Path: utzoo!attcan!uunet!lll-winken!lll-lcc!ames!oliveb!sun!chiba!khb
From: khb%chiba@Sun.COM (Keith Bierman - Sun Tactical Engineering)
Newsgroups: comp.arch
Subject: Re: MIPS supports 80- & 128-bit floats.
Message-ID: <83722@sun.uucp>
Date: 4 Jan 89 18:38:17 GMT
References: <10452@obiwan.mips.COM> <325@loligo.fsu.edu> <13142@cup.portal.com> <345@loligo.fsu.edu> <83596@sun.uucp> <350@loligo.fsu.edu>
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Reply-To: khb@sun.UUCP (Keith Bierman - Sun Tactical Engineering)
Organization: Sun Microsystems, Mountain View
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In article <350@loligo.fsu.edu> mccalpin@loligo.UUCP (John McCalpin) writes:
>
>An option that seems to be taken by many vendors is to adopt the IEEE
>*format* without adopting all of the *rules*.  Admittedly, this is a
>dangerous choice, but it does aid portability.  A particular example is
>to simply not calculate guard, round, and sticky bits in divides.  The
>user should try to replace divides with multiplies, which retain full
>IEEE precision.  If the divide can't be replaced, then you just get a
>less accurate answer (as on the Crays).  I don't know how to handle
>gradual underflow, though I agree it is important....
>
>The advantage of using the IEEE *formats* is that there is at least hope
>that binary data files could be read on the front end.  Many, many hours
>of CPU time on supercomputers are wasted on scalar data analysis/graphics
>programs that should be run on a more cost-effective front-end, which is
>often where the files are actually stored anyway.

If there is a 32-bit mode (and its being used) I would be very worried
about the quality of a non-ieee "algorithm" using ieee formatted
numbers. For 64-bit machines the problem is not as severe...at least
in my experience the "real world" is 32-bit (resolution of measuring
devices, combined with reasonable units) so the fact that the last
several bits are "corrupt" is not really a problem. But in 32-bit mode
all of the IEEE stuff is really a must....this is why so much work is
done in DP...32-bits of "crummy" arithmetic just wasn't good enough.
The sad thing is that many researchers insist on using their nice new
ieee machines in 64-bit mode only...




Keith H. Bierman
It's Not My Fault ---- I Voted for Bill & Opus