[C++] Inline Return

[R.a.B.B.i.T]

I've got some code (simply powers) which I'm inlining in assembly because I have nothing else to do right now.  I can't, however, get the result to be returned or printed to the console.  Can anyone help?

Code Select Expand

#include <iostream.h>

void power2(int num, int power, unsigned int outl)
{
__asm
{
mov eax, num
mov ecx, power
mov ebx, outl
shl eax, cl
out eax, outl
}
}

int main()
{
power2(5, 3, (unsigned int) sizeof(cout));
return 0;
}

[Arta]

Out is for device IO. You need to call printf (or equivalent) from your assembly code, or just return the value and printf it in main (that would be better).

[Adron]

I've got some code (simply powers) which I'm inlining in assembly because I have nothing else to do right now.  I can't, however, get the result to be returned or printed to the console.  Can anyone help?

Code Select Expand

#include <iostream.h>

void power2(int num, int power, unsigned int outl)
{
__asm
{
mov eax, num
mov ecx, power
mov ebx, outl
shl eax, cl
out eax, outl
}
}

int main()
{
power2(5, 3, (unsigned int) sizeof(cout));
return 0;
}

I like the novel idea of getting the size of cout and using that as the output port to send the data to. Must've required some creative thinking

[MyndFyre]

I like the novel idea of getting the size of cout and using that as the output port to send the data to. Must've required some creative thinking

Heh I noticed that too.  I was wondering how that was supposed to work.

[K]

Code Select Expand


#include <cstdio>

unsigned int power2(int num, int power)
{
__asm
{
mov eax, num
mov ecx, power
shl eax, cl
}
// return value is in eax already
}

int main()
{
std::printf("%d\r\n", power2(x, y));
return 0;
}


[R.a.B.B.i.T]

Thanks, K, that work's after some modification

I used sizeof(cout) because I knew out couldn't take an ostream as a parameter, but it didn't work ><

[Zakath]

The sizeof operator returns the size in bytes of its operand (or the length of the array if the operand is an array). Why would that be a valid device handle? It would just be the number of bytes an instance of class ostream occupies.

Think about what you're doing.

[R.a.B.B.i.T]

I needed to make it a number somehow

[Kp]

The sizeof operator returns the size in bytes of its operand (or the length of the array if the operand is an array).

So given this:

Code Select Expand

int x[10];
cout << sizeof(x) << endl;, it should print 10?   The length of the array is 10, but that's not its size...

[Mephisto]

I needed to make it a number somehow

Perhaps you could've taken the address of an object of type cout?

[R.a.B.B.i.T]

I don't know that much C++!

[MyndFyre]

I don't know that much C++!

If you don't know how to use pointers, you shouldn't be using C++ *or* assembly.

[R.a.B.B.i.T]

I know pointers, just not too well.  I'm still learning, remember.  And ACTUALLY, I learned Assembly first, during my electronics course.

[Zakath]

The sizeof operator returns the size in bytes of its operand (or the length of the array if the operand is an array).

So given this:

Code Select Expand

int x[10];
cout << sizeof(x) << endl;, it should print 10?   The length of the array is 10, but that's not its size...

My mistake. I was going from memory, and it appears that my memory has a leak in it.

It returns the total number of bytes occupied by the array, not the length of the array.

[Mephisto]

I was just curious though, why are you using inline assembler to create a power evaluation function?  Why not just use plain C++...

Code Select Expand

unsigned long EvaluatePower(unsigned long base, unsigned long exponent)
{
if(exponent == 0)
return 1;
else if(exponent == 1)
return base;
else {
unsigned long value = 0;
unsigned long tracker = base;

for(unsigned int i = 1; i < exponent; i++) {
value = base * tracker;
tracker = value;
}

return value;
}
}

Note: Does not support negative exponents.  If you want this supported you'll have to change the values to type signed and come up with some thinking as to how to process a negative exponent (e.g. taking the recipricol of the evaluated power).