hash_edge

src/delaunator.cpp

diff --git a/src/delaunator.cpp b/src/delaunator.cpp
index 6d5b0d1..ff00c2c 100644
--- a/src/delaunator.cpp
+++ b/src/delaunator.cpp
@@ -287,7 +287,23 @@
     for (int i = 0; i < m_hash_size; i++) m_hash.push_back(-1);
 
     std::deque<DelaunatorPoint>::iterator e = insert_node(m_hull, coords, i0);
+    hash_edge(e);
     // cout << i0 << endl;
     // cout << m_hull[0].i << endl;
 
 };
+
+long int Delaunator::hash_key(double x, double y) {
+    const double dx = x - m_center_x;
+    const double dy = y - m_center_y;
+    // use pseudo-angle: a measure that monotonically increases
+    // with real angle, but doesn't require expensive trigonometry
+    const double p = 1 - dx / (abs(dx) + abs(dy));
+    return floor((2 + (dy < 0 ? -p : p)) / 4 * m_hash_size);
+}
+
+void Delaunator::hash_edge(std::deque<DelaunatorPoint>::iterator e){
+    const long int pos = e - m_hull.begin();
+    const DelaunatorPoint p = m_hull[pos];
+    m_hash[hash_key(p.x, p.y)] = pos;
+}
\ No newline at end of file

src/delaunator.h

diff --git a/src/delaunator.h b/src/delaunator.h
index 12e5645..278f91c 100644
--- a/src/delaunator.h
+++ b/src/delaunator.h
@@ -19,4 +19,6 @@
         double m_hash_size;
         std::vector<int> m_hash;
         std::deque<DelaunatorPoint> m_hull;
+        long int hash_key(double x, double y);
+        void hash_edge(std::deque<DelaunatorPoint>::iterator e);
 };