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Groups > comp.lang.forth > #57179
| From | Spiros Bousbouras <spibou@gmail.com> |
|---|---|
| Newsgroups | comp.lang.forth, comp.lang.c |
| Subject | Re: LLVM and Forth |
| References | (10 earlier) <2017Apr9.165301@mips.complang.tuwien.ac.at> <xuAGA.661090$nT1.467590@fx44.am4> <ocerfl$5j4$1@dont-email.me> <HsLGA.931050$vF2.237690@fx46.am4> <4c1e8cea-0ec5-7fe5-d5fa-adc0b894f96f@verizon.net> |
| Message-ID | <K1xHA.311069$Fa7.217668@fx09.am4> (permalink) |
| Organization | virginmedia.com |
| Date | 2017-04-12 21:32 +0000 |
Cross-posted to 2 groups.
On Mon, 10 Apr 2017 11:51:37 -0400
"James R. Kuyper" <jameskuyper@verizon.net> wrote:
> On 04/10/2017 09:07 AM, Spiros Bousbouras wrote:
> > On Sun, 9 Apr 2017 22:46:04 -0400
> > James Kuyper <jameskuyper@verizon.net> wrote:
> ...
> >> Note: C++ requires that std::less<T*> must provide a total ordering of
> >> all pointers of type T*, even if the "<" operator does not provide such
> >> an ordering (20.9.5p14). C++ has a sufficiently strong shared heritage
> >> with C that the fact that the C++ standard can successfully impose this
> >> requirement strongly suggests that the C standard could impose a similar
> >> requirement.
> >> However, it's telling that C++ did NOT impose this requirement on the
> >> "<" operator itself, but only on std::less<T*>. That's because there are
> >> some systems where meeting this requirement makes std::less<T*>(p,q)
> >> substantially slower than p<q.
> >
> > I wonder if for Anton's purposes and for a big endian machine the following
> > would do
> >
> > int compare_pointers_to_void(void **p1 , void **p2) {
> > return memcmp(*p1 , *p2 , sizeof(void *)) ;
> > }
>
> <sidetrack>
> That seems unnecessarily complicated. To use it, if the pointers you
> want to compare are the values of expressions, you first have to store
> those values in void*. The same is true if you wan to compare pointers
> that are not of type "void*". Then you would have to pass pointers to
> those objects to compare_pointers_to_void(). Wouldn't it be simpler to
> define:
>
> int compare_pointers_to_void(void *p1, void *p2)
> {
> return memcmp(&p1, &p2, sizeof (void *));
> }
>
> This works on pointers of arbitrary types, which would all be implicitly
> converted to void* before the function call, and requires no extra work
> to apply it to a pointer-valued expression, rather than a pointer stored
> in an object.
> </sidetrack>
Yes , your version is better.
> It's unlikely that such a work-around would actually work as desired on
> any system where "<" would not - if the above code would in fact work,
> that's precisely how "<" should be implemented by the compiler.
Isn't it more likely that the compiler would compare pointers by a single
assembly instruction as opposed a call to memcmp() ? In any case , the
whole point of my code is that it's defined even if the pointers point to
different objects. Whereas using < , if the pointers point to different
objects then the behaviour is undefined. So if the compiler can prove they
point to different objects then instead of emitting the "obvious" assembly
instruction which presumably would do what Anton wants , it may decide
instead to be a smart ass and do something totally unpredictable.
[ If I ever write a C compiler I will consider adding a -smartass option.
Precise functionality to be decided. ]
> Implementations where "<" doesn't provide a total ordering generally use
> a pointer representation for which your function would sometimes give
> either the wrong order, or an order that is inconsistent.
When you say "wrong order" do you mean that for pointers pointing to the
same object , compare_pointers_to_void() might not give the same result
as < ? And what about inconsistent ? Do you mean not satisfy transitivity ?
> On some
> systems, pointers to the same location in memory can have different
> representations, so your function could even return a non-zero value for
> equivalent pointers.
Fascinating. Can you give an example ?
--
Apple Computer reported today that it has developed computer chips that
can store and play music inside women's breasts. This is considered to
be a major breakthrough because women are always complaining about men
staring at their breasts and not listening to them.
