diff --git a/src/kcas/kcas.ml b/src/kcas/kcas.ml
index 799e12cc..fb163659 100644
--- a/src/kcas/kcas.ml
+++ b/src/kcas/kcas.ml
@@ -685,83 +685,100 @@ module Xt = struct
     (* Fenceless is safe as we are accessing a private location. *)
     xt_r.mode == `Obstruction_free && 0 <= loc.id
 
-  let[@inline] update_new loc f xt lt gt =
-    (* Fenceless is safe inside transactions as each log update has a fence. *)
+  type (_, _) up =
+    | Get : (unit, 'a) up
+    | Fetch_and_add : (int, int) up
+    | Exchange : ('a, 'a) up
+    | Compare_and_swap : ('a * 'a, 'a) up
+    | Fn : ('a -> 'a, 'a) up
+
+  let[@inline] update :
+      type c a.
+      'x t -> a loc -> c -> (c, a) up -> tree -> tree -> a state -> a -> a =
+   fun xt loc c up lt gt state before ->
+    let after =
+      match up with
+      | Get -> before
+      | Fetch_and_add -> before + c
+      | Exchange -> c
+      | Compare_and_swap -> if fst c == before then snd c else before
+      | Fn -> begin
+          try c before
+          with exn ->
+            tree_as_ref xt := T (Node { loc; state; lt; gt; awaiters = [] });
+            raise exn
+        end
+    in
+    let state =
+      if before == after && is_obstruction_free xt loc then state
+      else { before; after; which = W xt; awaiters = [] }
+    in
+    tree_as_ref xt := T (Node { loc; state; lt; gt; awaiters = [] });
+    before
+
+  let[@inline] update_new :
+      type c a. 'x t -> a loc -> c -> (c, a) up -> tree -> tree -> a =
+   fun xt loc c up lt gt ->
     let state = fenceless_get (as_atomic loc) in
     let before = eval state in
-    match f before with
-    | after ->
-        let state =
-          if before == after && is_obstruction_free xt loc then state
-          else { before; after; which = W xt; awaiters = [] }
-        in
-        tree_as_ref xt := T (Node { loc; state; lt; gt; awaiters = [] });
-        before
-    | exception exn ->
-        tree_as_ref xt := T (Node { loc; state; lt; gt; awaiters = [] });
-        raise exn
-
-  let[@inline] update_top loc f xt state' lt gt =
-    let state = Obj.magic state' in
-    if is_cmp xt state then begin
-      let before = eval state in
-      let after = f before in
-      let state =
-        if before == after then state
-        else { before; after; which = W xt; awaiters = [] }
+    update xt loc c up lt gt state before
+
+  let[@inline] update_top :
+      type c a. 'x t -> a loc -> c -> (c, a) up -> 'b state -> tree -> tree -> a
+      =
+   fun xt loc c up state' lt gt ->
+    let state : a state = Obj.magic state' in
+    if is_cmp xt state then update xt loc c up lt gt state (eval state)
+    else
+      let before = state.after in
+      let after =
+        match up with
+        | Get -> before
+        | Fetch_and_add -> before + c
+        | Exchange -> c
+        | Compare_and_swap -> if fst c == before then snd c else before
+        | Fn -> c before
       in
+      let state = if before == after then state else { state with after } in
       tree_as_ref xt := T (Node { loc; state; lt; gt; awaiters = [] });
       before
-    end
-    else
-      let current = state.after in
-      let state = { state with after = f current } in
-      tree_as_ref xt := T (Node { loc; state; lt; gt; awaiters = [] });
-      current
 
-  let[@inline] unsafe_update ~xt loc f =
+  let unsafe_update ~xt loc c up =
     let loc = Loc.to_loc loc in
     maybe_validate_log xt;
     let x = loc.id in
     match !(tree_as_ref xt) with
-    | T Leaf -> update_new loc f xt (T Leaf) (T Leaf)
+    | T Leaf -> update_new xt loc c up (T Leaf) (T Leaf)
     | T (Node { loc = a; lt = T Leaf; _ }) as tree when x < a.id ->
-        update_new loc f xt (T Leaf) tree
+        update_new xt loc c up (T Leaf) tree
     | T (Node { loc = a; gt = T Leaf; _ }) as tree when a.id < x ->
-        update_new loc f xt tree (T Leaf)
+        update_new xt loc c up tree (T Leaf)
     | T (Node { loc = a; state; lt; gt; _ }) when Obj.magic a == loc ->
-        update_top loc f xt state lt gt
+        update_top xt loc c up state lt gt
     | tree -> begin
         match splay ~hit_parent:false x tree with
-        | l, T Leaf, r -> update_new loc f xt l r
-        | l, T (Node node_r), r -> update_top loc f xt node_r.state l r
+        | l, T Leaf, r -> update_new xt loc c up l r
+        | l, T (Node node_r), r -> update_top xt loc c up node_r.state l r
       end
 
-  let[@inline] protect xt f x =
-    let tree = !(tree_as_ref xt) in
-    let y = f x in
-    assert (!(tree_as_ref xt) == tree);
-    y
-
-  let get ~xt loc = unsafe_update ~xt loc Fun.id
-  let set ~xt loc after = unsafe_update ~xt loc (fun _ -> after) |> ignore
-  let modify ~xt loc f = unsafe_update ~xt loc (protect xt f) |> ignore
+  let get ~xt loc = unsafe_update ~xt loc () Get
+  let set ~xt loc after = unsafe_update ~xt loc after Exchange |> ignore
+  let modify ~xt loc f = unsafe_update ~xt loc f Fn |> ignore
 
   let compare_and_swap ~xt loc before after =
-    unsafe_update ~xt loc (fun actual ->
-        if actual == before then after else actual)
+    unsafe_update ~xt loc (before, after) Compare_and_swap
 
   let compare_and_set ~xt loc before after =
     compare_and_swap ~xt loc before after == before
 
-  let exchange ~xt loc after = unsafe_update ~xt loc (fun _ -> after)
-  let fetch_and_add ~xt loc n = unsafe_update ~xt loc (( + ) n)
-  let incr ~xt loc = unsafe_update ~xt loc inc |> ignore
-  let decr ~xt loc = unsafe_update ~xt loc dec |> ignore
-  let update ~xt loc f = unsafe_update ~xt loc (protect xt f)
+  let exchange ~xt loc after = unsafe_update ~xt loc after Exchange
+  let fetch_and_add ~xt loc n = unsafe_update ~xt loc n Fetch_and_add
+  let incr ~xt loc = unsafe_update ~xt loc 1 Fetch_and_add |> ignore
+  let decr ~xt loc = unsafe_update ~xt loc (-1) Fetch_and_add |> ignore
+  let update ~xt loc f = unsafe_update ~xt loc f Fn
   let swap ~xt l1 l2 = set ~xt l1 @@ exchange ~xt l2 @@ get ~xt l1
-  let unsafe_modify ~xt loc f = unsafe_update ~xt loc f |> ignore
-  let unsafe_update ~xt loc f = unsafe_update ~xt loc f
+  let unsafe_modify ~xt loc f = unsafe_update ~xt loc f Fn |> ignore
+  let unsafe_update ~xt loc f = unsafe_update ~xt loc f Fn
 
   let[@inline] to_blocking ~xt tx =
     match tx ~xt with None -> Retry.later () | Some value -> value