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Editorial Team
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Asked: 2026-05-13T23:15:38+00:00

I’ve written a custom hashing for my custom key in stdext::hash_map and would like

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I’ve written a custom hashing for my custom key in stdext::hash_map and would like to check whether the hasher is good. I’m using STL supplied with VS 2008. A typical check, as I know, is to check the uniformity of distribution among buckets.

How should I organize such a check correctly? A solution that comes to my mind is to modify STL sources to add a method to hash_map that walks through buckets and does the subject. Is there are any better ways?

Maybe, derive from hash_map and create there such method?

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  1. Editorial Team

    I’d run one (large) dataset through stl::hash_map. Once done, I’d collect the results for all buckets using the following method

    From hash_map:

    size_type elems_in_bucket (size_type __n) const;

    Finally, I would do compute the standard deviation (SD) of the elem-to-bucket distribution.

    I’d do the above for different hash functions. Whichever hash function results in minimum SD is the winner (for this dataset).

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