{- Copyright © 2007 Magnus Therning
-
- This file is part of dataenc.
-
- Dataenc is free software: you can redistribute it and/or modify it under
- the terms of the GNU Lesser General Public License as published by the
- Free Software Foundation, either version 3 of the License, or (at your
- option) any later version.
-
- Dataenc is distributed in the hope that it will be useful, but WITHOUT
- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
- License for more details.
-
- You should have received a copy of the GNU Lesser General Public License
- along with dataenc. If not, see
-}
-- | Base16 module.
--
-- Implemented as specified in RFC 4648
-- ().
module Codec.Binary.Base16
( encode
, decode
, decode'
, chop
, unchop
) where
import Control.Monad
import Data.Array
import Data.Bits
import Data.Maybe
import Data.Word
import qualified Data.Map as M
-- {{{1 enc/dec map
_encMap =
[ (0, '0'), (1, '1'), (2, '2'), (3, '3'), (4, '4')
, (5, '5'), (6, '6'), (7, '7'), (8, '8'), (9, '9')
, (10, 'A'), (11, 'B'), (12, 'C'), (13, 'D'), (14, 'E')
, (15, 'F') ]
-- {{{1 encodeArray
encodeArray :: Array Word8 Char
encodeArray = array (0, 64) _encMap
-- {{{1 decodeMap
decodeMap :: M.Map Char Word8
decodeMap = M.fromList [(snd i, fst i) | i <- _encMap]
-- {{{1 encode
-- | Encode data.
encode :: [Word8]
-> String
encode os = let
splitOctet o = [ o `shiftR` 4, o .&. 0xf ]
in map (encodeArray !) $ foldr (\ o l -> (splitOctet o) ++ l) [] os
-- {{{1 decode
-- | Decode data (lazy).
decode' :: String
-> [Maybe Word8]
decode' = let
dec [] = []
dec (Just o1:Just o2:os) =
Just (o1 `shiftL` 4 .|. o2) : dec os
dec _ = [Nothing]
in
dec . map (flip M.lookup decodeMap)
-- | Decode data (strict).
decode :: String
-> Maybe [Word8]
decode = sequence . decode'
-- {{{1 chop
-- | Chop up a string in parts.
--
-- The length given is rounded down to the nearest multiple of 2.
chop :: Int -- ^ length of individual lines
-> String
-> [String]
chop n "" = []
chop n s = let
enc_len | n < 2 = 2
| otherwise = n `div` 2 * 2
in (take enc_len s) : chop n (drop enc_len s)
-- {{{1 unchop
-- | Concatenate the strings into one long string.
unchop :: [String]
-> String
unchop = foldr (++) ""