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| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Objective C |
| Date | 2015-11-17 01:21 +0000 |
| Organization | A noiseless patient Spider |
| Message-ID | <877flhpgjh.fsf@bsb.me.uk> (permalink) |
| References | (9 earlier) <fff2ac89-757c-4d72-8307-9f48cd8327a6@googlegroups.com> <876111r86a.fsf@bsb.me.uk> <4e6ba271-859c-4d89-8603-2ea9fff9a1fc@googlegroups.com> <87k2phpoim.fsf@bsb.me.uk> <e43ebc47-dcd8-4424-94e5-837d3d40753d@googlegroups.com> |
supercat@casperkitty.com writes:
> On Monday, November 16, 2015 at 4:29:03 PM UTC-6, Ben Bacarisse wrote:
>> supercat writes:
>> I don't see the problem, but "used" is rather vague. To access the data
>> you need to know its effective type. Are you saying that one bit of
>> code has to work "bind" -- entirely unaware of the effective type of the
>> data? If so, I think your example is rather contrived.
>
> Targetting a 32-bit machine with linear address space, how would you write a
> function to fill a uint16_t[] with the value 12345 if speed was
> important?
I'd try:
void fill(int16_t *data, size_t n, int16_t val)
{
if (n) {
*data = val;
size_t copy_sz = 1, remaining = n - 1;
while (remaining >= copy_sz) {
memcpy(data + copy_sz, data, copy_sz * sizeof *data);
remaining -= copy_sz;
copy_sz *= 2;
}
memcpy(data + n - remaining, data, remaining * sizeof *data);
}
}
in the hope that memcpy is fast.
> My inclination would be to write a function which checks whether the
> received pointer is an odd multiple of 2, and if so store one value and
> decrement the count. Then cast the pointer to some type to which one can
> write 32 bits, store count/2 32-bit values, and then if the count was odd,
> store one uint16_t at the end. On many platforms, that would be about
> twice as fast as using uint16_t for everything, and on some it may be a lot
> faster than that.
>
> Some compilers might find the optimization if code was written using
> uint16_t* for everything, but a lot wouldn't. If a compiler doesn't find
> that optimization and performance is important, how should the code be
> written?
There's no aliasing issue here. What optimisation do you think a
"hyper-modern" compiler will do when you access the data in the obvious
way? Is your concern just the "shall" in the standard, or have you
found a case where this actually matters in the absence of all aliasing?
Despite the "shall" most people take the footnote to be significant
("The intent of this list is to specify those circumstances in which an
object may or may not be aliased.").
I can't tell if your concern is with the words (I'm sure the text could
be improved in this area) or with the type-based aliasing optimisation
that modern compiler do. You paint it as a practical problem (what
compilers do to your previously well-understood code) but do any of them
play up in this case?
<huge snip>
Can you confirm that agree with me about your other example at least?
Can I assume that when you cut an answer altogether it's because you
have no objection to it?
--
Ben.
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Objective C Alla _ <modelling.data@gmail.com> - 2015-11-10 09:10 -0800
Re: Objective C "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2015-11-10 09:16 -0800
Re: Objective C Richard Heathfield <rjh@cpax.org.uk> - 2015-11-10 17:17 +0000
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-10 09:32 -0800
Re: Objective C Mark Storkamp <mstorkamp@yahoo.com> - 2015-11-10 11:38 -0600
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-10 12:36 -0500
Re: Objective C Alla _ <modelling.data@gmail.com> - 2015-11-10 11:15 -0800
Re: Objective C Richard Heathfield <rjh@cpax.org.uk> - 2015-11-10 21:51 +0000
Re: Objective C Alla _ <modelling.data@gmail.com> - 2015-11-10 23:13 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-13 16:01 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-14 01:07 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-14 06:26 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-14 22:22 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-14 15:46 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 01:47 +0000
Re: Objective C BartC <bc@freeuk.com> - 2015-11-15 10:43 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-15 13:19 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 15:43 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-15 23:50 +0100
Re: Objective C gazelle@shell.xmission.com (Kenny McCormack) - 2015-11-16 00:05 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-15 19:10 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-16 09:11 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-16 11:57 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 20:38 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-16 13:20 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 22:28 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-16 15:33 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-16 15:56 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 01:43 +0000
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-17 01:21 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-16 18:11 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-16 20:12 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 00:59 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-18 22:46 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 14:25 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-19 07:58 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-19 22:13 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-19 15:29 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 08:44 -0800
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-17 01:26 +0000
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-16 21:48 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-16 20:27 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-17 13:58 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-17 12:28 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-18 13:00 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-18 12:31 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-18 16:43 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-18 15:57 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-19 19:09 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-19 19:05 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-20 15:00 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-20 15:30 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 17:11 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-22 15:53 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-23 13:51 -0600
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-24 12:00 +0000
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-17 10:26 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-17 06:20 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-17 16:41 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-17 12:08 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-17 16:27 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-17 14:55 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-18 13:59 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-18 13:06 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-24 14:24 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-24 15:11 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-26 17:02 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-27 07:26 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-18 21:56 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 02:17 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-22 07:16 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-26 17:11 -0600
