@@ -4,7 +4,6 @@
44-- |
55-- Module : Data.Binary.Bits.Get
66-- Copyright : (c) Lennart Kolmodin 2010-2011
7−-- (c) Sylvain Henry 2015
87-- License : BSD3-style (see LICENSE)
98--
109-- Maintainer : kolmodin@gmail.com
@@ -56,11 +55,14 @@ module Data.Binary.Bits.Get
5655 -- $bitget
5756
5857 BitGet
58+ , BitOrder(..)
5959 , runBitGet
60+ , getBitOrder
61+ , selectBitOrder
62+ , withBitOrder
6063
6164 -- ** Get bytes
6265 , getBool
63− , getBool#
6466 , getWord8
6567 , getWord16
6668 , getWord32
@@ -97,9 +99,6 @@ module Data.Binary.Bits.Get
9799
98100import Data.Binary.Get as B ( Get, getLazyByteString, isEmpty )
99101import Data.Binary.Get.Internal as B ( get, put, ensureN )
100−import Data.Binary.Bits.BitOrder
101−import Data.Binary.Bits.Internal
102−import Data.Binary.Bits.Alignment
103102
104103import Data.ByteString as B
105104import qualified Data.ByteString.Lazy as L
@@ -115,8 +114,12 @@ import Control.Applicative
115114import Control.Monad (when,foldM_)
116115
117116import Prelude as P
117+
118+#if defined(__GLASGOW_HASKELL__) && !defined(__HADDOCK__)
119+import GHC.Base
118120import GHC.Word
119−import GHC.Base (uncheckedShiftLWord8#, wordToWord8#, Int (..), andWord8#, Word8#, (-#), Int#, xorI#, eqWord8#, TYPE)
121+#endif
122+
120123
121124-- $bitget
122125-- Parse bits using a monad.
@@ -169,6 +172,16 @@ data S = S {-# UNPACK #-} !ByteString -- Input
169172 !BitOrder -- Bit order
170173 deriving (Show)
171174
175+-- | Compute bit offset (equivalent to x `mod` 8 but faster)
176+bit_offset :: Int -> Int
177+bit_offset n = make_mask 3 .&. n
178+{-# INLINE bit_offset #-}
179+
180+-- | Compute byte offset (equivalent to x `div` 8 but faster)
181+byte_offset :: Int -> Int
182+byte_offset n = n `shiftR` 3
183+{-# INLINE byte_offset #-}
184+
172185-- | Increment the current bit offset
173186incS :: Int -> S -> S
174187incS o (S bs n bo) = S (unsafeDrop d bs) n' bo
@@ -177,30 +190,58 @@ incS o (S bs n bo) = S (unsafeDrop d bs) n' bo
177190 !d = byte_offset o'
178191 !n' = bit_offset o'
179192
193+-- | Select the bit ordering
194+selectBitOrderS :: BitOrder -> S -> S
195+selectBitOrderS bo (S bs o _) = S bs o bo
196+
197+-- | make_mask 3 = 00000111
198+make_mask :: (Bits a, Num a) => Int -> a
199+make_mask n = (1 `shiftL` fromIntegral n) - 1
200+{-# SPECIALIZE make_mask :: Int -> Int #-}
201+{-# SPECIALIZE make_mask :: Int -> Word #-}
202+{-# SPECIALIZE make_mask :: Int -> Word8 #-}
203+{-# SPECIALIZE make_mask :: Int -> Word16 #-}
204+{-# SPECIALIZE make_mask :: Int -> Word32 #-}
205+{-# SPECIALIZE make_mask :: Int -> Word64 #-}
206+
207+-- | Keep only the n least-significant bits of the given value
208+mask :: (Bits a, Num a) => Int -> a -> a
209+mask n v = v .&. make_mask n
210+{-# INLINE mask #-}
211+
212+-- | Bit order
213+--
214+-- E.g. two words of 5 bits: ABCDE, VWXYZ
215+-- - BB: ABCDEVWX YZxxxxxx
216+-- - LB: XYZABCDE xxxxxxVW
217+-- - BL: EDCBAZYX WVxxxxxx
218+-- - LL: XWVEDCBA xxxxxxZY
219+data BitOrder = BB | LB | BL | LL deriving (Show)
220+
221+-- | Reverse the @n@ least important bits of the given value
222+reverseBits :: (Num a, FastBits a, Bits a) => Int -> a -> a
223+reverseBits n value = rec value n 0
224+ where
225+ -- rec v i r, where
226+ -- v is orginal value shifted
227+ -- i is the remaining number of bits
