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

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Message-ID: <CAHp75Vd2Lu110om-hPE2bx_XFa0zpNHHC4RC_uLsTBSywJO2KQ@mail.gmail.com>
Date:   Fri, 27 Jul 2018 13:39:22 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Zhaoxiu Zeng <zengzhaoxiu@....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()

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.

-- 
With Best Regards,
Andy Shevchenko