linux-kernel - Re: [PATCH] Optimize is_power_of

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 15 Jun 2007 21:47:50 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...putergmbh.de>
To:	Vegard Nossum <vegard.nossum@...il.com>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Robert P. J. Day" <rpjday@...dspring.com>
Subject: Re: [PATCH] Optimize is_power_of_2().



On Jun 15 2007 18:56, Vegard Nossum wrote:
> bool is_power_of_2(unsigned long n)
> {
>-	return (n != 0 && ((n & (n - 1)) == 0));
>+	return n * !(n & (n - 1));
> }

There is a third way which uses neither * nor &&, but []:

bool is_power_of_2(unsigned long n)
{
	static const bool yn[] = {
		[0] = false,
		[1 ... (8 * sizeof(n) - 1)] = true,
	};
	return yn[(n & (n - 1)) == 0];
}



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