utils/Encoding.hs

    {-# LANGUAGE BangPatterns, MagicHash, UnboxedTuples #-}
    {-# OPTIONS_GHC -O #-}
    -- We always optimise this, otherwise performance of a non-optimised
    -- compiler is severely affected

    -- -----------------------------------------------------------------------------
    --
    -- (c) The University of Glasgow, 1997-2006
    --
    -- Character encodings
    --
    -- -----------------------------------------------------------------------------

    module Encoding (
            -- * UTF-8
            utf8DecodeChar#,
            utf8PrevChar,
            utf8CharStart,
            utf8DecodeChar,
            utf8DecodeByteString,
            utf8DecodeStringLazy,
            utf8EncodeChar,
            utf8EncodeString,
            utf8EncodedLength,
            countUTF8Chars,

            -- * Z-encoding
            zEncodeString,
            zDecodeString,

            -- * Base62-encoding
            toBase62,
            toBase62Padded
      ) where

    import Foreign
    import Foreign.ForeignPtr.Unsafe
    import Data.Char
    import qualified Data.Char as Char
    import Numeric
    import GHC.IO

    import Data.ByteString (ByteString)
    import qualified Data.ByteString.Internal as BS

    import GHC.Exts

    -- -----------------------------------------------------------------------------
    -- UTF-8

    -- We can't write the decoder as efficiently as we'd like without
    -- resorting to unboxed extensions, unfortunately.  I tried to write
    -- an IO version of this function, but GHC can't eliminate boxed
    -- results from an IO-returning function.
    --
    -- We assume we can ignore overflow when parsing a multibyte character here.
    -- To make this safe, we add extra sentinel bytes to unparsed UTF-8 sequences
    -- before decoding them (see StringBuffer.hs).

    {-# INLINE utf8DecodeChar# #-}
    utf8DecodeChar# :: Addr# -> (# Char#, Int# #)
    utf8DecodeChar# a# =
      let !ch0 = word2Int# (indexWord8OffAddr# a# 0#) in
      case () of
        _ | isTrue# (ch0 <=# 0x7F#) -> (# chr# ch0, 1# #)

          | isTrue# ((ch0 >=# 0xC0#) `andI#` (ch0 <=# 0xDF#)) ->
            let !ch1 = word2Int# (indexWord8OffAddr# a# 1#) in
            if isTrue# ((ch1 <# 0x80#) `orI#` (ch1 >=# 0xC0#)) then fail 1# else
            (# chr# (((ch0 -# 0xC0#) `uncheckedIShiftL#` 6#) +#
                      (ch1 -# 0x80#)),
               2# #)

          | isTrue# ((ch0 >=# 0xE0#) `andI#` (ch0 <=# 0xEF#)) ->
            let !ch1 = word2Int# (indexWord8OffAddr# a# 1#) in
            if isTrue# ((ch1 <# 0x80#) `orI#` (ch1 >=# 0xC0#)) then fail 1# else
            let !ch2 = word2Int# (indexWord8OffAddr# a# 2#) in
            if isTrue# ((ch2 <# 0x80#) `orI#` (ch2 >=# 0xC0#)) then fail 2# else
            (# chr# (((ch0 -# 0xE0#) `uncheckedIShiftL#` 12#) +#
                     ((ch1 -# 0x80#) `uncheckedIShiftL#` 6#)  +#
                      (ch2 -# 0x80#)),
               3# #)

         | isTrue# ((ch0 >=# 0xF0#) `andI#` (ch0 <=# 0xF8#)) ->
            let !ch1 = word2Int# (indexWord8OffAddr# a# 1#) in
            if isTrue# ((ch1 <# 0x80#) `orI#` (ch1 >=# 0xC0#)) then fail 1# else
            let !ch2 = word2Int# (indexWord8OffAddr# a# 2#) in
            if isTrue# ((ch2 <# 0x80#) `orI#` (ch2 >=# 0xC0#)) then fail 2# else
            let !ch3 = word2Int# (indexWord8OffAddr# a# 3#) in
            if isTrue# ((ch3 <# 0x80#) `orI#` (ch3 >=# 0xC0#)) then fail 3# else
            (# chr# (((ch0 -# 0xF0#) `uncheckedIShiftL#` 18#) +#
                     ((ch1 -# 0x80#) `uncheckedIShiftL#` 12#) +#
                     ((ch2 -# 0x80#) `uncheckedIShiftL#` 6#)  +#
                      (ch3 -# 0x80#)),
               4# #)

          | otherwise -> fail 1#
      where
            -- all invalid sequences end up here:
            fail :: Int# -> (# Char#, Int# #)
            fail nBytes# = (# '\0'#, nBytes# #)
            -- '\xFFFD' would be the usual replacement character, but
            -- that's a valid symbol in Haskell, so will result in a
            -- confusing parse error later on.  Instead we use '\0' which
            -- will signal a lexer error immediately.

