path: root/compiler/utils/Binary.hs

{-# OPTIONS -cpp #-}
{-# OPTIONS_GHC -O -funbox-strict-fields #-}
-- We always optimise this, otherwise performance of a non-optimised
-- compiler is severely affected

--
-- (c) The University of Glasgow 2002-2006
--
-- Binary I/O library, with special tweaks for GHC
--
-- Based on the nhc98 Binary library, which is copyright
-- (c) Malcolm Wallace and Colin Runciman, University of York, 1998.
-- Under the terms of the license for that software, we must tell you
-- where you can obtain the original version of the Binary library, namely
--     http://www.cs.york.ac.uk/fp/nhc98/

module Binary
  ( {-type-}  Bin,
    {-class-} Binary(..),
    {-type-}  BinHandle,

   openBinIO, openBinIO_,
   openBinMem,
--   closeBin,

   seekBin,
   seekBy,
   tellBin,
   castBin,

   writeBinMem,
   readBinMem,
   fingerprintBinMem,

   isEOFBin,

   putAt, getAt,

   -- for writing instances:
   putByte,
   getByte,

   -- lazy Bin I/O
   lazyGet,
   lazyPut,

#ifdef __GLASGOW_HASKELL__
   -- GHC only:
   ByteArray(..),
   getByteArray,
   putByteArray,
#endif

   UserData(..), getUserData, setUserData,
   newReadState, newWriteState,
   putDictionary, getDictionary, putFS,
  ) where

#include "HsVersions.h"

-- The *host* architecture version:
#include "MachDeps.h"

import {-# SOURCE #-} Name (Name)
import FastString
import Panic
import UniqFM
import FastMutInt
import Fingerprint
import BasicTypes

import Foreign
import Data.Array
import Data.Bits
import Data.Int
import Data.Word
import Data.IORef
import Data.Char                ( ord, chr )
import Data.Typeable
import Control.Monad            ( when )
import System.IO as IO
import System.IO.Unsafe         ( unsafeInterleaveIO )
import System.IO.Error          ( mkIOError, eofErrorType )
import GHC.Real                 ( Ratio(..) )
import GHC.Exts
import GHC.Word                 ( Word8(..) )
import System.IO                ( openBinaryFile )

#if __GLASGOW_HASKELL__ >= 611
import GHC.IO ( IO(..) )
#else
import GHC.IOBase ( IO(..) )
#endif

type BinArray = ForeignPtr Word8

---------------------------------------------------------------
-- BinHandle
---------------------------------------------------------------

data BinHandle
  = BinMem {                     -- binary data stored in an unboxed array
     bh_usr :: UserData,         -- sigh, need parameterized modules :-)
     _off_r :: !FastMutInt,      -- the current offset
     _sz_r  :: !FastMutInt,      -- size of the array (cached)
     _arr_r :: !(IORef BinArray) -- the array (bounds: (0,size-1))
    }
        -- XXX: should really store a "high water mark" for dumping out
        -- the binary data to a file.

  | BinIO {                     -- binary data stored in a file
     bh_usr :: UserData,
     _off_r :: !FastMutInt,     -- the current offset (cached)
     _hdl   :: !IO.Handle       -- the file handle (must be seekable)
   }
        -- cache the file ptr in BinIO; using hTell is too expensive
        -- to call repeatedly.  If anyone else is modifying this Handle
        -- at the same time, we'll be screwed.

getUserData :: BinHandle -> UserData
getUserData bh = bh_usr bh

setUserData :: BinHandle -> UserData -> BinHandle
setUserData bh us = bh { bh_usr = us }


---------------------------------------------------------------
-- Bin
---------------------------------------------------------------

newtype Bin a = BinPtr Int
  deriving (Eq, Ord, Show, Bounded)

castBin :: Bin a -> Bin b
castBin (BinPtr i) = BinPtr i

---------------------------------------------------------------
-- class Binary
---------------------------------------------------------------

class Binary a where
    put_   :: BinHandle -> a -> IO ()
    put    :: BinHandle -> a -> IO (Bin a)
    get    :: BinHandle -> IO a

