[pulse][formula] swap order of constant and linear sum

Summary:
It is better for the derived comparison functions to start by comparing
the single offset `Q.t` instead of the map. The order of the pair
doesn't matter so the easiest way to achieve that is by putting the
offset first.

Reviewed By: skcho

Differential Revision: D26022080

fbshipit-source-id: 874ea5c66

infer/src/pulse/PulseFormula.ml

@@ -89,13 +89,13 @@ module LinArith : sig
   val subst_variables : t -> f:(Var.t -> subst_target) -> t
 end = struct
   (** invariant: the representation is always "canonical": coefficients cannot be [Q.zero] *)
-  type t = Q.t Var.Map.t * Q.t [@@deriving compare]
+  type t = Q.t * Q.t Var.Map.t [@@deriving compare, equal]
 
-  let yojson_of_t (vs, c) = `List [Var.Map.yojson_of_t Q.yojson_of_t vs; Q.yojson_of_t c]
+  let yojson_of_t (c, vs) = `List [Var.Map.yojson_of_t Q.yojson_of_t vs; Q.yojson_of_t c]
 
   type subst_target = QSubst of Q.t | VarSubst of Var.t | LinSubst of t
 
-  let pp pp_var fmt (vs, c) =
+  let pp pp_var fmt (c, vs) =
     if Var.Map.is_empty vs then Q.pp_print fmt c
     else
       let pp_c fmt c =
@@ -118,30 +118,30 @@ end = struct
       F.fprintf fmt "@[<h>%a%a@]" pp_vs vs pp_c c
 
 
-  let add (vs1, c1) (vs2, c2) =
-    ( Var.Map.union
+  let add (c1, vs1) (c2, vs2) =
+    ( Q.add c1 c2
+    , Var.Map.union
         (fun _v c1 c2 ->
           let c = Q.add c1 c2 in
           if Q.is_zero c then None else Some c )
-        vs1 vs2
-    , Q.add c1 c2 )
+        vs1 vs2 )
 
 
-  let minus (vs, c) = (Var.Map.map (fun c -> Q.neg c) vs, Q.neg c)
+  let minus (c, vs) = (Q.neg c, Var.Map.map (fun c -> Q.neg c) vs)
 
   let subtract l1 l2 = add l1 (minus l2)
 
-  let zero = (Var.Map.empty, Q.zero)
+  let zero = (Q.zero, Var.Map.empty)
 
-  let is_zero (vs, c) = Q.is_zero c && Var.Map.is_empty vs
+  let is_zero (c, vs) = Q.is_zero c && Var.Map.is_empty vs
 
-  let mult q ((vs, c) as l) =
+  let mult q ((c, vs) as l) =
     if Q.is_zero q then (* needed for correction: coeffs cannot be zero *) zero
     else if Q.is_one q then (* purely an optimisation *) l
-    else (Var.Map.map (fun c -> Q.mul q c) vs, Q.mul q c)
+    else (Q.mul q c, Var.Map.map (fun c -> Q.mul q c) vs)
 
 
-  let solve_eq_zero (vs, c) =
+  let solve_eq_zero (c, vs) =
     match Var.Map.min_binding_opt vs with
     | None ->
         if Q.is_zero c then Sat None else Unsat
@@ -154,18 +154,18 @@ end = struct
             vs Var.Map.empty
         in
         let c' = Q.div c d in
-        Sat (Some (x, (vs', c')))
+        Sat (Some (x, (c', vs')))
 
 
   let solve_eq l1 l2 = solve_eq_zero (subtract l1 l2)
 
-  let of_var v = (Var.Map.singleton v Q.one, Q.zero)
+  let of_var v = (Q.zero, Var.Map.singleton v Q.one)
 
-  let of_q q = (Var.Map.empty, q)
+  let of_q q = (q, Var.Map.empty)
 
-  let get_as_const (vs, c) = if Var.Map.is_empty vs then Some c else None
+  let get_as_const (c, vs) = if Var.Map.is_empty vs then Some c else None
 
-  let get_as_var (vs, c) =
+  let get_as_var (c, vs) =
     if Q.is_zero c then
       match Var.Map.is_singleton_or_more vs with
       | Singleton (x, cx) when Q.is_one cx ->
@@ -175,20 +175,20 @@ end = struct
     else None
 
 
-  let has_var x (vs, _) = Var.Map.mem x vs
+  let has_var x (_, vs) = Var.Map.mem x vs
 
-  let subst x y ((vs, c) as l) =
+  let subst x y ((c, vs) as l) =
     match Var.Map.find_opt x vs with
     | None ->
         l
     | Some cx ->
         let vs' = Var.Map.remove x vs |> Var.Map.add y cx in
-        (vs', c)
+        (c, vs')
 
 
   let of_subst_target = function QSubst q -> of_q q | VarSubst v -> of_var v | LinSubst l -> l
 
-  let fold_subst_variables ((vs_foreign, c) as l0) ~init ~f =
+  let fold_subst_variables ((c, vs_foreign) as l0) ~init ~f =
     let changed = ref false in
     let acc_f, l' =
       Var.Map.fold
@@ -197,7 +197,7 @@ end = struct
           (match op with VarSubst v when Var.equal v v_foreign -> () | _ -> changed := true) ;
           (acc_f, add (mult q0 (of_subst_target op)) l) )
         vs_foreign
-        (init, (Var.Map.empty, c))
+        (init, (c, Var.Map.empty))
     in
     let l' = if !changed then l' else l0 in
     (acc_f, l')
@@ -205,7 +205,7 @@ end = struct
 
   let subst_variables l ~f = fold_subst_variables l ~init:() ~f:(fun () v -> ((), f v)) |> snd
 
-  let get_variables (vs, _) = Var.Map.to_seq vs |> Seq.map fst
+  let get_variables (_, vs) = Var.Map.to_seq vs |> Seq.map fst
 end
 
 type subst_target = LinArith.subst_target =