Require Import Fcore.
Require Import Fcore_digits.
Require Import Fcalc_digits.
Require Import Fcalc_round.
Require Import Fcalc_bracket.
Require Import Fcalc_ops.
Require Import Fcalc_div.
Require Import Fcalc_sqrt.
Require Import Fprop_relative.

Section AnyRadix.

Inductive full_float :=
  | F754_zero : bool → full_float
  | F754_infinity : bool → full_float
  | F754_nan : bool → positive → full_float
  | F754_finite : bool → positive → Z → full_float.

Definition FF2R beta x :=
  match x with
  | F754_finite s m e ⇒ F2R (Float beta (cond_Zopp s (Zpos m)) e)
  | _ ⇒ R0
  end.

End AnyRadix.

Section Binary.

Implicit Arguments exist [[A] [P]].

Variable prec emax : Z.
Context (prec_gt_0_ : Prec_gt_0 prec).
Hypothesis Hmax : (prec < emax)%Z.

Let emin := (3 - emax - prec)%Z.
Let fexp := FLT_exp emin prec.
Instance fexp_correct : Valid_exp fexp := FLT_exp_valid emin prec.
Instance fexp_monotone : Monotone_exp fexp := FLT_exp_monotone emin prec.

Definition canonic_mantissa m e :=
  Zeq_bool (fexp (Zpos (digits2_pos m) + e)) e.

Definition bounded m e :=
  andb (canonic_mantissa m e) (Zle_bool e (emax - prec)).

Definition valid_binary x :=
  match x with
  | F754_finite _ m e ⇒ bounded m e
  | F754_nan _ pl ⇒ (Zpos (digits2_pos pl) <? prec)%Z
  | _ ⇒ true
  end.

Definition nan_pl := {pl | (Zpos (digits2_pos pl) <? prec)%Z = true}.

Inductive binary_float :=
  | B754_zero : bool → binary_float
  | B754_infinity : bool → binary_float
  | B754_nan : bool → nan_pl → binary_float
  | B754_finite : bool →
    ∀ (m : positive) (e : Z), bounded m e = true → binary_float.

Definition FF2B x :=
  match x as x return valid_binary x = true → binary_float with
  | F754_finite s m e ⇒ B754_finite s m e
  | F754_infinity s ⇒ fun _ ⇒ B754_infinity s
  | F754_zero s ⇒ fun _ ⇒ B754_zero s
  | F754_nan b pl ⇒ fun H ⇒ B754_nan b (exist pl H)
  end.

Definition B2FF x :=
  match x with
  | B754_finite s m e _ ⇒ F754_finite s m e
  | B754_infinity s ⇒ F754_infinity s
  | B754_zero s ⇒ F754_zero s
  | B754_nan b (exist pl _) ⇒ F754_nan b pl
  end.

Definition B2R f :=
  match f with
  | B754_finite s m e _ ⇒ F2R (Float radix2 (cond_Zopp s (Zpos m)) e)
  | _ ⇒ R0
  end.

Theorem FF2R_B2FF :
  ∀ x,
  FF2R radix2 (B2FF x) = B2R x.

Theorem B2FF_FF2B :
  ∀ x Hx,
  B2FF (FF2B x Hx) = x.

Theorem valid_binary_B2FF :
  ∀ x,
  valid_binary (B2FF x) = true.

Theorem FF2B_B2FF :
  ∀ x H,
  FF2B (B2FF x) H = x.

Theorem FF2B_B2FF_valid :
  ∀ x,
  FF2B (B2FF x) (valid_binary_B2FF x) = x.

Theorem B2R_FF2B :
  ∀ x Hx,
  B2R (FF2B x Hx) = FF2R radix2 x.

Theorem match_FF2B :
  ∀ {T} fz fi fn ff x Hx,
  match FF2B x Hx return T with
  | B754_zero sx ⇒ fz sx
  | B754_infinity sx ⇒ fi sx
  | B754_nan b (exist p _) ⇒ fn b p
  | B754_finite sx mx ex _ ⇒ ff sx mx ex
  end =
  match x with
  | F754_zero sx ⇒ fz sx
  | F754_infinity sx ⇒ fi sx
  | F754_nan b p ⇒ fn b p
  | F754_finite sx mx ex ⇒ ff sx mx ex
  end.

