Re: Using the GNU GMP Library for Bignums in Emacs

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

On 04/25/2018 03:40 PM, Richard Stallman wrote:
> If we were to support_only_  64-bit systems, this argument would cease
> to be valid.

That is easy to arrange; just configure --with-wide-int. This causes 
Emacs to use 64-bit words on all platforms (or wider, at least in 
theory). If we made --with-wide-int the default (which I'm more and more 
thinking would be a good thing, for this and other reasons), then 
#xffffffff would work and would format the same on all platforms by 
default, and this would happen regardless of whether we also add bignums 
to Emacs.

However, I don't see why assuming 64 bits would mean that the argument 
would cease to be valid. Even with that assumption, we would continue 
have the same problem with numbers like #xffffffffffffffff that exceed 
Emacs fixnum range when words are 64 bits.

> I responded to a statement about what happens in C.  Did you misread that
> as a proposal to change Emacs?
Yes, because after your response (which talked about what happens in C), 
you wrote "I contend that we want the same behavior in Emacs Lisp, too." 
Sorry if I misunderstood you.

I think part of the problem here, is that once we have bignums then 
there will no problem representing unsigned values that are too large to 
fit into (say) 30-bit signed integers, so there will be no problem in 
having %x treat integers like Common Lisp and Python do: programs that 
want to do I/O of numbers as hexadecimal strings will be able to read 
and print them with %x and they'll all work just fine even if the 
numbers contain 8 or 16 or more hexadecimal digits. The problem arises 
in Emacs Lisp only because it is limited to fixnums now.