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-22 19:09 +0000
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-17 23:28 -0600
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-18 15:33 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-18 23:06 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-19 09:12 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-19 09:25 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-19 21:06 +0100
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-20 13:49 -0800
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-21 05:01 -0600
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-21 05:09 -0600
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-21 03:31 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-21 17:43 -0600
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-21 16:00 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 01:12 -0600
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-27 16:42 +0000
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-27 12:38 -0500
Re: Objective C supercat@casperkitty.com - 2015-11-27 11:09 -0800
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-21 19:06 -0500
Re: Objective C supercat@casperkitty.com - 2015-11-21 17:00 -0800
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-22 14:44 +0000
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 01:55 -0600
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-22 00:03 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-22 10:18 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 03:21 -0800
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-22 10:53 -0500
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-22 20:28 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-22 18:52 -0800
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-23 11:58 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-23 15:24 -0800
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-23 09:46 -0500
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-23 08:13 -0800
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-23 12:04 -0500
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-23 11:52 -0600
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 16:05 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-24 09:09 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-08 08:48 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-12-08 10:40 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-09 12:34 -0800
Re: Objective C supercat@casperkitty.com - 2015-12-08 10:50 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-12-09 12:42 -0800
Re: Objective C supercat@casperkitty.com - 2015-12-09 13:38 -0800
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-12-10 19:54 +0000
Re: Objective C David Thompson <dave.thompson2@verizon.net> - 2015-12-06 08:02 -0500
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-22 14:36 -0800
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-23 00:41 -0600
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 07:39 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-22 14:23 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-17 10:24 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-18 15:40 +0100
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-20 16:02 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-21 15:53 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-21 08:58 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-22 22:14 +0100
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 03:39 -0800
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-23 13:24 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-26 09:39 -0800
Re: Objective C Robert Wessel <robertwessel2@yahoo.com> - 2015-11-26 13:16 -0600
Re: Objective C supercat@casperkitty.com - 2015-11-26 12:25 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 14:34 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-26 12:39 -0800
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-27 16:43 +0000
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-27 09:29 -0800
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 14:18 -0800
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-23 22:35 +0000
Re: Objective C James Kuyper <jameskuyper@verizon.net> - 2015-11-23 17:40 -0500
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-24 05:35 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-25 12:15 -0800
Re: Objective C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2015-11-25 22:49 +0000
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-27 16:44 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 14:03 -0800
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-29 09:29 +0000
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-22 19:01 +0000
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-23 07:31 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-23 07:43 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-23 08:17 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-23 17:34 +0100
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-23 22:02 +0000
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-24 10:12 +0100
Re: Objective C Tim Rentsch <txr@alumni.caltech.edu> - 2015-11-27 08:39 -0800
Re: Objective C Jorgen Grahn <grahn+nntp@snipabacken.se> - 2015-11-14 18:24 +0000
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 12:23 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-14 12:36 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 13:13 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-14 14:04 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 14:15 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-14 14:29 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-14 15:39 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-14 16:37 -0800
Re: Objective C Ian Collins <ian-news@hotmail.com> - 2015-11-15 13:46 +1300
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 02:06 +0000
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-15 03:25 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 12:56 +0000
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-15 07:53 -0600
Re: Objective C Stephen Sprunk <stephen@sprunk.org> - 2015-11-15 07:19 -0600
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-15 13:29 +0000
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-15 10:56 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-15 14:35 -0800
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-15 16:52 -0800
Re: Objective C supercat@casperkitty.com - 2015-11-15 19:49 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-16 11:02 +0000
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-16 10:36 -0800
Re: Objective C David Thompson <dave.thompson2@verizon.net> - 2015-12-06 08:03 -0500
Re: Objective C Melzzzzz <mel@zzzzz.com> - 2015-11-16 02:01 +0100
Re: Objective C supercat@casperkitty.com - 2015-11-15 19:34 -0800
Re: Objective C Chad <cdalten@gmail.com> - 2015-11-15 19:54 -0800
Re: Objective C raltbos@xs4all.nl (Richard Bos) - 2015-11-17 22:36 +0000
Re: Objective C supercat@casperkitty.com - 2015-11-17 15:27 -0800
Re: Objective C Malcolm McLean <malcolm.mclean5@btinternet.com> - 2015-11-17 21:15 -0800
Re: Objective C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-11-14 22:08 +0000
Re: Objective C fir <profesor.fir@gmail.com> - 2015-11-27 14:36 -0800
Re: Objective C David Brown <david.brown@hesbynett.no> - 2015-11-10 19:03 +0100
Re: Objective C Keith Thompson <kst-u@mib.org> - 2015-11-10 10:50 -0800
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