From: Eli Zaretskii <eliz@gnu.org>
To: Andreas Schwab <schwab@linux-m68k.org>
Cc: t_tuneyosi@hotmail.com, monnier@iro.umontreal.ca, emacs-devel@gnu.org
Subject: Re: macro FIXNUM_OVERFLOW_P in lisp.h is valid ?
Date: Sat, 24 Oct 2009 12:16:47 +0200 [thread overview]
Message-ID: <83pr8df65s.fsf@gnu.org> (raw)
In-Reply-To: <m2d44duo31.fsf@whitebox.home>
> From: Andreas Schwab <schwab@linux-m68k.org>
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>, t_tuneyosi@hotmail.com, emacs-devel@gnu.org
> Date: Sat, 24 Oct 2009 11:40:34 +0200
>
> >> (FIXNUM_OVERFLOW_P): Cast I to EMACS_INT in comparisons
> >> in case I is of some unsigned type, in which case
> >> MOST_NEGATIVE_FIXNUM will be converted to unsigned, and the
> >> comparison becomes bogus.
> >
> > Right, sorry for my failing memory.
> >
> > So I think the change made yesterday by Andreas should be reverted.
>
> The cast does not really fix the described problem anyway. Converting
> an unsigned value to a signed type when the value is out of range for
> the signed type results in an implementation defined value. That is
> less bad than undefined behaviour, but still not portable.
That's true, but I think we need to fix both problems. In any case, I
think having a small unsigned value is more frequent than having a
very large unsigned value, which is probably the reason why the former
was discovered in 2001, while the latter only now.
Maybe the solution is to use a real function rather than a macro.
next prev parent reply other threads:[~2009-10-24 10:16 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-10-23 17:51 macro FIXNUM_OVERFLOW_P in lisp.h is valid ? Toru TSUNEYOSHI
2009-10-23 19:33 ` Eli Zaretskii
2009-10-24 1:50 ` Toru TSUNEYOSHI
2009-10-24 9:05 ` Eli Zaretskii
2009-10-24 11:59 ` Toru TSUNEYOSHI
2009-10-24 13:00 ` Eli Zaretskii
2009-10-24 18:45 ` Toru TSUNEYOSHI
2009-10-24 15:14 ` Andreas Schwab
2009-10-24 18:39 ` Stefan Monnier
2009-10-26 14:48 ` Toru TSUNEYOSHI
[not found] ` <20091024.105033.100383844.t_tuneyosi@hotmail.com>
2009-10-24 6:07 ` Toru TSUNEYOSHI
[not found] ` <20091024.150744.186061320.t_tuneyosi@hotmail.com>
2009-10-24 7:46 ` Toru TSUNEYOSHI
2009-10-24 10:11 ` Eli Zaretskii
2009-10-23 20:57 ` Andreas Schwab
2009-10-23 22:02 ` Eli Zaretskii
2009-10-24 1:05 ` Stefan Monnier
2009-10-24 9:15 ` Eli Zaretskii
2009-10-24 9:40 ` Andreas Schwab
2009-10-24 10:16 ` Eli Zaretskii [this message]
2009-10-24 10:01 ` Andreas Schwab
2009-10-23 21:14 ` Stefan Monnier
2009-10-25 8:51 ` Toru TSUNEYOSHI
[not found] ` <20091025.175131.55657724.t_tuneyosi@hotmail.com>
2009-10-25 11:30 ` Toru TSUNEYOSHI
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