Proof with auto with typeclass_instances.
intros plus_nan m [sx|sx| |sx mx ex Hx] [sy|sy| |sy my ey Hy] Fx Fy ; try easy.
(* *)
rewrite Rplus_0_r, round_0, Rabs_R0, Rlt_bool_true...
simpl.
rewrite Rcompare_Eq by auto.
destruct sx, sy; try easy; now case m.
apply bpow_gt_0.
(* *)
rewrite Rplus_0_l, round_generic, Rlt_bool_true...
split... split...
simpl. unfold F2R.
erewrite <- Rmult_0_l, Rcompare_mult_r.
rewrite Rcompare_Z2R with (y:=0%Z).
destruct sy...
apply bpow_gt_0.
apply abs_B2R_lt_emax.
apply generic_format_B2R.
(* *)
rewrite Rplus_0_r, round_generic, Rlt_bool_true...
split... split...
simpl. unfold F2R.
erewrite <- Rmult_0_l, Rcompare_mult_r.
rewrite Rcompare_Z2R with (y:=0%Z).
destruct sx...
apply bpow_gt_0.
apply abs_B2R_lt_emax.
apply generic_format_B2R.
(* *)
clear Fx Fy.
simpl.
set (szero := match m with mode_DN => true | _ => false end).
set (ez := Zmin ex ey).
set (mz := (cond_Zopp sx (Zpos (fst (shl_align mx ex ez))) + cond_Zopp sy (Zpos (fst (shl_align my ey ez))))%Z).
assert (Hp: (F2R (Float radix2 (cond_Zopp sx (Zpos mx)) ex) +
F2R (Float radix2 (cond_Zopp sy (Zpos my)) ey))%R = F2R (Float radix2 mz ez)).
rewrite 2!F2R_cond_Zopp.
generalize (shl_align_correct mx ex ez).
generalize (shl_align_correct my ey ez).
generalize (snd_shl_align mx ex ez (Zle_min_l ex ey)).
generalize (snd_shl_align my ey ez (Zle_min_r ex ey)).
destruct (shl_align mx ex ez) as (mx', ex').
destruct (shl_align my ey ez) as (my', ey').
simpl.
intros H1 H2.
rewrite H1, H2.
clear H1 H2.
intros (H1, _) (H2, _).
rewrite H1, H2.
clear H1 H2.
rewrite <- 2!F2R_cond_Zopp.
unfold F2R. simpl.
now rewrite <- Rmult_plus_distr_r, <- Z2R_plus.
rewrite Hp.
assert (Sz: (bpow radix2 emax <= Rabs (round radix2 fexp (round_mode m) (F2R (Float radix2 mz ez))))%R -> sx = Rlt_bool (F2R (Float radix2 mz ez)) 0 /\ sx = sy).
(* . *)
rewrite <- Hp.
intros Bz.
destruct (Bool.bool_dec sx sy) as [Hs|Hs].
(* .. *)
refine (conj _ Hs).
rewrite Hs.
apply sym_eq.
case sy.
apply Rlt_bool_true.
rewrite <- (Rplus_0_r 0).
apply Rplus_lt_compat.
now apply F2R_lt_0_compat.
now apply F2R_lt_0_compat.
apply Rlt_bool_false.
rewrite <- (Rplus_0_r 0).
apply Rplus_le_compat.
now apply F2R_ge_0_compat.
now apply F2R_ge_0_compat.
(* .. *)
elim Rle_not_lt with (1 := Bz).
generalize (bounded_lt_emax _ _ Hx) (bounded_lt_emax _ _ Hy) (andb_prop _ _ Hx) (andb_prop _ _ Hy).
intros Bx By (Hx',_) (Hy',_).
generalize (canonic_canonic_mantissa sx _ _ Hx') (canonic_canonic_mantissa sy _ _ Hy').
clear -Bx By Hs prec_gt_0_.
intros Cx Cy.
destruct sx.
(* ... *)
destruct sy.
now elim Hs.
clear Hs.
apply Rabs_lt.
split.
apply Rlt_le_trans with (F2R (Float radix2 (cond_Zopp true (Zpos mx)) ex)).
rewrite F2R_Zopp.
now apply Ropp_lt_contravar.
apply round_ge_generic...
now apply generic_format_canonic.
pattern (F2R (Float radix2 (cond_Zopp true (Zpos mx)) ex)) at 1 ; rewrite <- Rplus_0_r.
apply Rplus_le_compat_l.
now apply F2R_ge_0_compat.
apply Rle_lt_trans with (2 := By).
apply round_le_generic...
now apply generic_format_canonic.
rewrite <- (Rplus_0_l (F2R (Float radix2 (Zpos my) ey))).
apply Rplus_le_compat_r.
now apply F2R_le_0_compat.
(* ... *)
destruct sy.
2: now elim Hs.
clear Hs.
apply Rabs_lt.
split.
apply Rlt_le_trans with (F2R (Float radix2 (cond_Zopp true (Zpos my)) ey)).
rewrite F2R_Zopp.
now apply Ropp_lt_contravar.
apply round_ge_generic...
now apply generic_format_canonic.
pattern (F2R (Float radix2 (cond_Zopp true (Zpos my)) ey)) at 1 ; rewrite <- Rplus_0_l.
apply Rplus_le_compat_r.
now apply F2R_ge_0_compat.
apply Rle_lt_trans with (2 := Bx).
apply round_le_generic...
now apply generic_format_canonic.
rewrite <- (Rplus_0_r (F2R (Float radix2 (Zpos mx) ex))).
apply Rplus_le_compat_l.
now apply F2R_le_0_compat.
(* . *)
generalize (binary_normalize_correct m mz ez szero).
case Rlt_bool_spec.
split; try easy. split; try easy.
destruct (Rcompare_spec (F2R (beta:=radix2) {| Fnum := mz; Fexp := ez |}) 0); try easy.
rewrite H1 in Hp.
apply Rplus_opp_r_uniq in Hp.
rewrite <- F2R_Zopp in Hp.
eapply canonic_unicity in Hp.
inversion Hp. destruct sy, sx, m; try discriminate H3; easy.
apply canonic_canonic_mantissa.
apply Bool.andb_true_iff in Hy. easy.
replace (-cond_Zopp sx (Z.pos mx))%Z with  (cond_Zopp (negb sx) (Z.pos mx))
by (destruct sx; auto).
apply canonic_canonic_mantissa.
apply Bool.andb_true_iff in Hx. easy.
intros Hz' Vz.
specialize (Sz Hz').
split.
rewrite Vz.
now apply f_equal.
apply Sz.
Qed.
(** Subtraction *)
Definition Bminus minus_nan m x y := Bplus minus_nan m x (Bopp pair y).

Theorem Bminus_correct :
forall 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)).