GNU bug report logs - #32252
[PATCH] %o and %x now format signed numbers

Previous Next

Full log

View this message in rfc822 format

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: 32252 <at> debbugs.gnu.org
Subject: bug#32252: [PATCH] %o and %x now format signed numbers
Date: Tue, 24 Jul 2018 07:22:52 -0700

Helmut Eller wrote:
> With your change %x will also have quite a different meaning in C11.

Not really, as Emacs (format "%x" N) agrees with C11 printf ("%x", N) in all 
values of N that are valid in both languages. In C11, negative values are not 
valid, as printf ("%x", N) has undefined behavior when N is negative. So we are 
discussing an area where Emacs Lisp can define behavior without introducing 
incompatibilities with C11.

If we changed (format "%x" -1) to signal an error instead, that would also be 
upward-compatible with C11. However, it's more useful for something like (format 
"#x%x" -1) to output a string that can 'read' can scan to get -1, something 
that's not true of Emacs now.

>> This seems like overkill for such a small
>> change to functionality that hardly ever matters; plus, %x, %X and %o
>> would continue to have problematic machine-dependent semantics and
>> would not be sensibly extensible to bignums.
> 
> If it doesn't matter to you then why make the change/break at all?

It does matter to me, actually. I think Emacs should have sensible behavior even 
in corner cases that hardly ever arise in real programs.

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.