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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: floating point comparison
Date: 1997/09/09
Message-ID: <dewar.873861647@merv>#1/1
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References: <33EA46CC.226@pseserv3.fw.hac.com>
 <871377938snz@nezumi.demon.co.uk> <EACHUS.97Sep5165959@spectre.mitre.org>
 <5usm7v$bui@redtail.cruzio.com>
Organization: New York University
Newsgroups: 
 comp.lang.ada,sci.math.num-analysis,comp.software-eng,comp.theory,sci.math
Date: 1997-09-09T00:00:00+00:00
List-Id: <comp.lang.ada>


schafly said, replying to Eachus

<<>    In general it is much more work to write fixed point than floating
> point code, but especially in Ada, the error analysis is easy.  Errors
> are only introduced by explicit conversions never by arithmetic
> operations.

Not true.  Try computing 1/3 in fixed point.>>

This shows a lack of appreciation for how things are done in Ada. if you
have two fixed-point values of 1.0 and 3.0, then the division 1.0/3.0
gives a semantically precise and exact answer. That is true of any
division of fixed-point values.

BUT, to do anything interesting with this exact value, it must be converted
to a specific fixed-point type, hence Eachus' comment that "errors" [that
word again :-)] are introduced only by conversions.

This approach greatly simplifies analysis of the propagation of these
"errors".