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

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From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Rich Felker <dalias <at> aerifal.cx>
Cc: 7928 <at> debbugs.gnu.org, bug-gnulib <at> gnu.org, Bruno Haible <bruno <at> clisp.org>, Eric Blake <eblake <at> redhat.com>
Subject: bug#7928: mktime test in configure: UB resulting in infinite loop
Date: Thu, 27 Jan 2011 23:42:25 -0800

On 01/27/2011 02:08 PM, Rich Felker wrote:
> 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?

Your version of the code provokes similar undefined behavior
when computing TYPE_MINIMUM, which means that overall it's
no more reliable than what's there now.  An advantage of
the current approach is that there's a clear relationship
between TYPE_MINIMUM and TYPE_MAXIMUM, and this aids understanding.
If it could be done just as clearly by other means, that would
be OK too.

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