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Groups > comp.lang.forth > #21666
| From | anton@mips.complang.tuwien.ac.at (Anton Ertl) |
|---|---|
| Newsgroups | comp.lang.forth |
| Subject | Re: Portability |
| Date | 2013-04-15 15:46 +0000 |
| Organization | Institut fuer Computersprachen, Technische Universitaet Wien |
| Message-ID | <2013Apr15.174615@mips.complang.tuwien.ac.at> (permalink) |
| References | (5 earlier) <Z66dnedz25l5HfjMnZ2dnUVZ_hKdnZ2d@supernews.com> <2013Apr10.175619@mips.complang.tuwien.ac.at> <g5udnV5YkqvfSvjMnZ2dnUVZ_uKdnZ2d@supernews.com> <2013Apr11.152441@mips.complang.tuwien.ac.at> <kkgt30$311$1@dont-email.me> |
rickman <gnuarm@gmail.com> writes:
>On 4/11/2013 9:24 AM, Anton Ertl wrote:
>> Signed comparison is not at all circular. Nor is unsigned comparison.
>> And there cannot be an overflow when you compare two numbers of the
>> same type. The two possible results are definitely representable in a
>> cell.
>
>Can you explain that? Comparison is done by subtracting.
On all architectures that I have programmed, it is done with a
comparison instruction; e.g., CMP on 6502, CMP on IA-32 and AMD64, CMP
on the 68000, SLT/SLTU (signed/unsigned) on MIPS, cmplt/cmpult on
Alpha etc.
>Even if you ignore the overflows and just work with the result you get,
>cases can't be distinguished. -32768 32767 - produces 1 as does 2 1 -,
>but they should produce different results in a comparison test. Do I
>have this wrong?
So, just doing a subtraction is obviously insufficient to achieve a
proper comparison. If you insist on not using a proper comparison
instruction, but have an overflow flag, you can do what Bernd
described. If you don't even have that, you can do it, e.g., thus
(untested):
: < { a b -- f }
a b xor 0< if \ different signs?
a 0<
else
a b - 0< \ for the same sign, circular should work.
then ;
- 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 2013: http://www.euroforth.org/ef13/
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Portability kenney@cix.compulink.co.uk - 2013-04-06 04:12 -0500
Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-06 11:31 +0000
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-06 10:34 -1000
Re: Portability "Ed" <invalid@nospam.com> - 2013-04-09 09:56 +1000
Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-09 01:30 +0000
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-09 07:21 +0000
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-08 22:18 -1000
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-09 12:41 +0000
Re: Portability Coos Haak <chforth@hccnet.nl> - 2013-04-09 17:21 +0200
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-09 08:06 -1000
Re: Portability Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-09 22:34 +0200
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-09 12:05 -1000
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-09 14:19 -1000
Re: Portability Chris <xrissmith@me.com> - 2013-04-09 20:45 -0700
Re: Portability "Ed" <invalid@nospam.com> - 2013-04-10 14:02 +1000
Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-09 23:00 -0700
Re: Portability "WJ" <w_a_x_man@yahoo.com> - 2013-04-12 14:41 +0000
Re: Portability "Ed" <invalid@nospam.com> - 2013-04-13 15:34 +1000
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-10 15:19 +0000
Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-10 11:46 +0000
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-10 15:03 +0000
Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-09 18:28 -0700
Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-09 17:00 -0700
Re: Portability "Ed" <invalid@nospam.com> - 2013-04-10 13:00 +1000
Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-10 11:55 +0000
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-10 10:10 -0500
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-10 15:56 +0000
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-10 16:18 -0500
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-11 13:24 +0000
Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-11 20:50 -0700
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-12 04:17 -0500
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-12 13:43 +0000
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-12 11:08 -0500
Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-12 18:50 +0000
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-13 03:57 -0500
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-13 11:59 +0000
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-13 14:47 -0500
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-12 10:44 -0400
Re: Portability Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-15 16:20 +0200
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-16 08:12 -1000
Re: Portability "A.K." <akk@nospam.org> - 2013-04-16 22:21 +0200
Re: Portability Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-16 22:33 +0200
Re: Portability "Ed" <invalid@nospam.com> - 2013-04-19 15:04 +1000
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-15 15:46 +0000
Re: Portability Sieur de Bienville <morrimichael@gmail.com> - 2013-04-15 19:19 -0700
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-16 12:53 +0000
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-16 17:29 -0400
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-16 11:44 -1000
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-16 18:00 -0400
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-16 17:33 -0500
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-16 12:46 -1000
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 13:09 -0400
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-17 12:20 -0500
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-17 07:38 -1000
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-17 16:43 -0500
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 20:03 -0400
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-18 16:53 -0500
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-18 18:02 -0400
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-19 03:30 -0500
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-19 15:31 -0400
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-22 09:59 +0000
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-22 07:28 -0500
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-22 15:27 +0000
Re: Portability Hugh Aguilar <hughaguilar96@yahoo.com> - 2013-04-22 18:16 -0700
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-17 10:23 +0000
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 13:46 -0400
Re: Portability anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2013-04-22 09:47 +0000
Re: Portability Brad Eckert <hwfwguy@gmail.com> - 2013-04-17 10:32 -0700
Re: Portability nobody@nowhere - 2013-04-17 17:36 +0000
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 14:21 -0400
Re: Portability Brad Eckert <hwfwguy@gmail.com> - 2013-04-17 15:03 -0700
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 18:22 -0400
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-17 18:24 -0400
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-18 00:51 -0400
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-18 17:19 -0400
Re: Portability Brad Eckert <hwfwguy@gmail.com> - 2013-04-19 12:37 -0700
Re: Portability rickman <gnuarm@gmail.com> - 2013-04-19 15:53 -0400
Re: Portability Lars Brinkhoff <lars.spam@nocrew.org> - 2013-04-17 19:26 +0200
Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-10 18:50 +0000
Re: Portability Bernd Paysan <bernd.paysan@gmx.de> - 2013-04-10 22:14 +0200
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-12 04:18 -0500
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-12 08:30 -1000
Re: Portability albert@spenarnc.xs4all.nl (Albert van der Horst) - 2013-04-12 18:58 +0000
Re: Portability "Elizabeth D. Rather" <erather@forth.com> - 2013-04-12 11:29 -1000
Re: Portability "Ed" <invalid@nospam.com> - 2013-04-13 14:57 +1000
Re: Portability Andrew Haley <andrew29@littlepinkcloud.invalid> - 2013-04-09 04:11 -0500
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