    -- define one of put_, put.  Use of put_ is recommended because it
    -- is more likely that tail-calls can kick in, and we rarely need the
    -- position return value.
    put_ bh a = do put bh a; return ()
    put bh a  = do p <- tellBin bh; put_ bh a; return p

putAt  :: Binary a => BinHandle -> Bin a -> a -> IO ()
putAt bh p x = do seekBin bh p; put bh x; return ()

getAt  :: Binary a => BinHandle -> Bin a -> IO a
getAt bh p = do seekBin bh p; get bh

openBinIO_ :: IO.Handle -> IO BinHandle
openBinIO_ h = openBinIO h

openBinIO :: IO.Handle -> IO BinHandle
openBinIO h = do
  r <- newFastMutInt
  writeFastMutInt r 0
  return (BinIO noUserData r h)

openBinMem :: Int -> IO BinHandle
openBinMem size
 | size <= 0 = error "Data.Binary.openBinMem: size must be >= 0"
 | otherwise = do
   arr <- mallocForeignPtrBytes size
   arr_r <- newIORef arr
   ix_r <- newFastMutInt
   writeFastMutInt ix_r 0
   sz_r <- newFastMutInt
   writeFastMutInt sz_r size
   return (BinMem noUserData ix_r sz_r arr_r)

tellBin :: BinHandle -> IO (Bin a)
tellBin (BinIO  _ r _)   = do ix <- readFastMutInt r; return (BinPtr ix)
tellBin (BinMem _ r _ _) = do ix <- readFastMutInt r; return (BinPtr ix)

seekBin :: BinHandle -> Bin a -> IO ()
seekBin (BinIO _ ix_r h) (BinPtr p) = do
  writeFastMutInt ix_r p
  hSeek h AbsoluteSeek (fromIntegral p)
seekBin h@(BinMem _ ix_r sz_r _) (BinPtr p) = do
  sz <- readFastMutInt sz_r
  if (p >= sz)
        then do expandBin h p; writeFastMutInt ix_r p
        else writeFastMutInt ix_r p

seekBy :: BinHandle -> Int -> IO ()
seekBy (BinIO _ ix_r h) off = do
  ix <- readFastMutInt ix_r
  let ix' = ix + off
  writeFastMutInt ix_r ix'
  hSeek h AbsoluteSeek (fromIntegral ix')
seekBy h@(BinMem _ ix_r sz_r _) off = do
  sz <- readFastMutInt sz_r
  ix <- readFastMutInt ix_r
  let ix' = ix + off
  if (ix' >= sz)
        then do expandBin h ix'; writeFastMutInt ix_r ix'
        else writeFastMutInt ix_r ix'

isEOFBin :: BinHandle -> IO Bool
isEOFBin (BinMem _ ix_r sz_r _) = do
  ix <- readFastMutInt ix_r
  sz <- readFastMutInt sz_r
  return (ix >= sz)
isEOFBin (BinIO _ _ h) = hIsEOF h

writeBinMem :: BinHandle -> FilePath -> IO ()
writeBinMem (BinIO _ _ _) _ = error "Data.Binary.writeBinMem: not a memory handle"
writeBinMem (BinMem _ ix_r _ arr_r) fn = do
  h <- openBinaryFile fn WriteMode
  arr <- readIORef arr_r
  ix  <- readFastMutInt ix_r
  withForeignPtr arr $ \p -> hPutBuf h p ix
  hClose h

readBinMem :: FilePath -> IO BinHandle
-- Return a BinHandle with a totally undefined State
readBinMem filename = do
  h <- openBinaryFile filename ReadMode
  filesize' <- hFileSize h
  let filesize = fromIntegral filesize'
  arr <- mallocForeignPtrBytes (filesize*2)
  count <- withForeignPtr arr $ \p -> hGetBuf h p filesize
  when (count /= filesize) $
       error ("Binary.readBinMem: only read " ++ show count ++ " bytes")
  hClose h
  arr_r <- newIORef arr
  ix_r <- newFastMutInt
  writeFastMutInt ix_r 0
  sz_r <- newFastMutInt
  writeFastMutInt sz_r filesize
  return (BinMem noUserData ix_r sz_r arr_r)

fingerprintBinMem :: BinHandle -> IO Fingerprint
fingerprintBinMem (BinIO _ _ _) = error "Binary.md5BinMem: not a memory handle"
fingerprintBinMem (BinMem _ ix_r _ arr_r) = do
  arr <- readIORef arr_r
  ix <- readFastMutInt ix_r
  withForeignPtr arr $ \p -> fingerprintData p ix

-- expand the size of the array to include a specified offset
expandBin :: BinHandle -> Int -> IO ()
expandBin (BinMem _ _ sz_r arr_r) off = do
   sz <- readFastMutInt sz_r
   let sz' = head (dropWhile (<= off) (iterate (* 2) sz))
   arr <- readIORef arr_r
   arr' <- mallocForeignPtrBytes sz'
   withForeignPtr arr $ \old ->
     withForeignPtr arr' $ \new ->
       copyBytes new old sz 
   writeFastMutInt sz_r sz'
   writeIORef arr_r arr'
   when False $ -- disabled
      hPutStrLn stderr ("Binary: expanding to size: " ++ show sz')
   return ()
expandBin (BinIO _ _ _) _ = return ()
-- no need to expand a file, we'll assume they expand by themselves.

