Adding floating point/double numbers in assembly

I am trying to experiment with inline assembly, and I am trying to add decimal numbers (no, NOT integers) in inline assembly. Issue is, when I call the following function:

inline double ADD(double num1, double num2) {
  double res;
_asm{

    push eax; push the former state of eax onto stack
    mov eax, num1;
    add eax, num2;
    mov res, eax;
    pop eax; restore the former state of eax now that we are done   
     }  return res;}

The compiler complains of improper operand size at the inline assembly (ALL lines of assembly excluding the push and pop instruction lines). So I have to change to an integer type, such as unsigned long, and then it works, but of course only supports integer types; decimal results are rounded.

Is there any way to add in assembly that allows for decimal results like 8.4?