From 22c27854529b1e5c5da2b4845ffac764f208326d Mon Sep 17 00:00:00 2001
From: Krzysztof Wrzalik <kwrzalik@gmail.com>
Date: Sun, 18 Sep 2016 17:44:45 +0200
Subject: [PATCH 1/2] Added tests for negative multi-span access.

---
 tests/multi_span_tests.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/tests/multi_span_tests.cpp b/tests/multi_span_tests.cpp
index f04ba84..69cb34b 100644
--- a/tests/multi_span_tests.cpp
+++ b/tests/multi_span_tests.cpp
@@ -1084,6 +1084,12 @@ SUITE(multi_span_tests)
 
         CHECK_THROW(av[10][2], fail_fast);
         CHECK_THROW((av[{10, 2}]), fail_fast);
+
+        CHECK_THROW(av[-1][0], fail_fast);
+        CHECK_THROW((av[{-1, 0}]), fail_fast);
+
+        CHECK_THROW(av[0][-1], fail_fast);
+        CHECK_THROW((av[{0, -1}]), fail_fast);
     }
 
     void overloaded_func(multi_span<const int, dynamic_range, 3, 5> exp, int expected_value)

From 6cb0e3082a2b475d2ef5e9b591c60ae98bb3c483 Mon Sep 17 00:00:00 2001
From: Krzysztof Wrzalik <kwrzalik@gmail.com>
Date: Sun, 18 Sep 2016 17:56:18 +0200
Subject: [PATCH 2/2] Added a fix for not flagging negative indices to
 multi_span.

---
 gsl/multi_span | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gsl/multi_span b/gsl/multi_span
index 0abc7c1..40752aa 100644
--- a/gsl/multi_span
+++ b/gsl/multi_span
@@ -443,7 +443,7 @@ namespace details
         template <typename T, size_t Dim = 0>
         size_type linearize(const T& arr) const
         {
-            Expects(arr[Dim] < CurrentRange); // Index is out of range
+            Expects(arr[Dim] >= 0 && arr[Dim] < CurrentRange); // Index is out of range
             return this->Base::totalSize() * arr[Dim] +
                    this->Base::template linearize<T, Dim + 1>(arr);
         }
@@ -1510,7 +1510,7 @@ public:
     template <bool Enabled = (Rank > 1), typename Ret = std::enable_if_t<Enabled, sliced_type>>
     constexpr Ret operator[](size_type idx) const noexcept
     {
-        Expects(idx < bounds_.size()); // index is out of bounds of the array
+        Expects(idx >= 0 && idx < bounds_.size()); // index is out of bounds of the array
         const size_type ridx = idx * bounds_.stride();
 
         // index is out of bounds of the underlying data