Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1261001

Re: [GIT] Networking

Show all headers | View raw

On Mon, Nov 2, 2015 at 1:19 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Mon, Nov 2, 2015 at 1:16 PM, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
>> On Mon, Nov 2, 2015 at 12:34 PM, Andy Lutomirski <luto@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 linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [GIT] Networking Andy Lutomirski <luto@kernel.org> - 2015-11-02 21:40 +0100
  Re: [GIT] Networking Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-02 22:20 +0100
    Re: [GIT] Networking Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-02 22:20 +0100
      Re: [GIT] Networking Andy Lutomirski <luto@amacapital.net> - 2015-11-02 22:40 +0100
        Re: [GIT] Networking Hannes Frederic Sowa <hannes@stressinduktion.org> - 2015-11-02 23:20 +0100
          Re: [GIT] Networking Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-03 00:30 +0100
        Re: [GIT] Networking Benjamin Herrenschmidt <benh@kernel.crashing.org> - 2015-11-03 02:00 +0100
          Re: [GIT] Networking Andy Lutomirski <luto@amacapital.net> - 2015-11-03 03:00 +0100
            Re: [GIT] Networking Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-03 03:40 +0100
              Re: [GIT] Networking Hannes Frederic Sowa <hannes@stressinduktion.org> - 2015-11-03 14:00 +0100
                Re: [GIT] Networking Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-03 21:10 +0100
                Re: [GIT] Networking Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-03 21:50 +0100
                RE: [GIT] Networking David Laight <David.Laight@ACULAB.COM> - 2015-11-06 16:30 +0100
                Re: [GIT] Networking Andy Lutomirski <luto@amacapital.net> - 2015-11-07 01:50 +0100
                Re: [GIT] Networking Ingo Molnar <mingo@kernel.org> - 2015-11-09 09:20 +0100
                Re: [GIT] Networking Hannes Frederic Sowa <hannes@stressinduktion.org> - 2015-11-09 11:40 +0100
                Re: [GIT] Networking Hannes Frederic Sowa <hannes@stressinduktion.org> - 2015-11-09 11:40 +0100
          Re: [GIT] Networking Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-03 03:00 +0100

csiph-web