1 files changed, 65 insertions, 70 deletions

diff --git a/src/ModularArithmetic/Pow2BaseProofs.v b/src/ModularArithmetic/Pow2BaseProofs.v
index a9b9fbdfc..da9bbac0d 100644
--- a/src/ModularArithmetic/Pow2BaseProofs.v
+++ b/src/ModularArithmetic/Pow2BaseProofs.v
@@ -35,7 +35,7 @@ Section Pow2BaseProofs.
   Lemma two_sum_firstn_limb_widths_nonzero n : 2^sum_firstn limb_widths n <> 0.
   Proof. pose proof (two_sum_firstn_limb_widths_pos n); omega. Qed.
 
-  Lemma base_from_limb_widths_step : forall i b w, (S i < length base)%nat ->
+  Lemma base_from_limb_widths_step : forall i b w, (S i < length limb_widths)%nat ->
     nth_error base i = Some b ->
     nth_error limb_widths i = Some w ->
     nth_error base (S i) = Some (two_p w * b).
@@ -43,7 +43,7 @@ Section Pow2BaseProofs.
     induction limb_widths; intros ? ? ? ? nth_err_w nth_err_b;
       unfold base_from_limb_widths in *; fold base_from_limb_widths in *;
       [rewrite (@nil_length0 Z) in *; omega | ].
-    simpl in *; rewrite map_length in *.
+    simpl in *.
     case_eq i; intros; subst.
     + subst; apply nth_error_first in nth_err_w.
       apply nth_error_first in nth_err_b; subst.
@@ -61,15 +61,14 @@ Section Pow2BaseProofs.
   Qed.
 
 
-  Lemma nth_error_base : forall i, (i < length base)%nat ->
+  Lemma nth_error_base : forall i, (i < length limb_widths)%nat ->
     nth_error base i = Some (two_p (sum_firstn limb_widths i)).
   Proof.
     induction i; intros.
     + unfold sum_firstn, base_from_limb_widths in *; case_eq limb_widths; try reflexivity.
       intro lw_nil; rewrite lw_nil, (@nil_length0 Z) in *; omega.
-    + assert (i < length base)%nat as lt_i_length by omega.
+    + assert (i < length limb_widths)%nat as lt_i_length by omega.
       specialize (IHi lt_i_length).
-      rewrite base_from_limb_widths_length in lt_i_length.
       destruct (nth_error_length_exists_value _ _ lt_i_length) as [w nth_err_w].
       erewrite base_from_limb_widths_step; eauto.
       f_equal.
@@ -87,19 +86,16 @@ Section Pow2BaseProofs.
         eapply nth_error_value_In; eauto.
   Qed.
 
-  Lemma nth_default_base : forall d i, (i < length base)%nat ->
+  Lemma nth_default_base : forall d i, (i < length limb_widths)%nat ->
     nth_default d base i = 2 ^ (sum_firstn limb_widths i).
   Proof.
     intros ? ? i_lt_length.
-    destruct (nth_error_length_exists_value _ _ i_lt_length) as [x nth_err_x].
-    unfold nth_default.
-    rewrite nth_err_x.
-    rewrite nth_error_base in nth_err_x by assumption.
-    rewrite two_p_correct in nth_err_x.
-    congruence.
+    apply nth_error_value_eq_nth_default.
+    rewrite nth_error_base, two_p_correct by assumption.
+    reflexivity.
   Qed.
 
