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Does C++ have a squared operator?


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21 replies to this topic

#1 LAURENT*   Members   -  Reputation: 289

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Posted 30 May 2014 - 03:04 PM

I mean something like 2^2 = 4 or 10^2 = 100. I'm programming physics and I kinda need it. If you have code that replicate exponents in math I would like to ask if you could give it to me. Thanks all for any support.



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#2 Washu   Senior Moderators   -  Reputation: 6761

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Posted 30 May 2014 - 03:30 PM

No, there is no operator for squaring, why would there be when you can simply do it yourself with the multiplication operator. And std::pow for doing arbitrary powers (with some limitations)


Edited by Washu, 30 May 2014 - 03:31 PM.

In time the project grows, the ignorance of its devs it shows, with many a convoluted function, it plunges into deep compunction, the price of failure is high, Washu's mirth is nigh.
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#3 LAURENT*   Members   -  Reputation: 289

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Posted 30 May 2014 - 03:38 PM

I guess you're right. I thought of that right I made the thread. I'm still trying out physics and the math isn't coming together like I hoped. I'm thinking about how the compiler will process my code and it look pretty inaccurate to me.



#4 Burnt_Fyr   Members   -  Reputation: 1454

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Posted 30 May 2014 - 03:46 PM

There is not an operator per se, but there is the pow function , which raises a base to an exponent.


Edited by Burnt_Fyr, 30 May 2014 - 05:26 PM.


#5 LAURENT*   Members   -  Reputation: 289

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Posted 30 May 2014 - 03:57 PM

You know what I'm so sorry for making this thread. We have a math and physics sub forum and my thread will serve it's purpose better there. Thank for incoming me about POW. I will research it.



#6 LightOfAnima   Members   -  Reputation: 121

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Posted 01 June 2014 - 02:32 PM

If you so want, you could always try creating a custom class that overloads the ^ operator, using pow internally happy.png


Edited by LightOfAnima, 01 June 2014 - 02:33 PM.


#7 L. Spiro   Crossbones+   -  Reputation: 20246

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Posted 01 June 2014 - 03:08 PM

Don’t use pow() unless necessary; there is no guarantee the compiler will optimize it away into “X*X” and when it doesn’t you will have a major performance problem.
Just use X*X.


L. Spiro

#8 Vortez   Crossbones+   -  Reputation: 2705

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Posted 02 June 2014 - 08:04 AM

I know most ppl here dont like macro, and i don't either most of the time, but i think that's a good case for one:

 

#define POW2(x) ((x)*(x))

 

or maybe an inline function if you dont like macros.



#9 Bacterius   Crossbones+   -  Reputation: 11354

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Posted 02 June 2014 - 08:36 AM

I know most ppl here dont like macro, and i don't either most of the time, but i think that's a good case for one:

 

#define POW2(x) ((x)*(x))

 

or maybe an inline function if you dont like macros.

 

This macro evaluates its operand twice though which is actually probably your enemy in situations where you would want to use this macro (compilers are not necessarily allowed to reorder operations or even do common subexpression elimination with floating-point math) so I would recommend against it.


“If I understand the standard right it is legal and safe to do this but the resulting value could be anything.”


#10 Cornstalks   Crossbones+   -  Reputation: 6999

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Posted 02 June 2014 - 12:10 PM

I know most ppl here dont like macro, and i don't either most of the time, but i think that's a good case for one:
 
#define POW2(x) ((x)*(x))
 
or maybe an inline function if you dont like macros.

My question is why you think this is good cause for a macro? What benefit does this provide over:
template <typename T>
T pow2(const T& x) {
  return x * x;
}

// Or, if using a more "modern" C++:
template <typename T>
constexpr T pow2(const T& x) {
  return x * x;
}

[ I was ninja'd 71 times before I stopped counting a long time ago ] [ f.k.a. MikeTacular ] [ My Blog ] [ SWFer: Gaplessly looped MP3s in your Flash games ]

#11 Vortez   Crossbones+   -  Reputation: 2705

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Posted 02 June 2014 - 02:02 PM

Well, for one it's extremely simple, compared to your method, and two, it's really fast since it's dosn't involve invoking a function, but it's just a sugestion after all, the op can choose whatever method he prefer, i was just pointing it out.



#12 Washu   Senior Moderators   -  Reputation: 6761

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Posted 02 June 2014 - 03:33 PM

Well, for one it's extremely simple, compared to your method, and two, it's really fast since it's dosn't involve invoking a function, but it's just a sugestion after all, the op can choose whatever method he prefer, i was just pointing it out.

Except that Cornstalks function will be inlined in any decent compiler. It also avoids a rather nasty trap that your macro has, which can result in hard to diagnose bugs and produce undefined behavior. I'll leave it up to you to figure out what the trap is...


Edited by Washu, 02 June 2014 - 03:35 PM.

In time the project grows, the ignorance of its devs it shows, with many a convoluted function, it plunges into deep compunction, the price of failure is high, Washu's mirth is nigh.
ScapeCode - Blog | SlimDX


#13 Chris_F   Members   -  Reputation: 2714

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Posted 02 June 2014 - 04:27 PM

Well, for one it's extremely simple, compared to your method, and two, it's really fast since it's dosn't involve invoking a function, but it's just a sugestion after all, the op can choose whatever method he prefer, i was just pointing it out.