    utf8DecodeChar :: Ptr Word8 -> (Char, Int)
    utf8DecodeChar (Ptr a#) =
      case utf8DecodeChar# a# of (# c#, nBytes# #) -> ( C# c#, I# nBytes# )

    -- UTF-8 is cleverly designed so that we can always figure out where
    -- the start of the current character is, given any position in a
    -- stream.  This function finds the start of the previous character,
    -- assuming there *is* a previous character.
    utf8PrevChar :: Ptr Word8 -> IO (Ptr Word8)
    utf8PrevChar p = utf8CharStart (p `plusPtr` (-1))

    utf8CharStart :: Ptr Word8 -> IO (Ptr Word8)
    utf8CharStart p = go p
     where go p = do w <- peek p
                     if w >= 0x80 && w < 0xC0
                            then go (p `plusPtr` (-1))
                            else return p

    utf8DecodeByteString :: ByteString -> [Char]
    utf8DecodeByteString (BS.PS ptr offset len)
      = utf8DecodeStringLazy ptr offset len

    utf8DecodeStringLazy :: ForeignPtr Word8 -> Int -> Int -> [Char]
    utf8DecodeStringLazy fptr offset len
      = unsafeDupablePerformIO $ unpack start
      where
        !start = unsafeForeignPtrToPtr fptr `plusPtr` offset
        !end = start `plusPtr` len

        unpack p
            | p >= end  = touchForeignPtr fptr >> return []
            | otherwise =
                case utf8DecodeChar# (unPtr p) of
                    (# c#, nBytes# #) -> do
                      rest <- unsafeDupableInterleaveIO $ unpack (p `plusPtr#` nBytes#)
                      return (C# c# : rest)

    countUTF8Chars :: Ptr Word8 -> Int -> IO Int
    countUTF8Chars ptr len = go ptr 0
      where
            !end = ptr `plusPtr` len

            go p !n
               | p >= end = return n
               | otherwise  = do
                    case utf8DecodeChar# (unPtr p) of
                      (# _, nBytes# #) -> go (p `plusPtr#` nBytes#) (n+1)

    unPtr :: Ptr a -> Addr#
    unPtr (Ptr a) = a

    plusPtr# :: Ptr a -> Int# -> Ptr a
    plusPtr# ptr nBytes# = ptr `plusPtr` (I# nBytes#)

    utf8EncodeChar :: Char -> Ptr Word8 -> IO (Ptr Word8)
    utf8EncodeChar c ptr =
      let x = ord c in
      case () of
        _ | x > 0 && x <= 0x007f -> do
              poke ptr (fromIntegral x)
              return (ptr `plusPtr` 1)
            -- NB. '\0' is encoded as '\xC0\x80', not '\0'.  This is so that we
            -- can have 0-terminated UTF-8 strings (see GHC.Base.unpackCStringUtf8).
          | x <= 0x07ff -> do
              poke ptr (fromIntegral (0xC0 .|. ((x `shiftR` 6) .&. 0x1F)))
              pokeElemOff ptr 1 (fromIntegral (0x80 .|. (x .&. 0x3F)))
              return (ptr `plusPtr` 2)
          | x <= 0xffff -> do
              poke ptr (fromIntegral (0xE0 .|. (x `shiftR` 12) .&. 0x0F))
              pokeElemOff ptr 1 (fromIntegral (0x80 .|. (x `shiftR` 6) .&. 0x3F))
              pokeElemOff ptr 2 (fromIntegral (0x80 .|. (x .&. 0x3F)))
              return (ptr `plusPtr` 3)
          | otherwise -> do
              poke ptr (fromIntegral (0xF0 .|. (x `shiftR` 18)))
              pokeElemOff ptr 1 (fromIntegral (0x80 .|. ((x `shiftR` 12) .&. 0x3F)))
              pokeElemOff ptr 2 (fromIntegral (0x80 .|. ((x `shiftR` 6) .&. 0x3F)))
              pokeElemOff ptr 3 (fromIntegral (0x80 .|. (x .&. 0x3F)))
              return (ptr `plusPtr` 4)

    utf8EncodeString :: Ptr Word8 -> String -> IO ()
    utf8EncodeString ptr str = go ptr str
      where go !_   []     = return ()
            go ptr (c:cs) = do
              ptr' <- utf8EncodeChar c ptr
              go ptr' cs

    utf8EncodedLength :: String -> Int
    utf8EncodedLength str = go 0 str
      where go !n [] = n
            go n (c:cs)
              | ord c > 0 && ord c <= 0x007f = go (n+1) cs
              | ord c <= 0x07ff = go (n+2) cs
              | ord c <= 0xffff = go (n+3) cs
              | otherwise       = go (n+4) cs

    -- -----------------------------------------------------------------------------
    -- The Z-encoding

    {-
    This is the main name-encoding and decoding function.  It encodes any
    string into a string that is acceptable as a C name.  This is done
    right before we emit a symbol name into the compiled C or asm code.
    Z-encoding of strings is cached in the FastString interface, so we
    never encode the same string more than once.