-  Lemma base_succ : forall i, ((S i) < length base)%nat ->
+  Lemma base_succ : forall i, ((S i) < length limb_widths)%nat ->
     nth_default 0 base (S i) mod nth_default 0 base i = 0.
   Proof.
     intros.
@@ -112,8 +108,7 @@ Section Pow2BaseProofs.
         apply limb_widths_nonneg.
         rewrite lw_eq.
         apply in_eq.
-      + assert (i < length base)%nat as i_lt_length by omega.
-        rewrite base_from_limb_widths_length in *.
+      + assert (i < length limb_widths)%nat as i_lt_length by omega.
         apply nth_error_length_exists_value in i_lt_length.
         destruct i_lt_length as [x nth_err_x].
         erewrite sum_firstn_succ; eauto.
@@ -127,6 +122,7 @@ Section Pow2BaseProofs.
    Proof.
      intros i b nth_err_b.
      pose proof (nth_error_value_length _ _ _ _ nth_err_b).
+     rewrite base_from_limb_widths_length in *.
      rewrite nth_error_base in nth_err_b by assumption.
      rewrite two_p_correct in nth_err_b.
      congruence.
@@ -169,19 +165,19 @@ Section Pow2BaseProofs.
   Section make_base_vector.
     Local Notation k := (sum_firstn limb_widths (length limb_widths)).
     Context (limb_widths_match_modulus : forall i j,
-                (i < length limb_widths)%nat ->
-                (j < length limb_widths)%nat ->
-                (i + j >= length limb_widths)%nat ->
+                (i < length base)%nat ->
+                (j < length base)%nat ->
+                (i + j >= length base)%nat ->
                 let w_sum := sum_firstn limb_widths in
-                k + w_sum (i + j - length limb_widths)%nat <= w_sum i + w_sum j)
+                k + w_sum (i + j - length base)%nat <= w_sum i + w_sum j)
             (limb_widths_good : forall i j, (i + j < length limb_widths)%nat ->
                                             sum_firstn limb_widths (i + j) <=
                                             sum_firstn limb_widths i + sum_firstn limb_widths j).
 
     Lemma base_matches_modulus: forall i j,
-      (i   <  length limb_widths)%nat ->
-      (j   <  length limb_widths)%nat ->
-      (i+j >= length limb_widths)%nat->
+      (i   <  length base)%nat ->
+      (j   <  length base)%nat ->
+      (i+j >= length base)%nat->
       let b := nth_default 0 base in
       let r := (b i * b j)  /   (2^k * b (i+j-length base)%nat) in
                 b i * b j = r * (2^k * b (i+j-length base)%nat).
@@ -189,20 +185,20 @@ Section Pow2BaseProofs.
       intros.
       rewrite (Z.mul_comm r).
       subst r.
+      rewrite base_from_limb_widths_length in *;
       assert (i + j - length limb_widths < length limb_widths)%nat by omega.
-      rewrite Z.mul_div_eq by (apply Z.gt_lt_iff; apply Z.mul_pos_pos;
-        subst b; rewrite ?nth_default_base; zero_bounds; rewrite ?base_from_limb_widths_length;
-        auto using sum_firstn_limb_widths_nonneg, limb_widths_nonneg).
+      rewrite Z.mul_div_eq by (apply Z.gt_lt_iff; subst b; rewrite ?nth_default_base; zero_bounds;
+        assumption).
       rewrite (Zminus_0_l_reverse (b i * b j)) at 1.
       f_equal.
       subst b.
-      repeat rewrite nth_default_base by (rewrite ?base_from_limb_widths_length; auto).
+      repeat rewrite nth_default_base by auto.
       do 2 rewrite <- Z.pow_add_r by auto using sum_firstn_limb_widths_nonneg.
       symmetry.
       apply Z.mod_same_pow.
       split.
       + apply Z.add_nonneg_nonneg; auto using sum_firstn_limb_widths_nonneg.
-      + rewrite base_from_limb_widths_length; auto using limb_widths_nonneg, limb_widths_match_modulus.
+      + auto using limb_widths_match_modulus.
     Qed.
 
     Lemma base_good : forall i j : nat,
@@ -212,7 +208,9 @@ Section Pow2BaseProofs.
                  b i * b j = r * b (i + j)%nat.
     Proof.
       intros; subst b r.
-      repeat rewrite nth_default_base by (omega || auto).
+      clear limb_widths_match_modulus.
+      rewrite base_from_limb_widths_length in *.
+      repeat rewrite nth_default_base by omega.
       rewrite (Z.mul_comm _ (2 ^ (sum_firstn limb_widths (i+j)))).
       rewrite Z.mul_div_eq by (apply Z.gt_lt_iff; zero_bounds;
         auto using sum_firstn_limb_widths_nonneg).
@@ -220,10 +218,11 @@ Section Pow2BaseProofs.
       rewrite Z.mod_same_pow; try ring.
       split; [ auto using sum_firstn_limb_widths_nonneg | ].
       apply limb_widths_good.
-      rewrite <-base_from_limb_widths_length; auto using limb_widths_nonneg.
+      assumption.
     Qed.
   End make_base_vector.
 End Pow2BaseProofs.
+Hint Rewrite @base_from_limb_widths_length : distr_length.
 
