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Diffstat (limited to 'theories/Numbers/DecimalPos.v')
-rw-r--r-- | theories/Numbers/DecimalPos.v | 383 |
1 files changed, 383 insertions, 0 deletions
diff --git a/theories/Numbers/DecimalPos.v b/theories/Numbers/DecimalPos.v new file mode 100644 index 00000000..722e73d9 --- /dev/null +++ b/theories/Numbers/DecimalPos.v @@ -0,0 +1,383 @@ +(************************************************************************) +(* * The Coq Proof Assistant / The Coq Development Team *) +(* v * INRIA, CNRS and contributors - Copyright 1999-2018 *) +(* <O___,, * (see CREDITS file for the list of authors) *) +(* \VV/ **************************************************************) +(* // * This file is distributed under the terms of the *) +(* * GNU Lesser General Public License Version 2.1 *) +(* * (see LICENSE file for the text of the license) *) +(************************************************************************) + +(** * DecimalPos + + Proofs that conversions between decimal numbers and [positive] + are bijections. *) + +Require Import Decimal DecimalFacts PArith NArith. + +Module Unsigned. + +Local Open Scope N. + +(** A direct version of [of_little_uint] *) +Fixpoint of_lu (d:uint) : N := + match d with + | Nil => 0 + | D0 d => 10 * of_lu d + | D1 d => 1 + 10 * of_lu d + | D2 d => 2 + 10 * of_lu d + | D3 d => 3 + 10 * of_lu d + | D4 d => 4 + 10 * of_lu d + | D5 d => 5 + 10 * of_lu d + | D6 d => 6 + 10 * of_lu d + | D7 d => 7 + 10 * of_lu d + | D8 d => 8 + 10 * of_lu d + | D9 d => 9 + 10 * of_lu d + end. + +Definition hd d := +match d with + | Nil => 0 + | D0 _ => 0 + | D1 _ => 1 + | D2 _ => 2 + | D3 _ => 3 + | D4 _ => 4 + | D5 _ => 5 + | D6 _ => 6 + | D7 _ => 7 + | D8 _ => 8 + | D9 _ => 9 +end. + +Definition tl d := + match d with + | Nil => d + | D0 d | D1 d | D2 d | D3 d | D4 d | D5 d | D6 d | D7 d | D8 d | D9 d => d +end. + +Lemma of_lu_eqn d : + of_lu d = hd d + 10 * (of_lu (tl d)). +Proof. + induction d; simpl; trivial. +Qed. + +Ltac simpl_of_lu := + match goal with + | |- context [ of_lu (?f ?x) ] => + rewrite (of_lu_eqn (f x)); simpl hd; simpl tl + end. + +Fixpoint usize (d:uint) : N := + match d with + | Nil => 0 + | D0 d => N.succ (usize d) + | D1 d => N.succ (usize d) + | D2 d => N.succ (usize d) + | D3 d => N.succ (usize d) + | D4 d => N.succ (usize d) + | D5 d => N.succ (usize d) + | D6 d => N.succ (usize d) + | D7 d => N.succ (usize d) + | D8 d => N.succ (usize d) + | D9 d => N.succ (usize d) + end. + +Lemma of_lu_revapp d d' : + of_lu (revapp d d') = + of_lu (rev d) + of_lu d' * 10^usize d. +Proof. + revert d'. + induction d; simpl; intro d'; [ now rewrite N.mul_1_r | .. ]; + unfold rev; simpl revapp; rewrite 2 IHd; + rewrite <- N.add_assoc; f_equal; simpl_of_lu; simpl of_lu; + rewrite N.pow_succ_r'; ring. +Qed. + +Definition Nadd n p := + match n with + | N0 => p + | Npos p0 => (p0+p)%positive + end. + +Lemma Nadd_simpl n p q : Npos (Nadd n (p * q)) = n + Npos p * Npos q. +Proof. + now destruct n. +Qed. + +Lemma of_uint_acc_eqn d acc : d<>Nil -> + Pos.of_uint_acc d acc = Pos.of_uint_acc (tl d) (Nadd (hd d) (10*acc)). +Proof. + destruct d; simpl; trivial. now destruct 1. +Qed. + +Lemma of_uint_acc_rev d acc : + Npos (Pos.of_uint_acc d acc) = + of_lu (rev d) + (Npos acc) * 10^usize d. +Proof. + revert acc. + induction d; intros; simpl usize; + [ simpl; now rewrite Pos.mul_1_r | .. ]; + rewrite N.pow_succ_r'; + unfold rev; simpl