Fix crash in ConvexHull::preSort (#1358)

* Add test for GH-1072

Resolves #1072

* ConvexHull: improve robustness of polarCompare

Author: dbaston

src/algorithm/ConvexHull.cpp

@@ -63,13 +63,21 @@ class RadiallyLessThen {
     polarCompare(const Coordinate* o, const Coordinate* p,
                  const Coordinate* q)
     {
-        int orient = Orientation::index(*o, *p, *q);
+        // To use this comparator in std::sort it must provide a stable ordering, such that
+        // if cmp(a, b) is true then cmp(b, a) is false. Unfortunately Orientation::index may
+        // not provide this guarantee when the inputs differ by many orders of magnitude. To
+        // guard against this, we normalize the order of P and Q before calling OrientationIndex
+        // and flip the result if the inputs were flipped.
+        const bool swap = geom::CoordinateLessThan()(p, q);
+
+        const int orient = swap ? Orientation::index(*o, *q, *p) : Orientation::index(*o, *p, *q);
 
         if(orient == Orientation::COUNTERCLOCKWISE) {
-            return 1;
+            return swap ? -1 : 1;
         }
+
         if(orient == Orientation::CLOCKWISE) {
-            return -1;
+            return swap ? 1 : -1;
         }
 
         /**
@@ -102,7 +110,7 @@ class RadiallyLessThen {
     RadiallyLessThen(const Coordinate* c): origin(c) {}
 
     bool
-    operator()(const Coordinate* p1, const Coordinate* p2)
+    operator()(const Coordinate* p1, const Coordinate* p2) const
     {
         return (polarCompare(origin, p1, p2) == -1);
     }

tests/unit/capi/GEOSMinimumBoundingCircleTest.cpp

@@ -129,5 +129,20 @@ void object::test<5>
     ensure("curved geometry not supported", result_ == nullptr);
 }
 
+template<>
+template<>
+void object::test<6>
+()
+{
+    set_test_name("https://github.com/libgeos/geos/issues/1072");
+
+    geom1_ =  fromWKT("LINESTRING(7777777777777777770 7777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777777770 1, 1 7 1,-2 1 2)");
+    geom2_ =  GEOSSingleSidedBuffer(geom1_, 1.0, 64, 1, 1.0, 1);
+    result_ =  GEOSMinimumBoundingCircle(geom2_, NULL, NULL);
+
+    // no segfault
+}
+
+
 } // namespace tut