netdev - Re: [PATCH 3/8] textsearch: fix Boyer-Moore algorithm for case insensitive searching

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Date:	Mon, 23 Jun 2008 13:41:54 -0700
From:	"Joonwoo Park" <joonwpark81@...il.com>
To:	"Pablo Neira Ayuso" <pablo@...filter.org>
Cc:	"Patrick McHardy" <kaber@...sh.net>,
	netdev <netdev@...r.kernel.org>,
	netfilter-devel <netfilter-devel@...r.kernel.org>,
	"Thomas Graf" <tgraf@...g.ch>
Subject: Re: [PATCH 3/8] textsearch: fix Boyer-Moore algorithm for case insensitive searching

2008/6/23 Pablo Neira Ayuso <pablo@...filter.org>:
> Patrick McHardy wrote:
>> Joonwoo Park wrote:
>>> 2008/6/21 Patrick McHardy <kaber@...sh.net>:
>>>>> +static void compute_prefix_tbl(struct ts_bm *bm, u8 icase)
>>>>>  {
>>>>>        int i, j, g;
>>>>>          for (i = 0; i < ASIZE; i++)
>>>>>                bm->bad_shift[i] = bm->patlen;
>>>>> -       for (i = 0; i < bm->patlen - 1; i++)
>>>>> +       for (i = 0; i < bm->patlen - 1; i++) {
>>>>>                bm->bad_shift[bm->pattern[i]] = bm->patlen - 1 - i;
>>>>> +               if (icase)
>>>>> +                       bm->bad_shift[tolower(bm->pattern[i])]
>>>>> +                           = bm->patlen - 1 - i;
>>>>> +       }
>>>> You use toupper() above and tolower() here, is that correct?
>>>>
>>>
>>> It should be, bm->pattern's characters are all upper case since It was
>>> altered before.
>>> So we should use toupper() for target string character to compare.
>>> And to ignore case, we should prepare one more bad_shift array
>>> calculation, opposite tolower() should be used for it.
>>
>> OK thanks. I'll wait for an ACK from Thomas before applying
>> them though.
>
> This is rather confusing. Why not set both the pattern and the bad_shift
> to lower or upper case?
>

To be honest, pattern can be set to lower or upper case, it doesn't matter.
But for bad_shift, we should add one more array for diffrence of case.
So bad_shift array should have both of lower and upper.

>>>>> +       for (i = 0; i < bm->patlen - 1; i++) {
>>>>>                bm->bad_shift[bm->pattern[i]] = bm->patlen - 1 - i;

Therefore, at here, this makes bad_shift for upper case,

>>>>> +               if (icase)
>>>>> +                       bm->bad_shift[tolower(bm->pattern[i])]
>>>>> +                           = bm->patlen - 1 - i;

At here, this makes bad_shift for lower case.
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