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Groups > comp.lang.c > #148270
| Subject | Re: OT: improve this simple algorithm? |
|---|---|
| Newsgroups | comp.lang.c |
| References | (9 earlier) <qqhtp6$m0m$1@dont-email.me> <7C%yF.190832$mB7.170245@fx32.am4> <qqj5lm$5qt$1@dont-email.me> <7cazF.64737$5W6.28259@fx13.am4> <qqjf8f$4dq$1@dont-email.me> |
| From | Bart <bc@freeuk.com> |
| Message-ID | <ELbzF.37452$3T6.9962@fx05.am4> (permalink) |
| Organization | virginmedia.com |
| Date | 2019-11-14 12:28 +0000 |
On 14/11/2019 11:53, David Brown wrote:
> On 14/11/2019 11:42, Bart wrote:
>> On 14/11/2019 09:10, David Brown wrote:
>>> On 13/11/2019 23:38, Bart wrote:
>>
>>> You know my answer here. You can predict it, I'm sure:
>>>
>>> gcc -Wvla
>>>
>>> warns if a VLA is used.
>>
>> Sure. Just add another option to every single invocation of gcc on the
>> off-chance that VLAs are use, to the other 198 options.
>
> Most people would rather use an option to a real compiler than your
> alternative - use a toy written by "someone off the internet" that
> compiles some bits of C. Oh, I forgot - it does it /really/ fast, and
> that is more important than anything else.
>
>>
>>> And
>>> gcc -Wvla-larger-than=10000
>>>
>>> warns if a VLA is bigger than 10000 bytes (or might be bigger than
>>> that). It is useful to have optimisation enabled to let the compiler
>>> work out bounds more accurately.
>>
>> It seems more like gcc acknowledges that VLAs, or VLAs used with
>> excessive sizes, can cause problems. (I couldn't get the second option
>> to work; that doesn't inspire much confidence. How does it work as a
>> /compile-time/ check anyway if a VLA size is determined at runtime?)
>>
>
> It seems like gcc acknowledges that some /programmers/ might want this
> check. And yes, some programmers /do/ want it. gcc acknowledges that
> the world does not revolve around Bart and his personal preferences,
> prejudices, requirements and pet hates. Thus it has lots of options to
> let people get the features /they/ want. It is not like "bcc" - a
> compiler written specifically for one person to use in one way, that
> doesn't need options.
>
>>
>>> There's your bug. You are getting unknown input from the outside, and
>>> not checking it for sane values.
>>
>> What /are/ the sane values? This checkedmalloc() will tell you!
>
> The sane values depend on the task in hand, obviously.
Not when it depends entirely on available memory. You can't determine
that (in portable code) with either heap or stack. But with the heap,
you can make a tentative allocation first. It is just more flexible,
/plus/ it typically has far higher limits.
>> It's completely obvious that VLAs can be far more dangerous than malloc
>> calls. Yet you are trying to brush the problems under the carpet.
>>
>
> It is obvious that you are failing to understand the issue. I'm not
> sure if it is because you are failing to apply even a modicum of thought
> to the process, or just trolling.
I don't think it's me failing to understand the issues. You have to
write a function that operates on a string like this:
int stringop(char* s, int length) {
}
The algorithm involves first making a temporary string of the same
length as s. Conditions:
* No upper limits are specified as to the length (except as limited by
the int type).
* The function can return a failure code if something went wrong or it
couldn't complete
* It needs to run as fast as possible
So, do you use a VLA or the heap, or something else?
