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Subject: Re: [PATCH] lib/int_sqrt.c: Optimize square root function
From: Joe Perches <joe@perches.com>
To: Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc: Anshul Garg <aksgarg1989@gmail.com>,
        Davidlohr Bueso <dave@stgolabs.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "anshul.g@samsung.com" <anshul.g@samsung.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Will Deacon <will.deacon@arm.com>
Date: Fri, 21 Jul 2017 05:15:10 -0700
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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?