On Thu, Jan 27, 2011 at 11:42:25PM -0800, Paul Eggert wrote: > On 01/27/2011 02:08 PM, Rich Felker wrote: > > I mean to say that left-shifting a negative value *at all* is > > undefined behavior. I doubt gcc will ever break it, but why not use my > > version of the code that's 100% safe and never invokes undefined > > behavior? > > Your version of the code provokes similar undefined behavior > when computing TYPE_MINIMUM, which means that overall it's > no more reliable than what's there now. An advantage of > the current approach is that there's a clear relationship > between TYPE_MINIMUM and TYPE_MAXIMUM, and this aids understanding. > If it could be done just as clearly by other means, that would > be OK too.
My version only computes the maximum. The minimum is -max if the type is sign/magnitude or ones complement and -max-1 if the type is twos complement. Testing which of the three allowable signed integer representations is used is easy: compare ~(t)1 against and -(t)1 and -(t)2. Rich
