linux-kernel - Re: [PATCH 1/1] lib: use sunday algorithm to do strstr() and strnstr()

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Date:   Sat, 28 Jul 2018 22:02:51 +0800
From:   Zhaoxiu Zeng <zengzhaoxiu@....com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Zhaoxiu Zeng <zhaoxiu.zeng@...il.com>
Subject: Re: [PATCH 1/1] lib: use sunday algorithm to do strstr() and
 strnstr()

在 2018/7/27 18:39, Andy Shevchenko 写道:
> On Fri, Jul 27, 2018 at 8:48 AM, Zhaoxiu Zeng <zengzhaoxiu@....com> wrote:
>> 在 2018/7/27 1:17, Zhaoxiu Zeng 写道:
>>> 在 2018/7/23 2:37, Greg Kroah-Hartman 写道:
>>>> On Mon, Jul 23, 2018 at 01:37:15AM +0800, Zhaoxiu Zeng wrote:
> 
>>>>> The Sunday algorithm is a variation of Boyer-Moore algorithm, it is easy and fast.
>>>>> For the Sunday algorithm, to see
>>>>>     http://www.inf.fh-flensburg.de/lang/algorithmen/pattern/sundayen.htm
>>>>
>>>> So you say, but what does this really buy us?  Why make this change?
>>>> How was it tested?  What is the downside of not taking this?
> 
>>> I use the following program to test on fc28.
>>> Compile with O2, the new version is almost 2X faster than the original.
> 
>>> The code size of the original is 0x80, the newer is 0xB0.
> 
> So, output of bloat-o-meter would be good to have in commit message.
> 
>>> The test result:
> 
> Compact performance statistics as well.
> 
>>> Thanks!
> 
>> The original strnstr might has a bug too!
>> For example, assume s1 is "123\0abc...." and s2 is "abc\0",
>> call strnstr(s1, s2, 7) will return &s1[4], but the correct result is NULL.
> 
> If there is a bug, send another patch to fix the bug first.
> 

The bug could be fixed by this patch.