Theorem canonic_canonic_mantissa :
  ∀ (sx : bool) mx ex,
  canonic_mantissa mx ex = true →
  canonic radix2 fexp (Float radix2 (cond_Zopp sx (Zpos mx)) ex).

Theorem generic_format_B2R :
  ∀ x,
  generic_format radix2 fexp (B2R x).

Theorem FLT_format_B2R :
  ∀ x,
  FLT_format radix2 emin prec (B2R x).

Theorem B2FF_inj :
  ∀ x y : binary_float,
  B2FF x = B2FF y →
  x = y.

Definition is_finite_strict f :=
  match f with
  | B754_finite _ _ _ _ ⇒ true
  | _ ⇒ false
  end.

Theorem B2R_inj:
  ∀ x y : binary_float,
  is_finite_strict x = true →
  is_finite_strict y = true →
  B2R x = B2R y →
  x = y.

Definition Bsign x :=
  match x with
  | B754_nan s _ ⇒ s
  | B754_zero s ⇒ s
  | B754_infinity s ⇒ s
  | B754_finite s _ _ _ ⇒ s
  end.

Definition sign_FF x :=
  match x with
  | F754_nan s _ ⇒ s
  | F754_zero s ⇒ s
  | F754_infinity s ⇒ s
  | F754_finite s _ _ ⇒ s
  end.

Theorem Bsign_FF2B :
  ∀ x H,
  Bsign (FF2B x H) = sign_FF x.

Definition is_finite f :=
  match f with
  | B754_finite _ _ _ _ ⇒ true
  | B754_zero _ ⇒ true
  | _ ⇒ false
  end.

Definition is_finite_FF f :=
  match f with
  | F754_finite _ _ _ ⇒ true
  | F754_zero _ ⇒ true
  | _ ⇒ false
  end.

Theorem is_finite_FF2B :
  ∀ x Hx,
  is_finite (FF2B x Hx) = is_finite_FF x.

Theorem is_finite_FF_B2FF :
  ∀ x,
  is_finite_FF (B2FF x) = is_finite x.

Theorem B2R_Bsign_inj:
  ∀ x y : binary_float,
    is_finite x = true →
    is_finite y = true →
    B2R x = B2R y →
    Bsign x = Bsign y →
    x = y.

Definition is_nan f :=
  match f with
  | B754_nan _ _ ⇒ true
  | _ ⇒ false
  end.

Definition is_nan_FF f :=
  match f with
  | F754_nan _ _ ⇒ true
  | _ ⇒ false
  end.

Theorem is_nan_FF2B :
  ∀ x Hx,
  is_nan (FF2B x Hx) = is_nan_FF x.

Theorem is_nan_FF_B2FF :
  ∀ x,
  is_nan_FF (B2FF x) = is_nan x.

Definition Bopp opp_nan x :=
  match x with
  | B754_nan sx plx ⇒
    let '(sres, plres) := opp_nan sx plx in B754_nan sres plres
  | B754_infinity sx ⇒ B754_infinity (negb sx)
  | B754_finite sx mx ex Hx ⇒ B754_finite (negb sx) mx ex Hx
  | B754_zero sx ⇒ B754_zero (negb sx)
  end.

Theorem Bopp_involutive :
  ∀ opp_nan x,
  is_nan x = false →
  Bopp opp_nan (Bopp opp_nan x) = x.

Theorem B2R_Bopp :
  ∀ opp_nan x,
  B2R (Bopp opp_nan x) = (- B2R x)%R.

Theorem is_finite_Bopp :
  ∀ opp_nan x,
  is_finite (Bopp opp_nan x) = is_finite x.

Theorem bounded_lt_emax :
  ∀ mx ex,
  bounded mx ex = true →
  (F2R (Float radix2 (Zpos mx) ex) < bpow radix2 emax)%R.

Theorem abs_B2R_lt_emax :
  ∀ x,
  (Rabs (B2R x) < bpow radix2 emax)%R.

Theorem bounded_canonic_lt_emax :
  ∀ mx ex,
  canonic radix2 fexp (Float radix2 (Zpos mx) ex) →
  (F2R (Float radix2 (Zpos mx) ex) < bpow radix2 emax)%R →
  bounded mx ex = true.

Record shr_record := { shr_m : Z ; shr_r : bool ; shr_s : bool }.

