2 files changed, 64 insertions, 40 deletions

diff --git a/lib/coq/Sail2_operators_mwords.v b/lib/coq/Sail2_operators_mwords.v
index 1d4eb906..5f9c15f4 100644
--- a/lib/coq/Sail2_operators_mwords.v
+++ b/lib/coq/Sail2_operators_mwords.v
@@ -15,14 +15,38 @@ Definition eq_dec := Z.eq_dec.
 End Z_eq_dec.
 Module ZEqdep := DecidableEqDep (Z_eq_dec).
 
-Definition cast_T {T : Z -> Type} {m n} (x : T m) (eq : m = n) : T n.
-rewrite <- eq.
-exact x.
+Fixpoint cast_positive (T : positive -> Type) (p q : positive) : T p -> p = q -> T q.
+refine (
+match p, q with
+| xH, xH => fun x _ => x
+| xO p', xO q' => fun x e => cast_positive (fun x => T (xO x)) p' q' x _
+| xI p', xI q' => fun x e => cast_positive (fun x => T (xI x)) p' q' x _
+| _, _ => _
+end); congruence.
 Defined.
 
+Definition cast_T {T : Z -> Type} {m n} : forall (x : T m) (eq : m = n), T n.
+refine (match m,n with
+| Z0, Z0 => fun x _ => x
+| Zneg p1, Zneg p2 => fun x e => cast_positive (fun p => T (Zneg p)) p1 p2 x _
+| Zpos p1, Zpos p2 => fun x e => cast_positive (fun p => T (Zpos p)) p1 p2 x _
+| _,_ => _
+end); congruence.
+Defined.
+
+Lemma cast_positive_refl : forall p T x (e : p = p),
+  cast_positive T p p x e = x.
+induction p.
+* intros. simpl. rewrite IHp; auto.
+* intros. simpl. rewrite IHp; auto.
+* reflexivity.
+Qed.
+
 Lemma cast_T_refl {T : Z -> Type} {m} {H:m = m} (x : T m) : cast_T x H = x.
-rewrite (ZEqdep.UIP _ _ H eq_refl).
-reflexivity.
+destruct m.
+* reflexivity.
+* simpl. rewrite cast_positive_refl. reflexivity.
+* simpl. rewrite cast_positive_refl. reflexivity.
 Qed.
 
 Definition autocast {T : Z -> Type} {m n} (x : T m) `{H:ArithFact (m = n)} : T n :=
@@ -31,27 +55,31 @@ Definition autocast {T : Z -> Type} {m n} (x : T m) `{H:ArithFact (m = n)} : T n
 Definition autocast_m {rv e m n} (x : monad rv (mword m) e) `{H:ArithFact (m = n)} : monad rv (mword n) e :=
   x >>= fun x => returnm (cast_T x (use_ArithFact H)).
 
-Definition cast_word {m n} (x : Word.word m) (eq : m = n) : Word.word n.
-rewrite <- eq.
-exact x.
-Defined.
+Definition cast_word {m n} (x : Word.word m) (eq : m = n) : Word.word n :=
+  DepEqNat.nat_cast _ eq x.
 
 Lemma cast_word_refl {m} {H:m = m} (x : word m) : cast_word x H = x.
 rewrite (UIP_refl_nat _ H).
-reflexivity.
+apply nat_cast_same.
 Qed.
 
-Definition mword_of_nat {m} (x : Word.word m) : mword (Z.of_nat m).
-destruct m.
-- exact x.
-- simpl. rewrite SuccNat2Pos.id_succ. exact x.
+Definition mword_of_nat {m} : Word.word m -> mword (Z.of_nat m).
+refine (match m return word m -> mword (Z.of_nat m) with
+| O => fun x => x
+| S m' => fun x => nat_cast _ _ x
+end).
+rewrite SuccNat2Pos.id_succ.
+reflexivity.
 Defined.
 
-Definition cast_to_mword {m n} (x : Word.word m) (eq : Z.of_nat m = n) : mword n.
-destruct n.
-- constructor.
-- rewrite <- eq. exact (mword_of_nat x).
-- exfalso. destruct m; simpl in *; congruence.
+Definition cast_to_mword {m n} (x : Word.word m) : Z.of_nat m = n -> mword n.
+refine (match n return Z.of_nat m = n -> mword n with
+| Z0 => fun _ => WO
+| Zpos p => fun eq => cast_T (mword_of_nat x) eq
+| Zneg p => _
+end).
+intro eq.
+exfalso. destruct m; simpl in *; congruence.
 Defined.
 
 (*
diff --git a/lib/coq/Sail2_values.v b/lib/coq/Sail2_values.v
index 30df0672..9c1173f1 100644
--- a/lib/coq/Sail2_values.v
+++ b/lib/coq/Sail2_values.v
@@ -870,29 +870,25 @@ match l with
 end.
 
 Local Open Scope nat.
-Program Definition fit_bbv_word {n m} (w : word n) : word m :=
-match Nat.compare m n with
-| Gt => extz w (m - n)
-| Eq => w
-| Lt => split2 (n - m) m w
-end.
-Next Obligation.
-symmetry in Heq_anonymous.
-apply nat_compare_gt in Heq_anonymous.
-omega.
-Defined.
-Next Obligation.
 
-symmetry in Heq_anonymous.
-apply nat_compare_eq in Heq_anonymous.
-omega.
-Defined.
-Next Obligation.
+Fixpoint nat_diff {T : nat -> Type} n m {struct n} :
+forall
+ (lt : forall p, T n -> T (n + p))
+ (eq : T m -> T m)
+ (gt : forall p, T (m + p) -> T m), T n -> T m :=
+(match n, m return (forall p, T n -> T (n + p)) -> (T m -> T m) -> (forall p, T (m + p) -> T m) -> T n -> T m with
+| O, O => fun lt eq gt => eq
+| S n', O => fun lt eq gt => gt _
+| O, S m' => fun lt eq gt => lt _
+| S n', S m' => @nat_diff (fun x => T (S x)) n' m'
+end).
+
+Definition fit_bbv_word {n m} : word n -> word m :=
+nat_diff n m
+ (fun p w => nat_cast _ (Nat.add_comm _ _) (extz w p))
+ (fun w => w)
+ (fun p w => split2 _ _ (nat_cast _ (Nat.add_comm _ _) w)).
 
-symmetry in Heq_anonymous.
-apply nat_compare_lt in Heq_anonymous.
-omega.
-Defined.
 Local Close Scope nat.
 
 (*** Bitvectors *)