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From: Stephen Leake <stephen.a.leake.1@gsfc.nasa.gov>
Newsgroups: comp.lang.ada
Subject: Re: Announce: Grace project site operational
Date: 16 May 2002 09:52:49 -0400
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Date: 2002-05-16T13:59:50+00:00
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John English <je@brighton.ac.uk> writes:

> Surely the "right" way to do it is to express each value as a tuple
> consisting of magnitude and the exponents of each dimension, so
> 9.8 m/s**2 is (9.8, length=>1, time=>-2). Then you just have at most
> three versions of each operation (tuple op tuple, tuple op magnitude,
> magnitude op tuple) or even just tuple op tuple with a conversion
> from magnitude to (magnitude, others=>0).

Yes, that is the easiest to implement, and covers all possible units.
But it has run-time overhead, which is just not acceptable in a
real-time system.

One approach is to use such a package during development and unit
testing, to help catch unit errors. Then switch to a flat "all types
are float" package for the final build and system test. If the switch
can be made cleanly, and yield _no_ runtime overhead, this might be
the best approach.

-- 
-- Stephe