Accessing data in structures

[adam23]

I've been using the basics of MASM for some time now, so I have started to try and optimize some of my C++ routines.

My question is, say for example you are using a D3DXVECTOR3 from the DirectX library.  The structure contains three floats x,y,z, and is stored on the stack.  How can I access those floating point values in asm code.  I realize that I will have to use the FPU, but it doesn't necessarily have to be floating points.

Say I have an INT_POINT with an int x, and int y value that can be accessed.

INT_POINT temp;
temp.x = 5;
temp.y = 7;

Now say I have a structure or object passed by reference can I access them the same way?

void fill(INT_POINT &temp)
{
temp.x = 5;
temp.y = 7;
}

I'd like to take and convert similar functions to assembly but the only way I have been successful is to do this.

void fill(INT_POINT &temp)
{
int tempX;
int tempY;
_asm
{
mov eax, 5
mov tempX, eax
mov eax, 7
mov tempY, eax
}
temp.x = tempX;
temp.y = tempY;
}
As you can see this is no way optimized, because I am copying the value to a temp location before using C++ again to store it where is should be put to begin with.

I'd really appreciate any help I can get on this, and if I'm not being clear enough just let me know.

Thanks in advance
Adam
http://adamwlarson.com

[PBrennick]

adam23,
The guy who knows all about this stuff is Raymond Filiatreault. You can visit his site here.

There are nice tutorials, etc.

Paul

[japheth]

you might also just view this sample, works with VC:

Code Select Expand



typedef struct {
    int x;
    int y;
} POINT;

int fill(POINT& temp)
{
    _asm {
        mov edx,temp
        mov (POINT [edx]).x,5
        mov (POINT [edx]).y,6
    }
    return 0;
}

int main()
{
  POINT p1;
  fill (p1);
  return 0;
}


[adam23]

That looks pretty easy, but I ran into a little problem trying to do it.  It does get me going in the right direction though.

Say that I want to do this inside of a class,
I have a class Vector3 defined with a simple Test function to try and fill with values.

void Vector3::Test()
{
   _asm
   {
      mov edx, this
      mov (Vector3 [edx]).x, 5
      mov (Vector3 [edx]).y, 7
   }
}

I get these errors
error C2420: 'Vector3' : illegal symbol in first operand

Thanks again for the help

[adam23]

Man do I feel stupid

It was really simple

void Vector3::Test()
{
   _asm
   {
      mov edx, this
      mov ([edx]).x, 5
      mov ([edx]).y, 7
   }
}