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

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Message-ID: <1500639310.14415.25.camel@perches.com>
Date:   Fri, 21 Jul 2017 05:15:10 -0700
From:   Joe Perches <joe@...ches.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Anshul Garg <aksgarg1989@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "anshul.g@...sung.com" <anshul.g@...sung.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] lib/int_sqrt.c: Optimize square root function

On Fri, 2017-07-21 at 13:40 +0200, Peter Zijlstra wrote:
> @@ -21,7 +22,11 @@ unsigned long int_sqrt(unsigned long x)
>  	if (x <= 1)
>  		return x;
>  
> -	m = 1UL << (BITS_PER_LONG - 2);
> +	m = 1UL << (__fls(x) & ~1U);
> +
> +	while (m > x)
> +		m >>= 2;

while (m > x) ?

Belt and suspenders if __fls is broken?