Foreign/Marshal/Array.hs

    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE NoImplicitPrelude, MagicHash, ScopedTypeVariables #-}

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Foreign.Marshal.Array
    -- Copyright   :  (c) The FFI task force 2001
    -- License     :  BSD-style (see the file libraries/base/LICENSE)
    --
    -- Maintainer  :  ffi@haskell.org
    -- Stability   :  provisional
    -- Portability :  portable
    --
    -- Marshalling support: routines allocating, storing, and retrieving Haskell
    -- lists that are represented as arrays in the foreign language
    --
    -----------------------------------------------------------------------------

    module Foreign.Marshal.Array (
      -- * Marshalling arrays

      -- ** Allocation
      --
      mallocArray,
      mallocArray0,

      allocaArray,
      allocaArray0,

      reallocArray,
      reallocArray0,

      callocArray,
      callocArray0,

      -- ** Marshalling
      --
      peekArray,
      peekArray0,

      pokeArray,
      pokeArray0,

      -- ** Combined allocation and marshalling
      --
      newArray,
      newArray0,

      withArray,
      withArray0,

      withArrayLen,
      withArrayLen0,

      -- ** Copying

      -- | (argument order: destination, source)
      copyArray,
      moveArray,

      -- ** Finding the length
      --
      lengthArray0,

      -- ** Indexing
      --
      advancePtr,
    ) where

    import Foreign.Ptr      (Ptr, plusPtr)
    import Foreign.Storable (Storable(alignment,sizeOf,peekElemOff,pokeElemOff))
    import Foreign.Marshal.Alloc (mallocBytes, callocBytes, allocaBytesAligned, reallocBytes)
    import Foreign.Marshal.Utils (copyBytes, moveBytes)

    import GHC.Num
    import GHC.List
    import GHC.Base

    -- allocation
    -- ----------

    -- |Allocate storage for the given number of elements of a storable type
    -- (like 'Foreign.Marshal.Alloc.malloc', but for multiple elements).
    --
    mallocArray :: forall a . Storable a => Int -> IO (Ptr a)
    mallocArray  size = mallocBytes (size * sizeOf (undefined :: a))

    -- |Like 'mallocArray', but add an extra position to hold a special
    -- termination element.
    --
    mallocArray0      :: Storable a => Int -> IO (Ptr a)
    mallocArray0 size  = mallocArray (size + 1)

    -- |Like 'mallocArray', but allocated memory is filled with bytes of value zero.
    --
    callocArray :: forall a . Storable a => Int -> IO (Ptr a)
    callocArray size = callocBytes (size * sizeOf (undefined :: a))

    -- |Like 'callocArray0', but allocated memory is filled with bytes of value
    -- zero.
    --
    callocArray0 :: Storable a => Int -> IO (Ptr a)
    callocArray0 size  = callocArray (size + 1)

    -- |Temporarily allocate space for the given number of elements
    -- (like 'Foreign.Marshal.Alloc.alloca', but for multiple elements).
    --
    allocaArray :: forall a b . Storable a => Int -> (Ptr a -> IO b) -> IO b
    allocaArray size = allocaBytesAligned (size * sizeOf (undefined :: a))
                                          (alignment (undefined :: a))

    -- |Like 'allocaArray', but add an extra position to hold a special
    -- termination element.
    --
    allocaArray0      :: Storable a => Int -> (Ptr a -> IO b) -> IO b
    allocaArray0 size  = allocaArray (size + 1)
    {-# INLINE allocaArray0 #-}
      -- needed to get allocaArray to inline into withCString, for unknown
      -- reasons --SDM 23/4/2010, see #4004 for benchmark

    -- |Adjust the size of an array
    --
    reallocArray :: forall a . Storable a => Ptr a -> Int -> IO (Ptr a)
    reallocArray ptr size = reallocBytes ptr (size * sizeOf (undefined :: a))

    -- |Adjust the size of an array including an extra position for the end marker.
    --
    reallocArray0          :: Storable a => Ptr a -> Int -> IO (Ptr a)
    reallocArray0 ptr size  = reallocArray ptr (size + 1)

    -- marshalling
    -- -----------

    -- |Convert an array of given length into a Haskell list.  The implementation
    -- is tail-recursive and so uses constant stack space.
    --
    peekArray          :: Storable a => Int -> Ptr a -> IO [a]
    peekArray size ptr | size <= 0 = return []
                     | otherwise = f (size-1) []
      where
        f 0 acc = do e <- peekElemOff ptr 0; return (e:acc)
        f n acc = do e <- peekElemOff ptr n; f (n-1) (e:acc)

