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make nextPermutation faster #497

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make nextPermutation faster #497

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5 changes: 2 additions & 3 deletions vector/src/Data/Vector/Generic/Mutable.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -1231,7 +1231,7 @@ a given permutation. It changes the given permutation in-place.
nextPermutation :: (PrimMonad m,Ord e,MVector v e) => v (PrimState m) e -> m Bool
nextPermutation v
| dim < 2 = return False
| otherwise = do
| otherwise = stToPrim $ do
val <- unsafeRead v 0
(k,l) <- loop val (-1) 0 val 1
if k < 0
Expand All @@ -1243,8 +1243,7 @@ nextPermutation v
| i == dim = return (k,l)
| otherwise = do
cur <- unsafeRead v i
-- TODO: make tuple unboxed
let (kval',k') = if prev < cur then (prev,i-1) else (kval,k)
let (!kval',!k') = if prev < cur then (prev,i-1) else (kval,k)
l' = if kval' < cur then i else l
loop kval' k' l' cur (i+1)
dim = length v
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