    {-# LANGUAGE MagicHash, UnliftedFFITypes #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Data.Array.IO
    -- Copyright   :  (c) The University of Glasgow 2001
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  libraries@haskell.org
    -- Stability   :  experimental
    -- Portability :  non-portable (uses Data.Array.MArray)
    --
    -- Mutable boxed and unboxed arrays in the IO monad.
    --
    -----------------------------------------------------------------------------

    module Data.Array.IO (
        -- * @IO@ arrays with boxed elements
        IOArray,             -- instance of: Eq, Typeable

        -- * @IO@ arrays with unboxed elements
        IOUArray,            -- instance of: Eq, Typeable

        -- * Overloaded mutable array interface
        module Data.Array.MArray,

        -- * Doing I\/O with @IOUArray@s
        hGetArray,           -- :: Handle -> IOUArray Int Word8 -> Int -> IO Int
        hPutArray,           -- :: Handle -> IOUArray Int Word8 -> Int -> IO ()
      ) where

    import Data.Array.Base
    import Data.Array.IO.Internals
    import Data.Array.MArray
    import System.IO.Error

    import Foreign
    import Foreign.C

    import GHC.Exts  (MutableByteArray#, RealWorld)
    import GHC.IO.Handle
    import GHC.IO.Exception

    -- ---------------------------------------------------------------------------
    -- hGetArray

    -- | Reads a number of 'Word8's from the specified 'Handle' directly
    -- into an array.
    hGetArray
            :: Handle               -- ^ Handle to read from
            -> IOUArray Int Word8   -- ^ Array in which to place the values
            -> Int                  -- ^ Number of 'Word8's to read
            -> IO Int
                    -- ^ Returns: the number of 'Word8's actually
                    -- read, which might be smaller than the number requested
                    -- if the end of file was reached.

    hGetArray handle (IOUArray (STUArray _l _u n ptr)) count
      | count == 0              = return 0
      | count < 0 || count > n  = illegalBufferSize handle "hGetArray" count
      | otherwise = do
          -- we would like to read directly into the buffer, but we can't
          -- be sure that the MutableByteArray# is pinned, so we have to
          -- allocate a separate area of memory and copy.
          allocaBytes count $ \p -> do
            r <- hGetBuf handle p count
            _ <- memcpy_ba_ptr ptr p (fromIntegral r)
            return r

    foreign import ccall unsafe "memcpy"
       memcpy_ba_ptr :: MutableByteArray# RealWorld -> Ptr a -> CSize -> IO (Ptr ())

    -- ---------------------------------------------------------------------------
    -- hPutArray

    -- | Writes an array of 'Word8' to the specified 'Handle'.
    hPutArray
            :: Handle                       -- ^ Handle to write to
            -> IOUArray Int Word8           -- ^ Array to write from
            -> Int                          -- ^ Number of 'Word8's to write
            -> IO ()

    hPutArray handle (IOUArray (STUArray _l _u n raw)) count
      | count == 0              = return ()
      | count < 0 || count > n  = illegalBufferSize handle "hPutArray" count
      | otherwise = do
          -- as in hGetArray, we would like to use the array directly, but
          -- we can't be sure that the MutableByteArray# is pinned.
         allocaBytes count $ \p -> do
           _ <- memcpy_ptr_ba p raw (fromIntegral count)
           hPutBuf handle p count

    foreign import ccall unsafe "memcpy"
       memcpy_ptr_ba :: Ptr a -> MutableByteArray# RealWorld -> CSize -> IO (Ptr ())

    -- ---------------------------------------------------------------------------
    -- Internal Utils

    illegalBufferSize :: Handle -> String -> Int -> IO a
    illegalBufferSize handle fn sz =
            ioException (ioeSetErrorString
                         (mkIOError InvalidArgument fn (Just handle) Nothing)
                         ("illegal buffer size " ++ showsPrec 9 (sz::Int) []))