revapp; try rewrite of_lu_revapp; simpl of_lu; + rewrite of_uint_acc_eqn by easy; simpl tl; simpl hd; + rewrite IHd, Nadd_simpl; ring. +Qed. + +Lemma of_uint_alt d : Pos.of_uint d = of_lu (rev d). +Proof. + induction d; simpl; trivial; unfold rev; simpl revapp; + rewrite of_lu_revapp; simpl of_lu; try apply of_uint_acc_rev. + rewrite IHd. ring. +Qed. + +Lemma of_lu_rev d : Pos.of_uint (rev d) = of_lu d. +Proof. + rewrite of_uint_alt. now rewrite rev_rev. +Qed. + +Lemma of_lu_double_gen d : + of_lu (Little.double d) = N.double (of_lu d) /\ + of_lu (Little.succ_double d) = N.succ_double (of_lu d). +Proof. + rewrite N.double_spec, N.succ_double_spec. + induction d; try destruct IHd as (IH1,IH2); + simpl Little.double; simpl Little.succ_double; + repeat (simpl_of_lu; rewrite ?IH1, ?IH2); split; reflexivity || ring. +Qed. + +Lemma of_lu_double d : + of_lu (Little.double d) = N.double (of_lu d). +Proof. + apply of_lu_double_gen. +Qed. + +Lemma of_lu_succ_double d : + of_lu (Little.succ_double d) = N.succ_double (of_lu d). +Proof. + apply of_lu_double_gen. +Qed. + +(** First bijection result *) + +Lemma of_to (p:positive) : Pos.of_uint (Pos.to_uint p) = Npos p. +Proof. + unfold Pos.to_uint. + rewrite of_lu_rev. + induction p; simpl; trivial. + - now rewrite of_lu_succ_double, IHp. + - now rewrite of_lu_double, IHp. +Qed. + +(** The other direction *) + +Definition to_lu n := + match n with + | N0 => Decimal.zero + | Npos p => Pos.to_little_uint p + end. + +Lemma succ_double_alt d : + Little.succ_double d = Little.succ (Little.double d). +Proof. + now induction d. +Qed. + +Lemma double_succ d : + Little.double (Little.succ d) = + Little.succ (Little.succ_double d). +Proof. + induction d; simpl; f_equal; auto using succ_double_alt. +Qed. + +Lemma to_lu_succ n : + to_lu (N.succ n) = Little.succ (to_lu n). +Proof. + destruct n; simpl; trivial. + induction p; simpl; rewrite ?IHp; + auto using succ_double_alt, double_succ. +Qed. + +Lemma nat_iter_S n {A} (f:A->A) i : + Nat.iter (S n) f i = f (Nat.iter n f i). +Proof. + reflexivity. +Qed. + +Lemma nat_iter_0 {A} (f:A->A) i : Nat.iter 0 f i = i. +Proof. + reflexivity. +Qed. + +Lemma to_ldec_tenfold p : + to_lu (10 * Npos p) = D0 (to_lu (Npos p)). +Proof. + induction p using Pos.peano_rect. + - trivial. + - change (N.pos (Pos.succ p)) with (N.succ (N.pos p)). + rewrite N.mul_succ_r. + change 10 at 2 with (Nat.iter 10%nat N.succ 0). + rewrite ?nat_iter_S, nat_iter_0. + rewrite !N.add_succ_r, N.add_0_r, !to_lu_succ, IHp. + destruct (to_lu (N.pos p)); simpl; auto. +Qed. + +Lemma of_lu_0 d : of_lu d = 0 <-> nztail d = Nil. +Proof. + induction d; try simpl_of_lu; split; trivial; try discriminate; + try (intros H; now apply N.eq_add_0 in H). + - rewrite N.add_0_l. intros H. + apply N.eq_mul_0_r in H; [|easy]. rewrite IHd in H. + simpl. now rewrite H. + - simpl. destruct (nztail d); try discriminate. + now destruct IHd as [_ ->]. +Qed. + +Lemma to_of_lu_tenfold d : + to_lu (of_lu d) = lnorm d -> + to_lu (10 * of_lu d) = lnorm (D0 d). +Proof. + intro IH. + destruct (N.eq_dec (of_lu d) 0) as [H|H]. + - rewrite H. simpl. rewrite of_lu_0 in H. + unfold lnorm. simpl. now rewrite H. + - destruct (of_lu d) eqn:Eq; [easy| ]. + rewrite to_ldec_tenfold; auto. rewrite IH. + rewrite <- Eq in H. rewrite of_lu_0 in H. + unfold lnorm. simpl. now destruct (nztail d). +Qed. + +Lemma Nadd_alt n m : n + m = Nat.iter (N.to_nat n) N.succ m. +Proof. + destruct