 

There are no disadvantages to the templated constexpr function. In Clang it is inlined at all optimizations levels except for -O0, and if you want to you could use __attribute__((always_inline)) to force it to inline under all circumstances. If you think macros are "fast" and functions are slow, you are using the wrong mindset.



#14 ilreh   Members   -  Reputation: 281

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Posted 02 June 2014 - 05:04 PM

I would stick with L. Spiro's suggestion. If you're using simple multiplications, a (good) compiler internally tries to solve this with bit shifting which is a very fast way of altering numbers. Adding stuff to the stack for such a simple operation is a waste.



#15 Vortez   Crossbones+   -  Reputation: 2705

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Posted 02 June 2014 - 05:25 PM


Except that Cornstalks function will be inlined in any decent compiler. It also avoids a rather nasty trap that your macro has, which can result in hard to diagnose bugs and produce undefined behavior. I'll leave it up to you to figure out what the trap is...

 

What's the trap?

 

I took it from a very good c++ book, not that i really care anyway lol. I don't mean to be rude, but it would be pretty dumb to not call this macro correctly.

 

The parentesis should be able to proctect from the bug you speak of, i believe. If not, then ill just shut my trap :)


Edited by Vortez, 02 June 2014 - 05:31 PM.


#16 ApochPiQ   Moderators   -  Reputation: 17624

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Posted 02 June 2014 - 05:27 PM

Hint: POW2(IncrementSomeNumberAndReturnIt()) does... what?



#17 Vortez   Crossbones+   -  Reputation: 2705

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Posted 02 June 2014 - 05:39 PM


Hint: POW2(IncrementSomeNumberAndReturnIt()) does... what?

 

???

 

I just compiled this and it worked just fine (Answer 9)

#include "stdio.h"

#define POW2(x) ((x)*(x))

int test()
{
	return 3;
}

int main()
{
	int x = POW2(test());	

	printf("%d\n", x);

	return 0;
}


#18 fastcall22   Crossbones+   -  Reputation: 5533

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Posted 02 June 2014 - 05:52 PM

Cool story, now try this one:
 
#include <iostream>
 
#define POW2(x) ((x)*(x))
 
class Foobar {
public:
    Foobar() : _a(5) { }
     
    int a() {
        return _a++;
    }
      
private:
    int _a;
};
 
int main() {
    using namespace std;
     
    Foobar f;
    int x = POW2(f.a());
     
    cout << x << endl;
}

Edited by fastcall22, 02 June 2014 - 05:55 PM.

QWxsIHRvYXN0LXRvYXN0aW5nIHRvYXN0ZXJzIGNhbiB0b2FzdCB0b2FzdGVkIHRvYXN0LCBhbHRob3Vn aCByZS10b2FzdGluZyB0b2FzdGVkIHRvYXN0IGlzIGdlbmVyYWxseSBub3QgcmVjb21tZW5kZWQgYnkg dGhlIG1hbnVmYWN0dXJlcnMgb2YgdG9hc3QtdG9hc3RpbmcgdG9hc3RlcnMuLi4=

#19 L. Spiro   Crossbones+   -  Reputation: 20246

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Posted 02 June 2014 - 05:55 PM

I just compiled this and it worked just fine (Answer 9)

#include "stdio.h"

#define POW2(x) ((x)*(x))

int test()
{
	return 3;
}

int main()
{
	int x = POW2(test());	

	printf("%d\n", x);

	return 0;
}

What happens if you try:
 

#include "stdio.h"

#define POW2(x) ((x)*(x))

int main()
{
	int y = 3;
	int x = POW2(++y);	

	printf("%d\n", x);

	return 0;
}




L. Spiro


Edited by L. Spiro, 02 June 2014 - 05:58 PM.


#20 Washu   Senior Moderators   -  Reputation: 6761

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Posted 02 June 2014 - 06:22 PM

 

I just compiled this and it worked just fine (Answer 9)

#include "stdio.h"

#define POW2(x) ((x)*(x))

int test()
{
	return 3;
}

int main()
{
	int x = POW2(test());	

	printf("%d\n", x);

	return 0;
}

What happens if you try:
 

#include "stdio.h"

#define POW2(x) ((x)*(x))

int main()
{
	int y = 3;
	int x = POW2(++y);	

	printf("%d\n", x);

	return 0;
}




L. Spiro

 

Cool story, now try this one:
 

#include <iostream>
 
#define POW2(x) ((x)*(x))
 
class Foobar {
public:
    Foobar() : _a(5) { }
     
    int a() {
        return _a++;
    }
      
private:
    int _a;
};
 
int main() {
    using namespace std;
     
    Foobar f;
    int x = POW2(f.a());
     
    cout << x << endl;
}

Hint: POW2(IncrementSomeNumberAndReturnIt()) does... what?

Three prime examples of the problems of using macros in this manner. Note that Spiro's results in undefined behavior.


In time the project grows, the ignorance of its devs it shows, with many a convoluted function, it plunges into deep compunction, the price of failure is high, Washu's mirth is nigh.
ScapeCode - Blog | SlimDX





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