XProfan

proc atan4

    parameters x!,y!
    var w!=0

    if x!>0

        if y!>0

            if x!>y!:w!=arctan(y!/x!)

                else :w!=1.57079632679489662-arctan(x!/y!)

            endif

        elseif y!<0

            if x!<-y!:w!=4.7123889803846899+arctan(x!/-y!)

                else :w!=6.28318530717958648-arctan(-y!/x!)

            endif

            else:w!=0'y=0

        endif

    elseif x!<0

        if y!>0

            if x!>-y!:w!=1.57079632679489662+arctan(-x!/y!)

                else :w!=3.1415926535897932-arctan(y!/-x!)

            endif

        elseif y!<0

            if x!<y!:w!=3.1415926535897932+arctan(-y!/-x!)

                else :w!=4.7123889803846899-arctan(-x!/-y!)

            endif

            else:w!=3.1415926535897932

        endif

    else'if x=0

        if y!>0:w!=1.57079632679489662

        elseif y!<0:w!=4.7123889803846899

            else:w!=0

        endif

    endif

    return w!

endproc