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## Does C++ have a squared operator?

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### #1LAURENT*  Members

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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.

### #2Washu  Senior Moderators

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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.

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### #3LAURENT*  Members

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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.

### #4Burnt_Fyr  Members

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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.

### #5LAURENT*  Members

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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.

### #6LightOfAnima  Members

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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

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

### #7L. Spiro  Members

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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

### #8Vortez  Members

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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.

### #9Bacterius  Members

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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.”

### #10Cornstalks  Members

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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;
}


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### #11Vortez  Members

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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.

### #12Washu  Senior Moderators

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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

### #13Chris_F  Members

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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.

### #14ilreh  Members

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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.

### #15Vortez  Members

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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.

### #16ApochPiQ  Moderators

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Posted 02 June 2014 - 05:27 PM

Wielder of the Sacred Wands

### #17Vortez  Members

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Posted 02 June 2014 - 05:39 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;
}


### #18fastcall22  Moderators

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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.

zlib: eJzVVLsSAiEQ6/1qCwoK i7PxA/2S2zMOZljYB1TO ZG7OhUtiduH9egZQCJH9 KcJyo4Wq9t0/RXkKmjx+ cgU4FIMWHhKCU+o/Nx2R LEPgQWLtnfcErbiEl0u4 0UrMghhZewgYcptoEF42 YMj+Z1kg+bVvqxhyo17h nUf+h4b2W4bR4XO01TJ7 qFNzA7jjbxyL71Avh6Tv odnFk4hnxxAf4w6496Kd OgH7/RxC

### #19L. Spiro  Members

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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;
}

Spoiler

L. Spiro

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

### #20Washu  Senior Moderators

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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;
}

Spoiler

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;
}


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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