Definition shr_1 mrs :=
  let '(Build_shr_record m r s) := mrs in
  let s := orb r s in
  match m with
  | Z0 ⇒ Build_shr_record Z0 false s
  | Zpos xH ⇒ Build_shr_record Z0 true s
  | Zpos (xO p) ⇒ Build_shr_record (Zpos p) false s
  | Zpos (xI p) ⇒ Build_shr_record (Zpos p) true s
  | Zneg xH ⇒ Build_shr_record Z0 true s
  | Zneg (xO p) ⇒ Build_shr_record (Zneg p) false s
  | Zneg (xI p) ⇒ Build_shr_record (Zneg p) true s
  end.

Definition loc_of_shr_record mrs :=
  match mrs with
  | Build_shr_record _ false false ⇒ loc_Exact
  | Build_shr_record _ false true ⇒ loc_Inexact Lt
  | Build_shr_record _ true false ⇒ loc_Inexact Eq
  | Build_shr_record _ true true ⇒ loc_Inexact Gt
  end.

Definition shr_record_of_loc m l :=
  match l with
  | loc_Exact ⇒ Build_shr_record m false false
  | loc_Inexact Lt ⇒ Build_shr_record m false true
  | loc_Inexact Eq ⇒ Build_shr_record m true false
  | loc_Inexact Gt ⇒ Build_shr_record m true true
  end.

Theorem shr_m_shr_record_of_loc :
  ∀ m l,
  shr_m (shr_record_of_loc m l) = m.

Theorem loc_of_shr_record_of_loc :
  ∀ m l,
  loc_of_shr_record (shr_record_of_loc m l) = l.

Definition shr mrs e n :=
  match n with
  | Zpos p ⇒ (iter_pos p _ shr_1 mrs, (e + n)%Z)
  | _ ⇒ (mrs, e)
  end.

Lemma inbetween_shr_1 :
  ∀ x mrs e,
  (0 ≤ shr_m mrs)%Z →
  inbetween_float radix2 (shr_m mrs) e x (loc_of_shr_record mrs) →
  inbetween_float radix2 (shr_m (shr_1 mrs)) (e + 1) x (loc_of_shr_record (shr_1 mrs)).

Theorem inbetween_shr :
  ∀ x m e l n,
  (0 ≤ m)%Z →
  inbetween_float radix2 m e x l →
  let '(mrs, e') := shr (shr_record_of_loc m l) e n in
  inbetween_float radix2 (shr_m mrs) e' x (loc_of_shr_record mrs).

Definition shr_fexp m e l :=
  shr (shr_record_of_loc m l) e (fexp (Zdigits2 m + e) - e).

Theorem shr_truncate :
  ∀ m e l,
  (0 ≤ m)%Z →
  shr_fexp m e l =
  let '(m', e', l') := truncate radix2 fexp (m, e, l) in (shr_record_of_loc m' l', e').

Inductive mode := mode_NE | mode_ZR | mode_DN | mode_UP | mode_NA.

Definition round_mode m :=
  match m with
  | mode_NE ⇒ ZnearestE
  | mode_ZR ⇒ Ztrunc
  | mode_DN ⇒ Zfloor
  | mode_UP ⇒ Zceil
  | mode_NA ⇒ ZnearestA
  end.

Definition choice_mode m sx mx lx :=
  match m with
  | mode_NE ⇒ cond_incr (round_N (negb (Zeven mx)) lx) mx
  | mode_ZR ⇒ mx
  | mode_DN ⇒ cond_incr (round_sign_DN sx lx) mx
  | mode_UP ⇒ cond_incr (round_sign_UP sx lx) mx
  | mode_NA ⇒ cond_incr (round_N true lx) mx
  end.

Global Instance valid_rnd_round_mode : ∀ m, Valid_rnd (round_mode m).

Definition overflow_to_inf m s :=
  match m with
  | mode_NE ⇒ true
  | mode_NA ⇒ true
  | mode_ZR ⇒ false
  | mode_UP ⇒ negb s
  | mode_DN ⇒ s
  end.

Definition binary_overflow m s :=
  if overflow_to_inf m s then F754_infinity s
  else F754_finite s (match (Zpower 2 prec - 1)%Z with Zpos p ⇒ p | _ ⇒ xH end) (emax - prec).

