[sledge] Add Arithmetic.solve_zero_eq

Reviewed By: jvillard

Differential Revision: D24532343

fbshipit-source-id: d7d2f6fd2

sledge/src/arithmetic.ml

@@ -7,9 +7,13 @@
 
 (** Arithmetic terms *)
 
+open Ses.Var_intf
 include Arithmetic_intf
 
-module Representation (Trm : INDETERMINATE) = struct
+module Representation
+    (Var : VAR)
+    (Trm : INDETERMINATE with type var := Var.t) =
+struct
   module Prod = struct
     include Multiset.Make
               (Int)
@@ -64,6 +68,16 @@ module Representation (Trm : INDETERMINATE) = struct
     (** [get_trm m] is [Some x] iff [equal m (of_ x 1)] *)
     let get_trm mono =
       match Prod.only_elt mono with Some (trm, 1) -> Some trm | _ -> None
+
+    (* traverse *)
+
+    let trms mono =
+      Iter.from_iter (fun f -> Prod.iter mono ~f:(fun trm _ -> f trm))
+
+    (* query *)
+
+    let vars p = Iter.flat_map ~f:Trm.vars (trms p)
+    let fv p = Var.Set.of_iter (vars p)
   end
 
   module Sum = struct
@@ -99,6 +113,8 @@ module Representation (Trm : INDETERMINATE) = struct
             (Sum.pp "@ + " pp_coeff_mono)
             poly
 
+    let pp = ppx (fun _ -> None)
+
     let mono_invariant mono =
       let@ () = Invariant.invariant [%here] mono [%sexp_of: Mono.t] in
       Prod.iter mono ~f:(fun base power ->
@@ -268,14 +284,72 @@ module Representation (Trm : INDETERMINATE) = struct
 
     (* traverse *)
 
-    let iter poly =
-      Iter.from_iter (fun f ->
-          Sum.iter poly ~f:(fun mono _ ->
-              Prod.iter mono ~f:(fun trm _ -> f trm) ) )
+    let monos poly =
+      Iter.from_iter (fun f -> Sum.iter poly ~f:(fun mono _ -> f mono))
+
+    let trms poly = Iter.flat_map ~f:Mono.trms (monos poly)
 
     type product = Prod.t
 
     let fold_factors = Prod.fold
     let fold_monomials = Sum.fold
+
+    (* query *)
+
+    let vars p = Iter.flat_map ~f:Trm.vars (trms p)
+
+    (* solve *)
+
+    let exists_fv_in vs poly = Iter.exists ~f:(Var.Set.mem vs) (vars poly)
+
+    (** [solve_for_mono r c m p] solves [0 = r + (c×m) + p] as [m = q]
+        ([Some (m, q)]) such that [r + (c×m) + p = m - q] *)
+    let solve_for_mono rejected_poly coeff mono poly =
+      if Mono.equal_one mono || exists_fv_in (Mono.fv mono) poly then None
+      else
+        Some
+          ( Sum.of_ mono Q.one
+          , mulc (Q.inv (Q.neg coeff)) (Sum.union rejected_poly poly) )
+
+    (** [solve_poly r p] solves [0 = r + p] as [m = q] ([Some (m, q)]) such
+        that [r + p = m - q] *)
+    let rec solve_poly rejected poly =
+      [%trace]
+        ~call:(fun {pf} -> pf "0 = (%a) + (%a)" pp rejected pp poly)
+        ~retn:(fun {pf} s ->
+          pf "%a"
+            (Option.pp "%a" (fun fs (v, q) ->
+                 Format.fprintf fs "%a ↦ %a" pp v pp q ))
+            s )
+      @@ fun () ->
+      let* mono, coeff, poly = Sum.pop_min_elt poly in
+      match solve_for_mono rejected coeff mono poly with
+      | Some _ as soln -> soln
+      | None -> solve_poly (Sum.add mono coeff rejected) poly
+
+    (* solve [0 = e] *)
+    let solve_zero_eq ?for_ e =
+      [%trace]
+        ~call:(fun {pf} ->
+          pf "0 = %a%a" Trm.pp e (Option.pp " for %a" Trm.pp) for_ )
+        ~retn:(fun {pf} s ->
+          pf "%a"
+            (Option.pp "%a" (fun fs (c, r) ->
+                 Format.fprintf fs "%a ↦ %a" pp c pp r ))
+            s ;
+          match (for_, s) with
+          | Some f, Some (c, _) -> assert (equal (trm f) c)
+          | _ -> () )
+      @@ fun () ->
+      let* a = Embed.get_arith e in
+      match for_ with
+      | None -> solve_poly Sum.empty a
+      | Some for_ -> (
+          let* for_poly = Embed.get_arith for_ in
+          match get_mono for_poly with
+          | Some m ->
+              let* c, p = Sum.find_and_remove m a in
+              solve_for_mono Sum.empty c m p
+          | _ -> None )
   end
 end

sledge/src/arithmetic.mli

@@ -7,9 +7,10 @@
 
 (** Arithmetic terms *)
 
