add bytes manipulation function

Crypto/Internal/Bytes.hs

@@ -0,0 +1,54 @@
+-- |
+-- Module      : Crypto.Internal.Bytes
+-- License     : BSD-style
+-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
+-- Stability   : experimental
+-- Portability : unknown
+--
+-- internal helpers function to manipulate sequence of bytes
+-- like ByteString and buffer.
+--
+module Crypto.Internal.Bytes
+    ( withByteStringPtr
+    , tempBufCreate
+    , bufCreate
+    , bufXor
+    ) where
+
+import Control.Applicative      ((<$>), (<*>))
+import Foreign.Ptr              (Ptr, plusPtr)
+import Foreign.ForeignPtr       (withForeignPtr)
+import Foreign.Storable         (peek, poke)
+import Foreign.Marshal.Alloc    (allocaBytesAligned)
+import Data.ByteString          (ByteString)
+import Data.ByteString.Internal (ByteString(..), mallocByteString)
+import Data.Bits                (xor)
+import Data.Word                (Word8)
+import Data.ByteString.Internal (toForeignPtr)
+
+withByteStringPtr :: ByteString -> (Ptr Word8 -> IO a) -> IO a
+withByteStringPtr b f =
+    withForeignPtr fptr $ \ptr -> f (ptr `plusPtr` off)
+  where (fptr, off, _) = toForeignPtr b
+
+-- | Create a buffer, and turns the final resulting ByteString
+bufCreate :: Int -> (Ptr Word8 -> IO ()) -> IO ByteString
+bufCreate size f = do
+    fptr <- mallocByteString size
+    withForeignPtr fptr f
+    return $! PS fptr 0 size
+    
+-- | Create a new temporary buffer
+tempBufCreate :: Int -> (Ptr Word8 -> IO a) -> IO a
+tempBufCreate size f = allocaBytesAligned size 8 f
+
+-- | xor bytes from source1 and source2 to destination
+-- 
+-- d = s1 xor s2
+--
+-- s1, nor s2 are modified unless
+bufXor :: Ptr Word8 -> Ptr Word8 -> Ptr Word8 -> Int -> IO ()
+bufXor _ _  _  0 = return ()
+bufXor d s1 s2 n = do
+    (xor <$> peek s1 <*> peek s2) >>= poke d
+    bufXor (d `plusPtr` 1) (s1 `plusPtr` 1) (s2 `plusPtr` 1) (n-1)

cryptonite.cabal

@@ -85,6 +85,7 @@ Library
                    , Crypto.Random.Entropy.Source
                    , Crypto.Random.Entropy.Backend
                    , Crypto.Internal.Compat
+                   , Crypto.Internal.Bytes
   Build-depends:     base >= 4.3 && < 5
                    , bytestring
                    , securemem >= 0.1.7