From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757509Ab3BGBQI (ORCPT ); Wed, 6 Feb 2013 20:16:08 -0500 Received: from mailout1.samsung.com ([203.254.224.24]:29859 "EHLO mailout1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755741Ab3BGBQE (ORCPT ); Wed, 6 Feb 2013 20:16:04 -0500 MIME-version: 1.0 Content-type: text/plain; charset=UTF-8 X-AuditID: cbfee61a-b7f7d6d000000f4e-94-51130051baf0 Content-transfer-encoding: 8BIT Message-id: <5113004D.9050107@samsung.com> Date: Thu, 07 Feb 2013 10:15:57 +0900 From: jonghwa3.lee@samsung.com User-Agent: Mozilla/5.0 (X11; Linux i686; rv:10.0.2) Gecko/20120216 Thunderbird/10.0.2 To: Stephen Warren Cc: Haojian Zhuang , Venu Byravarasu , "linux-kernel@vger.kernel.org" , "a.zummo@towertech.it" , Andrew Morton , "rtc-linux@googlegroups.com" Subject: Re: [PATCH] rtc: Modify leap year test for more simpler way References: <1360149775-19606-1-git-send-email-jonghwa3.lee@samsung.com> <51124FF2.2070605@samsung.com> <51129CC2.7040709@wwwdotorg.org> In-reply-to: <51129CC2.7040709@wwwdotorg.org> X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrBIsWRmVeSWpSXmKPExsVy+t8zTd1ABuFAg4l/xC0u75rD5sDo8XmT XABjFJdNSmpOZllqkb5dAlfGnQV32Qta+CuuNG5lbGB8yt3FyMkhIWAisf34PGYIW0ziwr31 bF2MXBxCAssYJf52zWLvYuQAK1pxJx8ivohRYvnThWwgDbwCghI/Jt9jAalhFpCXOHIpGyTM LKAuMWneImaI+i4mid8zNzFC1GtJXH41gQnEZhFQlfi7dT0riM0mICfxtukbI8gcUYEIiV/9 HCBhEaDySc/+MYLMYRbYyiRx8+dTZpAaYQEXiQk7dSDmT2OS+NtyHWwOp4CuROPaLWAPSAh0 s0vM3PqXHWKZgMS3yYdYIJ6Rldh0AOphSYmDK26wTGAUm4XknVkI78xC8s4CRuZVjKKpBckF xUnpuYZ6xYm5xaV56XrJ+bmbGCHxILWDcWWDxSFGAQ5GJR7eG0uFAoVYE8uKK3MPMUpwMCuJ 8GY/BQrxpiRWVqUW5ccXleakFh9iTAa6byKzlGhyPjBW80riDY0NjA0NLQ3NTC1NDUgTVhLn ZTz1JEBIID2xJDU7NbUgtQhmCxMHp1QD4yrpZ1r3PtVrFL02Mr7rHMYTWZxhFTNDk21CrPIO w6Y3S9foTT89zUrgnuWRyogVtik1yQeWbLffUK/nbctettdPviz6WHyZS72XEhOvdvSNxscn d2T3RZxaax2zWmLa9Ie3z+n57E2eM3NL9k+bKWY7ugJKxbqX3i162v3owPa1yuLP+xnilViK MxINtZiLihMBaTUlIssCAAA= X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFnrOIsWRmVeSWpSXmKPExsVy+t9jAd1ABuFAg/NzOC0u75rD5sDo8XmT XABjVAOjTUZqYkpqkUJqXnJ+SmZeuq2Sd3C8c7ypmYGhrqGlhbmSQl5ibqqtkotPgK5bZg7Q VCWFssScUqBQQGJxsZK+HaYJoSFuuhYwjRG6viFBcD1GBmggYR1jxp0Fd9kLWvgrrjRuZWxg fMrdxcjBISFgIrHiTn4XIyeQKSZx4d56ti5GLg4hgUWMEsufLmQDSfAKCEr8mHyPBaSeWUBe 4silbJAws4C6xKR5i5gh6ruYJH7P3MQIUa8lcfnVBCYQm0VAVeLv1vWsIDabgJzE26ZvjCBz RAUiJH71c4CERYDKJz37xwgyh1lgK5PEzZ9PmUFqhAVcJCbs1IGYP41J4m/LdbA5nAK6Eo1r t7BNYBSYheS8WQjnzUJy3gJG5lWMoqkFyQXFSem5hnrFibnFpXnpesn5uZsYwdH2TGoH48oG i0OMAhyMSjy8N5YKBQqxJpYVV+YeYpTgYFYS4c1+ChTiTUmsrEotyo8vKs1JLT7EmAz03ERm KdHkfGAiyCuJNzQ2MTOyNDIzNjE3NiZNWEmcl/HUkwAhgfTEktTs1NSC1CKYLUwcnFINjDvL mvI+hU4PalJWbd4/+e+Eg3tZl3yxnT9XOW31m8DHR1/7ZfBschPdeHj6c8ne5CutDpJTMs/1 eYQcbPk6JUE3rd5x9/e/cQ2O6lIPmhJkXpvf3f1OdmGZpwHf3bSejZnNb5klld2Eojqj939Y 0FW0U4Bt/b7eG5cDj1rwtKctygw5dPv0ViWW4oxEQy3mouJEANlDt2T6AgAA DLP-Filter: Pass X-MTR: 20000000000000000@CPGS X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2013년 02월 07일 03:11, Stephen Warren wrote: > On 02/06/2013 06:00 AM, Haojian Zhuang wrote: >> On Wed, Feb 6, 2013 at 8:43 PM, wrote: >>> On 2013년 02월 06일 20:42, Venu Byravarasu wrote: >>>> By definition, leap year is one, which is a divisible by 4 & 400, excluding multiples of 100s. >>>> Hence I feel this patch is not correct. >>> >>> No, I think you might misunderstood the it's meaning. The former code checks >>> whether if it is multiple of 4 or not. Formal mathematical way to verify multiple of 4 >>> is just checks the last two digits are multiple of 4. This '(!year % 4) && (year % 100)' >>> part does it. But with only that checking, it may miss the case of multiple of 400 which >>> is also multiple of 4. Then my modification checks in hexadecimal, whether if number >>> has any of 1st and 2nd bit with value 1. Because any number which has all bits above >>> the 3rd can be divided with 4(2^2). >>> (e.g. 44(0b101100) = 2^5+2^3+2^2 = 2^2(2^3 + 2 + 1)) >>> So It does same things with less instructions. >> >> I still can't understand your logic. >> >> Please check whether 200 year is leap year. >> >> 200(decimal) = 2b11001000 >> >> !(200 & 0x3) = 1 (Your condition said that 200 year is a leap year.) >> >> According to this logic in below. >> if year mod 4 = 0 and year mod 100 <> 0 or year mod 400 = 0, then >> it's a leap year. >> >> This tells us that 200 year isn't a leap year because 200 mod 100 == >> 0. So who is wrong? > > The rule is: it's a leap year if divisible by 4, unless it's divisible > by 100, but actually also including years divisible by 400. So, the > current code is correct, and the patch is wrong. > Sorry, I was wrong. I didn't know the definition of leap year not including multiple of 4. Sorry for making noise. Thanks, Jonghwa > http://en.wikipedia.org/wiki/Leap_year#Algorithm >