 Section BitwiseDecodeEncode.
   Context {limb_widths} (bv : BaseSystem.BaseVector (base_from_limb_widths limb_widths))
@@ -233,7 +232,7 @@ Section BitwiseDecodeEncode.
   Local Notation base := (base_from_limb_widths limb_widths).
   Local Notation upper_bound := (upper_bound limb_widths).
 
-  Lemma encode'_spec : forall x i, (i <= length base)%nat ->
+  Lemma encode'_spec : forall x i, (i <= length limb_widths)%nat ->
     encode' limb_widths x i = BaseSystem.encode' base x upper_bound i.
   Proof.
     induction i; intros.
@@ -241,13 +240,12 @@ Section BitwiseDecodeEncode.
     + rewrite encode'_succ, <-IHi by omega.
       simpl; do 2 f_equal.
       rewrite Z.land_ones, Z.shiftr_div_pow2 by auto using sum_firstn_limb_widths_nonneg.
-      match goal with H : (S _ <= length base)%nat |- _ =>
+      match goal with H : (S _ <= length limb_widths)%nat |- _ =>
         apply le_lt_or_eq in H; destruct H end.
       - repeat f_equal; rewrite nth_default_base by (omega || auto); reflexivity.
       - repeat f_equal; try solve [rewrite nth_default_base by (omega || auto); reflexivity].
-        rewrite nth_default_out_of_bounds by omega.
+        rewrite nth_default_out_of_bounds by (distr_length; omega).
         unfold Pow2Base.upper_bound.
-        rewrite <-base_from_limb_widths_length by auto.
         congruence.
   Qed.
 
@@ -259,20 +257,17 @@ Section BitwiseDecodeEncode.
   Lemma base_upper_bound_compatible : @base_max_succ_divide base upper_bound.
   Proof.
     unfold base_max_succ_divide; intros i lt_Si_length.
+    rewrite base_from_limb_widths_length in lt_Si_length.
     rewrite Nat.lt_eq_cases in lt_Si_length; destruct lt_Si_length;
       rewrite !nth_default_base by (omega || auto).
-    + erewrite sum_firstn_succ by (eapply nth_error_Some_nth_default with (x := 0);
-         rewrite <-base_from_limb_widths_length by auto; omega).
+    + erewrite sum_firstn_succ by (eapply nth_error_Some_nth_default with (x := 0); omega).
       rewrite Z.pow_add_r; auto using sum_firstn_limb_widths_nonneg.
       apply Z.divide_factor_r.
-    + rewrite nth_default_out_of_bounds by omega.
+    + rewrite nth_default_out_of_bounds by (distr_length; omega).
       unfold Pow2Base.upper_bound.
-      replace (length limb_widths) with (S (pred (length limb_widths))) by
-        (rewrite base_from_limb_widths_length in H by auto; omega).
-      replace i with (pred (length limb_widths)) by
-        (rewrite base_from_limb_widths_length in H by auto; omega).
-      erewrite sum_firstn_succ by (eapply nth_error_Some_nth_default with (x := 0);
-         rewrite <-base_from_limb_widths_length by auto; omega).
+      replace (length limb_widths) with (S (pred (length limb_widths))) by omega.
+      replace i with (pred (length limb_widths)) by omega.
+      erewrite sum_firstn_succ by (eapply nth_error_Some_nth_default with (x := 0); omega).
       rewrite Z.pow_add_r; auto using sum_firstn_limb_widths_nonneg.
       apply Z.divide_factor_r.
   Qed.
@@ -282,7 +277,7 @@ Section BitwiseDecodeEncode.
     BaseSystem.decode base (encodeZ limb_widths x) = x mod upper_bound.
   Proof.
     intros.
-    assert (length base = length limb_widths) by auto using base_from_limb_widths_length.
+    assert (length base = length limb_widths) by distr_length.
     unfold encodeZ; rewrite encode'_spec by omega.
     rewrite BaseSystemProofs.encode'_spec; unfold Pow2Base.upper_bound; try zero_bounds;
       auto using sum_firstn_limb_widths_nonneg.
@@ -522,7 +517,7 @@ Section carrying_helper.
   Local Notation base := (base_from_limb_widths limb_widths).
   Local Notation log_cap i := (nth_default 0 limb_widths i).
 