228+ -- r is current value
229+ rec 0 0 r = r
230+ rec 0 i r = r `fastShiftL` i
231+ rec v i r = rec (v `fastShiftR` 1) (i-1) ((r `fastShiftL` 1) .|. (v .&. 0x1))
232+
180233-- | Read a single bit
181234readBool :: S -> Bool
182235readBool (S bs o bo) = case bo of
183236 BB -> testBit (unsafeHead bs) (7-o)
184237 BL -> testBit (unsafeHead bs) (7-o)
185− LL -> testBit (unsafeHead bs) o
186238 LB -> testBit (unsafeHead bs) o
187−
188−-- | Read a single bit
189−readBool# :: S -> Int
190−readBool# (S bs (I# o) bo) = case bo of
191− BB -> testBit# (7# -# o)
192− BL -> testBit# (7# -# o)
193− LL -> testBit# o
194− LB -> testBit# o
195− where
196− !(W8# w) = unsafeHead bs
197− testBit# n = I# (((w `andWord8#` (wordToWord8# 1## `uncheckedShiftLWord8#` n)) `eqWord8#` wordToWord8# 0##) `xorI#` 1#)
198−
239+ LL -> testBit (unsafeHead bs) o
199240
200241-- | Extract a range of bits from (ws :: ByteString)
201242--
202243-- Constraint: 8 * (length ws -1 ) < o+n <= 8 * length ws
203−extract :: (Num a, FastBits a) => BitOrder -> ByteString -> Int -> Int -> a
244+extract :: (Num a, Bits a, FastBits a) => BitOrder -> ByteString -> Int -> Int -> a
204245extract bo bs o n
205246 | n == 0 = 0
206247 | B.length bs == 0 = error "Empty ByteString"
@@ -218,21 +259,21 @@ extract bo bs o n
218259
219260 -- shift offset depending on the byte position (0..B.length-1)
220261 off i = case bo of
221− LL -> 8*i - o
222262 LB -> 8*i - o
263+ LL -> 8*i - o
223264 BB -> (B.length bs -1 - i) * 8 - r
224265 BL -> (B.length bs -1 - i) * 8 - r
225266
226267 -- reverse bits if necessary
227268 rev = case bo of
228− LB -> reverseBits n
269+ LL -> reverseBits n
229270 BL -> reverseBits n
230271 BB -> id
231− LL -> id
272+ LB -> id
232273
233274
234275-- | Generic readWord
235−readWord :: (Num a, FastBits a) => Int -> S -> a
276+readWord :: (Num a, Bits a, FastBits a) => Int -> S -> a
236277readWord n (S bs o bo)
237278 | n == 0 = 0
238279 | otherwise = extract bo (unsafeTake nbytes bs) o n
@@ -240,7 +281,7 @@ readWord n (S bs o bo)
240281
241282-- | Check that the number of bits to read is not greater than the first parameter
242283{-# INLINE readWordChecked #-}
243−readWordChecked :: (Num a, FastBits a) => Int -> Int -> S -> a
284+readWordChecked :: (Num a, Bits a, FastBits a) => Int -> Int -> S -> a
244285readWordChecked m n s
245286 | n > m = error $ "Tried to read more than " ++ show m ++ " bits (" ++ show n ++")"
246287 | otherwise = readWord n s
@@ -249,23 +290,22 @@ readWordChecked m n s
249290--
250291-- Examples:
251292-- BB: xxxABCDE FGHIJKLM NOPxxxxx -> ABCDEFGH IJKLMNOP
252−-- LL: LMNOPxxx DEFGHIJK xxxxxABC -> ABCDEFGH IJKLMNOP
293+-- LB: LMNOPxxx DEFGHIJK xxxxxABC -> ABCDEFGH IJKLMNOP
253294-- BL: xxxPONML KJIHGFED CBAxxxxx -> ABCDEFGH IJKLMNOP
254−-- LB: EDCBAxxx MLKJIHGF xxxxxPON -> ABCDEFGH IJKLMNOP
295+-- LL: EDCBAxxx MLKJIHGF xxxxxPON -> ABCDEFGH IJKLMNOP
255296readByteString :: Int -> S -> ByteString
256297readByteString n (S bs o bo) =
257298 let
258− bs' = unsafeTake (n+1) bs
259− bs'' = unsafeTake n bs
260− rev = B.map (reverseBits 8)
299+ bs' = unsafeTake (n+1) bs
300+ rev = B.map (reverseBits 8)
261301 in case (o,bo) of
262− (0,BB) -> bs''
263− (0,LL) -> B.reverse bs''
264− (0,LB) -> rev bs''
265− (0,BL) -> rev . B.reverse $ bs''