-- -----------------------------------------------------------------------------
-- Low-level reading/writing of bytes

putWord8 :: BinHandle -> Word8 -> IO ()
putWord8 h@(BinMem _ ix_r sz_r arr_r) w = do
    ix <- readFastMutInt ix_r
    sz <- readFastMutInt sz_r
    -- double the size of the array if it overflows
    if (ix >= sz)
        then do expandBin h ix
                putWord8 h w
        else do arr <- readIORef arr_r
                withForeignPtr arr $ \p -> pokeByteOff p ix w
                writeFastMutInt ix_r (ix+1)
                return ()
putWord8 (BinIO _ ix_r h) w = do
    ix <- readFastMutInt ix_r
    hPutChar h (chr (fromIntegral w)) -- XXX not really correct
    writeFastMutInt ix_r (ix+1)
    return ()

getWord8 :: BinHandle -> IO Word8
getWord8 (BinMem _ ix_r sz_r arr_r) = do
    ix <- readFastMutInt ix_r
    sz <- readFastMutInt sz_r
    when (ix >= sz) $
        ioError (mkIOError eofErrorType "Data.Binary.getWord8" Nothing Nothing)
    arr <- readIORef arr_r
    w <- withForeignPtr arr $ \p -> peekByteOff p ix
    writeFastMutInt ix_r (ix+1)
    return w
getWord8 (BinIO _ ix_r h) = do
    ix <- readFastMutInt ix_r
    c <- hGetChar h
    writeFastMutInt ix_r (ix+1)
    return $! (fromIntegral (ord c)) -- XXX not really correct

putByte :: BinHandle -> Word8 -> IO ()
putByte bh w = put_ bh w

getByte :: BinHandle -> IO Word8
getByte = getWord8

-- -----------------------------------------------------------------------------
-- Primitve Word writes

instance Binary Word8 where
  put_ = putWord8
  get  = getWord8

instance Binary Word16 where
  put_ h w = do -- XXX too slow.. inline putWord8?
    putByte h (fromIntegral (w `shiftR` 8))
    putByte h (fromIntegral (w .&. 0xff))
  get h = do
    w1 <- getWord8 h
    w2 <- getWord8 h
    return $! ((fromIntegral w1 `shiftL` 8) .|. fromIntegral w2)


instance Binary Word32 where
  put_ h w = do
    putByte h (fromIntegral (w `shiftR` 24))
    putByte h (fromIntegral ((w `shiftR` 16) .&. 0xff))
    putByte h (fromIntegral ((w `shiftR` 8)  .&. 0xff))
    putByte h (fromIntegral (w .&. 0xff))
  get h = do
    w1 <- getWord8 h
    w2 <- getWord8 h
    w3 <- getWord8 h
    w4 <- getWord8 h
    return $! ((fromIntegral w1 `shiftL` 24) .|.
               (fromIntegral w2 `shiftL` 16) .|.
               (fromIntegral w3 `shiftL`  8) .|.
               (fromIntegral w4))

instance Binary Word64 where
  put_ h w = do
    putByte h (fromIntegral (w `shiftR` 56))
    putByte h (fromIntegral ((w `shiftR` 48) .&. 0xff))
    putByte h (fromIntegral ((w `shiftR` 40) .&. 0xff))
    putByte h (fromIntegral ((w `shiftR` 32) .&. 0xff))
    putByte h (fromIntegral ((w `shiftR` 24) .&. 0xff))
    putByte h (fromIntegral ((w `shiftR` 16) .&. 0xff))
    putByte h (fromIntegral ((w `shiftR`  8) .&. 0xff))
    putByte h (fromIntegral (w .&. 0xff))
  get h = do
    w1 <- getWord8 h
    w2 <- getWord8 h
    w3 <- getWord8 h
    w4 <- getWord8 h
    w5 <- getWord8 h
    w6 <- getWord8 h
    w7 <- getWord8 h
    w8 <- getWord8 h
    return $! ((fromIntegral w1 `shiftL` 56) .|.
               (fromIntegral w2 `shiftL` 48) .|.
               (fromIntegral w3 `shiftL` 40) .|.
               (fromIntegral w4 `shiftL` 32) .|.
               (fromIntegral w5 `shiftL` 24) .|.
               (fromIntegral w6 `shiftL` 16) .|.
               (fromIntegral w7 `shiftL`  8) .|.
               (fromIntegral w8))

