Unprototyped Functions
For functions not fully prototyped, the caller will pass integer values as integers and floating-point values as double precision. For floating-point values only, both the integer register and the floating-point register will contain the float value in case the callee expects the value in the integer registers.
func1();
func2() { // RCX = 2, RDX = XMM1 = 1.0, and R8 = 7
func1(2, 1.0, 7);
}