    The basic encoding scheme is this.

    * Tuples (,,,) are coded as Z3T

    * Alphabetic characters (upper and lower) and digits
            all translate to themselves;
            except 'Z', which translates to 'ZZ'
            and    'z', which translates to 'zz'
      We need both so that we can preserve the variable/tycon distinction

    * Most other printable characters translate to 'zx' or 'Zx' for some
            alphabetic character x

    * The others translate as 'znnnU' where 'nnn' is the decimal number
            of the character

            Before          After
            --------------------------
            Trak            Trak
            foo_wib         foozuwib
            >               zg
            >1              zg1
            foo#            foozh
            foo##           foozhzh
            foo##1          foozhzh1
            fooZ            fooZZ
            :+              ZCzp
            ()              Z0T     0-tuple
            (,,,,)          Z5T     5-tuple
            (# #)           Z1H     unboxed 1-tuple (note the space)
            (#,,,,#)        Z5H     unboxed 5-tuple
                    (NB: There is no Z1T nor Z0H.)
    -}

    type UserString = String        -- As the user typed it
    type EncodedString = String     -- Encoded form

    zEncodeString :: UserString -> EncodedString
    zEncodeString cs = case maybe_tuple cs of
                    Just n  -> n            -- Tuples go to Z2T etc
                    Nothing -> go cs
              where
                    go []     = []
                    go (c:cs) = encode_digit_ch c ++ go' cs
                    go' []     = []
                    go' (c:cs) = encode_ch c ++ go' cs

    unencodedChar :: Char -> Bool   -- True for chars that don't need encoding
    unencodedChar 'Z' = False
    unencodedChar 'z' = False
    unencodedChar c   =  c >= 'a' && c <= 'z'
                      || c >= 'A' && c <= 'Z'
                      || c >= '0' && c <= '9'

    -- If a digit is at the start of a symbol then we need to encode it.
    -- Otherwise package names like 9pH-0.1 give linker errors.
    encode_digit_ch :: Char -> EncodedString
    encode_digit_ch c | c >= '0' && c <= '9' = encode_as_unicode_char c
    encode_digit_ch c | otherwise            = encode_ch c

    encode_ch :: Char -> EncodedString
    encode_ch c | unencodedChar c = [c]     -- Common case first

    -- Constructors
    encode_ch '('  = "ZL"   -- Needed for things like (,), and (->)
    encode_ch ')'  = "ZR"   -- For symmetry with (
    encode_ch '['  = "ZM"
    encode_ch ']'  = "ZN"
    encode_ch ':'  = "ZC"
    encode_ch 'Z'  = "ZZ"

    -- Variables
    encode_ch 'z'  = "zz"
    encode_ch '&'  = "za"
    encode_ch '|'  = "zb"
    encode_ch '^'  = "zc"
    encode_ch '$'  = "zd"
    encode_ch '='  = "ze"
    encode_ch '>'  = "zg"
    encode_ch '#'  = "zh"
    encode_ch '.'  = "zi"
    encode_ch '<'  = "zl"
    encode_ch '-'  = "zm"
    encode_ch '!'  = "zn"
    encode_ch '+'  = "zp"
    encode_ch '\'' = "zq"
    encode_ch '\\' = "zr"
    encode_ch '/'  = "zs"
    encode_ch '*'  = "zt"
    encode_ch '_'  = "zu"
    encode_ch '%'  = "zv"
    encode_ch c    = encode_as_unicode_char c

    encode_as_unicode_char :: Char -> EncodedString
    encode_as_unicode_char c = 'z' : if isDigit (head hex_str) then hex_str
                                                               else '0':hex_str
      where hex_str = showHex (ord c) "U"
      -- ToDo: we could improve the encoding here in various ways.
      -- eg. strings of unicode characters come out as 'z1234Uz5678U', we
      -- could remove the 'U' in the middle (the 'z' works as a separator).

