From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753770Ab2IWSWO (ORCPT ); Sun, 23 Sep 2012 14:22:14 -0400 Received: from mail-wi0-f172.google.com ([209.85.212.172]:41837 "EHLO mail-wi0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752997Ab2IWSWM (ORCPT ); Sun, 23 Sep 2012 14:22:12 -0400 From: Michal Nazarewicz To: George Spelvin , vda.linux@googlemail.com Cc: hughd@google.com, linux-kernel@vger.kernel.org, linux@horizon.com Subject: Re: [PATCH 3/4] lib: vsprintf: Optimize put_dec_trunc8 In-Reply-To: <1343971271-13355-3-git-send-email-linux@horizon.com> Organization: Google Inc References: <1343971271-13355-1-git-send-email-linux@horizon.com> <1343971271-13355-3-git-send-email-linux@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: Sun, 23 Sep 2012 20:22:02 +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 Fri, Aug 03 2012, George Spelvin wrote: > If you're going to have a conditional branch after > each 32x32->64-bit multiply, might as well shrink the code > and make it a loop. > > This also avoids using the long multiply for small integers. > > (This leaves the comments in a confusing state, but that's a separate > patch to make review easier.) > > Signed-off-by: George Spelvin NAK. > --- > lib/vsprintf.c | 20 ++++++-------------- > 1 file changed, 6 insertions(+), 14 deletions(-) > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > index a8e7392..3ca77b8 100644 > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -174,20 +174,12 @@ char *put_dec_trunc8(char *buf, unsigned r) > unsigned q; >=20=20 > /* Copy of previous function's body with added early returns */ > - q =3D (r * (uint64_t)0x1999999a) >> 32; > - *buf++ =3D (r - 10 * q) + '0'; /* 2 */ > - if (q =3D=3D 0) > - return buf; > - r =3D (q * (uint64_t)0x1999999a) >> 32; > - *buf++ =3D (q - 10 * r) + '0'; /* 3 */ > - if (r =3D=3D 0) > - return buf; > - q =3D (r * (uint64_t)0x1999999a) >> 32; > - *buf++ =3D (r - 10 * q) + '0'; /* 4 */ > - if (q =3D=3D 0) > - return buf; > - r =3D (q * (uint64_t)0x1999999a) >> 32; > - *buf++ =3D (q - 10 * r) + '0'; /* 5 */ > + while (r >=3D 10000) { > + q =3D r + '0'; > + r =3D (r * (uint64_t)0x1999999a) >> 32; > + *buf++ =3D q - 10*r; > + } This loop looks nothing like the original code. Why are you adding '0' at the beginning? Also, the original code switches the role of q and r, the loop does not. > if (r =3D=3D 0) > return buf; > q =3D (r * 0x199a) >> 16; --=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) iQIcBAEBAgAGBQJQX1NKAAoJECBgQBJQdR/0OI0P/0fE8AOqbg2D+VIaanMH5WLO oDnXdJiRGHEEqEmEGOuE7PyJYfFZnd4ruEvJXZ/Vi4dTWXjwcWyG5T1QaVFieVYU RBGSYiFKc9GwIh6wKnayVBMjSuyPgqVh9IPulymbaf6D4+wrSbzWqLgvRibT95eL gA5Xne9tK9xE0vgmVru670Eo3zYScv9F6EKIZUOmPrqIPRxaN10ClG6/+ukHBEXT TtiT6ZWUkuWdtEWiIS5Kic8oXa0uz29qJ9WtqG2pGZRpc4eJCbL0la4HvVY+sOqw iOhsZZueonarrC/KEJj/neIZXJQEJgE7ePhlLQlnC5iHWfcD0i1zd3hClogbu9g8 vMjnovd9HIMAecYzhzOhRWcy7Vf0tKnYGFMdBKNBF3/Ec1rY80+Qa4BjSKcmlJag dLHiCFjlAWq4cnpH5JybQFxjKqAvak2kW4dfkvjTZR2Bf8v6BkE/HvPyiuLssknz uiDJUPcKn8zJ0GfP3i+4Jyr48dDrF5aG9SHFgyl7LF5o9G+J1emw8U5b5lR/3c1M kI4uXxLeOe7gNq8hYBnFhxeQGcxTb5/EBrPBKYRCr6/BPO6m81QKgglaIYWb6ZOp wTaQEYDk46wqy0U3dKLF7kmPiqr+FSXROQecRg4DruNqyGt55WjBAGTK8MJFdsnV wXYM5VQYo4wZqB9lMIFQ =KY+9 -----END PGP SIGNATURE----- --==-=-=-- --=-=-=--