{-# LANGUAGE CPP #-} -- | -- Copyright : (c) 2011 Simon Meier -- License : BSD3-style (see LICENSE) -- -- Maintainer : Simon Meier <iridcode@gmail.com> -- Stability : experimental -- Portability : GHC -- -- Hexadecimal encoding of nibbles (4-bit) and octets (8-bit) as ASCII -- characters. -- -- The current implementation is based on a table based encoding inspired by -- the code in the 'base64-bytestring' library by Bryan O'Sullivan. In our -- benchmarks on a 32-bit machine it turned out to be the fastest -- implementation option. -- module Data.ByteString.Builder.Prim.Internal.Base16 ( EncodingTable , lowerTable , encode8_as_16h ) where import qualified Data.ByteString as S import qualified Data.ByteString.Internal as S #if MIN_VERSION_base(4,4,0) #if MIN_VERSION_base(4,7,0) import Foreign #else import Foreign hiding (unsafePerformIO, unsafeForeignPtrToPtr) #endif import Foreign.ForeignPtr.Unsafe (unsafeForeignPtrToPtr) import System.IO.Unsafe (unsafePerformIO) #else import Foreign #endif -- Creating the encoding table ------------------------------ -- TODO: Use table from C implementation. -- | An encoding table for Base16 encoding. newtype EncodingTable = EncodingTable (ForeignPtr Word8) tableFromList :: [Word8] -> EncodingTable tableFromList xs = case S.pack xs of S.PS fp _ _ -> EncodingTable fp unsafeIndex :: EncodingTable -> Int -> IO Word8 unsafeIndex (EncodingTable table) = peekElemOff (unsafeForeignPtrToPtr table) base16EncodingTable :: EncodingTable -> IO EncodingTable base16EncodingTable alphabet = do xs <- sequence $ concat $ [ [ix j, ix k] | j <- [0..15], k <- [0..15] ] return $ tableFromList xs where ix = unsafeIndex alphabet {-# NOINLINE lowerAlphabet #-} lowerAlphabet :: EncodingTable lowerAlphabet = tableFromList $ map (fromIntegral . fromEnum) $ ['0'..'9'] ++ ['a'..'f'] -- | The encoding table for hexadecimal values with lower-case characters; -- e.g., deadbeef. {-# NOINLINE lowerTable #-} lowerTable :: EncodingTable lowerTable = unsafePerformIO $ base16EncodingTable lowerAlphabet -- | Encode an octet as 16bit word comprising both encoded nibbles ordered -- according to the host endianness. Writing these 16bit to memory will write -- the nibbles in the correct order (i.e. big-endian). {-# INLINE encode8_as_16h #-} encode8_as_16h :: EncodingTable -> Word8 -> IO Word16 encode8_as_16h (EncodingTable table) = peekElemOff (castPtr $ unsafeForeignPtrToPtr table) . fromIntegral