From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756302Ab2IXPGk (ORCPT ); Mon, 24 Sep 2012 11:06:40 -0400 Received: from mail-bk0-f46.google.com ([209.85.214.46]:56158 "EHLO mail-bk0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756200Ab2IXPGO (ORCPT ); Mon, 24 Sep 2012 11:06:14 -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 3/4] lib: vsprintf: Optimize put_dec_trunc8 In-Reply-To: <20120924134939.23197.qmail@science.horizon.com> Organization: Google Inc References: <20120924134939.23197.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: 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 X-PGP: 50751FF4 X-PGP-FP: AC1F 5F5C D418 88F8 CC84 5858 2060 4012 5075 1FF4 Date: Mon, 24 Sep 2012 17:06:04 +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: > Michal Nazarewicz wrote: >> static noinline_for_stack >> char *put_dec_trunc8(char *buf, unsigned r) { >> unsigned q; >>=20 >> if (r > 10000) { >> do { >> q =3D r + '0'; >> r =3D (r * (uint64_t)0x1999999a) >> 32; >> *buf++ =3D q - 10 * r; >> } while (r >=3D 10000); >> if (r =3D=3D 0) >> return buf; >> } >>=20 >> q =3D (r * 0x199a) >> 16; >> *buf++ =3D (r - 10 * q) + '0'; /* 6 */ [...] >> return buf; >> } > > Two bugs: > > 1) The initial "(r > 10000)" should be >=3D. > If you let r =3D=3D 10000 through to the remaining code, you'll get > ":000". Obviously... ;) > > 2) The "r =3D=3D 0" test isn't necessary. > Given that the loop divides r by 10 each time, r >=3D 10000 at the > beginning implies r >=3D 1000 at the end, so 1000 <=3D r < 10000 > when the loop exits. Yeah, I've just figured that out. :] --=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) iQIcBAEBAgAGBQJQYHbcAAoJECBgQBJQdR/0qmkP/35qV4DjlnI8cQ6eCs1wF6Uq aBY6h5ASH2YwEiXgybK/pl2GGTCH+T+eytYxL9LxtX+8diCjacmKwkOd9PULHcxD DZrPqffwIrePySVutlZSjC++T9mZCoueae9ekTcZe8sHcc/1bTEA0I725OFEHTF+ qW1DoQPyKHLYZ6rgnLEFvZiK2akVoD4igTUVUpwiWmM2wI4Zy5/MSZ/pUZjELwio RbDvrOq2KhOUuf6RNF1YnFvd7VN50cfi3/cufNCe/R/V6tFcdr5TA/c0+rr5BsK2 ccrB5/YSjhtCh6YWnS+YY1Qsi7p67BZ0a5+SUysRvWY0nP6kJ+zdC3qoHUsTd/FA c7x7Urz7I+Eg+HC/tXEXu6lXpaaDJHzasHjsW7BUVspGxUAOLgeCNRmXJrjia9+J yxztrG0bAqYLm8PCtiHoBGTHQePxKZ2noE2aF6efewmPZv1ohLR+6iqcLoYr4wuy dNfExze7RwZrrTgilLSWiVkDnqkSecTnj/hnAT/skONidpFdFSLpkVhwNQ6cibuN HXASRfaiUY3jjXxHOFHSA3sEGDZKpSse7kaRpGsycA7VRuyejxKONuTNZngvcKeo 0JmGT84zsaVmllVT5z39QfN/1rn+m2zIPlAn9DyrlOUc2kYgZEGfdUvtfVqXp0hd rLJKjlnNVcCpaZchAv3W =5htg -----END PGP SIGNATURE----- --==-=-=-- --=-=-=--