Require Recdef.
Require Coq.Strings.String.
Require Coq.Strings.Ascii.
(* LINEAR-TIME FUNCTIONAL VERSION OF SHA256 *)
Function zeros (n : Z) {measure Z.to_nat n} : list Int.int :=
if Z.gtb n 0 then Int.zero :: zeros (n-1) else nil.
Hint Rewrite length_zeros : norm.
Local Open Scope Z.
Definition padlen' (n: Z) : list Int.int :=
let q := (n+8)/64*16 + 15 - (n+8)/4   (* number of zero-pad words *)
in zeros q ++ [Int.repr (n * 8 / Int.modulus); Int.repr (n * 8)].
Transparent generate_word.

Lemma generate_word_plus:
forall msg a b, (16 <= length msg)%nat ->
generate_word msg (a+b) = generate_word (generate_word msg a) b.