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
59
60
61
|
-- |
-- Module : Data.Byteable
-- License : BSD-style
-- Maintainer : Vincent Hanquez <vincent@snarc.org>
-- Stability : experimental
-- Portability : good
--
module Data.Byteable
( Byteable(..)
, constEqBytes
) where
import Foreign.Ptr (Ptr, plusPtr)
import Foreign.ForeignPtr (withForeignPtr)
import Data.ByteString (ByteString)
import Data.List (foldl')
import Data.Word (Word8)
import qualified Data.ByteString as B (length, zipWith)
import qualified Data.ByteString.Internal as B (toForeignPtr)
-- | Class of things that can generate sequence of bytes
class Byteable a where
-- | Convert a byteable type to a bytestring
toBytes :: a -> ByteString
-- | Return the size of the byteable .
byteableLength :: a -> Int
byteableLength = B.length . toBytes
-- | Provide a way to look at the data of a byteable type with a ptr.
withBytePtr :: a -> (Ptr Word8 -> IO b) -> IO b
withBytePtr a f = withForeignPtr fptr $ \ptr -> f (ptr `plusPtr` off)
where (fptr, off, _) = B.toForeignPtr $ toBytes a
instance Byteable ByteString where
toBytes bs = bs
-- | A constant time equality test for 2 byteable objects.
--
-- If objects are of 2 different sizes, the function will abort early
-- without comparing any bytes.
--
-- compared to == , this function will go over all the bytes
-- present before yielding a result even when knowing the
-- overall result early in the processing.
constEqBytes :: Byteable a => a -> a -> Bool
constEqBytes a b = constEqByteString (toBytes a) (toBytes b)
{-# RULES "constEqBytes/ByteString" constEqBytes = constEqByteString #-}
{-# INLINE constEqByteString #-}
constEqByteString :: ByteString -> ByteString -> Bool
constEqByteString a b
| len /= B.length b = False
| otherwise = foldl' (&&!) True $ B.zipWith (==) a b
where len = B.length a
(&&!) :: Bool -> Bool -> Bool
True &&! True = True
True &&! False = False
False &&! True = False
False &&! False = False
|