Definition binary_round_aux mode sx mx ex lx :=
  let '(mrs', e') := shr_fexp (Zpos mx) ex lx in
  let '(mrs'', e'') := shr_fexp (choice_mode mode sx (shr_m mrs') (loc_of_shr_record mrs')) e' loc_Exact in
  match shr_m mrs'' with
  | Z0 ⇒ F754_zero sx
  | Zpos m ⇒ if Zle_bool e'' (emax - prec) then F754_finite sx m e'' else binary_overflow mode sx
  | _ ⇒ F754_nan false xH
  end.

Theorem binary_round_aux_correct :
  ∀ mode x mx ex lx,
  inbetween_float radix2 (Zpos mx) ex (Rabs x) lx →
  (ex ≤ fexp (Zdigits radix2 (Zpos mx) + ex))%Z →
  let z := binary_round_aux mode (Rlt_bool x 0) mx ex lx in
  valid_binary z = true ∧
  if Rlt_bool (Rabs (round radix2 fexp (round_mode mode) x)) (bpow radix2 emax) then
    FF2R radix2 z = round radix2 fexp (round_mode mode) x ∧
    is_finite_FF z = true ∧ sign_FF z = Rlt_bool x 0
  else
    z = binary_overflow mode (Rlt_bool x 0).

Lemma Bmult_correct_aux :
  ∀ m sx mx ex (Hx : bounded mx ex = true) sy my ey (Hy : bounded my ey = true),
  let x := F2R (Float radix2 (cond_Zopp sx (Zpos mx)) ex) in
  let y := F2R (Float radix2 (cond_Zopp sy (Zpos my)) ey) in
  let z := binary_round_aux m (xorb sx sy) (mx × my) (ex + ey) loc_Exact in
  valid_binary z = true ∧
  if Rlt_bool (Rabs (round radix2 fexp (round_mode m) (x × y))) (bpow radix2 emax) then
    FF2R radix2 z = round radix2 fexp (round_mode m) (x × y) ∧
    is_finite_FF z = true ∧ sign_FF z = xorb sx sy
  else
    z = binary_overflow m (xorb sx sy).

Definition Bmult mult_nan m x y :=
  let f pl := B754_nan (fst pl) (snd pl) in
  match x, y with
  | B754_nan _ _, _ | _, B754_nan _ _ ⇒ f (mult_nan x y)
  | B754_infinity sx, B754_infinity sy ⇒ B754_infinity (xorb sx sy)
  | B754_infinity sx, B754_finite sy _ _ _ ⇒ B754_infinity (xorb sx sy)
  | B754_finite sx _ _ _, B754_infinity sy ⇒ B754_infinity (xorb sx sy)
  | B754_infinity _, B754_zero _ ⇒ f (mult_nan x y)
  | B754_zero _, B754_infinity _ ⇒ f (mult_nan x y)
  | B754_finite sx _ _ _, B754_zero sy ⇒ B754_zero (xorb sx sy)
  | B754_zero sx, B754_finite sy _ _ _ ⇒ B754_zero (xorb sx sy)
  | B754_zero sx, B754_zero sy ⇒ B754_zero (xorb sx sy)
  | B754_finite sx mx ex Hx, B754_finite sy my ey Hy ⇒
    FF2B _ (proj1 (Bmult_correct_aux m sx mx ex Hx sy my ey Hy))
  end.

Theorem Bmult_correct :
  ∀ mult_nan m x y,
  if Rlt_bool (Rabs (round radix2 fexp (round_mode m) (B2R x × B2R y))) (bpow radix2 emax) then
    B2R (Bmult mult_nan m x y) = round radix2 fexp (round_mode m) (B2R x × B2R y) ∧
    is_finite (Bmult mult_nan m x y) = andb (is_finite x) (is_finite y) ∧
    (is_nan (Bmult mult_nan m x y) = false →
      Bsign (Bmult mult_nan m x y) = xorb (Bsign x) (Bsign y))
  else
    B2FF (Bmult mult_nan m x y) = binary_overflow m (xorb (Bsign x) (Bsign y)).

