On Fri, Nov 02, 2018 at 01:23:28PM +0100, Peter Zijlstra wrote: > On Fri, Nov 02, 2018 at 10:56:31AM +0000, David Laight wrote: > > From: Paul E. McKenney > > > Sent: 01 November 2018 17:02 > > ... > > > And there is a push to define C++ signed arithmetic as 2s complement, > > > but there are still 1s complement systems with C compilers. Just not > > > C++ compilers. Legacy... > > > > Hmmm... I've used C compilers for DSPs where signed integer arithmetic > > used the 'data registers' and would saturate, unsigned used the 'address > > registers' and wrapped. > > That was deliberate because it is much better to clip analogue values. > > Seems a dodgy heuristic if you ask me. > > > Then there was the annoying cobol run time that didn't update the > > result variable if the result wouldn't fit. > > Took a while to notice that the sum of a list of values was even wrong! > > That would be perfectly valid for C - if unexpected. > > That's just insane ;-) > > > > > But for us using -fno-strict-overflow which actually defines signed > > > > overflow > > > > I wonder how much real code 'strict-overflow' gets rid of? > > IIRC gcc silently turns loops like: > > int i; for (i = 1; i != 0; i *= 2) ... > > into infinite ones. > > Which is never what is required. > > Nobody said C was a 'safe' language. But less UB makes a better language > IMO. Ideally we'd get all UBs filled in -- but I realise C has a few > very 'interesting' ones that might be hard to get rid of. There has been an effort to reduce UB, but not sure how far they got. Thanx, Paul
