Partially revert #670

Bodigrim found a bug in the new `Ord` instance in #783. Put the
old one one back.

Fixes #783.

Author: treeowl

containers/src/Data/IntSet/Internal.hs

@@ -1215,156 +1215,8 @@ nequal _   _   = True
 --------------------------------------------------------------------}
 
 instance Ord IntSet where
-  compare Nil Nil = EQ
-  compare Nil _ = LT
-  compare _ Nil = GT
-  compare t1@(Tip _ _) t2@(Tip _ _)
-    = orderingOf $ relateTipTip t1 t2
-  compare xs ys
-    | (xsNeg, xsNonNeg) <- splitSign xs
-    , (ysNeg, ysNonNeg) <- splitSign ys
-    = case relate xsNeg ysNeg of
-       Less -> LT
-       Prefix -> if null xsNonNeg then LT else GT
-       Equals -> orderingOf (relate xsNonNeg ysNonNeg)
-       FlipPrefix -> if null ysNonNeg then GT else LT
-       Greater -> GT
-
--- | detailed outcome of lexicographic comparison of lists.
--- w.r.t. Ordering, there are two extra cases,
--- since (++) is not monotonic w.r.t. lex. order on lists
--- (which is used by definition):
--- consider comparison of  (Bin [0,3,4] [ 6] ) to  (Bin [0,3] [7] )
--- where [0,3,4] > [0,3]  but [0,3,4,6] < [0,3,7].
-
-data Relation
-  = Less  -- ^ holds for [0,3,4] [0,3,5,1]
-  | Prefix -- ^ holds for [0,3,4] [0,3,4,5]
-  | Equals -- ^  holds for [0,3,4] [0,3,4]
-  | FlipPrefix -- ^ holds for [0,3,4] [0,3]
-  | Greater -- ^ holds for [0,3,4] [0,2,5]
-  deriving (Show, Eq)
-   
-orderingOf :: Relation -> Ordering
-{-# INLINE orderingOf #-}
-orderingOf r = case r of
-  Less -> LT
-  Prefix -> LT
-  Equals -> EQ
-  FlipPrefix -> GT
-  Greater -> GT
-
--- | precondition: each argument is non-mixed
-relate :: IntSet -> IntSet -> Relation
-relate Nil Nil = Equals
-relate Nil _t2 = Prefix
-relate _t1 Nil = FlipPrefix
-relate t1@Tip{} t2@Tip{} = relateTipTip t1 t2
-relate t1@(Bin _p1 m1 l1 r1) t2@(Bin _p2 m2 l2 r2)
-  | succUpperbound t1 <= lowerbound t2 = Less
-  | lowerbound t1 >= succUpperbound t2 = Greater
-  | otherwise = case compare (natFromInt m1) (natFromInt m2) of
-      GT -> combine_left (relate l1 t2)
-      EQ -> combine (relate l1 l2) (relate r1 r2)
-      LT -> combine_right (relate t1 l2)
-relate t1@(Bin _p1 m1 l1 _r1) t2@(Tip p2 _bm2)
-  | succUpperbound t1 <= lowerbound t2 = Less
-  | lowerbound t1 >= succUpperbound t2 = Greater
-  | 0 == (m1 .&. p2) = combine_left (relate l1 t2)
-  | otherwise = Less
-relate t1@(Tip p1 _bm1) t2@(Bin _p2 m2 l2 _r2)
-  | succUpperbound t1 <= lowerbound t2 = Less
-  | lowerbound t1 >= succUpperbound t2 = Greater
-  | 0 == (p1 .&. m2) = combine_right (relate t1 l2)
-  | otherwise = Greater
-
-relateTipTip :: IntSet -> IntSet -> Relation
-{-# INLINE relateTipTip #-}
-relateTipTip (Tip p1 bm1) (Tip p2 bm2) = case compare p1 p2 of
-  LT -> Less
-  EQ -> relateBM bm1 bm2
-  GT -> Greater
-relateTipTip _ _ = error "relateTipTip"
-
-relateBM :: BitMap -> BitMap -> Relation
-{-# inline relateBM #-}
-relateBM w1 w2 | w1 == w2 = Equals
-relateBM w1 w2 =
-  let delta = xor w1 w2
-      lowest_diff_mask = delta .&. complement (delta-1)
-      prefix = (complement lowest_diff_mask + 1)
-            .&. (complement lowest_diff_mask)
-  in  if 0 == lowest_diff_mask .&. w1
-      then if 0 == w1 .&. prefix
-           then Prefix else Greater
-      else if 0 == w2 .&. prefix
-           then FlipPrefix else Less
-
--- | This function has the property
--- relate t1@(Bin p m l1 r1) t2@(Bin p m l2 r2) = combine (relate l1 l2) (relate r1 r2)
--- It is important that `combine` is lazy in the second argument (achieved by inlining)
-combine :: Relation -> Relation -> Relation
-{-# inline combine #-}
-combine r eq = case r of
-      Less -> Less
-      Prefix -> Greater
-      Equals -> eq
-      FlipPrefix -> Less
-      Greater -> Greater
-
--- | This function has the property
--- relate t1@(Bin p1 m1 l1 r1) t2 = combine_left (relate l1 t2)
--- under the precondition that the range of l1 contains the range of t2,
--- and r1 is non-empty
-combine_left :: Relation -> Relation
-{-# inline combine_left #-}
-combine_left r = case r of
-      Less -> Less
-      Prefix -> Greater
-      Equals -> FlipPrefix
-      FlipPrefix -> FlipPrefix
-      Greater -> Greater
-
--- | This function has the property
--- relate t1 t2@(Bin p2 m2 l2 r2) = combine_right (relate t1 l2)
--- under the precondition that the range of t1 is included in the range of l2,
--- and r2 is non-empty
-combine_right :: Relation -> Relation
-{-# inline combine_right #-}
-combine_right r = case r of
-      Less -> Less
-      Prefix -> Prefix
-      Equals -> Prefix
-      FlipPrefix -> Less
-      Greater -> Greater
-
--- | shall only be applied to non-mixed non-Nil trees
-lowerbound :: IntSet -> Int
-{-# INLINE lowerbound #-}
-lowerbound Nil = error "lowerbound: Nil"
-lowerbound (Tip p _) = p
-lowerbound (Bin p _ _ _) = p
-
--- | this is one more than the actual upper bound (to save one operation)
--- shall only be applied to non-mixed non-Nil trees
-succUpperbound :: IntSet -> Int
-{-# INLINE succUpperbound #-}
-succUpperbound Nil = error "succUpperbound: Nil"
-succUpperbound (Tip p _) = p + wordSize 
-succUpperbound (Bin p m _ _) = p + shiftR m 1
-
--- | split a set into subsets of negative and non-negative elements
-splitSign :: IntSet -> (IntSet,IntSet)
-{-# INLINE splitSign #-}
-splitSign t@(Tip kx _)
-  | kx >= 0 = (Nil, t)
-  | otherwise = (t, Nil)
-splitSign t@(Bin p m l r)
-  -- m < 0 is the usual way to find out if we have positives and negatives (see findMax)
-  | m < 0 = (r, l)
-  | p < 0 = (t, Nil)
-  | otherwise = (Nil, t)
-splitSign Nil = (Nil, Nil)
+    compare s1 s2 = compare (toAscList s1) (toAscList s2)
+    -- tentative implementation. See if more efficient exists.
 
 {--------------------------------------------------------------------
   Show