Re: Lisp reader syntax and bootstrap

[Paul Eggert <eggert@cs.ucla.edu>]

On 2023-07-14 19:10, Richard Stallman wrote:
> That's a bit of a kludge -- using those values might be wrong for
> some purposes...

Yes, though there are similar problems even for finite numbers, since 
they also behave differently on the VAX, sometimes significantly. E.g., 
VAX subtraction can underflow to zero via catastrophic cancellation, 
whereas IEEE subtraction cannot.

Though my change is indeed a hack, it is an improvement in that Emacs 
can now start up and load 'calculator' whereas formerly it could not. I 
"tested" this by manually setting IEEE_FLOATING_POINT to zero on x86-64, 
and compiling and running the result. Of course this is not the same as 
a real VAX.


>    > This patch shouldn't change behavior (or even the executable code) on
>    > today's platforms. It's purely for computer museums.
> 
> If that's true, maybe your solution is fine.

I surveyed the net and it appears to be true. The only Emacs platform 
that still insists on non-IEEE floating point is NetBSD/vax, and 
nowadays that platform seems to be run only for computer-museum-like 
purposes. These uses are rare even by computer-museum standards, as most 
hobbyist historians that simulate VAXes seem to prefer VMS to NetBSD, I 
expect partly because VMS "feels" older (it differs more from GNU :-). 
And VMS-using hobbyists can't run current Emacs, as Emacs 23 dropped VMS 
support.

PS. Are you aware of the licensing dispute over the emulator that 
hobbyists typically use to run VAX code? This emulator, SIMH, is based 
on software that dates back to the 1960s, so in some sense it's even 
older than Emacs. The dispute involves a license clause introduced a 
year ago that I've not seen before, and it's not clear to me that SIMH 
is free software any more. However, this change has been disputed and 
SIMH has forked off a new project Open SIMH that does not have the 
controversial clause. For details, please see:

https://groups.io/g/simh/topic/91528716#1659

The disputed licensing clause is at the end of this change:

https://github.com/simh/simh/commit/ce2adce632e1a22e6d76d4bf726d6b863373c550