On Tue, Jun 28, 2005 at 12:59:10PM -0400, Morten Welinder wrote: > > In particular, a very large number of C and C++ programs are written > > with the assumptions: > > >- signed and unsigned types are modulo, except in loop induction > > variables where it's bad taste > > Well, as demonstrated by INT_MIN/-1, gcc has NEVER fulfilled such assumptions > on i86 and, quite likely, neither has or will any other compiler. The > runtime > penalty would be too big and hurt performance numbers.
I meant "bad taste to rely on that", sorry. Not that it shouldn't overflow, but rather that overflowing shouldn't happen in a well-behaving program and and the compiler is allowed to go and slap you if it happens. > What I believe you can find examples of is that the more restricted claim of > "addition and perhaps subtraction of signed numbers is modulo" is being > assumed. That's cheap since (for 2-complement) signed addition is the same > operation as unsigned addition. Yes. OG.
