module Codec.Binary.UTF8.String (
encode
, decode
, encodeString
, decodeString
) where
import Data.Word (Word8)
import Data.Bits ((.|.),(.&.),shiftL,shiftR)
import Data.Char (chr,ord)
default(Int)
encodeString :: String -> String
encodeString xs = map (toEnum . fromEnum) (encode xs)
decodeString :: String -> String
decodeString xs = decode (map (toEnum . fromEnum) xs)
replacement_character :: Char
replacement_character = '\xfffd'
encode :: String -> [Word8]
encode = concatMap (map fromIntegral . go . ord)
where
go oc
| oc <= 0x7f = [oc]
| oc <= 0x7ff = [ 0xc0 + (oc `shiftR` 6)
, 0x80 + oc .&. 0x3f
]
| oc <= 0xffff = [ 0xe0 + (oc `shiftR` 12)
, 0x80 + ((oc `shiftR` 6) .&. 0x3f)
, 0x80 + oc .&. 0x3f
]
| otherwise = [ 0xf0 + (oc `shiftR` 18)
, 0x80 + ((oc `shiftR` 12) .&. 0x3f)
, 0x80 + ((oc `shiftR` 6) .&. 0x3f)
, 0x80 + oc .&. 0x3f
]
decode :: [Word8] -> String
decode [ ] = ""
decode (c:cs)
| c < 0x80 = chr (fromEnum c) : decode cs
| c < 0xc0 = replacement_character : decode cs
| c < 0xe0 = multi1
| c < 0xf0 = multi_byte 2 0xf 0x800
| c < 0xf8 = multi_byte 3 0x7 0x10000
| c < 0xfc = multi_byte 4 0x3 0x200000
| c < 0xfe = multi_byte 5 0x1 0x4000000
| otherwise = replacement_character : decode cs
where
multi1 = case cs of
c1 : ds | c1 .&. 0xc0 == 0x80 ->
let d = ((fromEnum c .&. 0x1f) `shiftL` 6) .|. fromEnum (c1 .&. 0x3f)
in if d >= 0x000080 then toEnum d : decode ds
else replacement_character : decode ds
_ -> replacement_character : decode cs
multi_byte :: Int -> Word8 -> Int -> [Char]
multi_byte i mask overlong = aux i cs (fromEnum (c .&. mask))
where
aux 0 rs acc
| overlong <= acc && acc <= 0x10ffff &&
(acc < 0xd800 || 0xdfff < acc) &&
(acc < 0xfffe || 0xffff < acc) = chr acc : decode rs
| otherwise = replacement_character : decode rs
aux n (r:rs) acc
| r .&. 0xc0 == 0x80 = aux (n1) rs
$ shiftL acc 6 .|. fromEnum (r .&. 0x3f)
aux _ rs _ = replacement_character : decode rs