utils/FastFunctions.lhs

Z% % (c) The University of Glasgow, 2000-2006 % \section{Fast functions} \begin{code}

    module FastFunctions (
        unsafeChr, inlinePerformIO, unsafeDupableInterleaveIO,
        indexWord8OffFastPtr,
        indexWord8OffFastPtrAsFastChar, indexWord8OffFastPtrAsFastInt,
        global, Global
      ) where

    #include "HsVersions.h"

    import FastTypes
    import Data.IORef
    import System.IO.Unsafe

    #if defined(__GLASGOW_HASKELL__)

    import GHC.Exts
    import GHC.Word
    import GHC.Base (unsafeChr)

    import GHC.IO   (IO(..), unsafeDupableInterleaveIO)

    -- Just like unsafePerformIO, but we inline it.
    {-# INLINE inlinePerformIO #-}
    inlinePerformIO :: IO a -> a
    inlinePerformIO (IO m) = case m realWorld# of (# _, r #)   -> r

    indexWord8OffFastPtr p i = W8# (indexWord8OffAddr# p i)
    indexWord8OffFastPtrAsFastChar p i = indexCharOffAddr# p i
    indexWord8OffFastPtrAsFastInt p i = word2Int# (indexWord8OffAddr# p i)
    -- or ord# (indexCharOffAddr# p i)

    #else /* ! __GLASGOW_HASKELL__ */

    import Foreign.Ptr
    import Data.Word

    -- hey, no harm inlining it, :-P
    {-# INLINE inlinePerformIO #-}
    inlinePerformIO :: IO a -> a
    inlinePerformIO = unsafePerformIO

    unsafeDupableInterleaveIO :: IO a -> IO a
    unsafeDupableInterleaveIO = unsafeInterleaveIO

    -- truly, these functions are unsafe: they assume
    -- a certain immutability of the pointer's target area.
    indexWord8OffFastPtr p i = inlinePerformIO (peekByteOff p n) :: Word8
    indexWord8OffFastPtrAsFastInt p i =
      iUnbox (fromIntegral (inlinePerformIO (peekByteOff p n) :: Word8))
    indexWord8OffFastPtrAsFastChar p i =
      fastChr (iUnbox (fromIntegral (inlinePerformIO (peekByteOff p n) :: Word8)))

    #endif /* ! __GLASGOW_HASKELL__ */

    --just so we can refer to the type clearly in a macro
    type Global a = IORef a
    global :: a -> Global a
    global a = unsafePerformIO (newIORef a)

    indexWord8OffFastPtr :: FastPtr Word8 -> FastInt -> Word8
    indexWord8OffFastPtrAsFastChar :: FastPtr Word8 -> FastInt -> FastChar
    indexWord8OffFastPtrAsFastInt :: FastPtr Word8 -> FastInt -> FastInt

\end{code}