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
_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') ]
encodeArray :: Array Word8 Char
encodeArray = array (0, 64) _encMap
decodeMap :: M.Map Char Word8
decodeMap = M.fromList [(snd i, fst i) | i <- _encMap]
encode :: [Word8]
-> String
encode os = let
splitOctet o = [ o `shiftR` 4, o .&. 0xf ]
in map (encodeArray !) $ foldr ((++) . splitOctet) [] os
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 :: String
-> Maybe [Word8]
decode = sequence . decode'
chop :: Int
-> 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)
unchop :: [String]
-> String
unchop = foldr (++) ""