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%
% (c) The GRASP Project, Glasgow University, 1994-1998
%
\section[BitSet]{An implementation of very small sets}
Bit sets are a fast implementation of sets of integers ranging from 0
to one less than the number of bits in a machine word (typically 31).
If any element exceeds the maximum value for a particular machine
architecture, the results of these operations are undefined. You have
been warned. If you put any safety checks in this code, I will have
to kill you.
Note: the Yale Haskell implementation won't provide a full 32 bits.
However, if you can handle the performance loss, you could change to
Integer and get virtually unlimited sets.
\begin{code}
module BitSet (
BitSet, -- abstract type
mkBS, listBS, emptyBS, unitBS,
unionBS, minusBS, intBS
) where
#include "HsVersions.h"
#ifdef __GLASGOW_HASKELL__
import GLAEXTS
-- nothing to import
#elif defined(__YALE_HASKELL__)
{-hide import from mkdependHS-}
import
LogOpPrims
#else
{-hide import from mkdependHS-}
import
Word
#endif
#ifdef __GLASGOW_HASKELL__
data BitSet = MkBS Word#
emptyBS :: BitSet
emptyBS = MkBS (int2Word# 0#)
mkBS :: [Int] -> BitSet
mkBS xs = foldr (unionBS . unitBS) emptyBS xs
unitBS :: Int -> BitSet
unitBS x = case x of
#if __GLASGOW_HASKELL__ >= 503
I# i# -> MkBS ((int2Word# 1#) `uncheckedShiftL#` i#)
#else
I# i# -> MkBS ((int2Word# 1#) `shiftL#` i#)
#endif
unionBS :: BitSet -> BitSet -> BitSet
unionBS (MkBS x#) (MkBS y#) = MkBS (x# `or#` y#)
minusBS :: BitSet -> BitSet -> BitSet
minusBS (MkBS x#) (MkBS y#) = MkBS (x# `and#` (not# y#))
#if 0
-- not used in GHC
isEmptyBS :: BitSet -> Bool
isEmptyBS (MkBS s#)
= case word2Int# s# of
0# -> True
_ -> False
intersectBS :: BitSet -> BitSet -> BitSet
intersectBS (MkBS x#) (MkBS y#) = MkBS (x# `and#` y#)
elementBS :: Int -> BitSet -> Bool
elementBS x (MkBS s#) = case x of
I# i# -> case word2Int# (((int2Word# 1#) `shiftL#` i#) `and#` s#) of
0# -> False
_ -> True
#endif
listBS :: BitSet -> [Int]
listBS s = listify s 0
where listify (MkBS s#) n =
case word2Int# s# of
0# -> []
_ -> let s' = (MkBS (s# `shiftr` 1#))
more = listify s' (n + 1)
in case word2Int# (s# `and#` (int2Word# 1#)) of
0# -> more
_ -> n : more
#if __GLASGOW_HASKELL__ >= 503
shiftr x y = uncheckedShiftRL# x y
#else
shiftr x y = shiftRL# x y
#endif
-- intBS is a bit naughty.
intBS :: BitSet -> Int
intBS (MkBS w#) = I# (word2Int# w#)
#elif defined(__YALE_HASKELL__)
data BitSet = MkBS Int
emptyBS :: BitSet
emptyBS = MkBS 0
mkBS :: [Int] -> BitSet
mkBS xs = foldr (unionBS . unitBS) emptyBS xs
unitBS :: Int -> BitSet
unitBS x = MkBS (1 `ashInt` x)
unionBS :: BitSet -> BitSet -> BitSet
unionBS (MkBS x) (MkBS y) = MkBS (x `logiorInt` y)
#if 0
-- not used in GHC
isEmptyBS :: BitSet -> Bool
isEmptyBS (MkBS s)
= case s of
0 -> True
_ -> False
intersectBS :: BitSet -> BitSet -> BitSet
intersectBS (MkBS x) (MkBS y) = MkBS (x `logandInt` y)
elementBS :: Int -> BitSet -> Bool
elementBS x (MkBS s)
= case logbitpInt x s of
0 -> False
_ -> True
#endif
minusBS :: BitSet -> BitSet -> BitSet
minusBS (MkBS x) (MkBS y) = MkBS (x `logandc2Int` y)
-- rewritten to avoid right shifts (which would give nonsense on negative
-- values.
listBS :: BitSet -> [Int]
listBS (MkBS s) = listify s 0 1
where listify s n m =
case s of
0 -> []
_ -> let n' = n+1; m' = m+m in
case logbitpInt s m of
0 -> listify s n' m'
_ -> n : listify (s `logandc2Int` m) n' m'
#else /* HBC, perhaps? */
data BitSet = MkBS Word
emptyBS :: BitSet
emptyBS = MkBS 0
mkBS :: [Int] -> BitSet
mkBS xs = foldr (unionBS . unitBS) emptyBS xs
unitBS :: Int -> BitSet
unitBS x = MkBS (1 `bitLsh` x)
unionBS :: BitSet -> BitSet -> BitSet
unionBS (MkBS x) (MkBS y) = MkBS (x `bitOr` y)
#if 0
-- not used in GHC
isEmptyBS :: BitSet -> Bool
isEmptyBS (MkBS s)
= case s of
0 -> True
_ -> False
intersectBS :: BitSet -> BitSet -> BitSet
intersectBS (MkBS x) (MkBS y) = MkBS (x `bitAnd` y)
elementBS :: Int -> BitSet -> Bool
elementBS x (MkBS s)
= case (1 `bitLsh` x) `bitAnd` s of
0 -> False
_ -> True
#endif
minusBS :: BitSet -> BitSet -> BitSet
minusBS (MkBS x) (MkBS y) = MkBS (x `bitAnd` (bitCompl y))
listBS :: BitSet -> [Int]
listBS (MkBS s) = listify s 0
where listify s n =
case s of
0 -> []
_ -> let s' = s `bitRsh` 1
more = listify s' (n + 1)
in case (s `bitAnd` 1) of
0 -> more
_ -> n : more
#endif
\end{code}
|
