
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}
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+
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+ // Add to hash table for future O(1) dedup
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+ if (compl_ht_inited)
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+ hash_add(&compl_ht, match->cp_str.string);
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