| Topic: |
DEVELOP > c-Plus-Plus |
| User: |
"" |
| Date: |
06 May 2006 10:25:21 AM |
| Object: |
Negate an integer |
Hi:
What is the protable way to negate an arithmetic integer?
template<typename T>
T negate(T t) {
return -t; // <-- problem
}
On my Intel machines, taking negation like the above is not
right if t is std::numeric_limits<T>::min()
So the question may be reduced to: how to detect to throw an error.
Thank you.
IJ. Wang
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| User: "osmium" |
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| Title: Re: Negate an integer |
06 May 2006 10:35:40 AM |
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<wij@seed.net.tw> wrote:
What is the protable way to negate an arithmetic integer?
I don't think a bulletproof way is possible. 0 is taken as a positive
number. Since there are an even number of numbers that can be represented
in binary, this is a problem.
template<typename T>
T negate(T t) {
return -t; // <-- problem
}
On my Intel machines, taking negation like the above is not
right if t is std::numeric_limits<T>::min()
So the question may be reduced to: how to detect to throw an error.
Why not do the obvious? Perhaps I don't understand what your problem is.
.
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| User: "" |
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| Title: Re: Negate an integer |
06 May 2006 08:09:57 PM |
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osmium wrote:
...
Why not do the obvious? Perhaps I don't understand what your problem is.
template<typename T>
T negate(T t) {
if(t==std::numeric_limits<T>::min()) {
throw error;
}
return -t;
}
1. I find no document clearly states when negate a value t yields
valid result or not.
2. The above method won't work for some machine not Intel CPU.
IJ. Wang
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| User: "osmium" |
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| Title: Re: Negate an integer |
06 May 2006 08:49:32 PM |
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<wij@seed.net.tw> wrote:
osmium wrote:
...
Why not do the obvious? Perhaps I don't understand what your problem is.
template<typename T>
T negate(T t) {
if(t==std::numeric_limits<T>::min()) {
throw error;
}
return -t;
}
1. I find no document clearly states when negate a value t yields
valid result or not.
2. The above method won't work for some machine not Intel CPU.
Are you implying that there is a compiler that lies about the value of
INT_MAX and/or INT_MIN in <climits>? I based what I said on the assumption
that they told the truth. I didn't look at your code; examining the
variables such as those two are what I had in mind. If you want an
alternative, you might be able to use one of the abs() functions somehow. I
have nothing else to offer.
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| User: "Rolf Magnus" |
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| Title: Re: Negate an integer |
06 May 2006 12:05:57 PM |
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wrote:
Hi:
What is the protable way to negate an arithmetic integer?
template<typename T>
T negate(T t) {
return -t; // <-- problem
}
On my Intel machines, taking negation like the above is not
right if t is std::numeric_limits<T>::min()
So the question may be reduced to: how to detect to throw an error.
Hmm, you mean how to detect that t is equal to
std::numeric_limits<T>::min()? Or did I miss anything?
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| User: "Alf P. Steinbach" |
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| Title: Re: Negate an integer |
06 May 2006 09:57:12 PM |
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* Rolf Magnus:
wij@seed.net.tw wrote:
What is the protable way to negate an arithmetic integer?
template<typename T>
T negate(T t) {
return -t; // <-- problem
}
On my Intel machines, taking negation like the above is not
right if t is std::numeric_limits<T>::min()
So the question may be reduced to: how to detect to throw an error.
Hmm, you mean how to detect that t is equal to
std::numeric_limits<T>::min()? Or did I miss anything?
He means, how to detect whether -std::numeric_limits<T>::min() exists.
Probably the most protable way to do that is to check whether
-(std::numeric_limits<T>::min()+1) == std::numeric_limits<T>::max().
Cheers.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
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| User: "" |
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| Title: Re: Negate an integer |
07 May 2006 03:53:28 AM |
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Alf P. Steinbach wrote:
..
He means, how to detect whether -std::numeric_limits<T>::min() exists.
..
Yes, that is what I meant. Thank you. (good rephrase)
IJ. Wang
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