-  Lemma update_nth_sum : forall n f us, (n < length us \/ n >= length base)%nat ->
+  Lemma update_nth_sum : forall n f us, (n < length us \/ n >= length limb_widths)%nat ->
     BaseSystem.decode base (update_nth n f us) =
     (let v := nth_default 0 us n in f v - v) * nth_default 0 base n + BaseSystem.decode base us.
   Proof.
@@ -541,17 +536,17 @@ Section carrying_helper.
       erewrite (nth_error_value_eq_nth_default _ _ us) by eassumption.
       rewrite firstn_length in Heqn0.
       rewrite Min.min_l in Heqn0 by omega; subst n0.
-      destruct (le_lt_dec (length base) n). {
-        rewrite (@nth_default_out_of_bounds _ _ base) by auto.
-        rewrite skipn_all by omega.
+      destruct (le_lt_dec (length limb_widths) n). {
+        rewrite (@nth_default_out_of_bounds _ _ base) by (distr_length; auto).
+        rewrite skipn_all by (rewrite base_from_limb_widths_length; omega).
         do 2 rewrite decode_base_nil.
         ring_simplify; auto.
       } {
-        rewrite (skipn_nth_default n base 0) by omega.
+        rewrite (skipn_nth_default n base 0) by (distr_length; omega).
         do 2 rewrite decode'_cons.
         ring_simplify; ring.
       } }
-    { rewrite (nth_default_out_of_bounds _ base) by omega; ring_simplify.
+    { rewrite (nth_default_out_of_bounds _ base) by (distr_length; omega); ring_simplify.
       etransitivity; rewrite BaseSystem.decode'_truncate; [ reflexivity | ].
       apply f_equal.
       autorewrite with push_firstn simpl_update_nth.
@@ -640,12 +635,12 @@ Section carrying_helper.
 
   Hint Rewrite @length_add_to_nth : distr_length.
 
-  Lemma set_nth_sum : forall n x us, (n < length us \/ n >= length base)%nat ->
+  Lemma set_nth_sum : forall n x us, (n < length us \/ n >= length limb_widths)%nat ->
     BaseSystem.decode base (set_nth n x us) =
     (x - nth_default 0 us n) * nth_default 0 base n + BaseSystem.decode base us.
   Proof. intros; unfold set_nth; rewrite update_nth_sum by assumption; reflexivity. Qed.
 
-  Lemma add_to_nth_sum : forall n x us, (n < length us \/ n >= length base)%nat ->
+  Lemma add_to_nth_sum : forall n x us, (n < length us \/ n >= length limb_widths)%nat ->
     BaseSystem.decode base (add_to_nth n x us) =
     x * nth_default 0 base n + BaseSystem.decode base us.
   Proof. intros; rewrite add_to_nth_set_nth, set_nth_sum; try ring_simplify; auto. Qed.
@@ -697,7 +692,7 @@ Section carrying.
   Proof. intros; unfold carry_simple; distr_length; reflexivity. Qed.
   Hint Rewrite @length_carry_simple : distr_length.
 
-  Lemma nth_default_base_succ : forall i, (S i < length base)%nat ->
+  Lemma nth_default_base_succ : forall i, (S i < length limb_widths)%nat ->
     nth_default 0 base (S i) = 2 ^ log_cap i * nth_default 0 base i.
   Proof.
     intros.
@@ -706,13 +701,13 @@ Section carrying.
   Qed.
 