-- -----------------------------------------------------------------------------
-- Primitve Int writes

instance Binary Int8 where
  put_ h w = put_ h (fromIntegral w :: Word8)
  get h    = do w <- get h; return $! (fromIntegral (w::Word8))

instance Binary Int16 where
  put_ h w = put_ h (fromIntegral w :: Word16)
  get h    = do w <- get h; return $! (fromIntegral (w::Word16))

instance Binary Int32 where
  put_ h w = put_ h (fromIntegral w :: Word32)
  get h    = do w <- get h; return $! (fromIntegral (w::Word32))

instance Binary Int64 where
  put_ h w = put_ h (fromIntegral w :: Word64)
  get h    = do w <- get h; return $! (fromIntegral (w::Word64))

-- -----------------------------------------------------------------------------
-- Instances for standard types

instance Binary () where
    put_ _ () = return ()
    get  _    = return ()
--    getF bh p  = case getBitsF bh 0 p of (_,b) -> ((),b)

instance Binary Bool where
    put_ bh b = putByte bh (fromIntegral (fromEnum b))
    get  bh   = do x <- getWord8 bh; return $! (toEnum (fromIntegral x))
--    getF bh p = case getBitsF bh 1 p of (x,b) -> (toEnum x,b)

instance Binary Char where
    put_  bh c = put_ bh (fromIntegral (ord c) :: Word32)
    get  bh   = do x <- get bh; return $! (chr (fromIntegral (x :: Word32)))
--    getF bh p = case getBitsF bh 8 p of (x,b) -> (toEnum x,b)

instance Binary Int where
#if SIZEOF_HSINT == 4
    put_ bh i = put_ bh (fromIntegral i :: Int32)
    get  bh = do
        x <- get bh
        return $! (fromIntegral (x :: Int32))
#elif SIZEOF_HSINT == 8
    put_ bh i = put_ bh (fromIntegral i :: Int64)
    get  bh = do
        x <- get bh
        return $! (fromIntegral (x :: Int64))
#else
#error "unsupported sizeof(HsInt)"
#endif
--    getF bh   = getBitsF bh 32

instance Binary a => Binary [a] where
    put_ bh l = do
        let len = length l
        if (len < 0xff)
          then putByte bh (fromIntegral len :: Word8)
          else do putByte bh 0xff; put_ bh (fromIntegral len :: Word32)
        mapM_ (put_ bh) l
    get bh = do
        b <- getByte bh
        len <- if b == 0xff
                  then get bh
                  else return (fromIntegral b :: Word32)
        let loop 0 = return []
            loop n = do a <- get bh; as <- loop (n-1); return (a:as)
        loop len

instance (Binary a, Binary b) => Binary (a,b) where
    put_ bh (a,b) = do put_ bh a; put_ bh b
    get bh        = do a <- get bh
                       b <- get bh
                       return (a,b)

instance (Binary a, Binary b, Binary c) => Binary (a,b,c) where
    put_ bh (a,b,c) = do put_ bh a; put_ bh b; put_ bh c
    get bh          = do a <- get bh
                         b <- get bh
                         c <- get bh
                         return (a,b,c)

instance (Binary a, Binary b, Binary c, Binary d) => Binary (a,b,c,d) where
    put_ bh (a,b,c,d) = do put_ bh a; put_ bh b; put_ bh c; put_ bh d
    get bh          = do a <- get bh
                         b <- get bh
                         c <- get bh
                         d <- get bh
                         return (a,b,c,d)

instance Binary a => Binary (Maybe a) where
    put_ bh Nothing  = putByte bh 0
    put_ bh (Just a) = do putByte bh 1; put_ bh a
    get bh           = do h <- getWord8 bh
                          case h of
                            0 -> return Nothing
                            _ -> do x <- get bh; return (Just x)

instance (Binary a, Binary b) => Binary (Either a b) where
    put_ bh (Left  a) = do putByte bh 0; put_ bh a
    put_ bh (Right b) = do putByte bh 1; put_ bh b
    get bh            = do h <- getWord8 bh
                           case h of
                             0 -> do a <- get bh ; return (Left a)
                             _ -> do b <- get bh ; return (Right b)

