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|
-- TODO: update documentation
-- |
-- Copyright : (c) Sam T. 2013
-- License : MIT
-- Maintainer : pxqr.sta@gmail.com
-- Stability : experimental
-- Portability : portable
--
--
-- Set of integers with atomic modification. Internally IntSet
-- represented as array of tightly packed bits.
--
-- Note that:
--
-- * Insertion, deletion are atomic, waitfree and failfree.
--
-- * You can avoid copying in conversion if you don't care about
-- referencial transparency or sure that after conversion bitfields
-- never modified.
--
--
{-# OPTIONS -fno-warn-unused-do-bind #-}
module Data.Bitfield.Mutable
( IntSet
-- * Construction
, empty, full
, create, releaseIntSet
-- * Query
-- , lookup, member, notMember
-- , size
, maxSize
, lookupUnsafe
-- * Modification
-- , insert, delete
, insertUnsafe, deleteUnsafe
-- * Conversion
, fromByteString, toByteString
, fromByteStringUnsafe, toByteStringUnsafe
) where
import Control.Applicative hiding (empty)
import Data.Bits.Atomic
import Data.ByteString (ByteString)
import qualified Data.ByteString as B
import qualified Data.ByteString.Internal as B
import Foreign
-- | Basically 'BitSet' is a wrapper on the 'ForeignPtr'.
data IntSet = IntSet {
sBasePtr :: {-# UNPACK #-} !(ForeignPtr Word8)
, sOffset :: {-# UNPACK #-} !Int
, sByteSize :: {-# UNPACK #-} !Int
, sMaxSize :: {-# UNPACK #-} !Int
} deriving Show
maxSize :: IntSet -> Int
maxSize = sMaxSize
create :: Int -> (Int -> Ptr Word8 -> IO a) -> IO IntSet
create n f = do
let byteSize = sizeInBytes n
fptr <- mallocForeignPtrBytes byteSize
withForeignPtr fptr (f byteSize)
return (IntSet fptr 0 byteSize n)
-- | Create a 'IntSet' with a given size in /bits/.
empty :: Int -> IO IntSet
empty n = create n $ \bn ptr ->
B.memset ptr 0 (fromIntegral bn)
full :: Int -> IO IntSet
full n = create n $ \bn ptr ->
B.memset ptr (error "IntSet.full") (fromIntegral bn)
-- | Should be used to free scarce resources immediately.
--
-- WARNING: After this call 'BitField' should not be used.
-- Also you can avoid using it at all if resource is not too scarce.
--
releaseIntSet :: IntSet -> IO ()
releaseIntSet = finalizeForeignPtr . sBasePtr
-- | Set nth bit in the given BifField to 1.
--
-- UNSAFE: no bound checking.
--
insertUnsafe :: Int -> IntSet -> IO ()
insertUnsafe i s =
withByte s i $ \ptr -> do
fetchAndOr ptr (bit (bitLoc i))
return ()
{-# INLINE insertUnsafe #-}
deleteUnsafe :: Int -> IntSet -> IO ()
deleteUnsafe i s =
withByte s i $ \ptr -> do
fetchAndAnd ptr (complement (bit (bitLoc i)))
return ()
{-# INLINE deleteUnsafe #-}
-- | Get nth bit in the given BitField.
--
-- UNSAFE: no bound checking.
--
lookupUnsafe :: Int -> IntSet -> IO Bool
lookupUnsafe n s = withByte s n $ \ptr -> (`testBit` bitLoc n) <$> peek ptr
{-# INLINE lookupUnsafe #-}
fromByteString :: Int -> ByteString -> IntSet
fromByteString n = fromByteStringUnsafe n . B.copy
{-# INLINE fromByteString #-}
toByteString :: IntSet -> ByteString
toByteString = B.copy . toByteStringUnsafe
{-# INLINE toByteString #-}
-- | Convert a 'BitField' to the 'ByteString' /without/ copying,
-- so we can write it to a socket or a file for exsample.
--
-- WARNING: Note that using the resulting 'ByteString' might (and even should)
-- BREAK REFERENCIAL TRANSPARENCY since we can change bits using 'setBitN'
-- after the conversion. Use this function wisely and if and only if
-- you understand the consequences, otherwise the really BAD THINGS WILL HAPPEN
-- or use safe version instead.
--
toByteStringUnsafe :: IntSet -> ByteString
toByteStringUnsafe = B.fromForeignPtr <$> sBasePtr <*> pure 0 <*> sByteSize
-- | Convert a 'ByteString' to 'BitField' /without/ copying,
-- so we can read it from a file or a socket.
--
-- WARNING: Please see 'toByteString' doc, the same apply to this function.
--
fromByteStringUnsafe :: Int -> ByteString -> IntSet
fromByteStringUnsafe n (B.PS fptr a b) = IntSet fptr a b n
baseSize :: (Bits a, Integral a) =>
a -- ^ Base, should be power of two.
-> a -- ^ Size.
-> a -- ^ Size in base.
baseSize base n = (n `div` base) + fromIntegral (fromEnum ((n .&. 0x7) > 0))
{-# SPECIALIZE baseSize :: Int -> Int -> Int #-}
{-# SPECIALIZE baseSize :: Word64 -> Word64 -> Word64 #-}
-------------------------------- internal --------------------------------------
sizeInBytes :: Int -- ^ Length in bits.
-> Int -- ^ Length in bytes aligned by size of word.
sizeInBytes = baseSize 8
{-# INLINE sizeInBytes #-}
-- TODO: see if shifts and bitwise ands are faster
-- and make portable version if not
byteLoc :: Int -> Int
byteLoc i = i `div` 8 * sizeOf (error "byteLoc" :: Word8)
{-# INLINE bitLoc #-}
bitLoc :: Int -> Int
bitLoc i = i `mod` 8 * sizeOf (error "bitLoc" :: Word8)
{-# INLINE byteLoc #-}
withByte :: IntSet -> Int -> (Ptr Word8 -> IO a) -> IO a
withByte s n action = do
let offset = sOffset s + byteLoc n
withForeignPtr (sBasePtr s) $ \ptr ->
action (ptr `advancePtr` offset)
{-# INLINE withByte #-}
|
