Re: Using the GNU GMP Library for Bignums in Emacs

[Paul Eggert]

On 04/24/2018 06:05 PM, Richard Stallman wrote:
>    > In such applications, it's routine to have hexadecimal numbers that are 
> wider
>    > than 32- or 64-bit words.
>
> What is the motive for using hexadecimal in a case like that?

It varies. One motivation is a desire to communicate a number via text 
more-efficiently than base 10 would provide.

>    > Even in the standard C library (which lacks bignums), the %x printf format 
> is
>    > supposed to be used only with unsigned integers.
>
> I think that's a misleading statement of what it does in C.  The rule
> is to use it with an unsigned _type_.  The type, not the value, is
> supposed to be unsigned.

In C, if the type is unsigned then the corresponding value is 
nonnegative. That is, in C there is no such thing as a negative value 
with an unsigned type. The %x format is supposed to be used only with 
unsigned types, i.e., only with nonnegative values.

> I contend that we want the same behavior in Emacs Lisp, too.

I certainly wouldn't want the behavior you suggest. Among other things, 
Emacs Lisp does not have unsigned types, and I'd rather not introduce 
such a concept into the language as it'd be needless complexity and an 
unnecessary divergence from other Lisps.

> In Emacs, 0xffffffff will be a bignum.

Whether 0xffffffff is a bignum will depend on the platform. On my 64-bit 
Emacs, 0xffffffff already is supported as a fixnum, and that wouldn't 
change if bignums were introduced to Emacs.

> Is it a bignum in those other systems?

It depends on the system, I expect (just as it would in Emacs).