Off-Topic Discussion > Programming

Key-value vector vs. padded/jagged vector

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CP5670:

--- Quote from: The E on May 28, 2015, 08:57:13 am ---Now, for those wise in the ways of STL containers, you might ask yourself "Why didn't z64555 consider using std::map or std::unordered_map"?

Which is a great question! Map containers are tailored for just this sort of application, and std::unordered_map has good performance characteristics after all. However, as this talk by Google's Chandler Carruth points out, those data structures play hell with CPU caching. Modern CPUs work most efficiently when dealing with contiguous data structures like arrays or vectors, structures which make explicit guarantees about using contiguous blocks of memory. Given that this is a part of the code that has to be iterated over per-frame, we want to be able to get through it as efficiently as possible, and while maps are really great and easy-to-use in non-critical code paths, they're not the right tool for this kind of thing.

--- End quote ---

Interesting, I use unordered_maps frequently but hadn't thought of this. There are apparently some third-party versions of it that are more efficient and are backward compatible.

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