Re: Ada.Containers Hash function for a set of small integers

["John B. Matthews" <nospam@nospam.invalid>]

In article 
<50701baa-7c05-450c-a42d-c699516ddc00@t14g2000prm.googlegroups.com>,
 Michael R <michael@zanyblue.com> wrote:

> Hi Folks,
> 
> I'd like to use the generic Hashed_Maps container to store mappings
> from a set of small integers (three) to Wide_Strings
> (Indefinite_Hashed_Maps):
> 
> (1, 10, 4) => "ABC",
> (10, 3, 5) => "XYZ",
> 
> Does anyone have recommendations on how best to implement the Hash
> function for keys like this?

I'd try something simple like shift and add, but it might depend on the 
definition of "small".

Whatever you decide, here's some code I used to examine the distribution 
of collisions in a map keyed by "/usr/share/dict/words":

$ ./collisions 
 0: 218586 (55.59%)
 1: 126250 (32.10%)
 2: 38432 (9.77%)
 3: 8362 (2.13%)
 4: 1354 (0.34%)
 5: 229 (0.06%)
 6: 24 (0.01%)
 7: 4 (0.00%)
 8: 1 (0.00%)

<http://home.roadrunner.com/~jbmatthews/jumble.html#sec2>

-- 
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>