Definition get_h (n: Z) :=
    Sset _t
        (Ederef
           (Ebinop Oadd
              (Efield
                 (Ederef (Etempvar _ctx (tptr t_struct_SHA256state_st))
                    t_struct_SHA256state_st) _h (tarray tuint 8))
              (Econst_int (Int.repr n) tint) (tptr tuint)) tuint).Definition add_h (n: Z) (i: ident) :=
   Sassign
       (Ederef
          (Ebinop Oadd
             (Efield
                (Ederef (Etempvar _ctx (tptr t_struct_SHA256state_st))
                   t_struct_SHA256state_st) _h (tarray tuint 8))
             (Econst_int (Int.repr n) tint) (tptr tuint)) tuint)
       (Ebinop Oadd (Etempvar _t tuint) (Etempvar i tuint) tuint).Fixpoint add_upto (k: nat) (u v: list int) {struct k} :=
 match k with
 | O => u
 | S k' => match u,v with
                | u1::us, v1::vs => Int.add u1 v1 :: add_upto k' us vs
                | _, _ => u
                end
 end.

Lemma force_lengthn_short: forall {A} i (b: list A) v, (i <= length b)%nat -> force_lengthn i b v = firstn i b.