Re: Ada Hash

["Randy Brukardt" <randy@rrsoftware.com>]

"markp" <markwork66@yahoo.com> wrote in message
news:1177429033.247571.9090@s33g2000prh.googlegroups.com...
> I need to use a hash table to store data using an integer as the key.
> I would like to use Ada.Containers.Hashed_Maps. Is there a default
> hash function for an integer that I can supply to the instantiation
> and could somebody provide a quick sample piece of code to do this?

There isn't a default function for this; but generally you don't need one -
the identity function would work fine unless your integers are distributed
unusually.

In any case, writing hash functions is an art; I generally test as many as a
dozen possibilities on sample data sets to see which one(s) work best. What
works best depends totally on your data; there is no such thing as a good
predefined hash function. (OTOH, if you don't have much data, anything might
be good enough -- but if that is true, why use the hashed container form at
all? The Ordered forms are easier to use and cost about the same on small
data sets.)

                                                Randy.