From ced436a707991a3e7018e0380bbbc2fc039c360b Mon Sep 17 00:00:00 2001
From: Mario Carneiro <di.gama@gmail.com>
Date: Tue, 11 Jul 2017 13:35:51 +0100
Subject: [PATCH] fix(library/vm/vm_nat): fix VM definition of nat.shiftr

fixes #1723
---
 src/library/vm/vm_nat.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/library/vm/vm_nat.cpp b/src/library/vm/vm_nat.cpp
index fd335c9fd6..e9d8f588cd 100644
--- a/src/library/vm/vm_nat.cpp
+++ b/src/library/vm/vm_nat.cpp
@@ -175,7 +175,8 @@ vm_obj nat_shiftl(vm_obj const & a1, vm_obj const & a2) {
 
 vm_obj nat_shiftr(vm_obj const & a1, vm_obj const & a2) {
     if (LEAN_LIKELY(is_simple(a1) && is_simple(a2))) {
-        return mk_vm_nat(cidx(a1) >> cidx(a2));
+        int v2 = cidx(a2);
+        return v2 < 32 ? mk_vm_nat(cidx(a1) >> v2) : mk_vm_simple(0);
     } else {
         mpz v1 = to_mpz1(a1);
         div2k(v1, v1, to_unsigned(a2));