Fixpoint intlist_to_bytelist (l: list int) : list byte :=
 match l with
 | nil => nil
 | i::r =>
     Byte.repr (Int.unsigned (Shr 24 i)) ::
     Byte.repr (Int.unsigned (Shr 16 i)) ::
     Byte.repr (Int.unsigned (Shr 8 i)) ::
     Byte.repr (Int.unsigned i) ::
     intlist_to_bytelist r
 end.Definition bytes_to_Int (a b c d : byte) : Int.int :=
  Int.or (Int.or (Int.or 
       (Int.shl (Int.repr (Byte.unsigned a)) (Int.repr 24))
      (Int.shl (Int.repr (Byte.unsigned b)) (Int.repr 16)))
       (Int.shl (Int.repr (Byte.unsigned c)) (Int.repr 8)))
         (Int.repr (Byte.unsigned d)).Fixpoint bytelist_to_intlist (nl: list byte) : list int :=
  match nl with
  | h1::h2::h3::h4::t => bytes_to_Int h1 h2 h3 h4 :: bytelist_to_intlist t
  | _ => nil
  end.

Lemma Ztest_Bytetest: forall a, Z.testbit (Byte.unsigned a) = Byte.testbit a.