Definition Bmult_FF mult_nan m x y :=
  let f pl := F754_nan (fst pl) (snd pl) in
  match x, y with
  | F754_nan _ _, _ | _, F754_nan _ _ ⇒ f (mult_nan x y)
  | F754_infinity sx, F754_infinity sy ⇒ F754_infinity (xorb sx sy)
  | F754_infinity sx, F754_finite sy _ _ ⇒ F754_infinity (xorb sx sy)
  | F754_finite sx _ _, F754_infinity sy ⇒ F754_infinity (xorb sx sy)
  | F754_infinity _, F754_zero _ ⇒ f (mult_nan x y)
  | F754_zero _, F754_infinity _ ⇒ f (mult_nan x y)
  | F754_finite sx _ _, F754_zero sy ⇒ F754_zero (xorb sx sy)
  | F754_zero sx, F754_finite sy _ _ ⇒ F754_zero (xorb sx sy)
  | F754_zero sx, F754_zero sy ⇒ F754_zero (xorb sx sy)
  | F754_finite sx mx ex, F754_finite sy my ey ⇒
    binary_round_aux m (xorb sx sy) (mx × my) (ex + ey) loc_Exact
  end.

Theorem B2FF_Bmult :
  ∀ mult_nan mult_nan_ff,
  ∀ m x y,
  mult_nan_ff (B2FF x) (B2FF y) = (let '(sr, exist plr _) := mult_nan x y in (sr, plr)) →
  B2FF (Bmult mult_nan m x y) = Bmult_FF mult_nan_ff m (B2FF x) (B2FF y).

Definition shl_align mx ex ex' :=
  match (ex' - ex)%Z with
  | Zneg d ⇒ (shift_pos d mx, ex')
  | _ ⇒ (mx, ex)
  end.

Theorem shl_align_correct :
  ∀ mx ex ex',
  let (mx', ex'') := shl_align mx ex ex' in
  F2R (Float radix2 (Zpos mx) ex) = F2R (Float radix2 (Zpos mx') ex'') ∧
  (ex'' ≤ ex')%Z.

Theorem snd_shl_align :
  ∀ mx ex ex',
  (ex' ≤ ex)%Z →
  snd (shl_align mx ex ex') = ex'.

Definition shl_align_fexp mx ex :=
  shl_align mx ex (fexp (Zpos (digits2_pos mx) + ex)).

Theorem shl_align_fexp_correct :
  ∀ mx ex,
  let (mx', ex') := shl_align_fexp mx ex in
  F2R (Float radix2 (Zpos mx) ex) = F2R (Float radix2 (Zpos mx') ex') ∧
  (ex' ≤ fexp (Zdigits radix2 (Zpos mx') + ex'))%Z.

Definition binary_round m sx mx ex :=
  let '(mz, ez) := shl_align_fexp mx ex in binary_round_aux m sx mz ez loc_Exact.

Theorem binary_round_correct :
  ∀ m sx mx ex,
  let z := binary_round m sx mx ex in
  valid_binary z = true ∧
  let x := F2R (Float radix2 (cond_Zopp sx (Zpos mx)) ex) in
  if Rlt_bool (Rabs (round radix2 fexp (round_mode m) x)) (bpow radix2 emax) then
    FF2R radix2 z = round radix2 fexp (round_mode m) x ∧
    is_finite_FF z = true ∧
    sign_FF z = sx
  else
    z = binary_overflow m sx.

Definition binary_normalize mode m e szero :=
  match m with
  | Z0 ⇒ B754_zero szero
  | Zpos m ⇒ FF2B _ (proj1 (binary_round_correct mode false m e))
  | Zneg m ⇒ FF2B _ (proj1 (binary_round_correct mode true m e))
  end.

Theorem binary_normalize_correct :
  ∀ m mx ex szero,
  if Rlt_bool (Rabs (round radix2 fexp (round_mode m) (F2R (Float radix2 mx ex)))) (bpow radix2 emax) then
    B2R (binary_normalize m mx ex szero) = round radix2 fexp (round_mode m) (F2R (Float radix2 mx ex)) ∧
    is_finite (binary_normalize m mx ex szero) = true ∧
    Bsign (binary_normalize m mx ex szero) =
      match Rcompare (F2R (Float radix2 mx ex)) 0 with
        | Eq ⇒ szero
        | Lt ⇒ true
        | Gt ⇒ false
      end
  else
    B2FF (binary_normalize m mx ex szero) = binary_overflow m (Rlt_bool (F2R (Float radix2 mx ex)) 0).

