Re: [PATCH RFC tip/core/rcu 13/20] rcu: increasesynchronize_sched_expedited() batching

[Peter Zijlstra]

On Sun, 2010-12-19 at 08:35 -0800, Paul E. McKenney wrote:
> >  (int)((unsigned)(a) - (unsigned)(b)) < 0
> 
> Unfortunately, no.  :-(
> 
> The (int) converts from unsigned to signed, and if the upper bit of
> the unsigned difference is non-zero, then the paragraph I quoted above
> applies, and the standard allows the compiler to do whatever it wants.
> 
As noted in the previous reply, that would render quite a lot of our
time-keeping code broken. I think its safe to assume this works.

Look at time_after() for example:

#define time_after(a,b)		\
	(typecheck(unsigned long, a) && \
	 typecheck(unsigned long, b) && \
	 ((long)(b) - (long)(a) < 0))

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