From 2b2ed5072128df9dc262fac1a5e40635a6ff71b3 Mon Sep 17 00:00:00 2001
From: Dennis Luxen <info@project-osrm.org>
Date: Wed, 25 Jun 2014 18:50:46 +0200
Subject: [PATCH] add a hash combine implementation that has some minor
 performance guarantees

---
 Util/StdHashExtensions.h | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/Util/StdHashExtensions.h b/Util/StdHashExtensions.h
index 29663f1d3..d2f2fc4fe 100644
--- a/Util/StdHashExtensions.h
+++ b/Util/StdHashExtensions.h
@@ -32,13 +32,41 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include <functional>
 
+// this is largely inspired by boost's hash combine
+template<typename T>
+inline void hash_combine(std::size_t &seed, const T& val)
+{
+    seed ^= std::hash<T>()(val) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
+}
+
+template<typename T>
+inline void hash_val(std::size_t &seed, const T& val)
+{
+    hash_combine(seed, val);
+}
+
+template<typename T, typename ... Types>
+inline void hash_val(std::size_t &seed, const T& val, const Types& ... args)
+{
+    hash_combine(seed, val);
+    hash_val(seed, args ...);
+}
+
+template<typename ... Types>
+inline std::size_t hash_val( const Types&... args)
+{
+    std::size_t seed = 0;
+    hash_val(seed, args...);
+    return seed;
+}
+
 namespace std
 {
 template <> struct hash<std::pair<NodeID, NodeID>>
 {
     size_t operator()(const std::pair<NodeID, NodeID> &pair) const
     {
-        return std::hash<int>()(pair.first) ^ std::hash<int>()(pair.second);
+        return hash_val(pair.first, pair.second);
     }
 };
 }