Introduce size-aware 'unsafeInsertWithInternal' function

Author: rockbmb

Data/HashMap/Base.hs

@@ -712,7 +712,10 @@ insertWith f k0 v0 m0 = go h0 k0 v0 0 m0
 -- | /O(log n)/ Associate the value with the key in this map.  If
 -- this map previously contained a mapping for the key, the old value
 -- is replaced by the result of applying the given function to the new
--- and old value.  Example:
+-- and old value. Returns a tuple where the first component is the
+-- difference in size between the old and new hashmaps, and the second
+-- is the new hashmap.
+-- Example:
 --
 -- > insertWithInternal f k v map
 -- >   where f new old = new + old
@@ -789,6 +792,48 @@ unsafeInsertWith f k0 v0 m0 = runST (go h0 k0 v0 0 m0)
         | otherwise = go h k x s $ BitmapIndexed (mask hy s) (A.singleton t)
 {-# INLINABLE unsafeInsertWith #-}
 
+-- | In-place update version of insertWithInternal
+unsafeInsertWithInternal :: forall k v. (Eq k, Hashable k)
+                 => (v -> v -> v) -> k -> v -> HashMap k v
+                 -> (Int, HashMap k v)
+unsafeInsertWithInternal f k0 v0 m0 = runST (go h0 k0 v0 0 m0)
+  where
+    h0 = hash k0
+    go :: Hash -> k -> v -> Shift -> HashMap k v -> ST s (Int, HashMap k v)
+    go !h !k x !_ Empty = return $! (1, Leaf h (L k x))
+    go h k x s (Leaf hy l@(L ky y))
+        | hy == h = if ky == k
+                    then return $! (0, Leaf h (L k (f x y)))
+                    else return $! (1, collision h l (L k x))
+        | otherwise = do
+              twoHm <- two s h k x hy ky y
+              return $! (1, twoHm)
+    go h k x s t@(BitmapIndexed b ary)
+        | b .&. m == 0 = do
+            ary' <- A.insertM ary i $! Leaf h (L k x)
+            return $! (1, bitmapIndexedOrFull (b .|. m) ary')
+        | otherwise = do
+            st <- A.indexM ary i
+            (sz, st') <- go h k x (s+bitsPerSubkey) st
+            A.unsafeUpdateM ary i st'
+            return (sz, t)
+      where m = mask h s
+            i = sparseIndex b m
+    go h k x s t@(Full ary) = do
+        st <- A.indexM ary i
+        (sz, st') <- go h k x (s+bitsPerSubkey) st
+        A.unsafeUpdateM ary i st'
+        return (sz, t)
+      where i = index h s
+    go h k x s t@(Collision hy v)
+        | h == hy   =
+            let !start = A.length v
+                !newV = updateOrSnocWith const k x v
+                !end = A.length newV
+            in return $! (end - start, Collision h newV)
+        | otherwise = go h k x s $ BitmapIndexed (mask hy s) (A.singleton t)
+{-# INLINABLE unsafeInsertWithInternal #-}
+
 -- | /O(log n)/ Remove the mapping for the specified key from this map
 -- if present.
 delete :: (Eq k, Hashable k) => k -> HashMap k v -> HashMap k v