Path: utzoo!utgpu!attcan!uunet!edsews!charette
From: charette@edsews.EDS.COM (Mark A. Charette)
Newsgroups: comp.lang.c
Subject: Re: x/10.0 vs x*0.1
Message-ID: <2888@edsews.EDS.COM>
Date: 14 Oct 88 02:52:59 GMT
References: <836@proxftl.UUCP> <3105@hubcap.UUCP> <1700@dataio.Data-IO.COM> <13969@mimsy.UUCP>
Organization: EDS/TSD - Troy, MI
Lines: 29

In article <13969@mimsy.UUCP>, chris@mimsy.UUCP (Chris Torek) writes:
> In article <1700@dataio.Data-IO.COM> Walter Bright suggests that one
> >>>Try very hard to replace divides with other operations, as in:
> >>>		x / 10
> >>>	with:
> >>>		x * .1
> 
> Yes (subject to the usual constraints, i.e., that you know what you are
> doing: if your input data has little precision, you can afford minor
> degredations in computations).

Some numerical analysts I associate with might argue that the propagation
of any error in floating point tends to be magnified as more operations
occur. I have had occasion to see the (small) precision in some data be
completely outweighed by using float instead of double (actually REAL
instead of DOUBLE PRECISION, but this is comp.lang.c ;') and really
whacking at the data (conversions back and forth between double and float).
 
> Yes (subject to the usual constraints, i.e., that you know what you are
> doing: 

Aye, there's the rub.


-- 
Mark Charette                   "On a clean disk you can seek forever" - 
Electronic Data Systems                  Thomas B. Steel Jr.
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