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Groups > comp.lang.forth > #38496
| From | anton@mips.complang.tuwien.ac.at (Anton Ertl) |
|---|---|
| Newsgroups | comp.lang.forth |
| Subject | Re: rhel 7 and kforth |
| Date | 2015-04-22 13:08 +0000 |
| Organization | Institut fuer Computersprachen, Technische Universitaet Wien |
| Message-ID | <2015Apr22.150859@mips.complang.tuwien.ac.at> (permalink) |
| References | (5 earlier) <ea58125a-3cc2-41a4-8481-b84c730218b9@googlegroups.com> <87d232wtfp.fsf@jester.gateway.pace.com> <630fc3d6-4917-426d-88f3-6e0179c1ad70@googlegroups.com> <878udqwq0s.fsf@jester.gateway.pace.com> <mh6hq7$qpq$1@dont-email.me> |
Bernd Paysan <bernd.paysan@gmx.de> writes:
>E.g. if I do a + in Forth on a two's complement system, it will wrap around,
>because + is defined for both signed and unsigned numbers, and what's an
>overflow for a signed number is a normal operation for the unsigned number
>and vice versa.
Forth-94 does not define integer overflow, neither for signed nor for
unsigned numbers, and Forth-2012 has not improved that. But as you
point out, it is hard to imagine a system where + does not wrap
around, because the same + works for both signed and unsigned numbers.
In particular, on 1s-complement and sign-magnitude systems you have
different addition operations for signed and unsigned addition.
I asked that question many years ago, and from the answer from a TC
member puzzled the following together: The way Forth-94 (2012) would
be implemented on a 1s-complement or sign-magnitude system would be to
have the signed addition as +, and the unsigned numbers as a subset of
the signed numbers (e.g., 17-bit signed numbers and 16-bit unsigned
numbers).
One could even test how viable that approach is on a 2s-complement
system, by implementing + as signed overflow-trapping operation.
Anyway, 2s-complement with wraparound is common practice, so we should
standardize it.
>IMHO the most obvious misconception of the C developers is that "undefined =
>fast". That's not the point. When you write a program, you want to express
>your algorithms, so it has to be well-defined.
I think it's a misconception of the miscompiler maintainers, not of C
developers (some developers may also suffer from this misconception as
a result from advocacy from miscompiler defenders). And the problem
is that the only programs they care about are those that are not being
developed, but were developed once upon a time and are now cast in
stone: benchmarks. So unlike production programs, where you solve a
performance problem by changing the source code, the only way to
improve performance for these programs is compiler heroics; and the
compiler can be the more heroic, the less complete the specification
is it has to satisfy. So what we get is that they use the C standard
as the only specification, plus adding those features that the SPEC
benchmarks use (but only in a very limited way, and of course
undocumented).
> If you don't check array
>bounds to gain speed, your compiler still can be well-defined: a[100] of an
>int a[something]; array is accessing the memory location 100 ints further
>from the start of a, no matter how big that "something" really is. That's
>defined behavior, undefined is only what kind of data there is at a[100],
>because if something<100, it's certainly not part of the array a[], and the
>memory layout of the rest of the system isn't easy to predict.
>
>A standard body of course simply writes "it's undefined", because vendor IBM
>AS/400 actually does implement array boundary checking even for C.
Even without array bounds checking, you can get a SIGSEGV, and on a
machine with array bounds checking, you get an exception, not an
endless loop.
A standards body writes "undefined behaviour" or "ambiguous condition"
because there is no common practice concerning the results, and they
therefore don't want to specify it any further. Taking that as excuse
for arbitrary miscompilation is the fault of the compiler maintainers
and their fault alone.
