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 11:21:17 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Vegard Nossum <vegard.nossum@...il.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Optimize is_power_of_2().

Vegard Nossum wrote:
> From: Vegard Nossum <vegard@...tkore.net>
> Date: Fri, 15 Jun 2007 18:35:49 +0200
> Subject: [PATCH] Optimize is_power_of_2().
> 
> Rationale: Removes one conditional branch and reduces icache footprint.
> Proof: If n is false, the product of n and any value is false. If n is
> true, the truth of (n * x) is the truth of x.
> 

You realize that on a lot of platforms, multiplication is done by an
out-of-line subroutine, and that even on those that aren't, it's
generally a long-pipeline operation, right?

	-hpa
-
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/