Re: hash_map

From:

"Maxim Yegorushkin" <maxim.yegorushkin@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

4 Oct 2006 08:52:42 -0400

Message-ID:

<1159946649.284251.215440@i42g2000cwa.googlegroups.com>

tat wrote:

Hi all,

Thanks very much for all of your comments about hash_map and various
issues around it.
Can someone suggest a good string hash function for a string of length
ranging from 7 to 13?

This one works well for me:

    size_t hash(char const* p)
    {
        size_t r = 0;

        // 31 is an empirical value obtained from hashing real logins
        // 6291469 buckets
        // 4142516 logins
        // 894278 collisions
        // 8 max bucket size

        for(;*p; ++p)
            r = r * 31 + *p;
        return r;
    }

I googled and found a webpage
(GeneralHashFunctions) of Arash Partow (http://www.partow.net) on which
there are a number of hash functions. I copied them below. I am not
sure which one is good for my case.

Can you profile it for your particular application to see which one
suits you needs best?

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