Path: utzoo!utgpu!watserv1!watmath!att!occrsh!uokmax!apple!julius.cs.uiuc.edu!zaphod.mps.ohio-state.edu!rpi!batcomputer!munnari.oz.au!goanna!ok
From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.arch
Subject: Re: Killer Micro II
Keywords: floating point, language
Message-ID: <3737@goanna.cs.rmit.oz.au>
Date: 12 Sep 90 03:24:56 GMT
References: <527@llnl.LLNL.GOV> <603@array.UUCP> <2482@l.cc.purdue.edu> <3785@osc.COM>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 31

In article <3785@osc.COM>, jgk@osc.COM (Joe Keane) writes:
> Suppose Fortran started out with three floating-point formats, and furthermore
> suppose that C also had this.  Then i bet you'd see a lot of machines today
> which directly support three different floating-point formats.

C *has* three floating-point types:  float, double, and long double.
Perhaps there aren't a lot of _architectures_ with three floating-point
types (although the VAX has four, and some IBM 370s have three), but a
lot of _machines_ have been shipped with IEEE single, double, and
extended formats (supported by a coprocessor chip).

> Another example is that Common Lisp has multi-precision integers and short
> floating-point types.  If you look at a Lisp machine, you'll find that these
> types are supported directly by the microcode.

Yes, but here it is a very clear case of the language driving the machine.
Bignums (integers which are whatever size they need to be, in a language
where your program doesn't have to _say_ what size they'll be) are there
because people were writing computer algebra programs and had a _use_ for
bignums.  On Xerox Lisp machines, bignums are actually handled in Lisp
code, _not_ in microcode.  Some models of the Xerox Lisp machines handled
floating-point in Lisp, some didn't.  It's an engineering tradeoff.

Many "stock" architectures (/370, 680x0, 80*86, 32?32, ... provide all
the primitives (add with carry, n*n -> 2n multiply, and so on) that are
needed to synthesise integer arithmetic of any size.  (Perhaps this is
a lingering relic of COBOL?)  I have never understood why Pascal compilers
don't exploit this to let you declare integers of whatever size you need.

-- 
Heuer's Law:  Any feature is a bug unless it can be turned off.