Data/ByteString/Builder/Prim/Internal/Base16.hs

    {-# LANGUAGE Trustworthy #-}
    {-# LANGUAGE MagicHash #-}
    -- |
    -- 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           Foreign
    import           GHC.Exts (Addr#, Ptr(..))

    -- Creating the encoding table
    ------------------------------

    -- | An encoding table for Base16 encoding.
    data EncodingTable = EncodingTable Addr#

    -- | The encoding table for hexadecimal values with lower-case characters;
    -- e.g., deadbeef.
    {-# NOINLINE lowerTable #-}
    lowerTable :: EncodingTable
    lowerTable = EncodingTable
        "000102030405060708090a0b0c0d0e0f\
        \101112131415161718191a1b1c1d1e1f\
        \202122232425262728292a2b2c2d2e2f\
        \303132333435363738393a3b3c3d3e3f\
        \404142434445464748494a4b4c4d4e4f\
        \505152535455565758595a5b5c5d5e5f\
        \606162636465666768696a6b6c6d6e6f\
        \707172737475767778797a7b7c7d7e7f\
        \808182838485868788898a8b8c8d8e8f\
        \909192939495969798999a9b9c9d9e9f\
        \a0a1a2a3a4a5a6a7a8a9aaabacadaeaf\
        \b0b1b2b3b4b5b6b7b8b9babbbcbdbebf\
        \c0c1c2c3c4c5c6c7c8c9cacbcccdcecf\
        \d0d1d2d3d4d5d6d7d8d9dadbdcdddedf\
        \e0e1e2e3e4e5e6e7e8e9eaebecedeeef\
        \f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff"#

    -- | 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 (Ptr table) . fromIntegral