For a felony defined by a statute of this state that is not in Title 9A RCW, unless otherwise provided:

(1) If the maximum sentence of imprisonment authorized by law upon a first conviction of such felony is twenty years or more, such felony shall be treated as a class A felony for purposes of this chapter;

(2) If the maximum sentence of imprisonment authorized by law upon a first conviction of such felony is eight years or more, but less than twenty years, such felony shall be treated as a class B felony for purposes of this chapter;

(3) If the maximum sentence of imprisonment authorized by law upon a first conviction of such felony is less than eight years, such felony shall be treated as a class C felony for purposes of this chapter.