module Endian (endianness, Endianness(..)) where

-- import Foreign.Marshal.Alloc
import Foreign.Marshal.Utils
import Foreign.Marshal.Array
import Foreign.Ptr
-- import Foreign.Storable
import Data.Word

-- | See http://en.wikipedia.org/wiki/Endianness
--   Some machines (luckily mostly historical) used endiannesses
--   other than strictly big-endian or strictly little-endian.
--   We will just try to ignore them since they are probably
--   entirely unsupported by other things including our libffi anyway.
data Endianness = BigEndian | LittleEndian -- | OtherEndianness
           deriving (Eq, Ord, Show)

-- | endianness returns the current environment's endianness.
--   It assumes that this is well-defined and always succeeds.
--   (Note: this could be changed so that an error is signalled
--   for, say, 4-byte integer-style quantities where the 1 is at
--   neither end, but this would not even be a complete test for
--   unusual endiannesses.)
endianness :: IO Endianness
endianness = with (1 :: Word16) $ \ptr16 -> do
  let ptr8 = castPtr ptr16 :: Ptr Word8
  bytes <- peekArray 2 ptr8
  case bytes of
    [1,0] -> return LittleEndian
    [0,1] -> return BigEndian
    _ -> fail $
          "endianness: something weird is going on; bytes of 1::Word16 are: "
           ++ show bytes