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From: lambert@mcvax.UUCP
Newsgroups: comp.lang.c
Subject: Re: C and Floating Point
Message-ID: <7350@boring.mcvax.cwi.nl>
Date: Wed, 15-Apr-87 17:27:34 EST
Article-I.D.: boring.7350
Posted: Wed Apr 15 17:27:34 1987
Date-Received: Fri, 17-Apr-87 06:17:36 EST
References: <15958@sun.uucp> <5716@brl-smoke.ARPA>
Reply-To: lambert@boring.UUCP (Lambert Meertens)
Organization: CWI, Amsterdam
Lines: 31
Keywords: C Fortran Floating Point Parenthases

>> For example, (foo / h_bar) / h_bar works, but the faster and
>> mathematically equivalent expression foo / (h_bar * h_bar) does not work.
> 
> So you should have measured "foo" in units of h_bar ...

Measures indicating h_bar units are hard to come by*. Of course you want
to do the computations in such units, but then you have to convert the
measurements first.
________
*I believe they keep a platinum h_bar in the Paris Bureau de Poids et
des Mesures, but I understand they are loath to lend it out.

Can we stop this discussion now? (Summary: From the point of view of people
who want to do serious numerical work it was a mistake that fp operations
were handled as if they were true to the algebraic properties of their
mathematical abstractions, which is good enough for most of the people all
of the time, and for all of the people (numerical analysts are not people)
most of the time, but not ... . But don't forget that C was really designed
for systems programming and such. There was already a work-around by using
assignments to temporaries, which was really hard on the people who wanted
to control the exact sequencing of the operations, and now there is this
kludge that no-one is really happy with but that sure makes life easier for
them.  Proposals to change the C semantics for fp operations only still
leave some other rearrangement problems unresolved and are probably not a
good idea anyway.  We'll have to live with it. As a consolation I can say
that the situation has not gotten worse because of the unary + and that
this is fortunately :-) not the worst problem with C anyway, far from it.)

-- 

Lambert Meertens, CWI, Amsterdam; lambert@cwi.nl