module Codec.Binary.Yenc
( encode
, decode
, decode'
, chop
, unchop
) where
import Data.Word
_criticals_in = [0xd6, 0xe0, 0xe3, 0x13]
_equal = 0x3d
encode :: [Word8]
-> [Word8]
encode (d:ds)
| d `elem` _criticals_in = _equal : d + 106 : encode ds
| otherwise = d + 42 : encode ds
encode _ = []
decode' :: [Word8]
-> [Maybe Word8]
decode' (0x3d:d:ds) = Just (d + 150) : decode' ds
decode' (d:ds) = Just (d + 214) : decode' ds
decode' _ = []
decode :: [Word8]
-> Maybe [Word8]
decode = sequence . decode'
chop :: Int
-> [Word8]
-> [[Word8]]
chop _ [] = []
chop n ws = let
(p1, p2) = splitAt n ws
in
if (last p1 == _equal)
then (p1 ++ (take 1 p2)) : chop n (drop 1 p2)
else p1 : chop n p2
unchop :: [[Word8]]
-> [Word8]
unchop = concat