n. trivial. + induction p using Pos.peano_rect. + - now rewrite N.add_1_l. + - change (N.pos (Pos.succ p)) with (N.succ (N.pos p)). + now rewrite N.add_succ_l, IHp, N2Nat.inj_succ. +Qed. + +Ltac simpl_to_nat := simpl N.to_nat; unfold Pos.to_nat; simpl Pos.iter_op. + +Lemma to_of_lu d : to_lu (of_lu d) = lnorm d. +Proof. + induction d; [reflexivity|..]; + simpl_of_lu; rewrite Nadd_alt; simpl_to_nat; + rewrite ?nat_iter_S, nat_iter_0, ?to_lu_succ, to_of_lu_tenfold by assumption; + unfold lnorm; simpl; destruct nztail; auto. +Qed. + +(** Second bijection result *) + +Lemma to_of (d:uint) : N.to_uint (Pos.of_uint d) = unorm d. +Proof. + rewrite of_uint_alt. + unfold N.to_uint, Pos.to_uint. + destruct (of_lu (rev d)) eqn:H. + - rewrite of_lu_0 in H. rewrite <- rev_lnorm_rev. + unfold lnorm. now rewrite H. + - change (Pos.to_little_uint p) with (to_lu (N.pos p)). + rewrite <- H. rewrite to_of_lu. apply rev_lnorm_rev. +Qed. + +(** Some consequences *) + +Lemma to_uint_nonzero p : Pos.to_uint p <> zero. +Proof. + intro E. generalize (of_to p). now rewrite E. +Qed. + +Lemma to_uint_nonnil p : Pos.to_uint p <> Nil. +Proof. + intros E. generalize (of_to p). now rewrite E. +Qed. + +Lemma to_uint_inj p p' : Pos.to_uint p = Pos.to_uint p' -> p = p'. +Proof. + intro E. + assert (E' : N.pos p = N.pos p'). + { now rewrite <- (of_to p), <- (of_to p'), E. } + now injection E'. +Qed. + +Lemma to_uint_pos_surj d : + unorm d<>zero -> exists p, Pos.to_uint p = unorm d. +Proof. + intros. + destruct (Pos.of_uint d) eqn:E. + - destruct H. generalize (to_of d). now rewrite E. + - exists p. generalize (to_of d). now rewrite E. +Qed. + +Lemma of_uint_norm d : Pos.of_uint (unorm d) = Pos.of_uint d. +Proof. + now induction d. +Qed. + +Lemma of_inj d d' : + Pos.of_uint d = Pos.of_uint d' -> unorm d = unorm d'. +Proof. + intros. rewrite <- !to_of. now f_equal. +Qed. + +Lemma of_iff d d' : Pos.of_uint d = Pos.of_uint d' <-> unorm d = unorm d'. +Proof. + split. apply of_inj. intros E. rewrite <- of_uint_norm, E. + apply of_uint_norm. +Qed. + +End Unsigned. + +(** Conversion from/to signed decimal numbers *) + +Module Signed. + +Lemma of_to (p:positive) : Pos.of_int (Pos.to_int p) = Some p. +Proof. + unfold Pos.to_int, Pos.of_int, norm. + now rewrite Unsigned.of_to. +Qed. + +Lemma to_of (d:int)(p:positive) : + Pos.of_int d = Some p -> Pos.to_int p = norm d. +Proof. + unfold Pos.of_int. + destruct d; [ | intros [=]]. + simpl norm. rewrite <- Unsigned.to_of. + destruct (Pos.of_uint d); now intros [= <-]. +Qed. + +Lemma to_int_inj p p' : Pos.to_int p = Pos.to_int p' -> p = p'. +Proof. + intro E. + assert (E' : Some p = Some p'). + { now rewrite <- (of_to p), <- (of_to p'), E. } + now injection E'. +Qed. + +Lemma to_int_pos_surj d : + unorm d <> zero -> exists p, Pos.to_int p = norm (Pos d). +Proof. + simpl. unfold Pos.to_int. intros H. + destruct (Unsigned.to_uint_pos_surj d H) as (p,Hp). + exists p. now f_equal. +Qed. + +Lemma of_int_norm d : Pos.of_int (norm d) = Pos.of_int d. +Proof. + unfold Pos.of_int. + destruct d. + - simpl. now rewrite Unsigned.of_uint_norm. + - simpl. now destruct (nzhead d) eqn:H. +Qed. + +Lemma of_inj_pos d d' : + Pos.of_int (Pos d) = Pos.of_int (Pos d') -> unorm d = unorm d'. +Proof. + unfold Pos.of_int. + destruct (Pos.of_uint d) eqn:Hd, (Pos.of_uint d') eqn:Hd'; + intros [=]. + - apply Unsigned.of_inj; now rewrite Hd, Hd'. + - apply Unsigned.of_inj; rewrite Hd, Hd'; now f_equal. +Qed. + +End Signed. |