Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!munnari.oz.au!goanna!ok
From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.arch
Subject: Re: 386 Clones [really: IEEE floating point & various approaches; long]
Message-ID: <4199@goanna.cs.rmit.oz.au>
Date: 5 Nov 90 03:55:01 GMT
References: <1990Oct26.015244.586@amd.com> <8464@scolex.sco.COM> <42677@mips.mips.COM>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 50

In article <42677@mips.mips.COM>, mash@mips.COM (John Mashey) writes:
> In article <4186@goanna.cs.rmit.oz.au> ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe) writes:

> 1) SVID, to be honest, was fairly irrelevant to this,

Eh?  Oh gosh, this means I have been fantastically stupid.
You see, when I tried to write numeric code that would run under "UNIX",
I used the SVID as a portability guide.  

> in that it described an interface, but gave as a future direction IEEE
> exception-handling.

Darn it, so _that_ was the answer.  Instead of trying to write programs
that would use the facilities available *now* (actually, *then*) I should
have waited for the future (no IEEE signal handling in V.3).

BSD UNIX *does* provide adequate information to an SIGFPE handler,
for my former purposes, except that the documentation could do with
improving (what is the difference between FPE_FLTOVF_FAULT and
FPE_FLTOVF_TRAP, for example?).  But if your code is to run on a V.2
box, that really doesn't help, it merely adds the pain of Tantalus
to that of Sisyphus.

> 2) People who've built IEEE-based computers who worried about FP
> have long ago included some approximation or other to full IEEE-signal
> handlers.  I'm sure Sun did; we did, and I'd assume others did also.

(a) Not all.  (I suppose it depends on how worried they were.)
(b) Certainly Sun did.  Twice.  And Sun's software FP on the 3/50 never
generated no signals nohow (I don't know about 4.x). People who wanted
their code to be portable *had* to write it so that it would work
without IEEE exception handling, even if they only wanted their code to
work on IEEE + 4.xBSD UNIX boxes, even if they further restricted
portability to MC680x0-based machines, because there wasn't a
*standard*, not even a de-facto standard, interface.  The really
horrible thing was that Sun were one of a very small number of companies
that obeyed the letter of IEEE 754 law and gave you the default
behaviour required by that standard, so not only could you not rely on
*getting* interrupts, you couldn't rely on *not* getting them either.


I suppose the contrast is between companies/universities/research units
that had serious number-crunching requirements and picked a UNIX system
to suit and inviduals who having a UNIX system ready to hand wanted to
get some number-crunching done and wanted it to work on whichever system
they'd be able to get time on next.

-- 
The problem about real life is that moving one's knight to QB3
may always be replied to with a lob across the net.  --Alasdair Macintyre.