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Groups > comp.lang.forth > #58089
| From | anton@mips.complang.tuwien.ac.at (Anton Ertl) |
|---|---|
| Newsgroups | comp.lang.forth |
| Subject | Re: mixed double and single signed division |
| Date | 2017-04-25 11:37 +0000 |
| Organization | Institut fuer Computersprachen, Technische Universitaet Wien |
| Message-ID | <2017Apr25.133713@mips.complang.tuwien.ac.at> (permalink) |
| References | (3 earlier) <f8a33236-78f6-462e-9bc1-67e2ca5c92b7@googlegroups.com> <2017Apr24.151206@mips.complang.tuwien.ac.at> <57830405-b5fe-4bf5-88dd-88a3838f1341@googlegroups.com> <2017Apr25.104007@mips.complang.tuwien.ac.at> <cd8cf26a-7424-4333-8023-f112c2ac7373@googlegroups.com> |
krishna.myneni@ccreweb.org writes:
>On Tuesday, April 25, 2017 at 4:03:12 AM UTC-5, Anton Ertl wrote:
>...
>> * works on signed and on unsigned numbers, and whether something is an
>> overflow depends on what kinds of numbers you work on, so your idea
>> cannot work for *.
>>=20
>
>* is a signed multiply.
From the standard:
|* ( n1 | u1 n2 | u2 -- n3 | u3 )
|
|Multiply n1 | u1 by n2 | u2 giving the product n3 | u3.
> I don't follow what you mean by the overflow depend=
>ing on the sign of the operands.
-1 -1 * is an overflow when you view it as an unsigned operation, but not when you view it as a signed operation.
$ffff $ffff * is an overflow on a 32-bit system when you view it as
signed operation but not when you view it as unsigned operation.
>> Moreover, the current draft for the next standard specifies that *
>> (among others) ignores overflow and uses modulo arithmetics.
>>=20
>
>Why would you do this for multiplication but not for division?
We don't do it for division for several reasons:
1) No hardware implements modulo arithmetic for division (and IIRC
that would only be defined for odd divisors anyway), and even if it
did, programs would probably usually prefer division-with-remainder.
2) Hardware diverges for division: There is hardware that produces an
exception for certain inputs, and hardware that doesn't.
By contrast, for *, all recent hardware that has a multiplication
instruction has one that does not produce an exception.
Modulo-arithmetic * is also an important operation in computing hash
functions. And if you want to be sure that there is no overflow, you
can make sure with M* or UM*.
- 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 2017: http://www.euroforth.org/ef17/
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mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-22 08:21 -0700
Re: mixed double and single signed division NN <november.nihal@gmail.com> - 2017-04-22 09:14 -0700
Re: mixed double and single signed division NN <november.nihal@gmail.com> - 2017-04-22 09:22 -0700
Re: mixed double and single signed division Coos Haak <htrofhc@gmail.com> - 2017-04-22 23:31 +0200
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-23 06:44 -0700
Re: mixed double and single signed division hughaguilar96@gmail.com - 2017-04-23 13:24 -0700
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-23 06:41 -0700
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-23 13:29 -0700
Re: mixed double and single signed division Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-22 11:40 -0500
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-23 06:52 -0700
Re: mixed double and single signed division "HAA" <someone@microsoft.com> - 2017-04-23 13:02 +1000
Re: mixed double and single signed division "Elizabeth D. Rather" <erather@forth.com> - 2017-04-22 17:58 -1000
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-23 13:36 -0700
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-23 16:33 -0700
Re: mixed double and single signed division anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-24 13:23 +0000
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-24 18:49 -0700
Re: mixed double and single signed division anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-24 13:12 +0000
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-24 18:35 -0700
Re: mixed double and single signed division "Elizabeth D. Rather" <erather@forth.com> - 2017-04-24 15:52 -1000
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-25 02:18 -0700
Re: mixed double and single signed division Paul Rubin <no.email@nospam.invalid> - 2017-04-25 02:25 -0700
Re: mixed double and single signed division anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-25 11:30 +0000
Re: mixed double and single signed division "Elizabeth D. Rather" <erather@forth.com> - 2017-04-25 08:08 -1000
Re: mixed double and single signed division anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-26 14:48 +0000
Re: mixed double and single signed division anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-25 08:40 +0000
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-25 02:25 -0700
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-25 03:00 -0700
Re: mixed double and single signed division anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-25 11:37 +0000
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-25 05:27 -0700
Re: mixed double and single signed division anton@mips.complang.tuwien.ac.at (Anton Ertl) - 2017-04-25 13:34 +0000
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-25 15:29 -0700
Re: mixed double and single signed division "HAA" <someone@microsoft.com> - 2017-04-27 14:02 +1000
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-27 16:00 -0700
Re: mixed double and single signed division "Elizabeth D. Rather" <erather@forth.com> - 2017-04-27 19:20 -1000
Re: mixed double and single signed division "HAA" <someone@microsoft.com> - 2017-04-28 22:41 +1000
Re: mixed double and single signed division Coos Haak <htrofhc@gmail.com> - 2017-04-25 15:32 +0200
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-25 15:22 -0700
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-23 06:55 -0700
Re: mixed double and single signed division "Elizabeth D. Rather" <erather@forth.com> - 2017-04-23 13:30 -1000
Re: mixed double and single signed division krishna.myneni@ccreweb.org - 2017-04-23 16:45 -0700
Re: mixed double and single signed division "HAA" <someone@microsoft.com> - 2017-04-24 10:56 +1000
Re: mixed double and single signed division "Elizabeth D. Rather" <erather@forth.com> - 2017-04-23 15:06 -1000
Re: mixed double and single signed division hughaguilar96@gmail.com - 2017-04-23 19:10 -0700
Re: mixed double and single signed division Paul Rubin <no.email@nospam.invalid> - 2017-04-23 19:12 -0700
Re: mixed double and single signed division "Elizabeth D. Rather" <erather@forth.com> - 2017-04-23 16:31 -1000
Re: mixed double and single signed division hughaguilar96@gmail.com - 2017-04-23 21:17 -0700
Re: mixed double and single signed division Paul Rubin <no.email@nospam.invalid> - 2017-04-23 21:47 -0700
Re: mixed double and single signed division hughaguilar96@gmail.com - 2017-04-23 22:58 -0700
Re: mixed double and single signed division hughaguilar96@gmail.com - 2017-04-23 23:22 -0700
Re: mixed double and single signed division Andrew Haley <andrew29@littlepinkcloud.invalid> - 2017-04-24 04:46 -0500
Re: mixed double and single signed division "HAA" <someone@microsoft.com> - 2017-04-24 12:59 +1000
Re: mixed double and single signed division "Elizabeth D. Rather" <erather@forth.com> - 2017-04-23 18:03 -1000
Re: mixed double and single signed division hughaguilar96@gmail.com - 2017-04-23 21:22 -0700
Re: mixed double and single signed division "HAA" <someone@microsoft.com> - 2017-04-25 12:53 +1000
Re: mixed double and single signed division "Elizabeth D. Rather" <erather@forth.com> - 2017-04-24 21:55 -1000
Re: mixed double and single signed division "HAA" <someone@microsoft.com> - 2017-04-25 20:00 +1000
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