   Lemma carry_gen_decode_eq : forall fc fi i' us
-                                     (i := fi (length base) i')
-                                     (Si := fi (length base) (S i)),
-    (length us = length base) ->
+                                     (i := fi i')
+                                     (Si := fi (S i)),
+    (length us = length limb_widths) ->
     BaseSystem.decode base (carry_gen limb_widths fc fi i' us)
     =  (fc (nth_default 0 us i / 2 ^ log_cap i) *
         (if eq_nat_dec Si (S i)
-         then if lt_dec (S i) (length base)
+         then if lt_dec (S i) (length limb_widths)
               then 2 ^ log_cap i * nth_default 0 base i
               else 0
          else nth_default 0 base Si)
@@ -720,29 +715,29 @@ Section carrying.
       + BaseSystem.decode base us.
   Proof.
     intros fc fi i' us i Si H; intros.
-    destruct (eq_nat_dec 0 (length base));
+    destruct (eq_nat_dec 0 (length limb_widths));
       [ destruct limb_widths, us, i; simpl in *; try congruence;
         break_match;
         unfold carry_gen, carry_single, add_to_nth;
         autorewrite with zsimplify simpl_nth_default simpl_set_nth simpl_update_nth distr_length;
         reflexivity
       | ].
-    (*assert (0 <= i < length base)%nat by (subst i; auto with arith).*)
+    (*assert (0 <= i < length limb_widths)%nat by (subst i; auto with arith).*)
     assert (0 <= log_cap i) by auto using log_cap_nonneg.
     assert (2 ^ log_cap i <> 0) by (apply Z.pow_nonzero; lia).
     unfold carry_gen, carry_single.
-    rewrite H; change (i' mod length base)%nat with i.
+     change (i' mod length limb_widths)%nat with i.
     rewrite add_to_nth_sum by (rewrite length_set_nth; omega).
     rewrite set_nth_sum by omega.
     unfold Z.pow2_mod.
     rewrite Z.land_ones by auto using log_cap_nonneg.
     rewrite Z.shiftr_div_pow2 by auto using log_cap_nonneg.
-    change (fi (length base) i') with i.
+    change (fi i') with i.
     subst Si.
     repeat first [ ring
                  | match goal with H : _ = _ |- _ => rewrite !H in * end
                  | rewrite nth_default_base_succ by omega
-                 | rewrite !(nth_default_out_of_bounds _ base) by omega
+                 | rewrite !(nth_default_out_of_bounds _ base) by (distr_length; omega)
                  | rewrite !(nth_default_out_of_bounds _ us) by omega
                  | rewrite Z.mod_eq by assumption
                  | progress distr_length
@@ -751,8 +746,8 @@ Section carrying.
   Qed.
 
   Lemma carry_simple_decode_eq : forall i us,
-    (length us = length base) ->
-    (i < (pred (length base)))%nat ->
+    (length us = length limb_widths) ->
+    (i < (pred (length limb_widths)))%nat ->
     BaseSystem.decode base (carry_simple limb_widths i us) = BaseSystem.decode base us.
   Proof.
     unfold carry_simple; intros; rewrite carry_gen_decode_eq by assumption.
@@ -791,11 +786,11 @@ Section carrying.
   Lemma nth_default_carry_gen_full fc fi d i n us
     : nth_default d (carry_gen limb_widths fc fi i us) n
       = if lt_dec n (length us)
-        then (if eq_nat_dec n (fi (length us) i)
+        then (if eq_nat_dec n (fi i)
               then Z.pow2_mod (nth_default 0 us n) (log_cap n)
               else nth_default 0 us n) +
-             if eq_nat_dec n (fi (length us) (S (fi (length us) i)))
-             then fc (nth_default 0 us (fi (length us) i) >> log_cap (fi (length us) i))
+             if eq_nat_dec n (fi (S (fi i)))
+             then fc (nth_default 0 us (fi i) >> log_cap (fi i))
              else 0
         else d.
   Proof.
@@ -827,11 +822,11 @@ Section carrying.
     : forall fc fi i us,
       (0 <= i < length us)%nat
       -> nth_default 0 (carry_gen limb_widths fc fi i us) i
-         = (if eq_nat_dec i (fi (length us) i)
+         = (if eq_nat_dec i (fi i)
             then Z.pow2_mod (nth_default 0 us i) (log_cap i)
             else nth_default 0 us i) +
-           if eq_nat_dec i (fi (length us) (S (fi (length us) i)))
-           then fc (nth_default 0 us (fi (length us) i) >> log_cap (fi (length us) i))
+           if eq_nat_dec i (fi (S (fi i)))
+           then fc (nth_default 0 us (fi i) >> log_cap (fi i))
            else 0.
   Proof.
     intros; autorewrite with push_nth_default natsimplify; break_match; omega.
@@ -849,7 +844,7 @@ Section carrying.
   Hint Rewrite @nth_default_carry_simple using (omega || distr_length; omega) : push_nth_default.
 End carrying.
 
-Hint Rewrite @length_carry_gen @base_from_limb_widths_length : distr_length.
+Hint Rewrite @length_carry_gen : distr_length.
 Hint Rewrite @length_carry_simple @length_carry_simple_sequence @length_make_chain @length_full_carry_chain @length_carry_simple_full : distr_length.
 Hint Rewrite @nth_default_carry_simple_full @nth_default_carry_gen_full : push_nth_default.
 Hint Rewrite @nth_default_carry_simple @nth_default_carry_gen using (omega || distr_length; omega) : push_nth_default.