Add splitUFM to UniqFM (used in a forthcoming patch)

splitUFM :: Uniquable key => UniqFM elt -> key -> (UniqFM elt, Maybe elt, UniqFM elt)
   -- Splits a UFM into things less than, equal to, and greater than the key

diff --git a/compiler/utils/UniqFM.lhs b/compiler/utils/UniqFM.lhs
index cc2d066..9a3d606 100644 (file)
--- a/compiler/utils/UniqFM.lhs
+++ b/compiler/utils/UniqFM.lhs
@@ -48,7 +48,7 @@ module UniqFM (
        isNullUFM,
        lookupUFM, lookupUFM_Directly,
        lookupWithDefaultUFM, lookupWithDefaultUFM_Directly,
-       eltsUFM, keysUFM,
+       eltsUFM, keysUFM, splitUFM,
        ufmToList 
     ) where
 
@@ -130,6 +130,8 @@ hashUFM             :: UniqFM elt -> Int
 elemUFM                :: Uniquable key => key -> UniqFM elt -> Bool
 elemUFM_Directly:: Unique -> UniqFM elt -> Bool
 
+splitUFM        :: Uniquable key => UniqFM elt -> key -> (UniqFM elt, Maybe elt, UniqFM elt)
+                  -- Splits a UFM into things less than, equal to, and greater than the key
 lookupUFM      :: Uniquable key => UniqFM elt -> key -> Maybe elt
 lookupUFM_Directly  -- when you've got the Unique already
                :: UniqFM elt -> Unique -> Maybe elt
@@ -137,7 +139,6 @@ lookupWithDefaultUFM
                :: Uniquable key => UniqFM elt -> elt -> key -> elt
 lookupWithDefaultUFM_Directly
                :: UniqFM elt -> elt -> Unique -> elt
-
 keysUFM                :: UniqFM elt -> [Unique]       -- Get the keys
 eltsUFM                :: UniqFM elt -> [elt]
 ufmToList      :: UniqFM elt -> [(Unique, elt)]
@@ -358,7 +359,7 @@ plusUFM_C f fm1 fm2 = mix_trees fm1 fm2
                        (mix_trees t2 t2')
                -- Now the 4 different other ways; all like this:
                --
-               -- Given j >^ j' (and, say,  j > j')
+ -- Given j >^ j' (and, say,  j > j')
                --
                --        j             j'                       j
                --       / \    +      / \      ==>             / \
@@ -608,6 +609,25 @@ lookUp fm i            = lookup_tree fm
          | otherwise   = lookup_tree t2
 
        lookup_tree EmptyUFM = panic "lookup Failed"
+
+-------------------
+splitUFM fm key = split fm (getKeyFastInt (getUnique key))
+
+split :: UniqFM a -> FastInt -> (UniqFM a, Maybe a, UniqFM a)
+-- Splits a UFM into things less than, equal to, and greater than the key
+split EmptyUFM _ = (EmptyUFM, Nothing, EmptyUFM)
+split fm i       = go fm
+  where
+    go (LeafUFM j b) | i <# j    = (EmptyUFM,    Nothing, LeafUFM j b)
+                            | i ># j    = (LeafUFM j b, Nothing, EmptyUFM)
+                     | otherwise = (EmptyUFM,    Just b,  EmptyUFM)
+                            
+    go (NodeUFM j p t1 t2) 
+      | j ># i 
+      , (lt, eq, gt) <- go t1 = (lt, eq, mkSLNodeUFM (NodeUFMData j p) gt t2)
+      | (lt, eq, gt) <- go t2 = (mkLSNodeUFM (NodeUFMData j p) t1 lt, eq, gt)
+
+    go EmptyUFM = panic "splitUFM failed"
 \end{code}
 
 folds are *wonderful* things.