GNU bug report logs - #7928
mktime test in configure: UB resulting in infinite loop

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Package: coreutils;

Reported by: Rich Felker <dalias <at> aerifal.cx>

Date: Thu, 27 Jan 2011 06:44:02 UTC

Severity: normal

Done: Paul Eggert <eggert <at> cs.ucla.edu>

Bug is archived. No further changes may be made.

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Message #26 received at 7928 <at> debbugs.gnu.org (full text, mbox):

From: Rich Felker <dalias <at> aerifal.cx>
To: Bruno Haible <bruno <at> clisp.org>
Cc: 7928 <at> debbugs.gnu.org, Rich Felker <dalias <at> aerifal.cx>, bug-gnulib <at> gnu.org,
	Eric Blake <eblake <at> redhat.com>
Subject: Re: bug#7928: mktime test in configure: UB resulting in infinite loop
Date: Thu, 27 Jan 2011 17:08:46 -0500

On Thu, Jan 27, 2011 at 07:42:10PM +0100, Bruno Haible wrote:
> Do you mean to say that GCC produces undefined behaviour for shifts of
> negative values, even those where the result is negative (no overflow)?
> I've never seen a sign of that.

I mean to say that left-shifting a negative value *at all* is
undefined behavior. I doubt gcc will ever break it, but why not use my
version of the code that's 100% safe and never invokes undefined
behavior?

Rich
This bug report was last modified 14 years and 177 days ago.

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