Re: Using the GNU GMP Library for Bignums in Emacs

[Ken Raeburn]

On May 5, 2018, at 23:12, Richard Stallman <address@hidden> wrote:
> 
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> 
>>> Another idea: %Nx with a negative number should output its 2's
>>> complement representation in 4N bits.
> 
>> That's already taken: A leading “-“ means to left-justify the output if the 
>> specified width is wider than required.
> 
> We are miscommunicating.  I'm talking about what %Nx should do when
> outputting an argument that is negative, as in (format "%16x" -63).
> 
> Sorry that wasn't clear.
> 
> You could try p/x -63 in GDB to see what I mean.

Oh, I see. Yes, I misunderstood. Apologies for my confusion.

So, in this case, would it truncate the output or use a wider field, if the 
value couldn’t “properly” be shown in the specified size?
E.g., -5000 would display in hex as …ffec78; with a format “%2x” should it 
return “78” or should it get enough digits to show the minimum number of bits 
needed to express the real value, much like formatting with “%2d” would still 
give you “-5000” instead of chopping off relevant digits?

Maybe we can supply both bit count and minimum field width in a format string… 
“%32!8x” to display the lowest 32 bits in 8 columns but with leading spaces 
rather than zeros? Or swap the positions of the numbers. And maybe one could be 
optional; “%32!x” could mean either “%32!8x” (eight columns, leading spaces) or 
“%32!1x” (minimum one column, i.e., no leading spaces or zeros added).

It would be logical to consider whether the same format extensions would be 
useful with %o or %d (or others?) being used to format bignums.

Ken