(** * Properties of compile-time approximations of values *)
Definition val_match_approx (a: approx) (v: val) : Prop :=
match a with
| Int1 => v = Val.zero_ext 1 v
| Int7 => v = Val.zero_ext 8 v /\ v = Val.sign_ext 8 v
| Int8u => v = Val.zero_ext 8 v
| Int8s => v = Val.sign_ext 8 v
| Int15 => v = Val.zero_ext 16 v /\ v = Val.sign_ext 16 v
| Int16u => v = Val.zero_ext 16 v
| Int16s => v = Val.sign_ext 16 v
| Float32 => v = Val.singleoffloat v
| Any => True
end.
Remark undef_match_approx: forall a, val_match_approx a Vundef.

Lemma approx_of_unop_sound:
forall op v1 v a1,
eval_unop op v1 = Some v ->
val_match_approx a1 v1 ->
val_match_approx (Approx.unop op a1) v.