On Mon, Nov 2, 2015 at 1:19 PM, Linus Torvalds <torva...@linux-foundation.org> wrote: > On Mon, Nov 2, 2015 at 1:16 PM, Linus Torvalds > <torva...@linux-foundation.org> wrote: >> On Mon, Nov 2, 2015 at 12:34 PM, Andy Lutomirski <l...@kernel.org> wrote: >>> >>> Getting overflow checking right in more complicated cases is a PITA. >> >> No it is not. Not for unsigned values. > > Just to clarify. The "oevrflow" test for unsigned subtracts of "a-b" > (it's really an underflow, but whatever) really is just > > (b > a) > > Really. That's it. Claiming that that is "complicated" and needs a > helper function is not something sane people do. A fifth-grader that > isn't good at math can understand that. > > In contrast, nobody sane understands "usub_overflow(a, b, &res)". > > So really. Stop making inane arguments.
I'll stop making inane arguments if you stop bashing arguments I didn't make. :) I said the helpers were useful for multiplication (by which I meant both signed and unsigned) and, to a lesser extent, for signed addition and subtraction. I don't believe I even tried to justify usub_overflow as anything other than an extremely minor optimization that probably isn't worthwhile. --Andy, who still has inline asm that does 'cmovo' and such in his code for work, sigh. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
