diff --git a/Data/Digest/CRC16.hs b/Data/Digest/CRC16.hs
new file mode 100644
--- /dev/null
+++ b/Data/Digest/CRC16.hs
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+{- | crc16 ccitt
+
+   1) MSB first 1021 x^16 + x^12 + x^5 + 1 
+
+   2) LSB first 8048
+
+-}
+module Data.Digest.CRC16 (
+     -- * CRC16 method
+     crc16_update
+    ) where
+
+import Data.Word(Word8,Word16)
+import Data.Bits
+
+
+-- | crc16 calculation
+-- This uses the simple method based on /bit shifting/.
+-- See the unittests for an example.
+--
+crc16_update :: Word16      -- ^ polynomial
+             -> Bool        -- ^ inverse bits 
+             -> Word16      -- ^ initial crc
+             -> Word8       -- ^ data byte
+             -> Word16      -- ^ new crc
+crc16_update poly rev crc b =
+    foldl (crc16_update_bit poly) new_crc [1..(bitSize b)]
+    where
+        new_crc = crc `xor` (shiftL (fromIntegral b' :: Word16) 8 )
+        b' = if rev
+                then reverse_bits b
+                else b
+
+
+
+
+crc16_update_bit :: Word16 -> Word16 -> Int -> Word16
+crc16_update_bit poly crc _ =
+    if (crc .&. 0x8000) /= 0x0000
+        then (shiftL crc 1) `xor` poly 
+        else shiftL crc 1
+
+
+
+-- | Reverse the bits in a byte
+--
+-- 7..0 becomes 0..7
+--
+reverse_bits :: Word8 -> Word8
+reverse_bits b =
+    (shiftL (b .&. 0x01) 7) .|. (shiftL (b .&. 0x02) 5) .|. (shiftL (b .&. 0x04) 3) .|. (shiftL (b .&. 0x08) 1) .|.
+    (shiftR (b .&. 0x10) 1) .|. (shiftR (b .&. 0x20) 3) .|. (shiftR (b .&. 0x40) 5) .|. (shiftR (b .&. 0x80) 7)
+
diff --git a/LICENSE b/LICENSE
new file mode 100644
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,29 @@
+Copyright (c) 2009, Joris Putcuyps
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+- Redistributions of source code must retain the above copyright
+notice, this list of conditions, and the following disclaimer.
+
+- Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions, and the following disclaimer in the
+documentation and/or other materials provided with the distribution.
+
+- The names of the copyright holders may not be used to endorse or
+promote products derived from this software without specific prior
+written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS "AS IS" AND ANY
+EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDERS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
+IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/Setup.hs b/Setup.hs
new file mode 100644
--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,10 @@
+import Distribution.Simple
+import Data.Digest.CRC16
+import Test.HUnit.Text
+import Tests
+
+main = 
+    defaultMainWithHooks ( simpleUserHooks { runTests = test_crc16 } )
+    where
+        test_crc16 _ _ _ _ = do runTestTT tests
+                                return ()
diff --git a/Tests.hs b/Tests.hs
new file mode 100644
--- /dev/null
+++ b/Tests.hs
@@ -0,0 +1,31 @@
+module Tests where
+
+import Test.HUnit.Base
+import Test.HUnit.Text
+import Data.Digest.CRC16
+import qualified Data.ByteString as B
+import Data.Word
+
+
+crc16 :: Word16 -> Bool -> Word16 -> [Word8] -> Word16
+crc16 poly inverse initial data_string =
+    B.foldl (crc16_update poly inverse) initial (B.pack data_string)
+
+
+-- | Test functions
+--
+-- Run with: 
+-- 
+-- > import Test.HUnit.Text
+-- > runTestTT tests
+--
+-- Checkout http://zorc.breitbandkatze.de/crc.html
+tests :: Test
+tests = "Basic" ~: [
+             0x29B1 ~=? crc16 0x1021 False 0xffff simple_string
+            ,0x89f6 ~=? crc16 0x1021 True 0xffff simple_string
+            ,0x31C3 ~=? crc16 0x1021 False 0x0000 simple_string
+        ]
+        where 
+            simple_string = [0x31,0x32,0x33,0x34,0x35,0x36,0x37,0x38,0x39] --string "123456789"
+
diff --git a/crc16.cabal b/crc16.cabal
new file mode 100644
--- /dev/null
+++ b/crc16.cabal
@@ -0,0 +1,20 @@
+name:           crc16 
+version:        0.1.0
+cabal-version:  >= 1.2
+build-Type:     Custom
+license:        BSD3
+license-file:	LICENSE
+copyright:      (c) 2009 Joris Putcuyps
+author:         Joris Putcuyps
+maintainer:     Joris.Putcuyps@gmail.com
+bug-reports:    mailto:Joris.Putcuyps@gmail.com
+synopsis:       Calculate the crc16-ccitt.
+description:    This module provides a method to calculate the crc16-ccitt using the slow bit shift way.
+category:       Cryptography
+extra-source-files: Tests.hs
+
+Library
+    Build-Depends:    base, bytestring, HUnit
+    Exposed-modules:  Data.Digest.CRC16
+    ghc-options:      -Wall
+