- anton
--
M. Anton Ertl http://www.complang.tuwien.ac.at/anton/home.html
comp.lang.forth FAQs: http://www.complang.tuwien.ac.at/forth/faq/toc.html
New standard: http://www.forth200x.org/forth200x.html
EuroForth 2014: http://www.euroforth.org/ef14/
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rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-15 11:20 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-15 19:09 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 04:13 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 04:55 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-16 12:08 +0000
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 05:29 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 07:07 -0700
Re: rhel 7 and kforth franck.bensusan@gmail.com - 2015-04-16 07:44 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 08:14 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-16 14:02 +0000
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 08:12 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 12:25 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 17:02 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 17:06 -0700
Re: rhel 7 and kforth foxaudioresearch@gmail.com - 2015-04-16 17:24 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 17:39 -0700
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-16 17:47 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 18:44 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 18:50 -0700
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-16 19:10 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 19:29 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-16 20:10 -0700
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-16 20:27 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 02:04 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-17 11:41 +0000
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 14:45 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 14:01 +0000
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-17 07:47 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 08:35 -0700
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-17 10:33 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 11:15 -0700
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-17 11:47 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 14:51 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 14:41 +0000
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-24 11:42 -0700
Re: rhel 7 and kforth "Elizabeth D. Rather" <erather@forth.com> - 2015-04-24 09:02 -1000
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-02 10:53 +0000
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-05-03 17:22 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-04 10:23 +0000
Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-22 00:10 +0200
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-21 17:45 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-22 13:08 +0000
Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-17 20:27 +0000
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 14:41 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 14:11 +0000
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-17 15:47 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-18 14:34 +0000
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-18 14:09 -0700
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-19 20:31 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-20 11:35 +0000
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-21 18:07 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-22 11:21 +0000
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-24 19:34 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-25 08:36 +0000
Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-25 11:36 +0000
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-25 16:29 +0000
Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-19 10:08 +0000
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-19 20:11 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-20 12:05 +0000
Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-22 01:27 +0200
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-21 18:18 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-22 11:00 +0000
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-24 11:28 -0700
Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-25 01:34 +0200
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-24 21:07 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-25 16:41 +0000
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-25 10:06 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-26 14:56 +0000
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-26 20:22 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-27 09:02 +0000
Re: rhel 7 and kforth mhx@iae.nl - 2015-04-27 03:59 -0700
Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-27 15:45 +0000
Re: rhel 7 and kforth "Rod Pemberton" <bork@lllljunkqwer.cpm> - 2015-04-27 18:09 -0400
Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-28 03:55 +0200
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-27 19:30 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-27 19:44 -0700
Re: rhel 7 and kforth "Rod Pemberton" <bork@lllljunkqwer.cpm> - 2015-04-28 02:03 -0400
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 01:44 -0700
Re: rhel 7 and kforth Mark Wills <markwills1970@gmail.com> - 2015-04-28 02:44 -0700
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-28 16:47 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 17:00 -0700
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-28 17:14 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 17:59 -0700
Re: rhel 7 and kforth Paul Rubin <no.email@nospam.invalid> - 2015-04-28 21:41 -0700
Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-29 03:07 +0200
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 18:13 -0700
Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-29 00:07 +0000
Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-28 22:22 +0200
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 14:23 -0700
Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-28 23:51 +0200
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-28 16:50 -0700
Re: rhel 7 and kforth David Thompson <dave.thompson2@verizon.net> - 2015-05-10 12:24 -0400
Re: rhel 7 and kforth mhx@iae.nl - 2015-04-26 22:16 -0700
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-04-27 09:19 +0000
Re: rhel 7 and kforth mhx@iae.nl - 2015-04-27 04:03 -0700
Re: rhel 7 and kforth "Rod Pemberton" <bork@lllljunkqwer.cpm> - 2015-04-27 18:21 -0400
Re: rhel 7 and kforth anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2015-05-01 14:46 +0000
Re: rhel 7 and kforth Bernd Paysan <bernd.paysan@gmx.de> - 2015-04-23 16:46 +0200
Re: rhel 7 and kforth albert@spenarnc.xs4all.nl (Albert van der Horst) - 2015-04-17 10:35 +0000
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 08:43 -0700
Re: rhel 7 and kforth krishna.myneni@ccreweb.org - 2015-04-17 08:41 -0700
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