linux-kernel - Re: [PATCH] lib/int_sqrt.c: optimize for small argument values

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Message-ID: <CAGXu5jL6g3QU4QshBiD=Zhf-5NJFX99eJ1sMkdOwn3ywW41TTA@mail.gmail.com>
Date:   Fri, 20 Oct 2017 07:18:51 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Joe Perches <joe@...ches.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Michael Davidson <md@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        David Miller <davem@...emloft.net>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lib/int_sqrt.c: optimize for small argument values

On Thu, Oct 19, 2017 at 11:13 PM, Joe Perches <joe@...ches.com> wrote:
> On Thu, 2017-10-19 at 13:31 -0700, Michael Davidson wrote:
>> int_sqrt() currently takes approximately constant time
>> regardless of the value of the argument. By using the
>> magnitude of the operand to set the initial conditions
>> for the calculation the cost becomes proportional to
>> log2 of the argument with the worst case behavior not
>> being measurably slower than it currently is.
>
> https://lkml.org/lkml/2017/7/24/408

Ah! Cool. I don't see this version queued up for -next. Where does
Peter's version stand?

-Kees

-- 
Kees Cook
Pixel Security