From 7033337149ea250b146cc0b464c23d181e357a76 Mon Sep 17 00:00:00 2001
From: Adam Wulkiewicz <adam.wulkiewicz@gmail.com>
Date: Mon, 24 Feb 2014 15:16:37 +0100
Subject: [PATCH] IP coordinates rounded to the nearest value instead of a cast
 in segments_intersection_points if coordinate_type is integer

---
 .../policies/relate/intersection_points.hpp   | 35 +++++++++++++++++--
 1 file changed, 32 insertions(+), 3 deletions(-)

diff --git a/include/boost/geometry/policies/relate/intersection_points.hpp b/include/boost/geometry/policies/relate/intersection_points.hpp
index ff8ec1949..8a315ef57 100644
--- a/include/boost/geometry/policies/relate/intersection_points.hpp
+++ b/include/boost/geometry/policies/relate/intersection_points.hpp
@@ -22,13 +22,42 @@
 #include <boost/geometry/util/select_calculation_type.hpp>
 #include <boost/geometry/util/select_most_precise.hpp>
 
-
 namespace boost { namespace geometry
 {
 
 namespace policies { namespace relate
 {
 
+template <typename Result, bool IsInteger = std::numeric_limits<Result>::is_integer>
+struct round_dispatch
+{
+    template <typename T>
+    static inline Result apply(T const& v)
+    {
+        return v < 0 ?
+               boost::numeric_cast<Result>(ceil(v - 0.5f)) :
+               boost::numeric_cast<Result>(floor(v + 0.5f));
+    }
+};
+
+template <typename Result>
+struct round_dispatch<Result, false>
+{
+    template <typename T>
+    static inline Result apply(T const& v)
+    {
+        return boost::numeric_cast<Result>(v);
+    }
+};
+
+template <typename Result, typename T>
+inline Result round(T const& v)
+{
+    // NOTE: boost::round() could be used instead but it throws in some situations
+
+    //BOOST_STATIC_ASSERT(!std::numeric_limits<T>::is_integer);
+    return round_dispatch<Result>::apply(v);
+}
 
 template <typename S1, typename S2, typename ReturnType, typename CalculationType = void>
 struct segments_intersection_points
@@ -60,9 +89,9 @@ struct segments_intersection_points
         return_type result;
         result.count = 1;
         set<0>(result.intersections[0],
-            boost::numeric_cast<return_coordinate_type>(R(s1x) + r * R(dx1)));
+            round<return_coordinate_type>(R(s1x) + r * R(dx1)));
         set<1>(result.intersections[0],
-            boost::numeric_cast<return_coordinate_type>(R(s1y) + r * R(dy1)));
+            round<return_coordinate_type>(R(s1y) + r * R(dy1)));
 
         return result;
     }