Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!ll-xn!husc6!bbn!rochester!ur-tut!ur-valhalla!micropen!dave
From: dave@micropen (David F. Carlson)
Newsgroups: comp.arch
Subject: Re: Performance increase - a suggestion
Message-ID: <408@micropen>
Date: 1 Feb 88 14:37:58 GMT
References: <235@unicom.UUCP> <28200089@ccvaxa> <3127@phri.UUCP>
Organization: Micropen Dirent Writing Systems, Pittsford, NY
Lines: 35
Summary: why single precision?

In article <3127@phri.UUCP>, roy@phri.UUCP (Roy Smith) writes:
> In article <28200089@ccvaxa> aglew@ccvaxa.UUCP writes:
> > I wonder how much interest might be out there for a true double-precision
> > floating point engine - one that did 64 bit floating point, or IEEE 80
> > bit extended floating point, or even 128 bit floating point, as its
> > native floating point mode, as fast as single precision on nearly any
> > other machine in its price range?
> 
> 	Given that we could do double floating math as fast as single
> floating math, the only advantage single would have left would be saving
> memory on large arrays.  Maybe we'd have to keep {load,store}
> Roy Smith, {allegra,cmcl2,philabs}!phri!roy
> System Administrator, Public Health Research Institute
> 455 First Avenue, New York, NY 10016

This is a question/problem that has been gnawing on me for a long time:
It is the case (K&R p184) that "All floating arithmetic in C is carried
out in double-precision;" regardless whether declared as single precision
or not.  Given that a large majority of code being written (at least at
a typical UNIX site) is in C, why not dispose of single precision floating
point altogether and concentrate the silicon real-estate to something
that my compiler might actaully use.  Alternately, perhaps hardware/arch.
people can convince C compiler writers that (as I often find) single
precision is more than sufficient for all but the most numerically nasty
problems and should be used for float arithmetic unless code directed
otherwise.  (It seems to go against UNIX philosophy to have a compiler
force a double precision arithmetic when source code clearly indicates
that single precision would suffice.)  I am willing to be that my FPA
has *never* executed a single precision arithmetic operation (other than
double->single and single->double)!!

-- 
David F. Carlson, Micropen, Inc.
...!{ames|harvard|rutgers|topaz|...}!rochester!ur-valhalla!micropen!dave

"The faster I go, the behinder I get." --Lewis Carroll