#if defined(__GLASGOW_HASKELL__) || 1
--to quote binary-0.3 on this code idea,
--
-- TODO  This instance is not architecture portable.  GMP stores numbers as
-- arrays of machine sized words, so the byte format is not portable across
-- architectures with different endianess and word size.
--
-- This makes it hard (impossible) to make an equivalent instance
-- with code that is compilable with non-GHC.  Do we need any instance
-- Binary Integer, and if so, does it have to be blazing fast?  Or can
-- we just change this instance to be portable like the rest of the
-- instances? (binary package has code to steal for that)
--
-- yes, we need Binary Integer and Binary Rational in basicTypes/Literal.lhs

instance Binary Integer where
    -- XXX This is hideous
    put_ bh i = put_ bh (show i)
    get bh = do str <- get bh
                case reads str of
                    [(i, "")] -> return i
                    _ -> fail ("Binary Integer: got " ++ show str)

    {-
    put_ bh (S# i#) = do putByte bh 0; put_ bh (I# i#)
    put_ bh (J# s# a#) = do
        putByte bh 1
        put_ bh (I# s#)
        let sz# = sizeofByteArray# a#  -- in *bytes*
        put_ bh (I# sz#)  -- in *bytes*
        putByteArray bh a# sz#

    get bh = do
        b <- getByte bh
        case b of
          0 -> do (I# i#) <- get bh
                  return (S# i#)
          _ -> do (I# s#) <- get bh
                  sz <- get bh
                  (BA a#) <- getByteArray bh sz
                  return (J# s# a#)
-}

-- As for the rest of this code, even though this module
-- exports it, it doesn't seem to be used anywhere else
-- in GHC!

putByteArray :: BinHandle -> ByteArray# -> Int# -> IO ()
putByteArray bh a s# = loop 0#
  where loop n#
           | n# ==# s# = return ()
           | otherwise = do
                putByte bh (indexByteArray a n#)
                loop (n# +# 1#)

getByteArray :: BinHandle -> Int -> IO ByteArray
getByteArray bh (I# sz) = do
  (MBA arr) <- newByteArray sz
  let loop n
           | n ==# sz = return ()
           | otherwise = do
                w <- getByte bh
                writeByteArray arr n w
                loop (n +# 1#)
  loop 0#
  freezeByteArray arr


data ByteArray = BA ByteArray#
data MBA = MBA (MutableByteArray# RealWorld)

newByteArray :: Int# -> IO MBA
newByteArray sz = IO $ \s ->
  case newByteArray# sz s of { (# s, arr #) ->
  (# s, MBA arr #) }

freezeByteArray :: MutableByteArray# RealWorld -> IO ByteArray
freezeByteArray arr = IO $ \s ->
  case unsafeFreezeByteArray# arr s of { (# s, arr #) ->
  (# s, BA arr #) }

writeByteArray :: MutableByteArray# RealWorld -> Int# -> Word8 -> IO ()
writeByteArray arr i (W8# w) = IO $ \s ->
  case writeWord8Array# arr i w s of { s ->
  (# s, () #) }

indexByteArray :: ByteArray# -> Int# -> Word8
indexByteArray a# n# = W8# (indexWord8Array# a# n#)

instance (Integral a, Binary a) => Binary (Ratio a) where
    put_ bh (a :% b) = do put_ bh a; put_ bh b
    get bh = do a <- get bh; b <- get bh; return (a :% b)
#endif

instance Binary (Bin a) where
  put_ bh (BinPtr i) = put_ bh i
  get bh = do i <- get bh; return (BinPtr i)

-- -----------------------------------------------------------------------------
-- Instances for Data.Typeable stuff

instance Binary TyCon where
    put_ bh ty_con = do
        let s = tyConString ty_con
        put_ bh s
    get bh = do
        s <- get bh
        return (mkTyCon s)

instance Binary TypeRep where
    put_ bh type_rep = do
        let (ty_con, child_type_reps) = splitTyConApp type_rep
        put_ bh ty_con
        put_ bh child_type_reps
    get bh = do
        ty_con <- get bh
        child_type_reps <- get bh
        return (mkTyConApp ty_con child_type_reps)