<S1895.ccc@netfunny.com>
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LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-01 06:36 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-01 14:57 +0000
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-01 11:55 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-02 15:24 +0000
Re: LLVM and Forth rickman <gnuarm@gmail.com> - 2017-04-01 11:21 -0400
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-01 11:57 -0700
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-02 04:02 -0500
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-02 06:35 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-02 14:41 +0000
Re: LLVM and Forth minforth@arcor.de - 2017-04-03 01:09 -0700
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-03 05:32 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-03 13:52 +0000
Re: LLVM and Forth minforth@arcor.de - 2017-04-03 07:59 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-03 16:08 +0000
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-03 12:22 -0500
Re: LLVM and Forth Paul Rubin <no.email@nospam.invalid> - 2017-04-03 20:10 -0700
Re: LLVM and Forth minforth@arcor.de - 2017-04-03 22:19 -0700
Re: LLVM and Forth albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-04 16:12 +0200
Re: LLVM and Forth Walter Banks <walter@bytecraft.com> - 2017-04-05 17:27 -0400
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-03 14:29 +0000
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-03 03:17 -0500
Re: LLVM and Forth minforth@arcor.de - 2017-04-03 05:04 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-03 12:55 +0000
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-03 10:08 -0500
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-03 17:05 +0000
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-04 11:29 -0500
Re: LLVM and Forth albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-04 19:11 +0200
Re: LLVM and Forth Paul Rubin <no.email@nospam.invalid> - 2017-04-04 21:29 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-05 15:01 +0000
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-05 18:42 +0100
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-06 04:01 -0500
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-06 18:48 +0000
Re: LLVM and Forth Joel Rees <joel.rees@gmail.com> - 2017-04-06 18:42 -0700
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-07 04:02 -0500
Re: LLVM and Forth Joel Rees <joel.rees@gmail.com> - 2017-04-08 21:18 -0700
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-08 22:43 +0000
Re: LLVM and Forth Joel Rees <joel.rees@gmail.com> - 2017-04-08 20:54 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-09 14:53 +0000
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-10 00:38 +0000
Re: LLVM and Forth James Kuyper <jameskuyper@verizon.net> - 2017-04-09 22:46 -0400
Re: LLVM and Forth Robert Wessel <robertwessel2@yahoo.com> - 2017-04-09 22:27 -0500
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-10 12:36 +0000
Re: LLVM and Forth Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-04-10 14:09 +0100
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-10 13:07 +0000
Re: LLVM and Forth Ben Bacarisse <ben.usenet@bsb.me.uk> - 2017-04-10 16:18 +0100
Re: LLVM and Forth "James R. Kuyper" <jameskuyper@verizon.net> - 2017-04-10 11:51 -0400
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-12 21:32 +0000
Re: LLVM and Forth "James R. Kuyper" <jameskuyper@verizon.net> - 2017-04-12 18:29 -0400
Re: LLVM and Forth hughaguilar96@gmail.com - 2017-04-12 15:29 -0700
Re: LLVM and Forth albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-13 02:55 +0200
Re: LLVM and Forth Joel Rees <joel.rees@gmail.com> - 2017-04-10 18:38 -0700
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-10 11:54 -0500
Re: LLVM and Forth Paul Rubin <no.email@nospam.invalid> - 2017-04-10 10:17 -0700
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-03 17:02 +0100
Re: LLVM and Forth hughaguilar96@gmail.com - 2017-04-03 10:03 -0700
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-04 03:25 -0700
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-04 11:24 +0000
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-04 04:55 -0700
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-04 12:28 +0000
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-04 16:16 +0000
Re: LLVM and Forth albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-04 15:38 +0200
Re: LLVM and Forth albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-04 16:06 +0200
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-04 17:57 -0700
Re: LLVM and Forth Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-05 00:44 -0400
