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Groups > comp.lang.c > #102358
| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Optimizing the code: way to reduce if, else if-s within the loop? |
| Date | 2017-01-22 21:54 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <87mveiwyjm.fsf@bsb.me.uk> (permalink) |
| References | (6 earlier) <o62bvj$ma5$1@dont-email.me> <lnlgu3f669.fsf@kst-u.example.com> <o62kre$sc7$1@dont-email.me> <87wpdmx6r0.fsf@bsb.me.uk> <o630f6$gfa$1@dont-email.me> |
BartC <bc@freeuk.com> writes:
> On 22/01/2017 18:57, Ben Bacarisse wrote:
>> BartC <bc@freeuk.com> writes:
>>
>>> On 22/01/2017 15:47, Keith Thompson wrote:
>>>> BartC <bc@freeuk.com> writes:
>>>>> On 22/01/2017 13:23, Ben Bacarisse wrote:
>>>>>> BartC <bc@freeuk.com> writes:
>>>> [...]
>>>>>>> This seems a common way of implementing it:
>>>>>>>
>>>>>>> #define offsetof(s,m) (int)&(((s *)0)->m)
>>>>>>
>>>>>> That would be wrong so I'm sorry to hear it's a common way.
>>>>>
>>>>> What's wrong with it?
>>>>
>>>> offsetof yields a result of type size_t. This macro yields a result of
>>>> type int. (It's also non-portable, but in a way that's likely to work
>>>> under most implementations.)
>>>
>>> Well, some use size_t in the cast, but this version came from a 32-bit
>>> compiler so was probably OK.
>>
>> Given struct s { int i; }; then
>>
>> assert(offsetof(struct s, i) - 1 > 0);
>>
>> should never fire, but if offsetof yields an int it will.
>
> The offset is zero.
>
> IIUC, if you subtract one from that offset, the correct behaviour is
> for that result to be greater than zero.
>
> If zero minus one is <= zero, then that's wrong.
>
> Okay....
I don't know what you mean by "wrong". You thought that offsetof being
int-valued would not matter on a 32-bit architecture. I'm just pointing
out that it does.
--
Ben.
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Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-21 08:52 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-21 09:35 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Barry Schwarz <schwarzb@dqel.com> - 2017-01-21 10:28 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-21 23:49 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 00:29 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-22 10:54 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 03:28 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Keith Thompson <kst-u@mib.org> - 2017-01-22 07:44 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 08:24 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Barry Schwarz <schwarzb@dqel.com> - 2017-01-22 10:43 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Keith Thompson <kst-u@mib.org> - 2017-01-22 12:22 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? BartC <bc@freeuk.com> - 2017-01-22 11:33 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-22 13:23 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? BartC <bc@freeuk.com> - 2017-01-22 13:28 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Keith Thompson <kst-u@mib.org> - 2017-01-22 07:47 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? BartC <bc@freeuk.com> - 2017-01-22 16:00 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? David Brown <david.brown@hesbynett.no> - 2017-01-22 18:23 +0100
Re: Optimizing the code: way to reduce if, else if-s within the loop? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-22 13:47 -0500
Re: Optimizing the code: way to reduce if, else if-s within the loop? Barry Schwarz <schwarzb@dqel.com> - 2017-01-22 10:43 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-22 13:53 -0500
Re: Optimizing the code: way to reduce if, else if-s within the loop? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-22 18:57 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? BartC <bc@freeuk.com> - 2017-01-22 19:18 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-22 21:54 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-23 02:41 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-23 11:20 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-23 03:53 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-23 12:12 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 03:24 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-22 13:16 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Barry Schwarz <schwarzb@dqel.com> - 2017-01-22 07:47 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 08:16 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? "James R. Kuyper" <jameskuyper@verizon.net> - 2017-01-22 11:54 -0500
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 11:23 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Barry Schwarz <schwarzb@dqel.com> - 2017-01-22 11:08 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 22:19 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 22:41 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Robert Wessel <robertwessel2@yahoo.com> - 2017-01-23 02:17 -0600
Re: Optimizing the code: way to reduce if, else if-s within the loop? Barry Schwarz <schwarzb@dqel.com> - 2017-01-23 02:16 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-23 03:59 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Keith Thompson <kst-u@mib.org> - 2017-01-23 08:44 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 08:23 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Barry Schwarz <schwarzb@dqel.com> - 2017-01-22 07:52 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-22 08:17 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Richard Heathfield <rjh@cpax.org.uk> - 2017-01-23 17:11 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-23 10:35 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-23 10:38 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? BartC <bc@freeuk.com> - 2017-01-23 19:06 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Barry Schwarz <schwarzb@dqel.com> - 2017-01-23 14:31 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-23 21:31 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Alla _ <modelling.data@gmail.com> - 2017-01-24 01:56 -0800
Re: Optimizing the code: way to reduce if, else if-s within the loop? Manfred <noname@invalid.add> - 2017-01-24 14:38 +0100
Re: Optimizing the code: way to reduce if, else if-s within the loop? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-24 13:57 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? BartC <bc@freeuk.com> - 2017-01-23 12:38 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-01-23 15:08 +0000
Re: Optimizing the code: way to reduce if, else if-s within the loop? m.labanowicz@gmail.com - 2017-01-23 07:08 -0800
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