266− (_,LL) -> readByteString n (S (B.reverse bs') (8-o) BB)
267− (_,BL) -> rev . B.reverse $ readByteString n (S bs' o BB)
268− (_,LB) -> rev . B.reverse $ readByteString n (S bs' o LL)
302+ (0,BB) -> unsafeTake n bs
303+ (0,LB) -> B.reverse (unsafeTake n bs)
304+ (0,BL) -> rev (unsafeTake n bs)
305+ (0,LL) -> rev (B.reverse (unsafeTake n bs))
306+ (_,BL) -> rev (readByteString n (S (B.reverse bs') o LB))
307+ (_,LL) -> rev (readByteString n (S (B.reverse bs') o BB))
308+ (_,LB) -> readByteString n (S (B.reverse bs') o BB)
269309 (_,BB) -> unsafePerformIO $ do
270310 let len = n+1
271311 ptr <- mallocBytes len
@@ -287,6 +327,7 @@ newtype BitGet a = B { runState :: S -> Get (S,a) }
287327
288328instance Monad BitGet where
289329 return x = B $ \s -> return (s,x)
330+ fail str = B $ \s -> putBackState s >> fail str
290331 (B f) >>= g = B $ \s -> do (s',a) <- f s
291332 runState (g a) s'
292333
@@ -297,29 +338,6 @@ instance Applicative BitGet where
297338 pure x = return x
298339 fm <*> m = fm >>= \f -> m >>= \v -> return (f v)
299340
300−instance BitOrderable BitGet where
301− setBitOrder bo = do
302− (S bs o _) <- getState
303− putState (S bs o bo)
304−
305− getBitOrder = do
306− (S _ _ bo) <- getState
307− return bo
308−
309−instance Alignable BitGet where
310− -- | Skip the given number of bits
311− skipBits n = do
312− ensureBits n
313− withState (incS n)
314−
315− -- | Skip bits if necessary to align to the next byte
316− alignByte = do
317− (S _ o _) <- getState
318− when (o /= 0) $
319− skipBits (8-o)
320−
321−
322−
323341-- | Run a 'BitGet' within the Binary packages 'Get' monad. If a byte has
324342-- been partially consumed it will be discarded once 'runBitGet' is finished.
325343runBitGet :: BitGet a -> Get a
@@ -354,6 +372,13 @@ withState f = do
354372 s <- getState
355373 putState $! f s
356374
375+-- | Get the bit ordering
376+getBitOrder :: BitGet BitOrder
377+getBitOrder = do
378+ (S _ _ bo) <- getState
379+ return bo
380+
381+
357382-- | Make sure there are at least @n@ bits.
358383ensureBits :: Int -> BitGet ()
359384ensureBits n = do
@@ -367,6 +392,33 @@ ensureBits n = do
367392 put B.empty
368393 return (S (bs`append`bs') o bo, ())
369394
395+-- | Skip the given number of bits
396+skipBits :: Int -> BitGet ()
397+skipBits n = do
398+ ensureBits n
399+ withState (incS n)
400+
401+-- | Skip bits if necessary to align to the next byte
402+alignByte :: BitGet ()
403+alignByte = do
404+ (S _ o _) <- getState
405+ when (o /= 0) $
406+ skipBits (8-o)
407+
408+-- | Select the bit ordering
409+selectBitOrder :: BitOrder -> BitGet ()
410+selectBitOrder = withState . selectBitOrderS
411+
412+withBitOrder :: BitOrder -> BitGet a -> BitGet a
413+withBitOrder bo f = do
414+ bo' <- getBitOrder
415+ selectBitOrder bo
416+ r <- f
417+ selectBitOrder bo'
418+ return r
419+
420+
421+
370422-- | Test whether all input has been consumed, i.e. there are no remaining
371423-- undecoded bytes.
372424isEmpty :: BitGet Bool
@@ -378,10 +430,6 @@ isEmpty = B $ \ (S bs o bo) -> if B.null bs
378430getBool :: BitGet Bool
379431getBool = block bool
380432
381−-- | Get 1 bit as a 'Bool'.
382−getBool# :: BitGet Int
383−getBool# = block bool#
384−
385433-- | Get @n@ bits as a 'Word8'. @n@ must be within @[0..8]@.
