-----------------------------------------------------------------------------
module Data.Bits (
- -- * The 'Bits' class
Bits(
(.&.), (.|.), xor, -- :: a -> a -> a
complement, -- :: a -> a
complementBit, -- :: a -> Int -> a
testBit, -- :: a -> Int -> Bool
bitSize, -- :: a -> Int
- isSigned -- :: a -> Bool
- ),
-
- -- * Shifts and rotates
-
- -- $shifts
- shiftL, shiftR, -- :: Bits a => a -> Int -> a
- rotateL, rotateR, -- :: Bits a => a -> Int -> a
+ isSigned, -- :: a -> Bool
+ shiftL, shiftR, -- :: a -> Int -> a
+ rotateL, rotateR -- :: a -> Int -> a
+ )
-- instance Bits Int
-- instance Bits Integer
{-| Reverse all the bits in the argument -}
complement :: a -> a
- {-| Signed shift the argument left by the specified number of bits.
- Right shifts are specified by giving a negative value. -}
+ {-| Shift the argument left by the specified number of bits.
+ Right shifts (signed) are specified by giving a negative value.
+
+ An instance can define either this unified 'shift' or 'shiftL' and
+ 'shiftR', depending on which is more convenient for the type in
+ question. -}
shift :: a -> Int -> a
- {-| Signed rotate the argument left by the specified number of bits.
+ x `shift` i | i<0 = x `shiftR` (-i)
+ | i==0 = x
+ | i>0 = x `shiftL` i
+
+ {-| Rotate the argument left by the specified number of bits.
Right rotates are specified by giving a negative value.
'rotate' is well defined only if 'bitSize' is also well defined
('bitSize' is undefined for 'Integer', for example).
- -}
+
+ An instance can define either this unified 'rotate' or 'rotateL' and
+ 'rotateR', depending on which is more convenient for the type in
+ question. -}
rotate :: a -> Int -> a
+ x `rotate` i | i<0 = x `rotateR` (-i)
+ | i==0 = x
+ | i>0 = x `rotateL` i
+
+ {-
+ -- Rotation can be implemented in terms of two shifts, but care is
+ -- needed for negative values. This suggested implementation assumes
+ -- 2's-complement arithmetic. It is commented out because it would
+ -- require an extra context (Ord a) on the signature of 'rotate'.
+ x `rotate` i | i<0 && isSigned x && x<0
+ = let left = i+bitSize x in
+ ((x `shift` i) .&. complement ((-1) `shift` left))
+ .|. (x `shift` left)
+ | i<0 = (x `shift` i) .|. (x `shift` (i+bitSize x))
+ | i==0 = x
+ | i>0 = (x `shift` i) .|. (x `shift` (i-bitSize x))
+ -}
+
-- | @bit i@ is a value with the @i@th bit set
bit :: Int -> a
value of the argument is ignored -}
isSigned :: a -> Bool
- bit i = 1 `shift` i
+ bit i = 1 `shiftL` i
x `setBit` i = x .|. bit i
x `clearBit` i = x .&. complement (bit i)
x `complementBit` i = x `xor` bit i
x `testBit` i = (x .&. bit i) /= 0
--- $shifts
--- These functions might sometimes be more convenient than the unified
--- versions 'shift' and 'rotate'.
+ {-| Shift the argument left by the specified number of bits
+ (which must be non-negative).
+
+ An instance can define either this and 'shiftR' or the unified
+ 'shift', depending on which is more convenient for the type in
+ question. -}
+ shiftL :: a -> Int -> a
+ x `shiftL` i = x `shift` i
+
+ {-| Shift the argument right (signed) by the specified number of bits
+ (which must be non-negative).
+
+ An instance can define either this and 'shiftL' or the unified
+ 'shift', depending on which is more convenient for the type in
+ question. -}
+ shiftR :: a -> Int -> a
+ x `shiftR` i = x `shift` (-i)
-shiftL, shiftR :: Bits a => a -> Int -> a
-rotateL, rotateR :: Bits a => a -> Int -> a
-x `shiftL` i = x `shift` i
-x `shiftR` i = x `shift` (-i)
-x `rotateL` i = x `rotate` i
-x `rotateR` i = x `rotate` (-i)
+ {-| Rotate the argument left by the specified number of bits
+ (which must be non-negative).
+
+ An instance can define either this and 'rotateR' or the unified
+ 'rotate', depending on which is more convenient for the type in
+ question. -}
+ rotateL :: a -> Int -> a
+ x `rotateL` i = x `rotate` i
+
+ {-| Rotate the argument right by the specified number of bits
+ (which must be non-negative).
+
+ An instance can define either this and 'rotateL' or the unified
+ 'rotate', depending on which is more convenient for the type in
+ question. -}
+ rotateR :: a -> Int -> a
+ x `rotateR` i = x `rotate` (-i)
#ifdef __GLASGOW_HASKELL__
instance Bits Int where
bitSize _ = error "Bits.bitSize(Integer)"
isSigned _ = True
#endif
+
+#ifdef __NHC__
+instance Bits Int where
+ (.&.) = nhc_primIntAnd
+ (.|.) = nhc_primIntOr
+ xor = nhc_primIntXor
+ complement = nhc_primIntCompl
+ shiftL = nhc_primIntLsh
+ shiftR = nhc_primIntRsh
+ bitSize _ = 32
+ isSigned _ = True
+
+foreign import ccall nhc_primIntAnd :: Int -> Int -> Int
+foreign import ccall nhc_primIntOr :: Int -> Int -> Int
+foreign import ccall nhc_primIntXor :: Int -> Int -> Int
+foreign import ccall nhc_primIntLsh :: Int -> Int -> Int
+foreign import ccall nhc_primIntRsh :: Int -> Int -> Int
+foreign import ccall nhc_primIntCompl :: Int -> Int
+
+instance Bits Integer where
+ -- (.&.) a b = undefined
+ -- (.|.) a b = undefined
+ -- xor a b = undefined
+ complement a = (-a)
+ x `shift` i | i<0 = x `div` (2^(-i))
+ | i==0 = x
+ | i>0 = x * (2^i)
+ x `rotate` i = x `shift` i -- an Integer never wraps
+ bitSize _ = error "Data.Bits: bitSize :: Integer -> Int"
+ isSigned _ = True
+
+#endif
+