Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755590Ab0HJHiQ (ORCPT ); Tue, 10 Aug 2010 03:38:16 -0400 Received: from mailout3.w1.samsung.com ([210.118.77.13]:47983 "EHLO mailout3.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752861Ab0HJHiL convert rfc822-to-8bit (ORCPT ); Tue, 10 Aug 2010 03:38:11 -0400 MIME-version: 1.0 Content-type: text/plain; charset=utf-8; format=flowed; delsp=yes Date: Tue, 10 Aug 2010 09:39:46 +0200 From: =?utf-8?B?TWljaGHFgiBOYXphcmV3aWN6?= Subject: Re: [PATCHv2 1/3] lib: vsprintf: optimised put_dec_trunc() and put_dec_full() In-reply-to: <201008100517.48231.vda.linux@googlemail.com> To: Michal Nazarewicz , Denys Vlasenko Cc: linux-kernel@vger.kernel.org, "Douglas W. Jones" , Andrew Morton Message-id: Organization: Samsung Electronics Content-transfer-encoding: 8BIT User-Agent: Opera Mail/10.60 (Linux) References: <6f90103dea29739de0f4f0ede3f3da68afe84343.1281295424.git.mina86@mina86.com> <201008100517.48231.vda.linux@googlemail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1571 Lines: 40 > On Sunday 08 August 2010 21:29, Michal Nazarewicz wrote: >> + /* >> + * '(x * 0xcccd) >> 19' is an approximation of 'x / 10' that >> + * gives correct results for all x < 81920. However, because >> + * intermediate result can be at most 32-bit we limit x to be >> + * 16-bit. >> + * >> + * Because of those, we check if we are dealing with a "big" >> + * number and if so, we make it smaller remembering to add to >> + * the most significant digit. >> + */ >> + if (q >= 50000) { >> + a = '5'; >> + q -= 50000; > ... >> + /* >> + * We need to check if q is < 65536 so we might as well check On Tue, 10 Aug 2010 05:17:48 +0200, Denys Vlasenko wrote: > You meant "need to check if q is < 81920"? No. 81920 is a 17 bit number and when we multiply it by 0xcccd we lose the most significant bit. Therefore we cannot use the '(x * 0xcccd) >> 19' approximation for numbers which are higher then 65535. >> + * if we can just call the _full version of this function. >> + */ >> + if (q > 9999) >> + return put_dec_full(buf, q); -- Best regards, _ _ | Humble Liege of Serenely Enlightened Majesty of o' \,=./ `o | Computer Science, Michał "mina86" Nazarewicz (o o) +----[mina86*mina86.com]---[mina86*jabber.org]----ooO--(_)--Ooo-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/