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From: Mark A Biggar <mark.a.biggar@lmco.com>
Subject: Re: Question for the folks who designed Ada95
Date: 1999/04/29
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Date: 1999-04-29T00:00:00+00:00
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Fraser Wilson wrote:
> 
> paene lacrimavi postquam Robert Dewar  scripsit:
> 
> >Now, *without* going to the Ada RM, let's see if we can
> >remember exactly what's going on with the etc here. Hands
> >up those who remember how NOT works on non-binary modular
> >types (hint: the above quote is wrong wrt NOT :-)
> 
> not X = Y: X + Y = 0 ?

That works.  The RM defines it as (Modulus - X) which is the same value.
 
> Here's a question: has anyone ever used a modular type which was not
> a power of 2, and lived to tell the tale?  What was the context?

Yeah, two different things: 

1) the index into a circular queue defined as:

type Queue_index is mod Queue_size;
type Queue is array (Queue_index) of Element;

(Actual implementation was a generic package)

2) Index type for a hash table where table size was largest prime < 32676.
This made the hash function very simple.

Sorry, I can't give detailed code examples as both cases involved code for
classified government projects.
--
Mark Biggar
mark.a.biggar@lmco.com