From 43e06e9040238e7eeda06240856358b9a75e9fb6 Mon Sep 17 00:00:00 2001
From: James O'Shannessy <12959316+joshanne@users.noreply.github.com>
Date: Thu, 4 Mar 2021 01:05:48 +1100
Subject: [PATCH] AC_Fence: Fix int32_t overflow with large longitude values

---
 libraries/AC_Fence/AC_PolyFence_loader.cpp | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libraries/AC_Fence/AC_PolyFence_loader.cpp b/libraries/AC_Fence/AC_PolyFence_loader.cpp
index d7a1d1d897..c89833dd41 100644
--- a/libraries/AC_Fence/AC_PolyFence_loader.cpp
+++ b/libraries/AC_Fence/AC_PolyFence_loader.cpp
@@ -1186,8 +1186,11 @@ bool AC_PolyFence_loader::get_return_point(Vector2l &ret)
         }
     }
 
-    ret.x = ((min_loc.x+max_loc.x)/2);
-    ret.y = ((min_loc.y+max_loc.y)/2);
+    // Potential for int32_t overflow when longitudes are beyond [-107, 107].
+    // As a result, the calculated return point's longitude is calculated using overflowed figure.
+    // Dividing first before adding avoids the potential overflow.
+    ret.x = (min_loc.x / 2) + (max_loc.x / 2);
+    ret.y = (min_loc.y / 2) + (max_loc.y / 2);
 
     return true;
 }