Message-ID: <1422904256.30476.11.camel@perches.com>
Subject: Re: [PATCH] lib/int_sqrt.c: Optimize square root function
From: Joe Perches <joe@perches.com>
To: Anshul Garg <aksgarg1989@gmail.com>
Cc: linux-kernel@vger.kernel.org, anshul.g@samsung.com,
        torvalds@linux-foundation.org
Date: Mon, 02 Feb 2015 11:10:56 -0800
In-Reply-To: <1422897162-111998-1-git-send-email-aksgarg1989@gmail.com>
References: <aksgarg1989@gmail.com>
	 <1422897162-111998-1-git-send-email-aksgarg1989@gmail.com>
Content-Type: text/plain; charset="ISO-8859-1"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1090
Lines: 41

On Mon, 2015-02-02 at 09:12 -0800, Anshul Garg wrote:
> From: Anshul Garg <aksgarg1989@gmail.com>
> 
> Unnecessary instructions are executing even though m is
> greater than x so added logic to make m less than equal to
> x before performing these operations.
> 
> Signed-off-by: Anshul Garg <aksgarg1989@gmail.com>
> ---
>  lib/int_sqrt.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/lib/int_sqrt.c b/lib/int_sqrt.c
[]
> @@ -22,6 +22,9 @@ unsigned long int_sqrt(unsigned long x)
>  		return x;
>  
>  	m = 1UL << (BITS_PER_LONG - 2);
> +
> +	while (m > x)
> +		m >>= 2;

Perhaps removing the while and using fls(x) would be better.

Perhaps something like:

	m = 1UL << min(sizeof(unsigned long) == sizeof(u64) ?
		       fls64(x) : fls(x),
		       BITS_PER_LONG - 2);

>  	while (m != 0) {
>  		b = y + m;
>  		y >>= 1;


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/