linux-kernel - Re: [PATCH v10 1/3] lib: Add strongly typed 64bit int

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Message-ID: <20171221141130.cdng2mysnjj6j4i6@hirez.programming.kicks-ass.net>
Date:   Thu, 21 Dec 2017 15:11:30 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Crt Mori' <cmo@...exis.com>, Jonathan Cameron <jic23@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Rusty Russell <rusty@...tcorp.com.au>,
        Ian Abbott <abbotti@....co.uk>,
        Larry Finger <Larry.Finger@...inger.net>,
        Niklas Soderlund <niklas.soderlund+renesas@...natech.se>,
        Thomas Gleixner <tglx@...utronix.de>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v10 1/3] lib: Add strongly typed 64bit int_sqrt

On Thu, Dec 21, 2017 at 01:56:55PM +0000, David Laight wrote:
> > This part above looks like FLS
> It also does the rest of the required shifts.

Still, fls() + shift is way faster on hardware that has an fls
instruction.

Writing out that binary search doesn't make sense.