From owner-svn-src-head@FreeBSD.ORG Mon Jan 26 03:07:29 2009 Return-Path: Delivered-To: svn-src-head@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E5D661065670 for ; Mon, 26 Jan 2009 03:07:29 +0000 (UTC) (envelope-from minimarmot@gmail.com) Received: from wf-out-1314.google.com (wf-out-1314.google.com [209.85.200.171]) by mx1.freebsd.org (Postfix) with ESMTP id B8EBE8FC22 for ; Mon, 26 Jan 2009 03:07:29 +0000 (UTC) (envelope-from minimarmot@gmail.com) Received: by wf-out-1314.google.com with SMTP id 24so6161482wfg.7 for ; Sun, 25 Jan 2009 19:07:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:cc:content-type :content-transfer-encoding; bh=PYKZFm/WIS62GQXRiyyMgqStE3+w5d9nOCbB/89lQkE=; b=pihny7kTsTyp2Ic3BNy2xLeRr7nSuPuGjppXU+boSYS+NEzwtEiGylGXg8RtQENbay NA0ChxPP2f9IL/i1p641lHUY0VnKO3zyJuX+AAJM/gQg0ayrwD96SMu55zEYRhOcsrTb F1jBODuJnMKGgUhXx1ZN2u0WWRmPgJzbu3YFA= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=pxKAwawqvYDBq2fNzuEsd69gD/eSXoN43C6HuKfFjqYweEDNIdAEKwQeLLVpaug2OG P0k5O5XaCB5TJnP0SQOOkZs0qTCQ9wE3N9OdZLil0umB+gwgawY98BNhP3xzGI+fOp1V pSz29ZOI2VI4S6xNYQSn8CQjRg8WFlF3KrLpw= MIME-Version: 1.0 Received: by 10.143.42.6 with SMTP id u6mr2075015wfj.144.1232937431738; Sun, 25 Jan 2009 18:37:11 -0800 (PST) In-Reply-To: <200901252308.n0PN8lvg030020@svn.freebsd.org> References: <200901252308.n0PN8lvg030020@svn.freebsd.org> Date: Sun, 25 Jan 2009 21:37:11 -0500 Message-ID: <47d0403c0901251837k4ea0fdk4ccaa8774c791634@mail.gmail.com> From: Ben Kaduk To: Xin LI Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r187700 - head/lib/libc/string X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 26 Jan 2009 03:07:30 -0000 On Sun, Jan 25, 2009 at 6:08 PM, Xin LI wrote: > Author: delphij > Date: Sun Jan 25 23:08:47 2009 > New Revision: 187700 > URL: http://svn.freebsd.org/changeset/base/187700 > > Log: > Rewrite of MI strlen(3) in a way that can better utilize modern hardware by > reducing branches and doing word-sized operation. > > The idea is taken from J.T. Conklin's x86_64 optimized version of strlen(3) > for NetBSD, and reimplemented in C by me. > > Discussed on: -arch@ > > Modified: > head/lib/libc/string/strlen.c > > Modified: head/lib/libc/string/strlen.c > ============================================================================== > --- head/lib/libc/string/strlen.c Sun Jan 25 21:27:31 2009 (r187699) > +++ head/lib/libc/string/strlen.c Sun Jan 25 23:08:47 2009 (r187700) > @@ -1,6 +1,6 @@ > /*- > - * Copyright (c) 1990, 1993 > - * The Regents of the University of California. All rights reserved. > + * Copyright (c) 2009 Xin LI > + * All rights reserved. > * > * Redistribution and use in source and binary forms, with or without > * modification, are permitted provided that the following conditions > @@ -10,14 +10,11 @@ > * 2. Redistributions in binary form must reproduce the above copyright > * notice, this list of conditions and the following disclaimer in the > * documentation and/or other materials provided with the distribution. > - * 4. Neither the name of the University nor the names of its contributors > - * may be used to endorse or promote products derived from this software > - * without specific prior written permission. > * > - * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND > + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND > * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE > * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE > - * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE > + * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE > * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL > * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS > * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) > @@ -27,21 +24,87 @@ > * SUCH DAMAGE. > */ > > -#if defined(LIBC_SCCS) && !defined(lint) > -static char sccsid[] = "@(#)strlen.c 8.1 (Berkeley) 6/4/93"; > -#endif /* LIBC_SCCS and not lint */ > #include > __FBSDID("$FreeBSD$"); > > +#include > +#include > #include > > +/* > + * Portable strlen() for 32-bit and 64-bit systems. > + * > + * Rationale: it is generally much more efficient to do word length > + * operations and avoid branches on modern computer systems, as > + * compared to byte-length operations with a lot of branches. > + * > + * The expression: > + * > + * ((x - 0x01....01) & ~x & 0x80....80) > + * > + * would evaluate to a non-zero value iff any of the bytes in the > + * original word is zero. However, we can further reduce ~1/3 of > + * time if we consider that strlen() usually operate on 7-bit ASCII > + * by employing the following expression, which allows false positive > + * when high bit of 1 and use the tail case to catch these case: > + * > + * ((x - 0x01....01) & 0x80....80) > + * > + * This is more than 5.2 times as compared to the raw implementation > + * on Intel T7300 under EM64T mode for strings longer than word length. The grammar is not quite right, here. Did you mean to say "more than 5.2 times as fast as the raw implementation [...]" -Ben Kaduk