1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
|
{-
Module : System.ByteOrder
Copyright : (c) Antoine Latter 2009
License : BSD3
Maintainer : Antoine Latter <aslatter@gmail.com>
-}
{-# OPTIONS_GHC -fno-cse #-}
module System.ByteOrder(byteOrder, ByteOrder(..)) where
import Foreign.Marshal.Alloc (alloca)
import Foreign.Marshal.Array (peekArray)
import Foreign.Ptr (castPtr)
import Foreign.Storable (poke)
import Data.Word
import System.IO.Unsafe (unsafePerformIO)
-- |Indicates the byte-ordering for a 4-byte value, where '1'
-- indicates the most-significant byte and '4' indicates the
-- least significant byte.
--
-- In this format, big endian byte order would be represented as:
-- (1,2,3,4).
--
-- For convinience, the most common cases (BigEndian and LittleEndian)
-- are provided their own constructors.
data ByteOrder
= BigEndian
| LittleEndian
| Mixed (Word8, Word8, Word8, Word8)
deriving (Eq, Show, Read, Ord)
input :: Word32
input = 0x01020304
-- |Returns the native byte ordering of the system.
byteOrder :: ByteOrder
byteOrder = unsafePerformIO byteOrderIO
{-# NOINLINE byteOrder #-}
byteOrderIO :: IO ByteOrder
byteOrderIO = bytesToByteOrder `fmap` wordToBytes input
wordToBytes :: Word32 -> IO (Word8,Word8,Word8,Word8)
wordToBytes word = alloca $ \wordPtr -> do
poke wordPtr word
[x1,x2,x3,x4] <- peekArray 4 (castPtr wordPtr)
return (x1,x2,x3,x4)
bytesToByteOrder :: (Word8,Word8,Word8,Word8) -> ByteOrder
bytesToByteOrder (1, 2, 3, 4) = BigEndian
bytesToByteOrder (4, 3, 2, 1) = LittleEndian
bytesToByteOrder (x1, x2, x3, x4) = Mixed (x1,x2,x3,x4)
|
