eeee054f1e
Now it's possible to change the character encoding while de-/encoding. Also, it's possible to use any data structure as a source or target of the de-/encoding process. darcs-hash:20090221203100-a4fee-6da31f2e37c30a3f5cd5f10af71984209488bb0b
82 lines
2.7 KiB
Haskell
82 lines
2.7 KiB
Haskell
{-# LANGUAGE DeriveDataTypeable #-}
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{- | This module implements UTF-16 encoding and decoding as in RFC 2781.
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See <http://en.wikipedia.org/wiki/UTF-16> for more information.
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-}
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module Data.Encoding.UTF16
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(UTF16(..)
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) where
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import Data.Encoding.Base
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import Data.Encoding.ByteSink
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import Data.Encoding.ByteSource
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import Data.Encoding.Exception
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import Control.Throws
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import Data.Bits
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import Data.Char
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import Data.Typeable
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import Data.Word
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data UTF16
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= UTF16 -- ^ Decodes big and little endian, encodes big endian.
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| UTF16BE -- ^ Big endian decoding and encoding, fails if the string isn\'t actually big endian.
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| UTF16LE -- ^ Little endian decoding and encoding.
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deriving (Eq,Show,Typeable)
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readBOM :: ByteSource m => m (Either Char UTF16)
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readBOM = do
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ch <- decodeChar UTF16
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case ch of
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'\xFEFF' -> return (Right UTF16BE)
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'\xFFFE' -> return (Right UTF16LE)
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_ -> return (Left ch)
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decodeUTF16 :: ByteSource m => (m Word16) -> m Char
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decodeUTF16 fetch = do
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w1 <- fetch
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if w1 < 0xD800 || w1 > 0xDFFF
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then return (chr $ fromIntegral w1)
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else (if w1 > 0xDBFF
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then throwException (IllegalCharacter (fromIntegral (w1 `shiftR` 8)))
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else (do
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w2 <- fetch
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if w2 < 0xDC00 || w2 > 0xDFFF
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then throwException (IllegalCharacter (fromIntegral (w2 `shiftR` 8)))
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else let v = ((fromIntegral (w1 .&. 0x3FF)) `shiftL` 10)
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.|. (fromIntegral (w2 .&. 0x3FF))
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in return $ chr (v+0x10000)
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)
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)
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encodeUTF16 :: ByteSink m => (Word16 -> m ()) -> Char -> m ()
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encodeUTF16 push ch
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| val<=0xDFFF && val>=0xD800 = throwException (HasNoRepresentation ch)
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| val<=0x0000FFFF = push $ fromIntegral val
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| val<=0x0010FFFF = let v = val - 0x10000
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w1 = (fromIntegral (v `shiftR` 10)) .|. 0xD800
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w2 = ((fromIntegral v) .&. 0x3FF) .|. 0xDC00
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in push w1 >> push w2
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| otherwise = throwException (HasNoRepresentation ch)
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where
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val = ord ch
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instance Encoding UTF16 where
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encodeChar UTF16LE = encodeUTF16 pushWord16le
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encodeChar _ = encodeUTF16 pushWord16be
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decodeChar UTF16LE = decodeUTF16 fetchWord16le
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decodeChar _ = decodeUTF16 fetchWord16be
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encode UTF16 str = do
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encodeChar UTF16 '\xFEFF'
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mapM_ (encodeChar UTF16) str
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encode enc str = mapM_ (encodeChar enc) str
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decode UTF16 = do
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res <- readBOM
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case res of
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Left c -> do
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cs <- untilM sourceEmpty (decodeChar UTF16BE)
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return (c:cs)
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Right bom -> decode bom
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decode enc = untilM sourceEmpty (decodeChar enc)
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