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|
-- |
-- Copyright : (c) Sam T. 2013
-- License : MIT
-- Maintainer : pxqr.sta@gmail.com
-- Stability : experimental
-- Portability : portable
--
--
-- This module provides Bitfield datatype used to represent sets of
-- piece indexes any peer have. All associated operations should be
-- defined here as well.
--
{-# LANGUAGE BangPatterns #-}
module Network.BitTorrent.PeerWire.Bitfield
-- TODO: move to Data.Bitfield
( Bitfield(..)
-- * Construction
, empty, full
, fromByteString, toByteString
-- * Query
, findMin, findMax
, union, intersection, difference, combine
, frequencies
-- * Serialization
, getBitfield, putBitfield, bitfieldByteCount
, aligned
) where
import Control.Applicative hiding (empty)
import Data.Array.Unboxed
import Data.Bits
import Data.ByteString (ByteString)
import qualified Data.ByteString as B
import qualified Data.ByteString.Internal as B
import Data.List as L hiding (union)
import Data.Maybe
import Data.Serialize
import Data.Word
import Foreign
import Network.BitTorrent.PeerWire.Block
import Data.Torrent
newtype Bitfield = MkBitfield {
bfBits :: ByteString
-- , bfSize :: Int
} deriving (Show, Eq, Ord)
empty :: Int -> Bitfield
empty n = MkBitfield $ B.replicate (sizeInBase n 8) 0
{-# INLINE empty #-}
full :: Int -> Bitfield
full n = MkBitfield $ B.replicate (sizeInBase n 8) (complement 0)
{-# INLINE full #-}
fromByteString :: ByteString -> Bitfield
fromByteString = MkBitfield
{-# INLINE fromByteString #-}
toByteString :: Bitfield -> ByteString
toByteString = bfBits
{-# INLINE toByteString #-}
getBitfield :: Int -> Get Bitfield
getBitfield n = MkBitfield <$> getBytes n
{-# INLINE getBitfield #-}
putBitfield :: Bitfield -> Put
putBitfield = putByteString . bfBits
{-# INLINE putBitfield #-}
bitfieldByteCount :: Bitfield -> Int
bitfieldByteCount = B.length . bfBits
{-# INLINE bitfieldByteCount #-}
type Mem a = (Ptr a, Int)
aligned :: Storable a => Mem Word8 -> (Mem Word8, Mem a, Mem Word8)
aligned (ptr, len) =
let lowPtr = ptr
lowLen = midPtr `minusPtr` ptr
midOff = lowLen
(midPtr, alg) = align (castPtr ptr)
midLen = alg * div (len - midOff) alg
midLenA = midLen `div` alg
hghOff = midOff + midLen
hghPtr = ptr `advancePtr` hghOff
hghLen = len - hghOff
in
((lowPtr, lowLen), (midPtr, midLenA), (hghPtr, hghLen))
where
align :: Storable a => Ptr a -> (Ptr a, Int)
align p = tie (alignPtr p) undefined
where
tie :: Storable a => (Int -> Ptr a) -> a -> (Ptr a, Int)
tie f a = (f (alignment a), (alignment a))
{-# INLINE aligned #-}
zipWithBS :: (Word8 -> Word8 -> Word8) -> ByteString -> ByteString -> ByteString
zipWithBS f a b =
let (afptr, aoff, asize) = B.toForeignPtr a
(bfptr, boff, bsize) = B.toForeignPtr b
size = min asize bsize in
B.unsafeCreate size $ \ptr -> do
withForeignPtr afptr $ \aptr -> do
withForeignPtr bfptr $ \bptr ->
zipBytes (aptr `plusPtr` aoff) (bptr `plusPtr` boff) ptr size
where
zipBytes :: Ptr Word8 -> Ptr Word8 -> Ptr Word8 -> Int -> IO ()
zipBytes aptr bptr rptr n = go 0
where
go :: Int -> IO ()
go i | i < n = do -- TODO unfold
av <- peekByteOff aptr i
bv <- peekByteOff bptr i
pokeByteOff rptr i (f av bv)
go (succ i)
| otherwise = return ()
zipWithBF :: (Word8 -> Word8 -> Word8) -> Bitfield -> Bitfield -> Bitfield
zipWithBF f a b = MkBitfield $ zipWithBS f (bfBits a) (bfBits b)
{-# INLINE zipWithBF #-}
findSet :: ByteString -> Maybe Int
findSet b =
let (fptr, off, len) = B.toForeignPtr b in
B.inlinePerformIO $ withForeignPtr fptr $ \_ptr -> do
let ptr = _ptr `advancePtr` off
let (low, mid, hgh) = aligned (ptr, len)
let lowOff = fst low `minusPtr` ptr
let midOff = fst mid `minusPtr` ptr
let hghOff = fst hgh `minusPtr` ptr
let resL = (lowOff +) <$> goFind low
let resM = (midOff +) <$> goFind (mid :: Mem Word) -- tune size here
-- TODO: with Word8
-- bytestring findIndex works 2
-- times faster.
let resH = (hghOff +) <$> goFind hgh
let res = resL <|> resM <|> resH
-- computation of res should not escape withForeignPtr
case res of
Nothing -> return ()
Just _ -> return ()
return res
where
goFind :: (Storable a, Eq a, Num a) => Mem a -> Maybe Int
goFind (ptr, n) = go 0
where
go :: Int -> Maybe Int
go i | i < n =
let v = B.inlinePerformIO (peekElemOff ptr i) in
if v /= 0
then Just i
else go (succ i)
| otherwise = Nothing
union :: Bitfield -> Bitfield -> Bitfield
union = zipWithBF (.|.)
{-# INLINE union #-}
intersection :: Bitfield -> Bitfield -> Bitfield
intersection = zipWithBF (.&.)
{-# INLINE intersection #-}
difference :: Bitfield -> Bitfield -> Bitfield
difference = zipWithBF diffWord8
where
diffWord8 :: Word8 -> Word8 -> Word8
diffWord8 a b = a .&. (a `xor` b)
{-# INLINE diffWord8 #-}
{-# INLINE difference #-}
combine :: [Bitfield] -> Maybe Bitfield
combine [] = Nothing
combine as = return $ foldr1 intersection as
-- | Get min index of piece that the peer have.
findMin :: Bitfield -> Maybe PieceIx
findMin (MkBitfield b) = do
byteIx <- findSet b
bitIx <- findMinWord8 (B.index b byteIx)
return $ byteIx * bitSize (undefined :: Word8) + bitIx
where
-- TODO: bit tricks
findMinWord8 :: Word8 -> Maybe Int
findMinWord8 byte = L.find (testBit byte) [0..bitSize (undefined :: Word8) - 1]
{-# INLINE findMinWord8 #-}
{-# INLINE findMin #-}
findMax :: Bitfield -> Maybe PieceIx
findMax (MkBitfield b) = do
-- TODO avoid reverse
byteIx <- (pred (B.length b) -) <$> findSet (B.reverse b)
bitIx <- findMaxWord8 (B.index b byteIx)
return $ byteIx * bitSize (undefined :: Word8) + bitIx
where
-- TODO: bit tricks
findMaxWord8 :: Word8 -> Maybe Int
findMaxWord8 byte = L.find (testBit byte)
(reverse [0 :: Int ..
bitSize (undefined :: Word8) - 1])
{-# INLINE findMax #-}
frequencies :: [Bitfield] -> UArray PieceIx Int
frequencies = undefined
|