386434getWord8 :: Int -> BitGet Word8
387435getWord8 n = block (word8 n)
@@ -457,10 +505,6 @@ block (Block i p) = do
457505bool :: Block Bool
458506bool = Block 1 readBool
459507
460−-- | Read a 1 bit 'Bool'.
461−bool# :: Block Int
462−bool# = Block 1 readBool#
463−
464508-- | Read @n@ bits as a 'Word8'. @n@ must be within @[0..8]@.
465509word8 :: Int -> Block Word8
466510word8 n = Block n (readWordChecked 8 n)
@@ -494,3 +538,84 @@ byteString :: Int -> Block ByteString
494538byteString n | n > 0 = Block (n*8) (readByteString n)
495539 | otherwise = Block 0 (\_ -> B.empty)
496540
541+
542+---------------------------------------------------------------------
543+-- Unchecked shifts, from the "binary" package
544+
545+-- | Class for types supporting fast bit shifting
546+class FastBits a where
547+ fastShiftR :: a -> Int -> a
548+ fastShiftL :: a -> Int -> a
549+
550+ {-# INLINE fastShift #-}
551+ fastShift :: a -> Int -> a
552+ fastShift x n
553+ | n > 0 = fastShiftL x n
554+ | n < 0 = fastShiftR x (negate n)
555+ | otherwise = x
556+
557+instance FastBits Word8 where
558+ fastShiftR = shiftr_w8
559+ fastShiftL = shiftl_w8
560+
561+instance FastBits Word16 where
562+ fastShiftR = shiftr_w16
563+ fastShiftL = shiftl_w16
564+
565+instance FastBits Word32 where
566+ fastShiftR = shiftr_w32
567+ fastShiftL = shiftl_w32
568+
569+instance FastBits Word64 where
570+ fastShiftR = shiftr_w64
571+ fastShiftL = shiftl_w64
572+
573+
574+shiftl_w8 :: Word8 -> Int -> Word8
575+shiftl_w16 :: Word16 -> Int -> Word16
576+shiftl_w32 :: Word32 -> Int -> Word32
577+shiftl_w64 :: Word64 -> Int -> Word64
578+
579+shiftr_w8 :: Word8 -> Int -> Word8
580+shiftr_w16 :: Word16 -> Int -> Word16
581+shiftr_w32 :: Word32 -> Int -> Word32
582+shiftr_w64 :: Word64 -> Int -> Word64
583+
584+#if defined(__GLASGOW_HASKELL__) && !defined(__HADDOCK__)
585+shiftl_w8 (W8# w) (I# i) = W8# (w `uncheckedShiftL#` i)
586+shiftl_w16 (W16# w) (I# i) = W16# (w `uncheckedShiftL#` i)
587+shiftl_w32 (W32# w) (I# i) = W32# (w `uncheckedShiftL#` i)
588+
589+shiftr_w8 (W8# w) (I# i) = W8# (w `uncheckedShiftRL#` i)
590+shiftr_w16 (W16# w) (I# i) = W16# (w `uncheckedShiftRL#` i)
591+shiftr_w32 (W32# w) (I# i) = W32# (w `uncheckedShiftRL#` i)
592+
593+
594+#if WORD_SIZE_IN_BITS < 64
595+shiftl_w64 (W64# w) (I# i) = W64# (w `uncheckedShiftL64#` i)
596+shiftr_w64 (W64# w) (I# i) = W64# (w `uncheckedShiftRL64#` i)
597+
598+#if __GLASGOW_HASKELL__ <= 606
599+-- Exported by GHC.Word in GHC 6.8 and higher
600+foreign import ccall unsafe "stg_uncheckedShiftL64"
601+ uncheckedShiftL64# :: Word64# -> Int# -> Word64#
602+foreign import ccall unsafe "stg_uncheckedShiftRL64"
603+ uncheckedShiftRL64# :: Word64# -> Int# -> Word64#
604+#endif
605+
606+#else
607+shiftl_w64 (W64# w) (I# i) = W64# (w `uncheckedShiftL#` i)
608+shiftr_w64 (W64# w) (I# i) = W64# (w `uncheckedShiftRL#` i)
609+#endif
610+
611+#else
612+shiftl_w8 = shiftL
613+shiftl_w16 = shiftL
614+shiftl_w32 = shiftL
615+shiftl_w64 = shiftL
616+
617+shiftr_w8 = shiftR
618+shiftr_w16 = shiftR
619+shiftr_w32 = shiftR
620+shiftr_w64 = shiftR
621+#endif