Library Coq.Strings.ByteVector

Require Import Ascii Basics Bvector String Vector.
Export VectorNotations.
Open Scope program_scope.
Open Scope string_scope.

Definition ByteVector := Vector.t ascii.

Definition ByteNil : ByteVector 0 := Vector.nil ascii.

Definition little_endian_to_string {n : nat} (v : ByteVector n) : string :=
  fold_right String v "".

Definition to_string {n : nat} : ByteVector n -> string :=
  little_endian_to_string ∘ rev.

Fixpoint little_endian_of_string (s : string) : ByteVector (length s) :=
  match s with
  | "" => ByteNil
  | String b s' => b :: little_endian_of_string s'
  end.

Definition of_string (s : string) : ByteVector (length s) :=
  rev (little_endian_of_string s).

Fixpoint to_Bvector {n : nat} (v : ByteVector n) : Bvector (n * 8) :=
  match v with
  | [] => []
  | Ascii b0 b1 b2 b3 b4 b5 b6 b7::v' =>
    b0::b1::b2::b3::b4::b5::b6::b7::to_Bvector v'
  end.

Fixpoint of_Bvector {n : nat} : Bvector (n * 8) -> ByteVector n :=
  match n with
  | 0 => fun _ => []
  | S _ =>
    fun v =>
      let (b0, v1) := uncons v in
      let (b1, v2) := uncons v1 in
      let (b2, v3) := uncons v2 in
      let (b3, v4) := uncons v3 in
      let (b4, v5) := uncons v4 in
      let (b5, v6) := uncons v5 in
      let (b6, v7) := uncons v6 in
      let (b7, v8) := uncons v7 in
      Ascii b0 b1 b2 b3 b4 b5 b6 b7::of_Bvector v8
  end.