content: {-# LANGUAGE MagicHash #-}
  
  -- |
  -- Module      : Data.Text.UnsafeShift
  -- Copyright   : (c) Bryan O'Sullivan 2009
  --
  -- License     : BSD-style
  -- Maintainer  : bos@serpentine.com, rtomharper@googlemail.com,
  --               duncan@haskell.org
  -- Stability   : experimental
  -- Portability : GHC
  --
  -- Fast, unchecked bit shifting functions.
  
  module Data.Text.UnsafeShift
      (
        UnsafeShift(..)
      ) where
  
  -- import qualified Data.Bits as Bits
  import GHC.Base
  import GHC.Word
  
  -- | This is a workaround for poor optimisation in GHC 6.8.2.  It
  -- fails to notice constant-width shifts, and adds a test and branch
  -- to every shift.  This imposes about a 10% performance hit.
  --
  -- These functions are undefined when the amount being shifted by is
  -- greater than the size in bits of a machine Int#.
  class UnsafeShift a where
      shiftL :: a -> Int -> a
      shiftR :: a -> Int -> a
  
  instance UnsafeShift Word16 where
      {-# INLINE shiftL #-}
      shiftL (W16# x#) (I# i#) = W16# (narrow16Word# (x# `uncheckedShiftL#` i#))
  
      {-# INLINE shiftR #-}
      shiftR (W16# x#) (I# i#) = W16# (x# `uncheckedShiftRL#` i#)
  
  instance UnsafeShift Word32 where
      {-# INLINE shiftL #-}
      shiftL (W32# x#) (I# i#) = W32# (narrow32Word# (x# `uncheckedShiftL#` i#))
  
      {-# INLINE shiftR #-}
      shiftR (W32# x#) (I# i#) = W32# (x# `uncheckedShiftRL#` i#)
  
  instance UnsafeShift Word64 where
      {-# INLINE shiftL #-}
      shiftL (W64# x#) (I# i#) = W64# (x# `uncheckedShiftL64#` i#)
  
      {-# INLINE shiftR #-}
      shiftR (W64# x#) (I# i#) = W64# (x# `uncheckedShiftRL64#` i#)
  
  instance UnsafeShift Int where
      {-# INLINE shiftL #-}
      shiftL (I# x#) (I# i#) = I# (x# `iShiftL#` i#)
  
      {-# INLINE shiftR #-}
      shiftR (I# x#) (I# i#) = I# (x# `iShiftRA#` i#)
  
  {-
  instance UnsafeShift Integer where
      {-# INLINE shiftL #-}
      shiftL = Bits.shiftL
  
      {-# INLINE shiftR #-}
      shiftR = Bits.shiftR
  -}
  