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diff --git a/intern/opensubdiv/internal/opensubdiv_edge_map.h b/intern/opensubdiv/internal/opensubdiv_edge_map.h
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+++ b/intern/opensubdiv/internal/opensubdiv_edge_map.h
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+// Copyright 2019 Blender Foundation. All rights reserved.
+//
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License
+// as published by the Free Software Foundation; either version 2
+// of the License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software Foundation,
+// Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+//
+// Author: Sergey Sharybin
+
+#ifndef OPENSUBDIV_EDGE_MAP_H_
+#define OPENSUBDIV_EDGE_MAP_H_
+
+#include "internal/opensubdiv_util.h"
+
+namespace opensubdiv_capi {
+
+// Helper class to ease dealing with edge indexing.
+// Simply takes care of ensuring order of vertices is strictly defined.
+class EdgeKey {
+ public:
+  inline EdgeKey();
+  inline EdgeKey(int v1, int v2);
+
+  inline size_t hash() const;
+  inline bool operator==(const EdgeKey& other) const;
+
+  // These indices are guaranteed to be so v1 < v2.
+  int v1;
+  int v2;
+};
+
+// Map from an edge defined by its verticies index to a custom tag value.
+template<typename T>
+class EdgeTagMap {
+ public:
+  typedef EdgeKey key_type;
+  typedef T value_type;
+
+  inline EdgeTagMap();
+
+  // Modifiers.
+  inline void clear();
+  inline void insert(const key_type& key, const value_type& value);
+  inline void insert(int v1, int v2, const value_type& value);
+
+  // Lookup.
+  value_type& at(const key_type& key);
+  value_type& at(key_type&& key);
+  value_type& at(int v1, int v2);
+
+  value_type& operator[](const key_type& key);
+  value_type& operator[](key_type&& key);
+
+ protected:
+  unordered_map<key_type, value_type> edge_tags_;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+// Implementation.
+
+// EdgeKey.
+
+EdgeKey::EdgeKey()
+    : v1(-1),
+      v2(-1) {
+}
+
+EdgeKey::EdgeKey(int v1, int v2) {
+  assert(v1 >= 0);
+  assert(v2 >= 0);
+  assert(v1 != v2);
+  if (v1 < v2) {
+    this->v1 = v1;
+    this->v2 = v2;
+  } else {
+    this->v1 = v2;
+    this->v2 = v1;
+  }
+}
+
+size_t EdgeKey::hash() const {
+  return (static_cast<uint64_t>(v1) << 32) | v2;
+}
+
+bool EdgeKey::operator==(const EdgeKey& other) const {
+  return v1 == other.v1 &&
+         v2 == other.v2;
+}
+
+// EdgeTagMap.
+
+template<typename T>
+EdgeTagMap<T>::EdgeTagMap() {
+}
+
+template<typename T>
+void EdgeTagMap<T>::clear() {
+  edge_tags_.clear();
+}
+
+template<typename T>
+void EdgeTagMap<T>::insert(const key_type& key, const value_type& value) {
+  edge_tags_.insert(make_pair(key, value));
+}
+
+template<typename T>
+void EdgeTagMap<T>::insert(int v1, int v2, const value_type& value) {
+  insert(EdgeKey(v1, v2), value);
+}
+
+template<typename T>
+typename EdgeTagMap<T>::value_type& EdgeTagMap<T>::at(const key_type& key) {
+  return edge_tags_.at[key];
+}
+
+template<typename T>
+typename EdgeTagMap<T>::value_type& EdgeTagMap<T>::at(key_type&& key) {
+  return edge_tags_.at[key];
+}
+
+template<typename T>
+typename EdgeTagMap<T>::value_type& EdgeTagMap<T>::at(int v1, int v2) {
+  return edge_tags_.at(EdgeKey(v1, v2));
+}
+
+template<typename T>
+typename EdgeTagMap<T>::value_type& EdgeTagMap<T>::operator[](
+    const key_type& key) {
+  return edge_tags_[key];
+}
+
+template<typename T>
+typename EdgeTagMap<T>::value_type& EdgeTagMap<T>::operator[](key_type&& key) {
+  return edge_tags_[key];
+}
+
+}  // namespace opensubdiv_capi
+
+namespace std {
+
+template <>
+struct hash<opensubdiv_capi::EdgeKey> {
+  std::size_t operator()(const opensubdiv_capi::EdgeKey& key) const {
+    return key.hash();
+  }
+};
+
+}  // namespace std
+
+#endif  // OPENSUBDIV_EDGE_MAP_H_