To properly call atan2 push two double precision floating 
points values onto the regular stack and then call atan2.
The answer in double precision is returned to the top of 
the floating point stack (st0). Below is an example code 
that takes two single precision floating point values 
(imaginary and magnitude) and calls atan2 and prints out
the result. Use the -lm option with gcc to link your .o file.

	
fld dword[imaginary]
sub esp ,16
fstp qword[esp]
fld  dword[magnitude]
fstp qword[esp+8]
call atan2  

Make_Local_Str flst_len1, flst_str1, 'atan2 is -> %.6e', 10, 0

sub esp, 8
fstp qword [esp]
push dword flst_str
call printf
add esp, 12