linux-kernel - Re: [PATCH] lib/int_sqrt.c: Optimize square root function

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Message-ID: <20170720141333.vqpeuzox7qusig2c@hirez.programming.kicks-ass.net>
Date:   Thu, 20 Jul 2017 16:13:33 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Anshul Garg <aksgarg1989@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        anshul.g@...sung.com, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] lib/int_sqrt.c: Optimize square root function

On Thu, Jul 20, 2017 at 04:52:49AM -0700, Joe Perches wrote:
> On Thu, 2017-07-20 at 13:24 +0200, Peter Zijlstra wrote:
> []
> > +	m = 1UL << ((fls(x) + 1) & ~1UL);
> 
> maybe 
> 
> #if BITS_PER_LONG == 64
> 	m = 1UL << ((fls64(x) + 1) & ~1UL);
> #else
> 	m = 1UL << ((fls(x) + 1) & ~1UL);
> #endif

We do seem to have __fls() which is defined on long.