From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755334Ab2IXMln (ORCPT ); Mon, 24 Sep 2012 08:41:43 -0400 Received: from mail-wi0-f178.google.com ([209.85.212.178]:64142 "EHLO mail-wi0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754199Ab2IXMlm (ORCPT ); Mon, 24 Sep 2012 08:41:42 -0400 From: Michal Nazarewicz To: George Spelvin , linux@horizon.com, vda.linux@googlemail.com Cc: hughd@google.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/4] lib: vsprintf: Optimize division by 10000 In-Reply-To: <20120924121614.5422.qmail@science.horizon.com> Organization: Google Inc References: <20120924121614.5422.qmail@science.horizon.com> User-Agent: Notmuch/0.14+22~g8bdc16b (http://notmuchmail.org) Emacs/24.2.50.1 (x86_64-unknown-linux-gnu) X-Face: PbkBB1w#)bOqd`iCe"Ds{e+!C7`pkC9a|f)Qo^BMQvy\q5x3?vDQJeN(DS?|-^$uMti[3D*#^_Ts"pU$jBQLq~Ud6iNwAw_r_o_4]|JO?]}P_}Nc&"p#D(ZgUb4uCNPe7~a[DbPG0T~!&c.y$Ur,=N4RT>]dNpd;KFrfMCylc}gc??'U2j,!8%xdD Face: iVBORw0KGgoAAAANSUhEUgAAADAAAAAwBAMAAAClLOS0AAAAJFBMVEWbfGlUPDDHgE57V0jUupKjgIObY0PLrom9mH4dFRK4gmjPs41MxjOgAAACQElEQVQ4jW3TMWvbQBQHcBk1xE6WyALX1069oZBMlq+ouUwpEQQ6uRjttkWP4CmBgGM0BQLBdPFZYPsyFUo6uEtKDQ7oy/U96XR2Ux8ehH/89Z6enqxBcS7Lg81jmSuujrfCZcLI/TYYvbGj+jbgFpHJ/bqQAUISj8iLyu4LuFHJTosxsucO4jSDNE0Hq3hwK/ceQ5sx97b8LcUDsILfk+ovHkOIsMbBfg43VuQ5Ln9YAGCkUdKJoXR9EclFBhixy3EGVz1K6eEkhxCAkeMMnqoAhAKwhoUJkDrCqvbecaYINlFKSRS1i12VKH1XpUd4qxL876EkMcDvHj3s5RBajHHMlA5iK32e0C7VgG0RlzFPvoYHZLRmAC0BmNcBruhkE0KsMsbEc62ZwUJDxWUdMsMhVqovoT96i/DnX/ASvz/6hbCabELLk/6FF/8PNpPCGqcZTGFcBhhAaZZDbQPaAB3+KrWWy2XgbYDNIinkdWAFcCpraDE/knwe5DBqGmgzESl1p2E4MWAz0VUPgYYzmfWb9yS4vCvgsxJriNTHoIBz5YteBvg+VGISQWUqhMiByPIPpygeDBE6elD973xWwKkEiHZAHKjhuPsFnBuArrzxtakRcISv+XMIPl4aGBUJm8Emk7qBYU8IlgNEIpiJhk/No24jHwkKTFHDWfPniR4iw5vJaw2nzSjfq2zffcE/GDjRC2dn0J0XwPAbDL84TvaFCJEU4Oml9pRyEUhR3Cl2t01AoEjRbs0sYugp14/4X5n4pU4EHHnMAAAAAElFTkSuQmCC X-PGP: 50751FF4 X-PGP-FP: AC1F 5F5C D418 88F8 CC84 5858 2060 4012 5075 1FF4 Date: Mon, 24 Sep 2012 14:41:32 +0200 Message-ID: MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="=-=-=" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --=-=-= Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Mon, Sep 24 2012, George Spelvin wrote: >> You are using a 64-bit multiply in a path that is designed for 32-bit >> processors, which makes me feel that it will be slower. > > Slower than the divide it's replacing? OK, granted, it might be faster after all. ;) Still, I'd love to see some benchmark. > The following 32-bit processors have 32x32->64-bit multiply: > > x86 > ARM (as of ARMv4 =3D ARM7TDMI, the lowest version in common use) > SPARCv7, SPARCv8 Didn't some SPARCs have 32x32->32 multiply? I remember reading some rant from a GMP developer about how SPARC is broken that way. > MIPS32 > MC68020 > PA-RISC 1.1 (XMPYU) > avr32 > PowerPC (MULHWU) > VAX (EMUL) > I could do some Kconfig hacking and make the code path > architecture-dependent. Do you think it's worth it? Definitely not. --=20 Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=3D./ `o ..o | Computer Science, Micha=C5=82 =E2=80=9Cmina86=E2=80=9D Nazarewicz = (o o) ooo +------------------ooO--(_)--Ooo-- --=-=-= Content-Type: multipart/signed; boundary="==-=-="; micalg=pgp-sha1; protocol="application/pgp-signature" --==-=-= Content-Type: text/plain --==-=-= Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQIcBAEBAgAGBQJQYFT8AAoJECBgQBJQdR/0tqkP/15WtAbkpAHJBBAeY9M3z18I DJ3vJy6fh4kdK7X22xHnbKxfAENd4U8yaKAUghAwrppmMHYOS5V0249moAu1J8Lx 3x+ar7u3Anv+C8U5fd6jtPIBPNBLa2zcYXwDGNCFozecGmrNuv4iJnWAfcIjKMNt Gey9b+RpUmmjpzdYHifbWL+2HDZEcRYiYb2VRenRkcN5IfX90G6LixY+ZeriGboX HW4cpYEksKHCS1E9d3FUUVCn2YEY7ZixnThuHktZD0eeotrWz9q1Vt2B4Bv9XGvP VNP62YRy1G3W+CFUuNmCEZ260zv+d0l218oRoAFcuxtfyIfZUwdkcrvUYCfPFPMP gVfertBV4Yim/679XmWFpWC4rfYELNZUWNBFvF5QFjI3mD2zuV/rZEmw6QRI2m1i CjKdBFRDu3L9pMTS3jnLkVVREOTA2TO35FNb85SSwzvxL1M4d6xJt5JewANZ4Zb6 Q0C4Qh7G3rNkTFM3Ub6x6dlRQVCdYRhATbdWpUPIiP+4uslkUifqAcESDtyfPijU Jdh9SrY2c9Am4Q3P4TErqqXskXIvp8E0agniSWzwbm61oASIIGyygWHsCdW8gt/0 umgEEpkdWXTSk8ysEY6s0qBRfbpTkblYn7KQOxtyrh3/ZVsOqwICGt3sFBGd2Zer WaAgEZBUedbg/A8YYYQw =ZuWm -----END PGP SIGNATURE----- --==-=-=-- --=-=-=--