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|
{-# LANGUAGE ForeignFunctionInterface #-}
module Network.HPACK.Huffman.ByteString (
unpack4bits,
copy,
) where
import Foreign.C.Types (CSize (..))
import Foreign.Ptr (Ptr, plusPtr)
import Foreign.Storable (peek)
import System.IO.Unsafe (unsafeDupablePerformIO)
import Imports
-- $setup
-- >>> import qualified Data.ByteString as BS
-- |
--
-- >>> let bs = BS.pack [0x12,0x34,0xf3,0xab]
-- >>> unpack4bits bs
-- [1,2,3,4,15,3,10,11]
-- >>> unpack4bits $ BS.tail bs
-- [3,4,15,3,10,11]
unpack4bits :: ByteString -> [Word8]
unpack4bits (PS fptr off len) = unsafeDupablePerformIO $
withForeignPtr fptr $ \ptr -> do
let lim = ptr `plusPtr` (off - 1)
end = ptr `plusPtr` (off + len - 1)
go lim end []
where
go lim p ws
| lim == p = return ws
| otherwise = do
w <- peek p
let w0 = w `shiftR` 4
w1 = w .&. 0xf
go lim (p `plusPtr` (-1)) (w0 : w1 : ws)
copy :: Ptr Word8 -> ByteString -> IO ()
copy dst (PS fptr off len) = withForeignPtr fptr $ \ptr -> do
let beg = ptr `plusPtr` off
memcpy dst beg (fromIntegral len)
foreign import ccall unsafe "string.h memcpy"
c_memcpy
:: Ptr Word8 -> Ptr Word8 -> CSize -> IO (Ptr Word8)
memcpy :: Ptr Word8 -> Ptr Word8 -> Int -> IO ()
memcpy dst src s = void $ c_memcpy dst src (fromIntegral s)
|
