Library Coq.Numbers.Cyclic.DoubleCyclic.DoubleSub

Set Implicit Arguments.

Require Import ZArith.
Require Import BigNumPrelude.
Require Import DoubleType.
Require Import DoubleBase.

Local Open Scope Z_scope.

Section DoubleSub.
Variable w : Type.
Variable w_0 : w.
Variable w_Bm1 : w.
Variable w_WW : w -> w -> zn2z w.
Variable ww_Bm1 : zn2z w.
Variable w_opp_c : w -> carry w.
Variable w_opp_carry : w -> w.
Variable w_pred_c : w -> carry w.
Variable w_sub_c : w -> w -> carry w.
Variable w_sub_carry_c : w -> w -> carry w.
Variable w_opp : w -> w.
Variable w_pred : w -> w.
Variable w_sub : w -> w -> w.
Variable w_sub_carry : w -> w -> w.

Definition ww_opp_c x :=
  match x with
  | W0 => C0 W0
  | WW xh xl =>
    match w_opp_c xl with
    | C0 _ =>
      match w_opp_c xh with
      | C0 h => C0 W0
      | C1 h => C1 (WW h w_0)
      end
    | C1 l => C1 (WW (w_opp_carry xh) l)
    end
  end.

Definition ww_opp x :=
  match x with
  | W0 => W0
  | WW xh xl =>
    match w_opp_c xl with
    | C0 _ => WW (w_opp xh) w_0
    | C1 l => WW (w_opp_carry xh) l
    end
  end.

Definition ww_opp_carry x :=
  match x with
  | W0 => ww_Bm1
  | WW xh xl => w_WW (w_opp_carry xh) (w_opp_carry xl)
  end.

Definition ww_pred_c x :=
  match x with
  | W0 => C1 ww_Bm1
  | WW xh xl =>
    match w_pred_c xl with
    | C0 l => C0 (w_WW xh l)
    | C1 _ =>
      match w_pred_c xh with
      | C0 h => C0 (WW h w_Bm1)
      | C1 _ => C1 ww_Bm1
      end
    end
  end.

Definition ww_pred x :=
  match x with
  | W0 => ww_Bm1
  | WW xh xl =>
    match w_pred_c xl with
    | C0 l => w_WW xh l
    | C1 l => WW (w_pred xh) w_Bm1
    end
  end.

Definition ww_sub_c x y :=
  match y, x with
  | W0, _ => C0 x
  | WW yh yl, W0 => ww_opp_c (WW yh yl)
  | WW yh yl, WW xh xl =>
    match w_sub_c xl yl with
    | C0 l =>
      match w_sub_c xh yh with
      | C0 h => C0 (w_WW h l)
      | C1 h => C1 (WW h l)
      end
    | C1 l =>
      match w_sub_carry_c xh yh with
      | C0 h => C0 (WW h l)
      | C1 h => C1 (WW h l)
      end
    end
  end.

Definition ww_sub x y :=
  match y, x with
  | W0, _ => x
  | WW yh yl, W0 => ww_opp (WW yh yl)
  | WW yh yl, WW xh xl =>
    match w_sub_c xl yl with
    | C0 l => w_WW (w_sub xh yh) l
    | C1 l => WW (w_sub_carry xh yh) l
    end
  end.

Definition ww_sub_carry_c x y :=
  match y, x with
  | W0, W0 => C1 ww_Bm1
  | W0, WW xh xl => ww_pred_c (WW xh xl)
  | WW yh yl, W0 => C1 (ww_opp_carry (WW yh yl))
  | WW yh yl, WW xh xl =>
    match w_sub_carry_c xl yl with
    | C0 l =>
      match w_sub_c xh yh with
      | C0 h => C0 (w_WW h l)
      | C1 h => C1 (WW h l)
      end
    | C1 l =>
      match w_sub_carry_c xh yh with
      | C0 h => C0 (w_WW h l)
      | C1 h => C1 (w_WW h l)
      end
    end
  end.

