On Mon, Sep 14, 2015 at 11:46:32PM -0400, Tejun Heo wrote: > Hello, > > On Mon, Sep 14, 2015 at 08:27:08PM -0700, John Stultz wrote: > > Yea. The above make sense to me, but I suspect there's some very > > subtle reason for the existing separated logic. > > But I'd have to defer to akpm for hints on that. > > Hmmm... people could be using it for calculating the distance between > two unsigned values and in that case the original behavior would be > the correct one. e.g. > > unsigned diff, a, b; > diff = abs(a - b);
This kind of construct can overflow whether a and b are signed or unsigned. Only a two-argument function can correctly return the absolute difference of two integers. At my day job, we arranged for abs(unsigned type) to be a compile-time error and supplied a two args function absdiff for use in these situations -- absdiff(a,b) is the same as abs(a-b) except it avoids overflow and returns an unsigned type. (though I have no doubt that some instances of abs(a - b) still exist where a and b are signed and the intermediate could still overflow...) Jeff -- 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/
