* Re: infinite loop in boyer_moore()
@ 2009-04-02 22:26 Chong Yidong
2009-04-16 4:51 ` Chong Yidong
0 siblings, 1 reply; 4+ messages in thread
From: Chong Yidong @ 2009-04-02 22:26 UTC (permalink / raw)
To: emacs-devel; +Cc: 2844
> Gnus has been entering infinite loops for me while splitting mail.
> Today I got a chance to look into it. The problem is in
> boyer_moore(), in search.c:
> /* Use signed comparison if appropriate
> to make cursor+infinity sure to be > p_limit.
> Assuming that the buffer lies in a range of addresses
> that are all "positive" (as ints) or all "negative",
> either kind of comparison will work as long
> as we don't step by infinity. So pick the kind
> that works when we do step by infinity. */
> if ((EMACS_INT) (p_limit + infinity) > (EMACS_INT) p_limit)
> while ((EMACS_INT) cursor <= (EMACS_INT) p_limit)
> cursor += BM_tab[*cursor];
> else
> while ((EMACS_UINT) cursor <= (EMACS_UINT) p_limit)
> cursor += BM_tab[*cursor];
> it takes the signed (EMACS_INT) loop, but that fails because cursor is
> (unsigned char *) 0x7fffc440, whereas p_limit is (unsigned char *)
> 0x80001260.
> infinity, computed earlier in that function, is 0x37dac21, but I don't
> see how a positive value would have helped. It seems to me that we
> have to check that we won't be crossing this boundary starting at
> cursor rather than p_limit, or maybe both. I haven't thought much
> about it.
Checking with cursor as well as p_limit sounds about right to be, but I
am far from familiar with this part of the code. Does anyone one this
list have an opinion?
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: infinite loop in boyer_moore()
2009-04-02 22:26 infinite loop in boyer_moore() Chong Yidong
@ 2009-04-16 4:51 ` Chong Yidong
2009-04-16 9:32 ` Andreas Schwab
0 siblings, 1 reply; 4+ messages in thread
From: Chong Yidong @ 2009-04-16 4:51 UTC (permalink / raw)
To: emacs-devel; +Cc: 2844
Ping. Anyone have an opinion?
>> Gnus has been entering infinite loops for me while splitting mail.
>> Today I got a chance to look into it. The problem is in
>> boyer_moore(), in search.c:
>
>> /* Use signed comparison if appropriate
>> to make cursor+infinity sure to be > p_limit.
>> Assuming that the buffer lies in a range of addresses
>> that are all "positive" (as ints) or all "negative",
>> either kind of comparison will work as long
>> as we don't step by infinity. So pick the kind
>> that works when we do step by infinity. */
>> if ((EMACS_INT) (p_limit + infinity) > (EMACS_INT) p_limit)
>> while ((EMACS_INT) cursor <= (EMACS_INT) p_limit)
>> cursor += BM_tab[*cursor];
>> else
>> while ((EMACS_UINT) cursor <= (EMACS_UINT) p_limit)
>> cursor += BM_tab[*cursor];
>
>> it takes the signed (EMACS_INT) loop, but that fails because cursor is
>> (unsigned char *) 0x7fffc440, whereas p_limit is (unsigned char *)
>> 0x80001260.
>
>> infinity, computed earlier in that function, is 0x37dac21, but I don't
>> see how a positive value would have helped. It seems to me that we
>> have to check that we won't be crossing this boundary starting at
>> cursor rather than p_limit, or maybe both. I haven't thought much
>> about it.
>
> Checking with cursor as well as p_limit sounds about right to be, but I
> am far from familiar with this part of the code. Does anyone one this
> list have an opinion?
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2009-04-16 13:42 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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2009-04-02 22:26 infinite loop in boyer_moore() Chong Yidong
2009-04-16 4:51 ` Chong Yidong
2009-04-16 9:32 ` Andreas Schwab
2009-04-16 13:42 ` Chong Yidong
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