    zDecodeString :: EncodedString -> UserString
    zDecodeString [] = []
    zDecodeString ('Z' : d : rest)
      | isDigit d = decode_tuple   d rest
      | otherwise = decode_upper   d : zDecodeString rest
    zDecodeString ('z' : d : rest)
      | isDigit d = decode_num_esc d rest
      | otherwise = decode_lower   d : zDecodeString rest
    zDecodeString (c   : rest) = c : zDecodeString rest

    decode_upper, decode_lower :: Char -> Char

    decode_upper 'L' = '('
    decode_upper 'R' = ')'
    decode_upper 'M' = '['
    decode_upper 'N' = ']'
    decode_upper 'C' = ':'
    decode_upper 'Z' = 'Z'
    decode_upper ch  = {-pprTrace "decode_upper" (char ch)-} ch

    decode_lower 'z' = 'z'
    decode_lower 'a' = '&'
    decode_lower 'b' = '|'
    decode_lower 'c' = '^'
    decode_lower 'd' = '$'
    decode_lower 'e' = '='
    decode_lower 'g' = '>'
    decode_lower 'h' = '#'
    decode_lower 'i' = '.'
    decode_lower 'l' = '<'
    decode_lower 'm' = '-'
    decode_lower 'n' = '!'
    decode_lower 'p' = '+'
    decode_lower 'q' = '\''
    decode_lower 'r' = '\\'
    decode_lower 's' = '/'
    decode_lower 't' = '*'
    decode_lower 'u' = '_'
    decode_lower 'v' = '%'
    decode_lower ch  = {-pprTrace "decode_lower" (char ch)-} ch

    -- Characters not having a specific code are coded as z224U (in hex)
    decode_num_esc :: Char -> EncodedString -> UserString
    decode_num_esc d rest
      = go (digitToInt d) rest
      where
        go n (c : rest) | isHexDigit c = go (16*n + digitToInt c) rest
        go n ('U' : rest)           = chr n : zDecodeString rest
        go n other = error ("decode_num_esc: " ++ show n ++  ' ':other)

    decode_tuple :: Char -> EncodedString -> UserString
    decode_tuple d rest
      = go (digitToInt d) rest
      where
            -- NB. recurse back to zDecodeString after decoding the tuple, because
            -- the tuple might be embedded in a longer name.
        go n (c : rest) | isDigit c = go (10*n + digitToInt c) rest
        go 0 ('T':rest)     = "()" ++ zDecodeString rest
        go n ('T':rest)     = '(' : replicate (n-1) ',' ++ ")" ++ zDecodeString rest
        go 1 ('H':rest)     = "(# #)" ++ zDecodeString rest
        go n ('H':rest)     = '(' : '#' : replicate (n-1) ',' ++ "#)" ++ zDecodeString rest
        go n other = error ("decode_tuple: " ++ show n ++ ' ':other)

    {-
    Tuples are encoded as
            Z3T or Z3H
    for 3-tuples or unboxed 3-tuples respectively.  No other encoding starts
            Z<digit>

    * "(# #)" is the tycon for an unboxed 1-tuple (not 0-tuple)
      There are no unboxed 0-tuples.

    * "()" is the tycon for a boxed 0-tuple.
      There are no boxed 1-tuples.
    -}

    maybe_tuple :: UserString -> Maybe EncodedString

    maybe_tuple "(# #)" = Just("Z1H")
    maybe_tuple ('(' : '#' : cs) = case count_commas (0::Int) cs of
                                     (n, '#' : ')' : _) -> Just ('Z' : shows (n+1) "H")
                                     _                  -> Nothing
    maybe_tuple "()" = Just("Z0T")
    maybe_tuple ('(' : cs)       = case count_commas (0::Int) cs of
                                     (n, ')' : _) -> Just ('Z' : shows (n+1) "T")
                                     _            -> Nothing
    maybe_tuple _                = Nothing

    count_commas :: Int -> String -> (Int, String)
    count_commas n (',' : cs) = count_commas (n+1) cs
    count_commas n cs         = (n,cs)

    {-
    ************************************************************************
    *                                                                      *
                            Base 62
    *                                                                      *
    ************************************************************************

    Note [Base 62 encoding 128-bit integers]
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Instead of base-62 encoding a single 128-bit integer
    (ceil(21.49) characters), we'll base-62 a pair of 64-bit integers
    (2 * ceil(10.75) characters).  Luckily for us, it's the same number of
    characters!
    -}

    --------------------------------------------------------------------------
    -- Base 62

    -- The base-62 code is based off of 'locators'
    -- ((c) Operational Dynamics Consulting, BSD3 licensed)

    -- | Size of a 64-bit word when written as a base-62 string
    word64Base62Len :: Int
    word64Base62Len = 11

    -- | Converts a 64-bit word into a base-62 string
    toBase62Padded :: Word64 -> String
    toBase62Padded w = pad ++ str
      where
        pad = replicate len '0'
        len = word64Base62Len - length str -- 11 == ceil(64 / lg 62)
        str = toBase62 w

    toBase62 :: Word64 -> String
    toBase62 w = showIntAtBase 62 represent w ""
      where
        represent :: Int -> Char
        represent x
            | x < 10 = Char.chr (48 + x)
            | x < 36 = Char.chr (65 + x - 10)
            | x < 62 = Char.chr (97 + x - 36)
            | otherwise = error "represent (base 62): impossible!"