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Linear getByteString #76

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Merged
kolmodin merged 2 commits into from
May 28, 2015
Merged

Linear getByteString #76

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e46b7b6
Remove quadratic behaviour in `ensureN`.
bitonic May 27, 2015
f947333
Make `ensureN` more inliner-friendly...
bitonic May 28, 2015
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24 changes: 16 additions & 8 deletions src/Data/Binary/Get/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -382,15 +382,23 @@ readN !n f = ensureN n >> unsafeReadN n f
-- computation will escape with 'Partial'.
ensureN :: Int -> Get ()
ensureN !n0 = C $ \inp ks -> do
if B.length inp >= n0
let inpLen = B.length inp
if inpLen >= n0
then ks inp ()
else runCont (go n0) inp ks
where -- might look a bit funny, but plays very well with GHC's inliner.
-- GHC won't inline recursive functions, so we make ensureN non-recursive
go n = C $ \inp ks -> do
if B.length inp >= n
then ks inp ()
else runCont (demandInput >> go n) inp ks
else runCont (go n0 []) inp ks
where
go !remaining0 bss0 = C $ \inp ks ->
let remaining = remaining0 - B.length inp
bss = inp : bss0
in if remaining <= 0
then ks (B.concat $ reverse bss) ()
else
Partial $ \mbBs -> case mbBs of
Just bs -> runCont (go remaining bss) bs ks
-- We keep the error message referencing @demandInput@,
-- for legacy reasons -- people have been seeing this for
-- years.
Nothing -> Fail (B.concat $ reverse bss) "demandInput: not enough bytes"
{-# INLINE ensureN #-}

unsafeReadN :: Int -> (B.ByteString -> a) -> Get a
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