On 01/27/11 10:15, Eric Blake wrote: > In other words, the problem is not about overflow, but about undefined > behavior.
You're right that the behavior is not defined, but this should not be a problem in practice, any more than the * CHAR_BIT business should be a problem in practice (that also relies a not-guaranteed- by-the-standard assumption). Currently the code assumes that if time_t values are signed, then they use either two's complement, ones' complement, or signed magnitude representation internally, that left shift shifts those bits left, and that there are no padding bits. The assumptions about left-shift and no padding bits are not guaranteed by the C standard, but they are portable in practice, even when using the latest GCC with all the optimization bells and whistles enabled. It's unlikely that GCC will ever break expressions like -1 << 1 merely because the C standard lets it do that.
