From 535c5bb5b20d1b35d63b54d927b22e45b55b5aa1 Mon Sep 17 00:00:00 2001
From: Laurent Rineau <laurent.rineau@cgal.org>
Date: Wed, 6 Apr 2016 16:03:55 +0200
Subject: [PATCH] Speed-up Triangulation_3::read_cells...

... by a factor 5 for big triangulations! The old code was using:

    std::map<size_t, Vertex_handle> V;
    std::map<size_t, Cell_handle> C;

whereas the indices are contiguous: from 0 to n. `std::vector` is a lot
better for that use case!
---
 .../include/CGAL/Triangulation_file_input.h     |  4 ++--
 .../CGAL/Triangulation_data_structure_3.h       | 17 ++++++++++-------
 Triangulation_3/include/CGAL/Triangulation_3.h  |  4 ++--
 3 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/Polyhedron/demo/Polyhedron/include/CGAL/Triangulation_file_input.h b/Polyhedron/demo/Polyhedron/include/CGAL/Triangulation_file_input.h
index af08e43db88..a7dd3dc32cb 100644
--- a/Polyhedron/demo/Polyhedron/include/CGAL/Triangulation_file_input.h
+++ b/Polyhedron/demo/Polyhedron/include/CGAL/Triangulation_file_input.h
@@ -66,7 +66,7 @@ std::istream& file_input(std::istream& is, Tr2 &tr,
   if(!is) return is;
   tr.tds().set_dimension(d);
 
-  std::map< std::size_t, Vertex_handle > V;
+  std::vector< Vertex_handle > V(n+1);
   V[0] = tr.infinite_vertex();
   // the infinite vertex is numbered 0
 
@@ -80,7 +80,7 @@ std::istream& file_input(std::istream& is, Tr2 &tr,
     }
   }
 
-  std::map< std::size_t, Cell_handle > C;
+  std::vector< Cell_handle > C;
 
   std::size_t m;
   tr.tds().read_cells(is, V, m, C);
diff --git a/TDS_3/include/CGAL/Triangulation_data_structure_3.h b/TDS_3/include/CGAL/Triangulation_data_structure_3.h
index fbdd537dd6a..0eb95a8a97c 100644
--- a/TDS_3/include/CGAL/Triangulation_data_structure_3.h
+++ b/TDS_3/include/CGAL/Triangulation_data_structure_3.h
@@ -334,8 +334,8 @@ public:
     }
 
   // not documented
-  void read_cells(std::istream& is, std::map< std::size_t, Vertex_handle > &V,
-                  std::size_t & m, std::map< std::size_t, Cell_handle > &C );
+  void read_cells(std::istream& is, const std::vector< Vertex_handle > &V,
+                  std::size_t & m, std::vector< Cell_handle > &C);
   // not documented
   void print_cells(std::ostream& os,
                    const Unique_hash_map<Vertex_handle, std::size_t> &V ) const;
@@ -1684,7 +1684,7 @@ operator>>(std::istream& is, Triangulation_data_structure_3<Vb,Cb,Ct>& tds)
   if(n == 0)
     return is;
 
-  std::map<std::size_t , Vertex_handle > V;
+  std::vector<Vertex_handle > V(n);
 
   // creation of the vertices
   for (std::size_t i=0; i < n; i++) {
@@ -1694,7 +1694,7 @@ operator>>(std::istream& is, Triangulation_data_structure_3<Vb,Cb,Ct>& tds)
     V[i] = tds.create_vertex();
   }
 
-  std::map< std::size_t, Cell_handle > C;
+  std::vector< Cell_handle > C;
   std::size_t m;
 
   tds.read_cells(is, V, m, C);
@@ -2231,8 +2231,8 @@ flip_really( Cell_handle c, int i, int j,
 template <class Vb, class Cb, class Ct>
 void
 Triangulation_data_structure_3<Vb,Cb,Ct>::
-read_cells(std::istream& is, std::map< std::size_t, Vertex_handle > &V,
-           std::size_t & m, std::map< std::size_t, Cell_handle > &C)
+read_cells(std::istream& is, const std::vector< Vertex_handle > &V,
+           std::size_t & m, std::vector< Cell_handle > &C)
 {
   // creation of the cells and neighbors
   switch (dimension()) {
@@ -2245,6 +2245,8 @@ read_cells(std::istream& is, std::map< std::size_t, Vertex_handle > &V,
       else
         read(is, m);
 
+      C.resize(m);
+
       for(std::size_t i = 0; i < m; i++) {
         Cell_handle c = create_cell();
         for (int k=0; k<=dimension(); ++k) {
@@ -2274,7 +2276,7 @@ read_cells(std::istream& is, std::map< std::size_t, Vertex_handle > &V,
   case 0:
     {
       m = 2;
-
+      C.resize(m);
       //      CGAL_triangulation_assertion( n == 2 );
       for (int i=0; i < 2; i++) {
         Cell_handle c = create_face(V[i], Vertex_handle(), Vertex_handle());
@@ -2290,6 +2292,7 @@ read_cells(std::istream& is, std::map< std::size_t, Vertex_handle > &V,
   case -1:
     {
       m = 1;
+      C.resize(m);
       //      CGAL_triangulation_assertion( n == 1 );
       Cell_handle c = create_face(V[0], Vertex_handle(), Vertex_handle());
       C[0] = c;
diff --git a/Triangulation_3/include/CGAL/Triangulation_3.h b/Triangulation_3/include/CGAL/Triangulation_3.h
index 743593cf4fb..01bfdbae6a2 100644
--- a/Triangulation_3/include/CGAL/Triangulation_3.h
+++ b/Triangulation_3/include/CGAL/Triangulation_3.h
@@ -2121,7 +2121,7 @@ operator>> (std::istream& is, Triangulation_3<GT, Tds, Lds> &tr)
   if(!is) return is;
   tr._tds.set_dimension(d);
 
-  std::map< std::size_t, Vertex_handle > V;
+  std::vector< Vertex_handle > V(n+1);
   V[0] = tr.infinite_vertex();
   // the infinite vertex is numbered 0
 
@@ -2130,7 +2130,7 @@ operator>> (std::istream& is, Triangulation_3<GT, Tds, Lds> &tr)
     if(!(is >> *V[i])) return is;
   }
 
-  std::map< std::size_t, Cell_handle > C;
+  std::vector< Cell_handle > C;
 
   std::size_t m;
   tr._tds.read_cells(is, V, m, C);