Definition Bplus plus_nan m x y :=
  let f pl := B754_nan (fst pl) (snd pl) in
  match x, y with
  | B754_nan _ _, _ | _, B754_nan _ _ ⇒ f (plus_nan x y)
  | B754_infinity sx, B754_infinity sy ⇒
    if Bool.eqb sx sy then x else f (plus_nan x y)
  | B754_infinity _, _ ⇒ x
  | _, B754_infinity _ ⇒ y
  | B754_zero sx, B754_zero sy ⇒
    if Bool.eqb sx sy then x else
    match m with mode_DN ⇒ B754_zero true | _ ⇒ B754_zero false end
  | B754_zero _, _ ⇒ y
  | _, B754_zero _ ⇒ x
  | B754_finite sx mx ex Hx, B754_finite sy my ey Hy ⇒
    let ez := Zmin ex ey in
    binary_normalize m (Zplus (cond_Zopp sx (Zpos (fst (shl_align mx ex ez)))) (cond_Zopp sy (Zpos (fst (shl_align my ey ez)))))
      ez (match m with mode_DN ⇒ true | _ ⇒ false end)
  end.

Theorem Bplus_correct :
  ∀ plus_nan m x y,
  is_finite x = true →
  is_finite y = true →
  if Rlt_bool (Rabs (round radix2 fexp (round_mode m) (B2R x + B2R y))) (bpow radix2 emax) then
    B2R (Bplus plus_nan m x y) = round radix2 fexp (round_mode m) (B2R x + B2R y) ∧
    is_finite (Bplus plus_nan m x y) = true ∧
    Bsign (Bplus plus_nan m x y) =
      match Rcompare (B2R x + B2R y) 0 with
        | Eq ⇒ match m with mode_DN ⇒ orb (Bsign x) (Bsign y)
                                 | _ ⇒ andb (Bsign x) (Bsign y) end
        | Lt ⇒ true
        | Gt ⇒ false
      end
  else
    (B2FF (Bplus plus_nan m x y) = binary_overflow m (Bsign x) ∧ Bsign x = Bsign y).

Definition Bminus minus_nan m x y := Bplus minus_nan m x (Bopp pair y).

Theorem Bminus_correct :
  ∀ minus_nan m x y,
  is_finite x = true →
  is_finite y = true →
  if Rlt_bool (Rabs (round radix2 fexp (round_mode m) (B2R x - B2R y))) (bpow radix2 emax) then
    B2R (Bminus minus_nan m x y) = round radix2 fexp (round_mode m) (B2R x - B2R y) ∧
    is_finite (Bminus minus_nan m x y) = true ∧
    Bsign (Bminus minus_nan m x y) =
      match Rcompare (B2R x - B2R y) 0 with
        | Eq ⇒ match m with mode_DN ⇒ orb (Bsign x) (negb (Bsign y))
                                 | _ ⇒ andb (Bsign x) (negb (Bsign y)) end
        | Lt ⇒ true
        | Gt ⇒ false
      end
  else
    (B2FF (Bminus minus_nan m x y) = binary_overflow m (Bsign x) ∧ Bsign x = negb (Bsign y)).

Definition Fdiv_core_binary m1 e1 m2 e2 :=
  let d1 := Zdigits2 m1 in
  let d2 := Zdigits2 m2 in
  let e := (e1 - e2)%Z in
  let (m, e') :=
    match (d2 + prec - d1)%Z with
    | Zpos p ⇒ (Z.shiftl m1 (Zpos p), e + Zneg p)%Z
    | _ ⇒ (m1, e)
    end in
  let '(q, r) := Zfast_div_eucl m m2 in
  (q, e', new_location m2 r loc_Exact).

Lemma Bdiv_correct_aux :
  ∀ m sx mx ex sy my ey,
  let x := F2R (Float radix2 (cond_Zopp sx (Zpos mx)) ex) in
  let y := F2R (Float radix2 (cond_Zopp sy (Zpos my)) ey) in
  let z :=
    let '(mz, ez, lz) := Fdiv_core_binary (Zpos mx) ex (Zpos my) ey in
    match mz with
    | Zpos mz ⇒ binary_round_aux m (xorb sx sy) mz ez lz
    | _ ⇒ F754_nan false xH
    end in
  valid_binary z = true ∧
  if Rlt_bool (Rabs (round radix2 fexp (round_mode m) (x / y))) (bpow radix2 emax) then
    FF2R radix2 z = round radix2 fexp (round_mode m) (x / y) ∧
    is_finite_FF z = true ∧ sign_FF z = xorb sx sy
  else
    z = binary_overflow m (xorb sx sy).

