Bug in Bob Supnik's Emulator!

[Pete Turnbull]

On Apr 3, 15:41, Greg Lehey wrote:
> Subject: Re: Bug in Bob Supnik's Emulator!
> On Thu,  2 April 1998 at 16:00:40 -0800, Tim Shoppa wrote:
> >> I suspect the FP emulation in Bob's Emulator, so it might be worth
> >> watching the floating point values in the program. Bob mailed me during
> >> the week, and I sent him a virgin binary of factor so he could verify that
> >> there is a bug.

I'd be very surprised if factor used FP.  My 7th Edition system's offline ATM,
so I can't check the source.

> > More evidence of a bug is that 'vi' doesn't work right under Bob
> > Supnik's emulator, either.  At one point Steven Schultz made some
> > private speculations to me about where the problem might be, but
> > I've forgotten the details.  Is it possible that these two bugs
> > are both due to FP emulation?  Does the 2.11BSD 'vi' even use
> > the FP registers?

Dunno, but I'd be surprised.

> applied multiple patches to the system.  I did have some as yet
> unexplained problems with the assembler, which Steven Schultz
> considers to be due to the emulator (more specifically, instruction
> restart), but Hartmut Brandt (the principal author) thinks this is
> unlikely.

Well, it is one of the areas that causes trouble on different flavours of
PDP-11.  Both DEC and Unix O/S's had all sorts of games being played in the
trap recovery code, according to which processor the O/S thought it was running
under.  But AFAIK, that code only gets called if an instruction is aborted,
which I wouldn't expect would happen exactly the same way every time factor was
run (but again, I'm speculating without having looked at the code).

-- 

Pete						Peter Turnbull
						Dept. of Computer Science
						University of York

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