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Re: FP emulation patch available

To: Dominic Sweetman <dom@algor.co.uk>
Subject: Re: FP emulation patch available
From: "Kevin D. Kissell" <KevinK@mips.com>
Date: Wed, 15 Mar 2000 15:35:17 +0100
Cc: "Andrew R. Baker" <andrewb@uab.edu>, Ralf Baechle <ralf@oss.sgi.com>, Harald Koerfgen <Harald.Koerfgen@home.ivm.de>, linux-mips@vger.rutgers.edu, linux-mips@fnet.fr, Linux SGI <linux@cthulhu.engr.sgi.com>
Organization: MIPS Technologies, Inc.
References: <20000313144657.E845@uni-koblenz.de> <Pine.LNX.3.96.1000314123742.24923A-100000@lithium> <200003142317.XAA00644@gladsmuir.algor.co.uk>
Sender: owner-linuxmips@oss.sgi.com
Dominic Sweetman wrote:

> Andrew R. Baker (andrewb@uab.edu) writes:
>
> > ... It will also only handle operations that should produce an
> > unimplemented exception (this is not quite all of the fp ops).
>
> Denormalised operands (for example) will cause any computational
> operation to blow up (change sign, load, store and move will survive -
> can you think of much else?).  The requirement for MIPS hardware is
> something like "you can throw an unimplemented exception in response
> to any combination of operands and operation you don't like, so long
> as it's rare".  That's why a complete emulator is probably a good
> idea.
>
> Dominic Sweetman
> dom@algor.co.uk

OK, I'm convinced.  I believe I know how to make the Algorithmics
emulator SMP-safe *and* more efficient in the general case, thanks
in part to a suggestion from Ralf.  Time permitting, I will also wire it
up to the unimplemented operation handler.  Give me a week or so
to accumulate enough spare time...



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