Re: Using the GNU GMP Library for Bignums in Emacs

[Paul Eggert]

Richard Stallman wrote:
> In practice, I think, the cases where one wants hexadecimal
> are cases where there is a word width.

Although that is true in traditional usage where word width is assumed, it's not 
true for most applications using bignums, the original context of this thread. 
In such applications, it's routine to have hexadecimal numbers that are wider 
than 32- or 64-bit words. And these numbers (when printed without a sign) are 
routinely treated as nonnegative, not as negative. For an example of this sort 
of application, see the OpenSSL C code that deals with bignums: e.g., BN_bn2hex 
generates a leading "-" when converting a negative number to a hexadecimal string.

Even in the standard C library (which lacks bignums), the %x printf format is 
supposed to be used only with unsigned integers. Nowadays GCC even optionally 
warns about using %x on signed integers.

> The reason to invent a special syntax is to get the commonly desired
> result in a simpler way.

If it turns out to be useful to have a shorthand printf format for formatting 
the least N bits of an argument, we can add it as needed. I have my doubts, 
though, as other bignum formatters seem to get along fine without such a feature.