[Simh] Looking for a milestone

[Leo Broukhis]

On Mon, 17 Oct 2016 15:29:10 -0600, Kevin Handy <khandy21yo at gmail.com>
wrote:

How close are the simh emulators to the real hardware's floating point? How
> exct is the emulation of FPU's?
> Does simh emulate the real hardware close enough that you can use it to
> analyze the original hardware floating point processors? (For those that
> actually had FPUs instead of doing it in software).
> Or does it do it using "modern" methods (IEEE style FPUs) that could
> calculate different results than the original hardware did?
>

I can tell that the engineering ALU test passes in the BESM-6 emulator.

Addition and multiplication produce 80 bit of mantissa and had to be
emulated with integers; division produces 40 bit, but using IEEE double and
truncating or rounding the result causes the test to fail; I had to
implement the non-restoring division algorithm exactly as described in the
docs to make it work.

It;s probably not a big deal for most users, but if the simh FPU hardware
>  might operate any different;y than the real hardware it should at least be
> documented somewhere.
>

If other machines emulated by SIMH use IEEE for speed, it would be
interesting to run their engineering tests, if available, to see if there
are any failures.

Leo
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