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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: function hash
Date: 31 May 2001 20:21:17 +0100
Organization: CodeFella
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Date: 2001-05-31T19:21:17+00:00
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Florian Weimer <fw@deneb.enyo.de> writes:

> Jeffrey Carter <jrcarter@acm.org> writes:
> 
> > Florian Weimer wrote:
> > > 
> > > A hash function returning only 256 different values?  Are there any
> > > applications for it?
> > 
> > Given the original poster's requirements of handling 500-1000 elements,
> > that's only 2-4 per bin, so it seemed suitable.
> 
> In particular with long strings, this will result in a measurable
> performance degradation in comparison to a real hash function because
> of the necessity to perform additional key comparisons.

I don't understand. If there are only 256 bins (not unreasonable) then
there are *bound* to be collisions for a large key space (eg all the
sentences in Jane Eyre).

If you need a perfect hash (eg for the reserved words in Ada) that's
quite a different problem.