+open Ses.Var_intf
 include module type of Arithmetic_intf
 
-module Representation (Indeterminate : INDETERMINATE) :
-  REPRESENTATION
-    with type var := Indeterminate.var
-    with type trm := Indeterminate.trm
+module Representation
+    (Var : VAR)
+    (Indeterminate : INDETERMINATE with type var := Var.t) :
+  REPRESENTATION with type var := Var.t with type trm := Indeterminate.trm

sledge/src/arithmetic_intf.ml

@@ -61,8 +61,15 @@ module type S = sig
 
   (** Traverse *)
 
-  val iter : t -> trm iter
-  (** [iter a] enumerates the indeterminate terms appearing in [a] *)
+  val trms : t -> trm iter
+  (** [trms a] enumerates the indeterminate terms appearing in [a] *)
+
+  (** Solve *)
+
+  val solve_zero_eq : ?for_:trm -> trm -> (t * t) option
+  (** [solve_zero_eq d] is [Some (e, f)] if [0 = d] can be equivalently
+      expressed as [e = f] for some monomial subterm [e] of [d]. If [for_]
+      is passed, then the subterm [e] must be [for_]. *)
 
   (**/**)
 
@@ -79,6 +86,8 @@ module type INDETERMINATE = sig
   type var
 
   val ppx : var Var.strength -> trm pp
+  val pp : trm pp
+  val vars : trm -> var iter
 end
 
 (** An embedding of arithmetic terms [t] into indeterminates [trm],

sledge/src/trm.ml

@@ -40,12 +40,13 @@ end
 
 and Arith0 :
   (Arithmetic.REPRESENTATION with type var := Var.t with type trm := Trm.t) =
-Arithmetic.Representation (struct
-  type trm = Trm.t [@@deriving compare, equal, sexp]
-  type var = Var.t
+  Arithmetic.Representation
+    (Var)
+    (struct
+      include Trm
 
-  let ppx = Trm.ppx
-end)
+      type trm = t [@@deriving compare, equal, sexp]
+    end)
 
 and Arith :
   (Arithmetic.S
@@ -89,6 +90,7 @@ and Trm : sig
   [@@deriving compare, equal, sexp]
 
   val ppx : Var.t Var.strength -> t pp
+  val pp : t pp
   val _Var : int -> string -> t
   val _Z : Z.t -> t
   val _Q : Q.t -> t
@@ -106,6 +108,7 @@ and Trm : sig
   val sub : t -> t -> t
   val seq_size_exn : t -> t
   val seq_size : t -> t option
+  val vars : t -> Var.t iter
 end = struct
   type t =
     | Var of {id: int; name: string}
@@ -198,12 +201,12 @@ end = struct
       | Trm _ | Const _ -> assert false )
     | _ -> ()
 
-  (* destructors *)
+  (** Destruct *)
 
   let get_z = function Z z -> Some z | _ -> None
   let get_q = function Q q -> Some q | Z z -> Some (Q.of_z z) | _ -> None
 
-  (* constructors *)
+  (** Construct *)
 
   let _Var id name = Var {id; name} |> check invariant
 
@@ -361,6 +364,26 @@ end = struct
     | Some c -> c
     | None -> Apply (f, es) )
     |> check invariant
+
+  (** Traverse *)
+
+  let rec iter_vars e ~f =
+    match e with
+    | Var _ as v -> f (Var.of_ v)
+    | Z _ | Q _ | Ancestor _ -> ()
+    | Splat x | Select {rcd= x} -> iter_vars ~f x
+    | Sized {seq= x; siz= y} | Update {rcd= x; elt= y} ->
+        iter_vars ~f x ;
+        iter_vars ~f y
+    | Extract {seq= x; off= y; len= z} ->
+        iter_vars ~f x ;
+        iter_vars ~f y ;
+        iter_vars ~f z
+    | Concat xs | Record xs | Apply (_, xs) ->
+        Array.iter ~f:(iter_vars ~f) xs
+    | Arith a -> Iter.iter ~f:(iter_vars ~f) (Arith.trms a)
+
+  let vars e = Iter.from_labelled_iter (iter_vars e)
 end
 
 type arith = Arith.t
@@ -424,22 +447,3 @@ let rec map_vars e ~f =
   | Record xs -> mapN (map_vars ~f) e _Record xs
   | Ancestor _ -> e
   | Apply (g, xs) -> mapN (map_vars ~f) e (_Apply g) xs
-
-(** Traverse *)
-
-let rec iter_vars e ~f =
-  match e with
-  | Var _ as v -> f (Var.of_ v)
-  | Z _ | Q _ | Ancestor _ -> ()
-  | Splat x | Select {rcd= x} -> iter_vars ~f x
-  | Sized {seq= x; siz= y} | Update {rcd= x; elt= y} ->
-      iter_vars ~f x ;
-      iter_vars ~f y
-  | Extract {seq= x; off= y; len= z} ->
-      iter_vars ~f x ;
-      iter_vars ~f y ;
-      iter_vars ~f z
-  | Concat xs | Record xs | Apply (_, xs) -> Array.iter ~f:(iter_vars ~f) xs
-  | Arith a -> Iter.iter ~f:(iter_vars ~f) (Arith.iter a)
-
-let vars e = Iter.from_labelled_iter (iter_vars e)