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Date: Mon, 2 Nov 2015 13:30:28 -0800 From: Andy Lutomirski <luto@...capital.net> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Andy Lutomirski <luto@...nel.org>, David Miller <davem@...emloft.net>, Hannes Frederic Sowa <hannes@...essinduktion.org>, Andrew Morton <akpm@...ux-foundation.org>, Network Development <netdev@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [GIT] Networking On Mon, Nov 2, 2015 at 1:19 PM, Linus Torvalds <torvalds@...ux-foundation.org> wrote: > On Mon, Nov 2, 2015 at 1:16 PM, Linus Torvalds > <torvalds@...ux-foundation.org> wrote: >> On Mon, Nov 2, 2015 at 12:34 PM, Andy Lutomirski <luto@...nel.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 linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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