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Here's a curiosity I've been investigating. The .NET Dictionary class performs ridiculously fast compared to the STL unordered_map in a test I keep running, and I can't figure out why. (0.5 seconds vs. 4 seconds on my machine) (.NET 3.5 SP1 vs. Visual Studio 2008 Express SP1's STL) On the other hand, if I implement my own hash table in C# and C++, the C++ version is about twice as fast as the C# one, which is fine because it reinforces my common sense that native machine code is sometimes faster. (See. I said "sometimes".) Me being the same person in both languages, I wonder what tricks was the C# coder from Microsoft able to play that the C++ coder from Microsoft wasn't? I'm having trouble imagining how a compiler could play such tricks on its own, going through the trouble of optimizing what should look to it to be arbitrary function calls. It's a simple test, storing and retrieving integers. C#: const int total = (1 << 20); int sum = 0; Dictionary<int, int> dict = new Dictionary<int, int>(); for(int i = 0; i < total; i++) { dict.Add(i, i * 7); } for(int j = 0; j < (1 << 3); j++) { int i = total; while(i > 0) { i--; sum += dict[i]; } } Console.WriteLine(sum); C++: const int total = (1 << 20); int sum = 0; std::tr1::unordered_map<int, int> dict; for(int i = 0; i < total; i++) { dict.insert(pair<int, int>(i, i * 7)); } for(int j = 0; j < (1 << 3); j++) { int i = total; while(i > 0) { i--; std::tr1::unordered_map<int, int>::const_iterator found = dict.find(i); sum += found->second; } } cout << sum << endl;

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