------- Comment #4 from pinskia at gmail dot com 2008-03-29 19:27 ------- Subject: Re: apparent integer math bug
Sent from my iPhone On Mar 29, 2008, at 12:16, "regehr at cs dot utah dot edu" <[EMAIL PROTECTED] > wrote: > > > ------- Comment #3 from regehr at cs dot utah dot edu 2008-03-29 > 19:16 ------- > Subject: Re: apparent integer math bug > >> This multiplication overflows so the resulting behavior is undefined. > > Right-- but always in the past it has been (or seemed) fine to assume > two's complement overflow behavior for signed arithmetic under gcc on > two's complement platforms. > > I have seen the "strict overflow" options and those seem quite > reasonable. However, changing overflow behavior for multiply seems > risky! > > Is it still reasonable at least to rely on two's complement behavior > for > signed addition and subtraction? > It never was reasonable to depend on this behaviour, just GCC got better at optimizing these cases. We have had the option -fwrapv since at least 3.3 so that people can use that option if the want full wrapping behavior with signed types. Note the C standard is over 18 years old now so I had hoped people would still not making the mistake of thinking signed interger being wrapping types. > Thanks, > > John Regehr > > > -- > > > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35753 > -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35753
