dons:
claus.reinke:
I noticed that ByteString is drastically slower than String if I use cons a lot. according to the source, that is expected because of the memcpy for the second parameter.
Just a quick response, before I consider this in detail, in the stream fusion branch of Data.ByteString cons is fusible:
cons :: Word8 -> ByteString -> ByteString cons c (PS x s l) = unsafeCreate (l+1) $ \p -> withForeignPtr x $ \f -> do poke p c memcpy (p `plusPtr` 1) (f `plusPtr` s) (fromIntegral l) {-# INLINE [1] cons #-}
{-# RULES "FPS cons -> fused" [~1] forall w. cons w = F.strTransformerUp (F.consS w) "FPS cons -> unfused" [1] forall w. F.strTransformerUp (F.consS w) = cons w #-}
strTransformerUp :: (Stream -> Stream) -> (ByteString -> ByteString) strTransformerUp f = writeStrUp . f . readStrUp {-# INLINE [0] strTransformerUp #-}
consS :: Word8 -> Stream -> Stream consS w (Stream nextx xs0 len) = Stream next' (True :*: xs0) (len+1) where next' (True :*: xs) = Yield w (False :*: xs) next' (_ :*: xs) = case nextx xs of Done -> Done Skip xs' -> Skip (False :*: xs') Yield x xs' -> Yield x (False :*: xs') {-# INLINE [0] consS #-}
Oh, this is slower than it should be, too. Those Bools get in the way of GHC's specConstr optimisation. Instead it shoudl use a strict Either. consS :: Word8 -> Stream -> Stream consS w (Stream nextx xs0 len) = Stream next' (RightS xs0) (len+1) where next' (RightS xs) = Yield w (LeftS xs) next' (LeftS xs) = case nextx xs of Done -> Done Skip xs' -> Skip (LeftS xs') Yield x xs' -> Yield x (LeftS xs') {-# INLINE [0] consS #-} where data EitherS a b = LeftS !a | RightS !b deriving (Eq, Ord ) that should help a bit with the stripping away of constructors in consS. -- Don