netdev - Re: [GIT] Networking

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrUxU_AVcQheeCXc0qTh=o2tmDbDct27QfTCb_+G6qc3gQ@mail.gmail.com>
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 netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html