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OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-12 15:55 -0500
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-12 21:20 +0000
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-12 23:28 -0500
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 10:52 +0100
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-13 10:16 -0500
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 16:53 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 11:18 +0000
Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-12 23:30 +0000
Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 05:12 +1300
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 16:34 +0000
Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 10:07 +1300
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 22:25 +0000
Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 12:02 +1300
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 23:27 +0000
Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 19:06 +1300
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-15 10:45 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-15 13:28 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-15 12:58 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-15 15:39 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-15 15:04 +0000
Re: OT: improve this simple algorithm? Richard Damon <Richard@Damon-Family.org> - 2019-11-15 12:19 -0500
Re: OT: improve this simple algorithm? Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2019-11-15 09:46 -0800
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-15 18:59 +0000
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-16 11:59 +0000
Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-16 09:02 +1300
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-15 11:17 +0100
Re: OT: improve this simple algorithm? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2019-11-15 21:38 +0000
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 11:44 -0500
Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-14 18:11 +0000
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 13:33 -0500
Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-15 01:49 +0000
Re: OT: improve this simple algorithm? Barry Schwarz <schwarzb@delq.com> - 2019-11-14 10:38 -0800
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 12:56 -0500
Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-14 13:50 -0500
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 14:42 -0500
Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-14 15:25 -0500
Re: OT: improve this simple algorithm? Barry Schwarz <schwarzb@delq.com> - 2019-11-14 11:03 -0800
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-14 16:08 -0500
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-15 11:30 +0100
Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-15 11:17 +0000
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-15 17:35 -0500
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-15 17:39 -0500
Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-15 23:19 +0000
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-15 18:53 -0500
Re: OT: improve this simple algorithm? Richard Damon <Richard@Damon-Family.org> - 2019-11-15 19:08 -0500
Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-16 01:30 +0000
Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-16 07:39 -0500
Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-16 07:37 -0500
Re: OT: improve this simple algorithm? James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-11-15 09:46 -0500
Re: OT: improve this simple algorithm? Richard Damon <Richard@Damon-Family.org> - 2019-11-15 12:38 -0500
Re: OT: improve this simple algorithm? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-11-15 23:07 +0000
Re: OT: improve this simple algorithm? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-28 16:54 -0800
Re: OT: improve this simple algorithm? Richard Damon <Richard@Damon-Family.org> - 2019-11-28 20:17 -0500
Re: OT: improve this simple algorithm? Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-11-29 06:08 -0800
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 20:45 +0100
Re: OT: improve this simple algorithm? Keith Thompson <kst-u@mib.org> - 2019-11-14 10:10 -0800
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 20:19 +0100
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-12 23:57 -0500
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 10:34 +0100
Re: OT: improve this simple algorithm? DFS <nospam@dfs.com> - 2019-11-13 23:57 -0500
Re: OT: improve this simple algorithm? Barry Schwarz <schwarzb@delq.com> - 2019-11-13 23:00 -0800
Re: OT: improve this simple algorithm? Ike Naar <ike@sdf.lonestar.org> - 2019-11-14 07:53 +0000
Re: OT: improve this simple algorithm? guinness.tony@gmail.com - 2019-11-14 02:34 -0800
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 10:01 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 11:27 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 12:46 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 12:01 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 14:05 +0100
Re: OT: improve this simple algorithm? Barry Schwarz <schwarzb@delq.com> - 2019-11-12 18:34 -0800
Re: OT: improve this simple algorithm? Keith Thompson <kst-u@mib.org> - 2019-11-12 19:01 -0800
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 17:08 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 17:06 +0000
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 19:11 +0000
Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-15 05:15 +1300
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 18:13 +0000
Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-14 20:16 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 20:03 +0000
Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-15 04:51 +0100
Re: OT: improve this simple algorithm? Keith Thompson <kst-u@mib.org> - 2019-11-14 10:15 -0800
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 20:52 +0100
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 10:57 +0100
Re: OT: improve this simple algorithm? Ian Collins <ian-news@hotmail.com> - 2019-11-13 23:23 +1300
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 11:53 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 14:02 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 13:40 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 17:01 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 16:28 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-13 22:49 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 22:38 +0000
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-13 23:06 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 10:10 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 10:42 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 12:53 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 12:28 +0000
Re: OT: improve this simple algorithm? David Brown <david.brown@hesbynett.no> - 2019-11-14 14:21 +0100
Re: OT: improve this simple algorithm? Bart <bc@freeuk.com> - 2019-11-14 14:28 +0000
Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-14 15:38 +0100
Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-14 13:37 +0100
Re: OT: improve this simple algorithm? Bonita Montero <Bonita.Montero@gmail.com> - 2019-11-14 13:38 +0100
Re: OT: improve this simple algorithm? Thiago Adams <thiago.adams@gmail.com> - 2019-11-13 05:21 -0800
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