Use UArray instead of Set for builtin availability check#7736
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Use UArray instead of Set for builtin availability check#7736
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The builtin availability check in `scriptCBORDecoder` was using `Set DefaultFun` for O(log n) membership, with a TODO suggesting `IntSet`. A `UArray DefaultFun Bool` is a better fit: since `DefaultFun` derives `Ix`, lookup is a true O(1) unboxed array index with no conversion at the lookup site. The array is built once per call via `runSTUArray`, folding over the `Set` through its `Foldable` instance (no intermediate list). The array covers all ~100 `DefaultFun` constructors.
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Unclear this is an improvement. Try |
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/benchmark validation-decode |
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/benchmark validation-full |
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Click here to check the status of your benchmark. |
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Comparing benchmark results of 'validation-decode' on '0468c1c57d' (base) and 'f2742c451c' (PR) Results table
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Unisay
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Apr 27, 2026
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Nice cleanup on the TODO.
Worth noting that the lookup is O(1) now, but the array itself gets rebuilt on every scriptCBORDecoder call. (ll, pv) ranges over a small finite set (four ledger languages times the handful of known protocol versions), so caching the array at module level costs almost nothing. Each decode then does a Map lookup instead of newArray plus a mapM_ over the Set.
Roughly:
availableBuiltinsArr
:: PlutusLedgerLanguage -> MajorProtocolVersion -> UArray DefaultFun Bool
availableBuiltinsArr =
let cache = Map.fromList
[((ll, pv), build ll pv) | ll <- [minBound .. maxBound], pv <- knownPVs]
build ll pv = runSTUArray $ do
arr <- newArray (minBound, maxBound) False
mapM_ (\f -> writeArray arr f True) (builtinsAvailableIn ll pv)
pure arr
in \ll pv -> Map.findWithDefault emptyArr (ll, pv) cacheMajorProtocolVersion doesn't have a meaningful Bounded instance, so knownPVs has to be listed by hand from Common/Versions.hs: alonzoPV, vasilPV, changPV, plominPV, vanRossemPV.
Whichever variant lands, it would be nice to see the win show up in plutus-benchmark:validation numbers before merging.
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Comparing benchmark results of 'validation-full' on '0468c1c57d' (base) and 'f2742c451c' (PR) Results table
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I'll defer this to @kwxm |
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Summary
Addresses the
TODOinSerialisedScript.hs:202suggesting a better data structure for the builtin availability check inscriptCBORDecoder.Previously
checkBuiltindid an O(log n)Set.memberon aSet DefaultFun.DefaultFunalready derivesIx, so aUArray DefaultFun Boolgives a true O(1) unboxed array index with nofromEnum/hash at the lookup site (GHC'sIxinstance handles the offset).