------- Comment #36 from rguenther at suse dot de 2010-02-21 13:37 ------- Subject: Re: numeric_limits<signed>::is_modulo is inconsistent with gcc
On Sun, 21 Feb 2010, veksler at il dot ibm dot com wrote: > > Or suspend it. I think this warrants a defect report anyway since I think > > is_modulo was intended to describe CPU behavior as otherwise defining > > signed integer overflow as undefined in one piece of the standard and > > then requiring a sane answer for is_modulo in another part sounds > > like a conflict of interest. > > > Maybe it is better to make things clear, but I am not so sure of the > outcome. I think that is_modulo is meaningful only if it is true, otherwise, > when false user's code can't rely on any specific behavior. > Maybe is_modulo=false is the right answer even for -fwrapv after all. Or maybe is_modulo=true has only practical meaning for code that doesn't invoke undefined behavior anyway (like adding two signed integers when the operation will overflow). That also avoids the /-1 and %-1 issues. It really depends on how is_modulo was supposed to be used. Richard. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=22200
