[Haskell-cafe] UTF-16

[Bulat Ziganshin]

Hello Donald,

Thursday, July 26, 2007, 8:13:37 AM, you wrote:
>> I don't know if anybody cares, but... Today a wrote some trivial code to
>> decode (not encode) UTF-16.

These functions already exist in win-specific part of base:

cWcharsToChars :: [CWchar] -> [Char]
charsToCWchars :: [Char] -> [CWchar]

#ifdef mingw32_HOST_OS

-- On Windows, wchar_t is 16 bits wide and CWString uses the UTF-16 encoding.

-- coding errors generate Chars in the surrogate range
cWcharsToChars = map chr . fromUTF16 . map fromIntegral
 where
  fromUTF16 (c1:c2:wcs)
    | 0xd800 <= c1 && c1 <= 0xdbff && 0xdc00 <= c2 && c2 <= 0xdfff =
      ((c1 - 0xd800)*0x400 + (c2 - 0xdc00) + 0x10000) : fromUTF16 wcs
  fromUTF16 (c:wcs) = c : fromUTF16 wcs
  fromUTF16 [] = []

charsToCWchars = foldr utf16Char [] . map ord
 where
  utf16Char c wcs
    | c < 0x10000 = fromIntegral c : wcs
    | otherwise   = let c' = c - 0x10000 in
                    fromIntegral (c' `div` 0x400 + 0xd800) :
                    fromIntegral (c' `mod` 0x400 + 0xdc00) : wcs




-- 
Best regards,
 Bulat                            mailto:Bulat.Ziganshin at gmail.com