-- -----------------------------------------------------------------------------
-- Lazy reading/writing

lazyPut :: Binary a => BinHandle -> a -> IO ()
lazyPut bh a = do
    -- output the obj with a ptr to skip over it:
    pre_a <- tellBin bh
    put_ bh pre_a       -- save a slot for the ptr
    put_ bh a           -- dump the object
    q <- tellBin bh     -- q = ptr to after object
    putAt bh pre_a q    -- fill in slot before a with ptr to q
    seekBin bh q        -- finally carry on writing at q

lazyGet :: Binary a => BinHandle -> IO a
lazyGet bh = do
    p <- get bh -- a BinPtr
    p_a <- tellBin bh
    a <- unsafeInterleaveIO (getAt bh p_a)
    seekBin bh p -- skip over the object for now
    return a

-- -----------------------------------------------------------------------------
-- UserData
-- -----------------------------------------------------------------------------

data UserData =
   UserData {
        -- for *deserialising* only:
        ud_dict   :: Dictionary,
        ud_symtab :: SymbolTable,

        -- for *serialising* only:
        ud_put_name :: BinHandle -> Name       -> IO (),
        ud_put_fs   :: BinHandle -> FastString -> IO ()
   }

newReadState :: Dictionary -> IO UserData
newReadState dict = do
  return UserData { ud_dict     = dict,
                    ud_symtab   = undef "symtab",
                    ud_put_name = undef "put_name",
                    ud_put_fs   = undef "put_fs"
                   }

newWriteState :: (BinHandle -> Name       -> IO ()) 
              -> (BinHandle -> FastString -> IO ())
              -> IO UserData
newWriteState put_name put_fs = do
  return UserData { ud_dict     = undef "dict",
                    ud_symtab   = undef "symtab",
                    ud_put_name = put_name,
                    ud_put_fs   = put_fs
                   }

noUserData :: a
noUserData = undef "UserData"

undef :: String -> a
undef s = panic ("Binary.UserData: no " ++ s)

---------------------------------------------------------
-- The Dictionary
---------------------------------------------------------

type Dictionary = Array Int FastString -- The dictionary
                                       -- Should be 0-indexed

putDictionary :: BinHandle -> Int -> UniqFM (Int,FastString) -> IO ()
putDictionary bh sz dict = do
  put_ bh sz
  mapM_ (putFS bh) (elems (array (0,sz-1) (eltsUFM dict)))

getDictionary :: BinHandle -> IO Dictionary
getDictionary bh = do
  sz <- get bh
  elems <- sequence (take sz (repeat (getFS bh)))
  return (listArray (0,sz-1) elems)

---------------------------------------------------------
-- The Symbol Table
---------------------------------------------------------

-- On disk, the symbol table is an array of IfaceExtName, when
-- reading it in we turn it into a SymbolTable.

type SymbolTable = Array Int Name

---------------------------------------------------------
-- Reading and writing FastStrings
---------------------------------------------------------

putFS :: BinHandle -> FastString -> IO ()
putFS bh (FastString _ l _ buf _) = do
  put_ bh l
  withForeignPtr buf $ \ptr ->
    let
        go n | n == l    = return ()
             | otherwise = do
                b <- peekElemOff ptr n
                putByte bh b
                go (n+1)
   in
   go 0

{- -- possible faster version, not quite there yet:
getFS bh@BinMem{} = do
  (I# l) <- get bh
  arr <- readIORef (arr_r bh)
  off <- readFastMutInt (off_r bh)
  return $! (mkFastSubStringBA# arr off l)
-}
getFS :: BinHandle -> IO FastString
getFS bh = do
  l <- get bh
  fp <- mallocForeignPtrBytes l
  withForeignPtr fp $ \ptr -> do
  let
        go n | n == l = mkFastStringForeignPtr ptr fp l
             | otherwise = do
                b <- getByte bh
                pokeElemOff ptr n b
                go (n+1)
  --
  go 0

instance Binary FastString where
  put_ bh f =
    case getUserData bh of
        UserData { ud_put_fs = put_fs } -> put_fs bh f

  get bh = do
        j <- get bh
        return $! (ud_dict (getUserData bh) ! j)

-- Here to avoid loop

instance Binary Fingerprint where
  put_ h (Fingerprint w1 w2) = do put_ h w1; put_ h w2
  get  h = do w1 <- get h; w2 <- get h; return (Fingerprint w1 w2)

instance Binary FunctionOrData where
    put_ bh IsFunction = putByte bh 0
    put_ bh IsData     = putByte bh 1
    get bh = do
        h <- getByte bh
        case h of
          0 -> return IsFunction
          1 -> return IsData
          _ -> panic "Binary FunctionOrData"