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
encodeArray :: Array Word8 Char
encodeArray = array (0, 64) [
(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') ]
decodeMap :: M.Map Char Word8
decodeMap = M.fromList [
('0', 0), ('1', 1), ('2', 2), ('3', 3), ('4', 4),
('5', 5), ('6', 6), ('7', 7), ('8', 8), ('9', 9),
('A', 10), ('B', 11), ('C', 12), ('D', 13), ('E', 14),
('F', 15) ]
encode :: [Word8]
-> String
encode os = let
splitOctet o = [ o `shiftR` 4, o .&. 0xf ]
in map (encodeArray !) $ foldr (\ o l -> (splitOctet o) ++ l) [] 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 (++) ""