Re: LLVM and Forth minforth@arcor.de - 2017-04-05 00:00 -0700
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-05 08:47 -0700
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-05 11:04 -0500
Re: LLVM and Forth john <anon@example.com> - 2017-04-05 18:04 +0100
Re: LLVM and Forth hughaguilar96@gmail.com - 2017-04-05 13:04 -0700
Re: LLVM and Forth Paul Rubin <no.email@nospam.invalid> - 2017-04-05 18:20 -0700
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-05 20:14 -0700
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-06 12:33 +0000
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-06 10:49 -0700
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-06 18:55 +0100
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-06 20:41 +0000
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-06 21:47 +0100
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-06 21:56 +0100
Re: LLVM and Forth Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-06 23:59 -0400
Re: LLVM and Forth Joel Rees <joel.rees@gmail.com> - 2017-04-06 17:10 -0700
Re: LLVM and Forth Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-07 03:33 -0400
Re: LLVM and Forth Spiros Bousbouras <spibou@gmail.com> - 2017-04-08 22:48 +0000
Re: LLVM and Forth Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-09 15:06 -0400
Re: LLVM and Forth Joel Rees <joel.rees@gmail.com> - 2017-04-08 22:45 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-09 14:27 +0000
Re: LLVM and Forth Joel Rees <joel.rees@gmail.com> - 2017-04-09 21:26 -0700
Re: LLVM and Forth Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-09 13:35 -0400
Re: LLVM and Forth Paul Rubin <no.email@nospam.invalid> - 2017-04-09 14:07 -0700
Re: LLVM and Forth minforth@arcor.de - 2017-04-05 12:16 -0700
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-05 20:27 -0700
Re: LLVM and Forth Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-06 05:24 -0400
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-06 03:26 -0700
Re: LLVM and Forth minforth@arcor.de - 2017-04-06 04:05 -0700
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-06 06:50 -0500
Re: LLVM and Forth Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-06 05:23 -0400
Re: LLVM and Forth Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-06 04:44 -0500
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-06 10:57 +0100
Re: LLVM and Forth peter.m.falth@gmail.com - 2017-04-05 05:29 -0700
Re: LLVM and Forth "Rudy Velthuis" <newsgroups@rvelthuis.de> - 2017-04-14 02:04 +0000
Re: LLVM and Forth albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-15 14:03 +0200
Re: LLVM and Forth "Rudy Velthuis" <newsgroups@rvelthuis.de> - 2017-04-16 00:44 +0000
Re: LLVM and Forth alex@rivadpm.com - 2017-04-16 05:53 -0700
Re: LLVM and Forth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-16 15:43 +0000
Re: LLVM and Forth "Rudy Velthuis" <newsgroups@rvelthuis.de> - 2017-04-16 22:27 +0000
Re: LLVM and Forth albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-18 02:45 +0200
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-18 18:26 +0100
Re: LLVM and Forth albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-20 19:51 +0200
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-20 19:08 +0100
Re: LLVM and Forth albert@cherry.spenarnc.xs4all.nl (Albert van der Horst) - 2017-04-20 20:42 +0200
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-20 20:29 +0100
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-20 20:48 +0100
Re: LLVM and Forth "Rudy Velthuis" <newsgroups@rvelthuis.de> - 2017-04-21 11:49 +0000
Re: LLVM and Forth Rod Pemberton <NeedNotReplyHere@xrsevnneqk.cem> - 2017-04-03 20:39 -0400
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-02 21:15 +0100
Re: LLVM and Forth hughaguilar96@gmail.com - 2017-04-02 15:18 -0700
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-03 13:07 +0100
Re: LLVM and Forth hughaguilar96@gmail.com - 2017-04-03 09:45 -0700
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-03 22:52 +0100
Re: LLVM and Forth hughaguilar96@gmail.com - 2017-04-03 15:25 -0700
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-06 09:35 +0100
Re: LLVM and Forth antispam@math.uni.wroc.pl - 2017-04-06 01:36 +0000
Re: LLVM and Forth minforth@arcor.de - 2017-04-05 22:00 -0700
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-06 09:52 +0100
Re: LLVM and Forth hughaguilar96@gmail.com - 2017-04-06 20:15 -0700
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-03 05:20 -0700
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-03 17:11 +0100
Re: LLVM and Forth Alex <alex@rivadpm.com> - 2017-04-06 17:43 +0100
Re: LLVM and Forth krishna.myneni@ccreweb.org - 2017-04-06 10:53 -0700
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