Definition Bdiv div_nan m x y :=
  let f pl := B754_nan (fst pl) (snd pl) in
  match x, y with
  | B754_nan _ _, _ | _, B754_nan _ _ ⇒ f (div_nan x y)
  | B754_infinity sx, B754_infinity sy ⇒ f (div_nan x y)
  | B754_infinity sx, B754_finite sy _ _ _ ⇒ B754_infinity (xorb sx sy)
  | B754_finite sx _ _ _, B754_infinity sy ⇒ B754_zero (xorb sx sy)
  | B754_infinity sx, B754_zero sy ⇒ B754_infinity (xorb sx sy)
  | B754_zero sx, B754_infinity sy ⇒ B754_zero (xorb sx sy)
  | B754_finite sx _ _ _, B754_zero sy ⇒ B754_infinity (xorb sx sy)
  | B754_zero sx, B754_finite sy _ _ _ ⇒ B754_zero (xorb sx sy)
  | B754_zero sx, B754_zero sy ⇒ f (div_nan x y)
  | B754_finite sx mx ex _, B754_finite sy my ey _ ⇒
    FF2B _ (proj1 (Bdiv_correct_aux m sx mx ex sy my ey))
  end.

Theorem Bdiv_correct :
  ∀ div_nan m x y,
  B2R y ≠ R0 →
  if Rlt_bool (Rabs (round radix2 fexp (round_mode m) (B2R x / B2R y))) (bpow radix2 emax) then
    B2R (Bdiv div_nan m x y) = round radix2 fexp (round_mode m) (B2R x / B2R y) ∧
    is_finite (Bdiv div_nan m x y) = is_finite x ∧
    (is_nan (Bdiv div_nan m x y) = false →
      Bsign (Bdiv div_nan m x y) = xorb (Bsign x) (Bsign y))
  else
    B2FF (Bdiv div_nan m x y) = binary_overflow m (xorb (Bsign x) (Bsign y)).

Definition Fsqrt_core_binary m e :=
  let d := Zdigits2 m in
  let s := Zmax (2 × prec - d) 0 in
  let e' := (e - s)%Z in
  let (s', e'') := if Zeven e' then (s, e') else (s + 1, e' - 1)%Z in
  let m' :=
    match s' with
    | Zpos p ⇒ Z.shiftl m (Zpos p)
    | _ ⇒ m
    end in
  let (q, r) := Z.sqrtrem m' in
  let l :=
    if Zeq_bool r 0 then loc_Exact
    else loc_Inexact (if Zle_bool r q then Lt else Gt) in
  (q, Zdiv2 e'', l).

Lemma Bsqrt_correct_aux :
  ∀ m mx ex (Hx : bounded mx ex = true),
  let x := F2R (Float radix2 (Zpos mx) ex) in
  let z :=
    let '(mz, ez, lz) := Fsqrt_core_binary (Zpos mx) ex in
    match mz with
    | Zpos mz ⇒ binary_round_aux m false mz ez lz
    | _ ⇒ F754_nan false xH
    end in
  valid_binary z = true ∧
  FF2R radix2 z = round radix2 fexp (round_mode m) (sqrt x) ∧
  is_finite_FF z = true ∧ sign_FF z = false.

Definition Bsqrt sqrt_nan m x :=
  let f pl := B754_nan (fst pl) (snd pl) in
  match x with
  | B754_nan sx plx ⇒ f (sqrt_nan x)
  | B754_infinity false ⇒ x
  | B754_infinity true ⇒ f (sqrt_nan x)
  | B754_finite true _ _ _ ⇒ f (sqrt_nan x)
  | B754_zero _ ⇒ x
  | B754_finite sx mx ex Hx ⇒
    FF2B _ (proj1 (Bsqrt_correct_aux m mx ex Hx))
  end.

Theorem Bsqrt_correct :
  ∀ sqrt_nan m x,
  B2R (Bsqrt sqrt_nan m x) = round radix2 fexp (round_mode m) (sqrt (B2R x)) ∧
  is_finite (Bsqrt sqrt_nan m x) = match x with B754_zero _ ⇒ true | B754_finite false _ _ _ ⇒ true | _ ⇒ false end ∧
  (is_nan (Bsqrt sqrt_nan m x) = false → Bsign (Bsqrt sqrt_nan m x) = Bsign x).

End Binary.