-- |
-- Module      : Crypto.Internal.Compat
-- License     : BSD-style
-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
-- Stability   : stable
-- Portability : Good
--
-- This module try to keep all the difference between versions of base
-- or other needed packages, so that modules don't need to use CPP
--
{-# LANGUAGE CPP #-}
module Crypto.Internal.Compat
    ( unsafeDoIO
    , popCount
    ) where

import System.IO.Unsafe
#if MIN_VERSION_base(4,5,0)
import Data.Bits (popCount)
#else
import Data.Word (Word64)
import Data.Bits (testBit, shiftR)
#endif

-- | perform io for hashes that do allocation and ffi.
-- unsafeDupablePerformIO is used when possible as the
-- computation is pure and the output is directly linked
-- to the input. we also do not modify anything after it has
-- been returned to the user.
unsafeDoIO :: IO a -> a
#if __GLASGOW_HASKELL__ > 704
unsafeDoIO = unsafeDupablePerformIO
#else
unsafeDoIO = unsafePerformIO
#endif

#if !(MIN_VERSION_base(4,5,0))
popCount :: Word64 -> Int
popCount n = loop 0 n
  where loop c 0 = c
        loop c i = loop (c + if testBit c 0 then 1 else 0) (i `shiftR` 1)
#endif