proc  _pow, x,y
        fld             QWORD [y]
        fld             QWORD [x]
        fyl2x
        fld1
        fld             st1
        fprem
        f2xm1
        faddp   st1,st0
        fscale
        fxch    st1
        fstp    st0
        ret
  endp
    

Since any parameters are pushed on the stack as double words when
calling such procedures, the labels for parameters are defined to mark the
double word data by default, however you can you specify the sizes for the
parameters if you want, by following the name of parameter with colon and
the size operator. The previous sample can be rewritten this way, which is
again equivalent:
proc WindowProc, hwnd:DWORD, wmsg:DWORD, wparam:DWORD, lparam:DWORD
If you specify a size smaller than double word, the given label applies to the
smaller portion of the whole double word stored on stack. If you you specify
a larger size, like far pointer of quad word, the two double word parameters
are defined to hold this value, but are labelled as one variable.