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Optimize Eq and Ord for LazyByteString using pointer equality #404

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Optimize Eq and Ord for LazyByteString using pointer equality #404

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37 changes: 20 additions & 17 deletions Data/ByteString/Lazy/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE DeriveLift #-}
{-# LANGUAGE MagicHash #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE Unsafe #-}
{-# OPTIONS_HADDOCK not-home #-}
Expand Down Expand Up @@ -68,7 +69,7 @@ import Data.String (IsString(..))
import Data.Typeable (Typeable)
import Data.Data (Data(..), mkNoRepType)

import GHC.Exts (IsList(..))
import GHC.Exts (IsList(..), isTrue#, reallyUnsafePtrEquality#)

import qualified Language.Haskell.TH.Syntax as TH

Expand Down Expand Up @@ -230,27 +231,29 @@ eq :: ByteString -> ByteString -> Bool
eq Empty Empty = True
eq Empty _ = False
eq _ Empty = False
eq (Chunk a@(S.BS ap al) as) (Chunk b@(S.BS bp bl) bs) =
case compare al bl of
LT -> a == S.BS bp al && eq as (Chunk (S.BS (S.plusForeignPtr bp al) (bl - al)) bs)
EQ -> a == b && eq as bs
GT -> S.BS ap bl == b && eq (Chunk (S.BS (S.plusForeignPtr ap bl) (al - bl)) as) bs
eq ac@(Chunk a@(S.BS ap al) as) bc@(Chunk b@(S.BS bp bl) bs)
| isTrue# (reallyUnsafePtrEquality# ac bc) = True
| otherwise = case compare al bl of
LT -> a == S.BS bp al && eq as (Chunk (S.BS (S.plusForeignPtr bp al) (bl - al)) bs)
EQ -> a == b && eq as bs
GT -> S.BS ap bl == b && eq (Chunk (S.BS (S.plusForeignPtr ap bl) (al - bl)) as) bs
Comment on lines +236 to +239
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In the LT and GT cases, we'd recursively run the pointer equality checks on freshly allocated Chunks – which is totally wasteful

It might be better to call an "inner" function here which doesn't perform the pointer equality check.

cmp has the same issue.


cmp :: ByteString -> ByteString -> Ordering
cmp Empty Empty = EQ
cmp Empty _ = LT
cmp _ Empty = GT
cmp (Chunk a@(S.BS ap al) as) (Chunk b@(S.BS bp bl) bs) =
case compare al bl of
LT -> case compare a (S.BS bp al) of
EQ -> cmp as (Chunk (S.BS (S.plusForeignPtr bp al) (bl - al)) bs)
result -> result
EQ -> case compare a b of
EQ -> cmp as bs
result -> result
GT -> case compare (S.BS ap bl) b of
EQ -> cmp (Chunk (S.BS (S.plusForeignPtr ap bl) (al - bl)) as) bs
result -> result
cmp ac@(Chunk a@(S.BS ap al) as) bc@(Chunk b@(S.BS bp bl) bs)
| isTrue# (reallyUnsafePtrEquality# ac bc) = EQ
| otherwise = case compare al bl of
LT -> case compare a (S.BS bp al) of
EQ -> cmp as (Chunk (S.BS (S.plusForeignPtr bp al) (bl - al)) bs)
result -> result
EQ -> case compare a b of
EQ -> cmp as bs
result -> result
GT -> case compare (S.BS ap bl) b of
EQ -> cmp (Chunk (S.BS (S.plusForeignPtr ap bl) (al - bl)) as) bs
result -> result

append :: ByteString -> ByteString -> ByteString
append xs ys = foldrChunks Chunk ys xs
Expand Down