use actual upper bound, not its successor, as this might overflow

Author: Johannes Waldmann

containers/src/Data/IntSet/Internal.hs

@@ -1261,20 +1261,20 @@ relate Nil t2 = Prefix
 relate t1 Nil = FlipPrefix
 relate t1@(Tip p1 bm1) t2@(Tip p2 bm2) = 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
+  | upperbound t1 < lowerbound t2 = Less
+  | lowerbound t1 > upperbound 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 _)
-  | succUpperbound t1 <= lowerbound t2 = Less
-  | lowerbound t1 >= succUpperbound t2 = Greater
+  | upperbound t1 < lowerbound t2 = Less
+  | lowerbound t1 > upperbound t2 = Greater
   | 0 == (m1 .&. p2) = combine_left (relate l1 t2)
   | otherwise = Less
 relate t1@(Tip p1 _) t2@(Bin p2 m2 l2 r2)
-  | succUpperbound t1 <= lowerbound t2 = Less
-  | lowerbound t1 >= succUpperbound t2 = Greater
+  | upperbound t1 < lowerbound t2 = Less
+  | lowerbound t1 > upperbound t2 = Greater
   | 0 == (p1 .&. m2) = combine_right (relate t1 l2)
   | otherwise = Greater
 
@@ -1343,12 +1343,11 @@ lowerbound :: IntSet -> Int
 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 (Tip p _) = p + wordSize 
-succUpperbound (Bin p m _ _) = p + shiftL m 1
+-- | shall only be applied to non-mixed non-Nil trees
+upperbound :: IntSet -> Int
+{-# INLINE upperbound #-}
+upperbound (Tip p _) = p + (wordSize - 1)
+upperbound (Bin p m _ _) = p + (shiftL m 1 - 1)
 
 -- | split a set into subsets of negative and non-negative elements
 splitSign :: IntSet -> (IntSet,IntSet)