GHC/Data/FastMutInt.hs

    {-# LANGUAGE BangPatterns, MagicHash, UnboxedTuples #-}
    {-# OPTIONS_GHC -O2 #-}
    -- We always optimise this, otherwise performance of a non-optimised
    -- compiler is severely affected
    --
    -- (c) The University of Glasgow 2002-2006
    --
    -- Unboxed mutable Ints

    module GHC.Data.FastMutInt(
            FastMutInt, newFastMutInt,
            readFastMutInt, writeFastMutInt,
            atomicFetchAddFastMut
      ) where

    import GHC.Prelude

    import Data.Bits
    import GHC.Base

    data FastMutInt = FastMutInt !(MutableByteArray# RealWorld)

    newFastMutInt :: Int -> IO FastMutInt
    newFastMutInt n = do
        x <- create
        writeFastMutInt x n
        return x
      where
        !(I# size) = finiteBitSize (0 :: Int) `unsafeShiftR` 3
        create = IO $ \s ->
          case newByteArray# size s of
            (# s, arr #) -> (# s, FastMutInt arr #)

    readFastMutInt :: FastMutInt -> IO Int
    readFastMutInt (FastMutInt arr) = IO $ \s ->
      case readIntArray# arr 0# s of
        (# s, i #) -> (# s, I# i #)

    writeFastMutInt :: FastMutInt -> Int -> IO ()
    writeFastMutInt (FastMutInt arr) (I# i) = IO $ \s ->
      case writeIntArray# arr 0# i s of
        s -> (# s, () #)

    atomicFetchAddFastMut :: FastMutInt -> Int -> IO Int
    atomicFetchAddFastMut (FastMutInt arr) (I# i) = IO $ \s ->
      case fetchAddIntArray# arr 0# i s of
        (# s, n #) -> (# s, I# n #)