perf: replace sort-based epssPercentile with O(n) linear scan#3316
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matiasinsaurralde wants to merge 1 commit intoanchore:mainfrom
Open
perf: replace sort-based epssPercentile with O(n) linear scan#3316matiasinsaurralde wants to merge 1 commit intoanchore:mainfrom
matiasinsaurralde wants to merge 1 commit intoanchore:mainfrom
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Finding max of a slice doesn't require sorting. The previous implementation called sort.Slice (O(n log n), 4 heap allocations) on every sort comparison. The linear scan is O(n) with zero allocations. It also removes a subtle mutation side-effect: sort.Slice was sorting the caller's EPSS slice in-place, silently modifying the match struct during output rendering. In practice EPSS slices are almost always length 0–1 (both paths remain O(1) for those), so the main value of this change is correctness (no mutation) and the allocation reduction on the multi-entry path. Benchmark (Apple M4): small (3 items): 100.6 ns/op → 2.2 ns/op (45x), 4 allocs → 0 large (100 items): 1131 ns/op → 62 ns/op (18x), 4 allocs → 0 Signed-off-by: Matías Insaurralde <matias@insaurral.de>
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Summary
epssPercentilewas callingsort.Sliceto find the maximum value in a slice — O(n log n) with 4 heap allocations — when a single linear pass suffices.This replaces it with an O(n), zero-allocation loop.
Bonus fix:
sort.Slicesorted the caller's slice in-place, silently mutatinga.Vulnerability.EPSSduring output rendering as a sideeffect. The linear scan is pure (read-only).Benchmarks (Apple M4 Pro)
In practice, EPSS slices are length 0–1 per CVE (both implementations are already O(1) there), so the primary value of this change is the removal of the mutation side-effect and the allocation savings on any multi-entry path
Test plan
TestEPSSPercentileunit tests pass unchangedgrype/presenter/modelspassepss_bench_test.goFeel free to leave the benchmark out from the PR if it's not relevant