On Sat, 2013-07-27 at 15:58 -0700, Paul E. McKenney wrote: > According to the C standard 3.4.3p3, overflow of a signed integer results > in undefined behavior. This commit therefore changes the definitions > of time_after() and time_after_eq() to avoid this undefined behavior. > The trick is that the subtraction is done using unsigned arithmetic, > which according to 6.2.5p9 cannot overflow because it is defined as > modulo arithmetic. This has the added (though admittedly quite small) > benefit of shortening two lines of code by four characters each. > > Note that the C standard considers the cast from signed to > unsigned to be implementation-defined, see 6.3.1.3p3. However, on a > two-complement system, an implementation that defines anything other > than a reinterpretation of the bits is free come to me, and I will be > happy to act as a witness for its being committed to an insane asylum. > (Although I have nothing against saturating arithmetic or signals in > some cases, these things really should not be the default.) > > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > Cc: John Stultz <john.stu...@linaro.org> > Cc: "David S. Miller" <da...@davemloft.net> > Cc: Arnd Bergmann <a...@arndb.de> > Cc: Ingo Molnar <mi...@kernel.org> > Cc: Linus Torvalds <torva...@linux-foundation.org> > > diff --git a/include/linux/jiffies.h b/include/linux/jiffies.h > index 97ba4e7..97967ba 100644 > --- a/include/linux/jiffies.h > +++ b/include/linux/jiffies.h > @@ -101,13 +101,13 @@ static inline u64 get_jiffies_64(void) > #define time_after(a,b) \ > (typecheck(unsigned long, a) && \ > typecheck(unsigned long, b) && \ > - ((long)(b) - (long)(a) < 0)) > + ((long)((b) - (a)) < 0)) > #define time_before(a,b) time_after(b,a) > > #define time_after_eq(a,b) \ > (typecheck(unsigned long, a) && \ > typecheck(unsigned long, b) && \ > - ((long)(a) - (long)(b) >= 0)) > + ((long)((a) - (b)) >= 0)) > #define time_before_eq(a,b) time_after_eq(b,a) >
time_after64() & time_after_eq64() probably need the same. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
