From d899f83728a04091bd60a43e774702f02fd59e28 Mon Sep 17 00:00:00 2001
From: David Monniaux <david.monniaux@univ-grenoble-alpes.fr>
Date: Wed, 15 May 2019 10:32:57 +0200
Subject: more lemmas on division

---
 mppa_k1c/ExtValues.v | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 55 insertions(+), 1 deletion(-)

(limited to 'mppa_k1c/ExtValues.v')

diff --git a/mppa_k1c/ExtValues.v b/mppa_k1c/ExtValues.v
index e9b2610c..1eb0bb89 100644
--- a/mppa_k1c/ExtValues.v
+++ b/mppa_k1c/ExtValues.v
@@ -474,4 +474,58 @@ Proof.
     }
   }
 
-*)
\ No newline at end of file
+ *)
+
+Require Import Coq.ZArith.Zquot.
+Lemma Z_quot_pos_pos_bound: forall a b m,
+    0 <= a <= m -> 1 <= b -> 0 <= Z.quot a b <= m.
+Proof.
+  intros.
+  split.
+  { rewrite <- (Z.quot_0_l b) by omega.
+    apply Z_quot_monotone; omega.
+  }
+  apply Z.le_trans with (m := a).
+  {
+    apply Z_quot_le; tauto.
+  }
+  tauto.
+Qed.
+Lemma Z_quot_neg_pos_bound: forall a b m,
+    m <= a <= 0 -> 1 <= b -> m <= Z.quot a b <= 0.
+  intros.
+  assert (0 <= - (a ÷ b) <= -m).
+  {
+    rewrite <- Z.quot_opp_l by omega.
+    apply Z_quot_pos_pos_bound; omega.
+  }
+  omega.
+Qed.
+
+Lemma Z_quot_signed_pos_bound: forall a b,
+    Int.min_signed <= a <= Int.max_signed -> 1 <= b ->
+    Int.min_signed <= Z.quot a b <= Int.max_signed.
+Proof.
+  intros.
+  destruct (Z_lt_ge_dec a 0).
+  {
+    split.
+    { apply Z_quot_neg_pos_bound; omega. }
+    { eapply Z.le_trans with (m := 0).
+      { apply Z_quot_neg_pos_bound with (m := Int.min_signed); trivial.
+        split. tauto. auto with zarith.
+      }
+      discriminate.
+    }
+  }
+  { split.
+    { eapply Z.le_trans with (m := 0).
+      discriminate.
+      apply Z_quot_pos_pos_bound with (m := Int.max_signed); trivial.
+      split. omega. tauto.
+    }
+    { apply Z_quot_pos_pos_bound; omega.
+    }
+  }
+Qed.
+
-- 
cgit