(** A few helper functions used during proofs *)

Definition hd d :=
  match d with
  | Nil => 0x0
  | D0 _ => 0x0
  | D1 _ => 0x1
  | D2 _ => 0x2
  | D3 _ => 0x3
  | D4 _ => 0x4
  | D5 _ => 0x5
  | D6 _ => 0x6
  | D7 _ => 0x7
  | D8 _ => 0x8
  | D9 _ => 0x9
  | Da _ => 0xa
  | Db _ => 0xb
  | Dc _ => 0xc
  | Dd _ => 0xd
  | De _ => 0xe
  | Df _ => 0xf
  end.Definition tl d :=
  match d with
  | Nil => d
  | D0 d | D1 d | D2 d | D3 d | D4 d | D5 d | D6 d | D7 d | D8 d | D9 d
  | Da d | Db d | Dc d | Dd d | De d | Df d => d
  end.Fixpoint usize (d:uint) : nat :=
  match d with
  | Nil => 0
  | D0 d => S (usize d)
  | D1 d => S (usize d)
  | D2 d => S (usize d)
  | D3 d => S (usize d)
  | D4 d => S (usize d)
  | D5 d => S (usize d)
  | D6 d => S (usize d)
  | D7 d => S (usize d)
  | D8 d => S (usize d)
  | D9 d => S (usize d)
  | Da d => S (usize d)
  | Db d => S (usize d)
  | Dc d => S (usize d)
  | Dd d => S (usize d)
  | De d => S (usize d)
  | Df d => S (usize d)
  end.(** A direct version of [to_little_uint], not tail-recursive *)
Fixpoint to_lu n :=
  match n with
  | 0 => Hexadecimal.zero
  | S n => Little.succ (to_lu n)
  end.(** A direct version of [of_little_uint] *)
Fixpoint of_lu (d:uint) : nat :=
  match d with
  | Nil => 0x0
  | D0 d => 0x10 * of_lu d
  | D1 d => 0x1 + 0x10 * of_lu d
  | D2 d => 0x2 + 0x10 * of_lu d
  | D3 d => 0x3 + 0x10 * of_lu d
  | D4 d => 0x4 + 0x10 * of_lu d
  | D5 d => 0x5 + 0x10 * of_lu d
  | D6 d => 0x6 + 0x10 * of_lu d
  | D7 d => 0x7 + 0x10 * of_lu d
  | D8 d => 0x8 + 0x10 * of_lu d
  | D9 d => 0x9 + 0x10 * of_lu d
  | Da d => 0xa + 0x10 * of_lu d
  | Db d => 0xb + 0x10 * of_lu d
  | Dc d => 0xc + 0x10 * of_lu d
  | Dd d => 0xd + 0x10 * of_lu d
  | De d => 0xe + 0x10 * of_lu d
  | Df d => 0xf + 0x10 * of_lu d
  end.

Lemma of_lu_eqn d : of_lu d = hd d + 0x10 * of_lu (tl d).