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UnsafeShift.hs
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UnsafeShift.hs
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{-# 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
-}