    -- |Convert an array terminated by the given end marker into a Haskell list
    --
    peekArray0            :: (Storable a, Eq a) => a -> Ptr a -> IO [a]
    peekArray0 marker ptr  = do
      size <- lengthArray0 marker ptr
      peekArray size ptr

    -- |Write the list elements consecutive into memory
    --
    pokeArray :: Storable a => Ptr a -> [a] -> IO ()
    pokeArray ptr vals0 = go vals0 0#
      where go [] _          = return ()
            go (val:vals) n# = do pokeElemOff ptr (I# n#) val; go vals (n# +# 1#)

    -- |Write the list elements consecutive into memory and terminate them with the
    -- given marker element
    --
    pokeArray0 :: Storable a => a -> Ptr a -> [a] -> IO ()
    pokeArray0 marker ptr vals0 = go vals0 0#
      where go [] n#         = pokeElemOff ptr (I# n#) marker
            go (val:vals) n# = do pokeElemOff ptr (I# n#) val; go vals (n# +# 1#)

    -- combined allocation and marshalling
    -- -----------------------------------

    -- |Write a list of storable elements into a newly allocated, consecutive
    -- sequence of storable values
    -- (like 'Foreign.Marshal.Utils.new', but for multiple elements).
    --
    newArray      :: Storable a => [a] -> IO (Ptr a)
    newArray vals  = do
      ptr <- mallocArray (length vals)
      pokeArray ptr vals
      return ptr

    -- |Write a list of storable elements into a newly allocated, consecutive
    -- sequence of storable values, where the end is fixed by the given end marker
    --
    newArray0             :: Storable a => a -> [a] -> IO (Ptr a)
    newArray0 marker vals  = do
      ptr <- mallocArray0 (length vals)
      pokeArray0 marker ptr vals
      return ptr

    -- |Temporarily store a list of storable values in memory
    -- (like 'Foreign.Marshal.Utils.with', but for multiple elements).
    --
    withArray :: Storable a => [a] -> (Ptr a -> IO b) -> IO b
    withArray vals = withArrayLen vals . const

    -- |Like 'withArray', but the action gets the number of values
    -- as an additional parameter
    --
    withArrayLen :: Storable a => [a] -> (Int -> Ptr a -> IO b) -> IO b
    withArrayLen vals f  =
      allocaArray len $ \ptr -> do
          pokeArray ptr vals
          f len ptr
      where
        len = length vals

    -- |Like 'withArray', but a terminator indicates where the array ends
    --
    withArray0 :: Storable a => a -> [a] -> (Ptr a -> IO b) -> IO b
    withArray0 marker vals = withArrayLen0 marker vals . const

    -- |Like 'withArrayLen', but a terminator indicates where the array ends
    --
    withArrayLen0 :: Storable a => a -> [a] -> (Int -> Ptr a -> IO b) -> IO b
    withArrayLen0 marker vals f  =
      allocaArray0 len $ \ptr -> do
          pokeArray0 marker ptr vals
          res <- f len ptr
          return res
      where
        len = length vals

    -- copying (argument order: destination, source)
    -- -------

    -- |Copy the given number of elements from the second array (source) into the
    -- first array (destination); the copied areas may /not/ overlap
    --
    copyArray :: forall a . Storable a => Ptr a -> Ptr a -> Int -> IO ()
    copyArray dest src size = copyBytes dest src (size * sizeOf (undefined :: a))

    -- |Copy the given number of elements from the second array (source) into the
    -- first array (destination); the copied areas /may/ overlap
    --
    moveArray :: forall a . Storable a => Ptr a -> Ptr a -> Int -> IO ()
    moveArray  dest src size = moveBytes dest src (size * sizeOf (undefined :: a))

    -- finding the length
    -- ------------------

    -- |Return the number of elements in an array, excluding the terminator
    --
    lengthArray0            :: (Storable a, Eq a) => a -> Ptr a -> IO Int
    lengthArray0 marker ptr  = loop 0
      where
        loop i = do
            val <- peekElemOff ptr i
            if val == marker then return i else loop (i+1)

    -- indexing
    -- --------

    -- |Advance a pointer into an array by the given number of elements
    --
    advancePtr :: forall a . Storable a => Ptr a -> Int -> Ptr a
    advancePtr ptr i = ptr `plusPtr` (i * sizeOf (undefined :: a))