Definition ww_sub_carry x y :=
  match y, x with
  | W0, W0 => ww_Bm1
  | W0, WW xh xl => ww_pred (WW xh xl)
  | WW yh yl, W0 => ww_opp_carry (WW yh yl)
  | WW yh yl, WW xh xl =>
    match w_sub_carry_c xl yl with
    | C0 l => w_WW (w_sub xh yh) l
    | C1 l => w_WW (w_sub_carry xh yh) l
    end
  end.

  Variable w_digits : positive.
  Variable w_to_Z : w -> Z.

  Notation wB := (base w_digits).
  Notation wwB := (base (ww_digits w_digits)).
  Notation "[| x |]" := (w_to_Z x) (at level 0, x at level 99).
  Notation "[+| c |]" :=
   (interp_carry 1 wB w_to_Z c) (at level 0, x at level 99).
  Notation "[-| c |]" :=
   (interp_carry (-1) wB w_to_Z c) (at level 0, x at level 99).

  Notation "[[ x ]]" := (ww_to_Z w_digits w_to_Z x)(at level 0, x at level 99).
  Notation "[+[ c ]]" :=
   (interp_carry 1 wwB (ww_to_Z w_digits w_to_Z) c)
   (at level 0, x at level 99).
  Notation "[-[ c ]]" :=
   (interp_carry (-1) wwB (ww_to_Z w_digits w_to_Z) c)
   (at level 0, x at level 99).

  Variable spec_w_0 : [|w_0 |] = 0.
  Variable spec_w_Bm1 : [|w_Bm1 |] = wB - 1.
  Variable spec_ww_Bm1 : [[ww_Bm1 ]] = wwB - 1.
  Variable spec_to_Z : forall x, 0 <= [|x |] < wB.
  Variable spec_w_WW : forall h l, [[w_WW h l ]] = [|h |] * wB + [|l |].

  Variable spec_opp_c : forall x, [-|w_opp_c x |] = -[|x |].
  Variable spec_opp : forall x, [|w_opp x |] = (-[|x |]) mod wB.
  Variable spec_opp_carry : forall x, [|w_opp_carry x |] = wB - [|x |] - 1.

  Variable spec_pred_c : forall x, [-|w_pred_c x |] = [|x |] - 1.
  Variable spec_sub_c : forall x y, [-|w_sub_c x y |] = [|x |] - [|y |].
  Variable spec_sub_carry_c :
   forall x y, [-|w_sub_carry_c x y |] = [|x |] - [|y |] - 1.

  Variable spec_pred : forall x, [|w_pred x |] = ([|x |] - 1) mod wB.
  Variable spec_sub : forall x y, [|w_sub x y |] = ([|x |] - [|y |]) mod wB.
  Variable spec_sub_carry :
         forall x y, [|w_sub_carry x y |] = ([|x |] - [|y |] - 1) mod wB.

  Lemma spec_ww_opp_c : forall x, [-[ww_opp_c x ]] = -[[x ]].

  Lemma spec_ww_opp : forall x, [[ww_opp x ]] = (-[[x ]]) mod wwB.

  Lemma spec_ww_opp_carry : forall x, [[ww_opp_carry x ]] = wwB - [[x ]] - 1.

  Lemma spec_ww_pred_c : forall x, [-[ww_pred_c x ]] = [[x ]] - 1.

  Lemma spec_ww_sub_c : forall x y, [-[ww_sub_c x y ]] = [[x ]] - [[y ]].

  Lemma spec_ww_sub_carry_c :
     forall x y, [-[ww_sub_carry_c x y ]] = [[x ]] - [[y ]] - 1.

  Lemma spec_ww_pred : forall x, [[ww_pred x ]] = ([[x ]] - 1) mod wwB.

  Lemma spec_ww_sub : forall x y, [[ww_sub x y ]] = ([[x ]] - [[y ]]) mod wwB.

  Lemma spec_ww_sub_carry :
         forall x y, [[ww_sub_carry x y ]] = ([[x ]] - [[y ]] - 1) mod wwB.

End DoubleSub.

Library Coq.Numbers.Cyclic.DoubleCyclic.DoubleSub

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